Alterations in cortical somatostatin (SST)-containing GABAergic interneurons are among the most consistently replicated molecular findings in schizophrenia. Whether these alterations primarily reflect intrinsic cellular vulnerabilities, regional circuit context, or an interaction between the two remains unclear. To address this question, we examined a transcriptionally distinct SST neuron subtype that selectively expresses chondrolectin (CHODL), referred to as CHODL-SST neurons, across two brain regions with markedly different circuit organization: deep layer 6 and adjacent subcortical white matter of the dorsolateral prefrontal cortex (DLPFC) and the caudate nucleus.Using multiplex fluorescent in situ hybridization in postmortem tissue from 18 matched pairs of schizophrenia and unaffected comparison individuals, we quantified mRNA levels of CHODL, SST, neuropeptide Y (NPY), and nitric oxide synthase (NOS1) within CHODL-SST neurons in both regions.In the DLPFC, CHODL-SST neurons exhibited lower mRNA levels for all four transcripts in schizophrenia, with small-to-medium effect sizes (-0.29 to -0.52). In contrast, effect sizes in the caudate were nominal (-0.13 to 0.03), with Bayesian analyses providing strong evidence for no difference in schizophrenia. For every transcript, a significant diagnosis-by-region interaction (all p < 0.005) highlighted a striking dissociation between cortical and striatal CHODL-SST neurons.These findings indicate that schizophrenia-associated molecular alterations in CHODL-SST neurons are regionally selective and preferentially affect cortical populations. Rather than reflecting uniform cell-intrinsic vulnerability, these results support a model in which differential vulnerability emerges from the interaction between subtype-specific molecular features and regional circuit context, with implications for understanding SST neuron dysfunction and developing circuit-informed therapeutic strategies.

Microglia exhibit complex and dynamic morphology that is linked to function. Altered microglia function has been implicated in multiple diseases of the brain, including elevated phagocytosis of neuronal dendritic spines in schizophrenia. However, understanding the relationship between altered microglia and pathophysiology first requires a clearer picture of microglia morphology in the non-diseased brain, which has yet to be fully established. Here, we deploy immunostaining and confocal microscopy to sample over 1,300 microglia from two prefrontal cortex (PFC) subregions in postmortem human brain (3 males, 3 females). We use Neurolucida 360 to trace the 3-dimensional structure of these microglia and quantify interactions with dendritic spines. We find that PFC microglia in male subjects display overall more complex branching than in female subjects, and subgenual anterior cingulate cortex (sgACC) microglia are more complexly branched with more round somas than those in the dorsolateral PFC (DLPFC), irrespective of sex. Furthermore, a lower proportion of phagocytic burden in sgACC microglia involves engulfment of dendritic spines compared to DLPFC. Overall, our results paint a detailed and nuanced picture of microglia morphology and function in subjects unaffected by psychiatric or neurologic illness that can be used as a benchmark for future studies of the diseased brain.

Importance:Schizophrenia (SZ) is characterized by deficits in visual-spatial working memory, a function dependent on a distributed cortical network that includes nodes in the primary visual (V1), posterior parietal (PPC), and dorsolateral prefrontal (DLPFC) cortices. The connections across these regions involve excitatory synapses on the dendritic spines of pyramidal neurons in layer 3 (L3). Objective:To assess whether SZ is associated with regional differences in the magnitude or nature of L3 spine alterations. Design, Setting, and Participants:This case-control study examined brain tissue from 20 individuals with SZ and 20 matched unaffected comparison (UC) individuals, obtained by the Allegheny County Office of the Medical Examiner (Pittsburgh, Pennsylvania). Dendritic spines were labeled using fluorescent phalloidin (for F-actin) and immunolabeling for spinophilin and imaged by confocal microscopy. Exposure:Schizophrenia. Main Outcomes and Measures:Primary outcomes were between-group differences in L3 dendritic spine density and size across V1, PPC, and DLPFC. Secondary outcomes included spine fluorescence intensities of phalloidin and spinophilin. Results:Forty individuals were studied (20 UC: 14 [70%] male and 6 [30%] female; mean [SD] age, 47.7 [9.6] years; 20 SZ: 14 [70%] male and 6 [30%] female; mean [SD] age, 45.6 [9.5] years). Dendritic spine density reductions in individuals with SZ varied by spine size across regions, with lower densities of small spines in V1 (-18%; 95% CI, -31% to -5%; P = .009), medium spines in PPC (-16%; 95% CI, -28% to -4%; P = .01) and DLPFC (-13%; 95% CI, -21% to -4%; P = .009), and large spines in PPC (-38%; 95% CI, -58% to -17%; P < .001) and DLPFC (-30%; 95% CI, -50% to -11%; P = .004). Phalloidin fluorescence was lower in small (-9.5%; 95% CI, -17% to -1%; P = .04) and medium (-9.8%; 95% CI, -18% to -1%; P = .04) V1 spines and higher in large DLPFC spines (9.5%; 95% CI, 0.4% to 19%; P = .049). Spinophilin fluorescence was lower across all spine sizes and regions (a range from -13%; 95% CI, -24% to -2%, to -34%; 95% CI, -46% to -21%; P values ranging .02 to <.001). Conclusions and Relevance:L3 dendritic spine density differs by diagnosis and cortical region in SZ. Because dendritic spine size is associated with synaptic stability (large/medium spines) and plasticity (small spines), regional differences in the sizes of affected spines in SZ may reflect differing functional impairments in the primary sensory and association regions of the cortical visual-spatial working memory network.

Age-related dopamine (DA) neuron loss is a primary feature of Parkinson’s disease. However, whether similar biological processes occur during healthy aging, but to a lesser degree, remains unclear. We therefore determined whether midbrain DA neurons degenerate during aging in mice and humans. In mice, we identified no difference in midbrain neuron numbers throughout aging. Despite this, we found age-related decreases in midbrain mRNA expression of tyrosine hydroxylase (Th), the rate limiting enzyme of DA synthesis. Among midbrain glutamatergic cells, we similarly identified age-related declines in vesicular glutamate transporter 2 (Vglut2) mRNA expression. In co-transmitting Th+/Vglut2+ neurons, Th and Vglut2 transcripts decreased with aging. However, Th and Vglut2 protein levels in striatal synaptic release sites (e.g., terminals and axonal projections) did not differ throughout aging. Similar to the mouse, an initial study of human brain showed no effect of aging on midbrain neuron number with a concomitant decrease in TH and VGLUT2 mRNA expression. Unlike in mice, the density of striatal TH+ dopaminergic terminals was lower in aged human subjects. However, TH and VGLUT2 protein levels were unaffected in the remaining striatal boutons. Finally, in contrast to Th and Vglut2 mRNA, expression of most ribosomal genes in Th+ neurons was either maintained or even upregulated during aging. This suggests a homeostatic mechanism where age-related declines in transcriptional efficiency are overcome by ongoing ribosomal translation. Overall, we demonstrate species-conserved transcriptional effects of aging in midbrain dopaminergic and glutamatergic neurons that are not accompanied by marked cell death or lower striatal protein expression. This opens the door to novel therapeutic approaches to maintain neurotransmission and bolster neuronal resilience.

BACKGROUND:Certain cognitive processes require inhibition provided by the somatostatin (SST) class of GABA (gamma-aminobutyric acid) neurons in the dorsolateral prefrontal cortex (DLPFC). This inhibition onto pyramidal neuron dendrites depends on both SST and GABA signaling. Although SST messenger RNA (mRNA) levels are lower in the DLPFC in schizophrenia, it is not known whether SST neurons exhibit alterations in the capacity to synthesize GABA, principally via the 67-kilodalton isoform of glutamic acid decarboxylase (GAD67). METHODS:GAD67 and SST mRNA levels were quantified in individual SST neurons using fluorescence in situ hybridization in DLPFC layers 2/superficial 3, where SST neurons are enriched, in individuals with schizophrenia (n = 46) and unaffected comparison (n = 46) individuals. Findings were compared with GAD67 and SST mRNA levels quantified by polymerase chain reaction and to final educational attainment, a proxy measure for cognitive functioning. RESULTS:GAD67 (F1,84 = 13.1, p = .0005, Cohen's d = -0.78) and SST (F1,84 = 10.1, p = .002, Cohen's d = -0.64) mRNA levels in SST neurons were lower in schizophrenia, with no group differences in the relative density of SST neurons (F1,84 = 0.21, p = .65). A presynaptic index of dendritic inhibition, derived by summing the alterations in GAD67 and SST mRNAs, was lower in 80.4% of individuals with schizophrenia and was associated with final educational attainment (adjusted odds ratio = 1.44, p = .022). CONCLUSIONS:Deficits in both GAD67 and SST mRNAs within SST neurons indicate that these neurons have a markedly reduced ability to inhibit postsynaptic pyramidal neuron dendrites in schizophrenia. These alterations likely contribute to cognitive dysfunction in schizophrenia.

Summary: Understanding how neurons regulate cerebral blood flow (CBF) is crucial for interpreting brain hemodynamic imaging signals. Although parvalbumin (PV) interneurons strongly influence network activity, their effects on CBF appear variable, particularly during natural sensory stimulation and resting state. Using two-photon imaging in awake mice, we assessed PV interneuron effects on vascular tone across cortical depths during evoked and spontaneous activity. Optogenetic PV activation produced rapid vasodilation in the superficial cortex (<250 μm) and slow, delayed vasodilation in the middle cortex (250–400 μm). Chemogenetic PV suppression revealed that PV interneurons did not drive the rapid hemodynamic increase to sustained sensory input but did contribute to superficial vasodilation following brief stimuli. During spontaneous activity, synchronized PV interneuron activity predicted depth-specific arteriolar changes more strongly than non-PV neurons. These findings demonstrate a depth-dependent role for PV interneurons in regulating CBF and refine our understanding of neurovascular coupling.

Parkinson's disease (PD) targets some dopamine (DA) neurons more than others. Sex differences offer insights, with females more protected from DA neurodegeneration. The mammalian vesicular glutamate transporter VGLUT2 and Drosophila ortholog dVGLUT have been implicated as modulators of DA neuron resilience. However, the mechanisms by which VGLUT2/dVGLUT protects DA neurons remain unknown. We discovered DA neuron dVGLUT knockdown increased mitochondrial reactive oxygen species in a sexually dimorphic manner in response to depolarization or paraquat-induced stress, males being especially affected. DA neuron dVGLUT also reduced ATP biosynthetic burden during depolarization. RNA sequencing of VGLUT+ DA neurons in mice and flies identified candidate genes that we functionally screened to further dissect VGLUT-mediated DA neuron resilience across PD models. We discovered transcription factors modulating dVGLUT-dependent DA neuroprotection and identified dj-1β as a regulator of sex-specific DA neuron dVGLUT expression. Overall, VGLUT protects DA neurons from PD-associated degeneration by maintaining mitochondrial health.

In schizophrenia, layer 3 pyramidal neurons (L3PNs) in the dorsolateral prefrontal cortex (DLPFC) are thought to receive fewer excitatory synaptic inputs and to have lower expression levels of activity-dependent genes and of genes involved in mitochondrial energy production. In concert, these findings from previous studies suggest that DLPFC L3PNs are hypoactive in schizophrenia, disrupting the patterns of activity that are crucial for working memory, which is impaired in the illness. However, whether lower PN activity produces alterations in inhibitory and/or excitatory synaptic strength has not been tested in the primate DLPFC. Here, we decreased PN excitability in rhesus monkey DLPFC in vivo using adeno-associated viral vectors (AAVs) to produce Cre recombinase-mediated overexpression of Kir2.1 channels, a genetic silencing tool that efficiently decreases neuronal excitability. In acute slices prepared from DLPFC 7-12 weeks post-AAV microinjections, Kir2.1-overexpressing PNs had a significantly reduced excitability largely attributable to highly specific effects of the AAV-encoded Kir2.1 channels. Moreover, recordings of synaptic currents showed that Kir2.1-overexpressing DLPFC PNs had reduced strength of excitatory synapses whereas inhibitory synaptic inputs were not affected. The decrease in excitatory synaptic strength was not associated with changes in dendritic spine number, suggesting that excitatory synapse quantity was unaltered in Kir2.1-overexpressing DLPFC PNs. These findings suggest that, in schizophrenia, the excitatory synapses on hypoactive L3PNs are weaker and thus might represent a substrate for novel therapeutic interventions. Significance Statement:In schizophrenia, dorsolateral prefrontal cortex (DLPFC) pyramidal neurons (PNs) have both transcriptional and structural alterations that suggest they are hypoactive. PN hypoactivity is thought to produce synaptic alterations in schizophrenia, however the effects of lower neuronal activity on synaptic function in primate DLPFC have not been examined. Here, we used, for the first time in primate neocortex, adeno-associated viral vectors (AAVs) to reduce PN excitability with Kir2.1 channel overexpression and tested if this manipulation altered the strength of synaptic inputs onto the Kir2.1-overexpressing PNs. Recordings in DLPFC slices showed that Kir2.1 overexpression depressed excitatory (but not inhibitory), synaptic currents, suggesting that, in schizophrenia, the hypoactivity of PNs might be exacerbated by reduced strength of the excitatory synapses they receive.

Aims Vein grafts are used for many indications, including bypass graft surgery and arteriovenous fistula (AVF) formation. However, patency following vein grafting or AVF formation is suboptimal for various reasons, including thrombosis, neointimal hyperplasia, and adverse remodelling. Recently, endothelial-to-mesenchymal transition (EndMT) was found to contribute to neointimal hyperplasia in mouse vein grafts. We aimed to evaluate the clinical potential of inhibiting EndMT and developed the first dedicated preclinical model to study the efficacy of local EndMT inhibition immediately prior to AVF creation. Methods and results We first undertook pilot studies to optimize the creation of a femoral AVF in pigs and verify that EndMT contributes to neointimal formation. We then developed a method to achieve local in vivo SMAD3 knockdown by dwelling a lentiviral construct containing SMAD3 shRNA in the femoral vein prior to AVF creation. Next, in Phase 1, six pigs were randomized to SMAD3 knockdown or control lentivirus to evaluate the effectiveness of SMAD3 knockdown and EndMT inhibition 8 days after AVF creation. In Phase 2, 16 pigs were randomized to SMAD3 knockdown or control lentivirus and were evaluated to assess longer-term effects on AVF diameter, patency, and related measures at 30 days after AVF creation. In Phase 1, compared with controls, SMAD3 knockdown achieved a 75% reduction in the proportion of CD31+ endothelial cells co-expressing SMAD3 (P < 0.001) and also a significant reduction in the extent of EndMT (P < 0.05). In Phase 2, compared with controls, SMAD3 knockdown was associated with an increase in the minimum diameter of the venous limb of the AVF (1.56 ± 1.66 vs. 4.26 ± 1.71 mm, P < 0.01) and a reduced degree of stenosis (P < 0.01). Consistent with this, neointimal thickness was reduced in the SMAD3 knockdown group (0.88 ± 0.51 vs. 0.45 ± 0.19 mm, P < 0.05). Furthermore, endothelial integrity (the proportion of luminal cells expressing endothelial markers) was improved in the SMAD3 knockdown group (P < 0.05). Conclusion EndMT inhibition in a preclinical AVF model by local SMAD3 knockdown using gene therapy led to reduced neointimal hyperplasia, increased endothelialization, and a reduction in the degree of AVF stenosis. This provides important proof of concept to pursue this approach as a clinical strategy to improve the patency of AVFs and other vein grafts.

The primate dorsolateral prefrontal cortex (DLPFC) displays unique in vivo activity patterns, but how in vivo activity regulates DLPFC pyramidal neuron (PN) properties remains unclear. We assessed the effects of in vivo Kir2.1 overexpression, a genetic silencing tool, on synapses in monkey DLPFC PNs. We show for the first time that recombinant ion channel expression successfully modifies the excitability of primate cortex neurons, producing effects on synaptic properties apparently different from those in the rodent cortex.

Background: Dorsolateral prefrontal cortex (DLPFC) dysfunction in schizophrenia appears to reflect alterations in layer 3 pyramidal neurons (L3PNs), including smaller cell bodies and lower expression of mitochondrial energy production genes. However, prior somal size studies used biased strategies for identifying L3PNs, and somal size and levels of energy production markers have not been assessed in individual L3PNs. Study design: We combined fluorescent in situ hybridization (FISH) of vesicular glutamate transporter 1 (VGLUT1) mRNA and immunohistochemical-labeling of NeuN to determine if the cytoplasmic distribution of VGLUT1 mRNA permits the unbiased identification and somal size quantification of L3PNs. Dual-label FISH for VGLUT1 mRNA and cytochrome C oxidase subunit 4I1 (COX4I1) mRNA, a marker of energy production, was used to assess somal size and COX4I1 transcript levels in individual DLPFC L3PNs from schizophrenia (12 males; 2 females) and unaffected comparison (13 males; 1 female) subjects. Study results: Measures of L3PN somal size with NeuN immunohistochemistry or VGLUT1 mRNA provided nearly identical results (ICC = 0.96, p < 0.0001). Mean somal size of VGLUT1-identified L3PNs was 8.7% smaller (p = 0.004) and mean COX4I1 mRNA levels per L3PN were 16.7% lower (p = 0.01) in schizophrenia. These measures were correlated across individual L3PNs in both subject groups (rrm = 0.81-0.86). Conclusions: This preliminary study presents a novel method for combining unbiased neuronal identification with quantitative assessments of somal size and mRNA levels. We replicated findings of smaller somal size and lower COX4I1 mRNA levels in DLPFC L3PNs in schizophrenia. The normal scaling of COX4I1 mRNA levels with somal size in schizophrenia suggests that lower markers of energy production are secondary to L3PN morphological alterations in the illness.

Deficient gamma oscillations in prefrontal cortex (PFC) of individuals with schizophrenia appear to involve impaired inhibitory drive from parvalbumin-expressing interneurons (PVIs). Inhibitory drive from PVIs is regulated, in part, by RNA binding fox-1 homolog 1 (Rbfox1). Rbfox1 is spliced into nuclear or cytoplasmic isoforms, which regulate alternative splicing or stability of their target transcripts, respectively. One major target of cytoplasmic Rbfox1 is vesicle associated membrane protein 1 (Vamp1). Vamp1 mediates GABA release probability from PVIs, and the loss of Rbfox1 reduces Vamp1 levels which in turn impairs cortical inhibition. In this study, we investigated if the Rbfox1-Vamp1 pathway is altered in PVIs in PFC of individuals with schizophrenia by utilizing a novel strategy that combines multi-label in situ hybridization and immunohistochemistry. In the PFC of 20 matched pairs of schizophrenia and comparison subjects, cytoplasmic Rbfox1 protein levels were significantly lower in PVIs in schizophrenia and this deficit was not attributable to potential methodological confounds or schizophrenia-associated co-occurring factors. In a subset of this cohort, Vamp1 mRNA levels in PVIs were also significantly lower in schizophrenia and were predicted by lower cytoplasmic Rbfox1 protein levels across individual PVIs. To investigate the functional impact of Rbfox1-Vamp1 alterations in schizophrenia, we simulated the effect of lower GABA release probability from PVIs on gamma power in a computational model network of pyramidal neurons and PVIs. Our simulations showed that lower GABA release probability reduces gamma power by disrupting network synchrony while minimally affecting network activity. Finally, lower GABA release probability synergistically interacted with lower strength of inhibition from PVIs in schizophrenia to reduce gamma power non-linearly. Together, our findings suggest that the Rbfox1-Vamp1 pathway in PVIs is impaired in schizophrenia and that this alteration likely contributes to deficient PFC gamma power in the illness.

To meet the high energy demands of brain function, cerebral blood flow (CBF) parallels changes in neuronal activity by a mechanism known as neurovascular coupling (NVC). However, which neurons play a role in mediating NVC is not well understood. Here, we identify in mice and humans a specific population of cortical GABAergic neurons that co-express neuronal nitric oxide synthase and tachykinin receptor 1 (Tacr1). Through whole-tissue clearing, we demonstrate that Tacr1 neurons extend local and long-range projections across functionally connected cortical areas. We show that whisker stimulation elicited Tacr1 neuron activity in the barrel cortex through feedforward excitatory pathways. Additionally, through optogenetic experiments, we demonstrate that Tacr1 neurons are instrumental in mediating CBF through the relaxation of mural cells in a similar fashion to whisker stimulation. Finally, by electron microscopy, we observe that Tacr1 processes contact astrocytic endfeet. These findings suggest that Tacr1 neurons integrate cortical activity to mediate NVC.

Working memory impairment in people with schizophrenia appears to be associated with neuronal morphological alterations, such as smaller somal sizes, shorter dendritic arbors, and fewer dendritic spines, in layer 3 pyramidal neurons (L3PNs) of the dorsolateral prefrontal cortex (DLPFC). Consequently, L3PNs are thought to receive fewer excitatory inputs, resulting in lower activity and reduced drive for mitochondrial energy production. However, the relationship between somal size and energy production has not been assessed in individual L3PNs.

The lifetime effects of space irradiation (IR) on left ventricular (LV) function are unknown. The cardiac effects induced by space-type IR, specifically 5-ion simplified galactic cosmic ray simulation (simGCRsim), are yet to be discovered. Three-month-old, age-matched, male C57BL/6J mice were irradiated with 137Cs gamma (γ; 100, 200 cGy) and simGCRsim (50 and 100 cGy). LV function was assessed via transthoracic echocardiography at 14 and 28 days (early), and at 365, 440, and 660 (late) days post IR. We measured the endothelial function marker brain natriuretic peptide in plasma at three late timepoints. We assessed the mRNA expression of the genes involved in cardiac remodeling, fibrosis, inflammation, and calcium handling in LVs harvested at 660 days post IR. All IR groups had impaired global LV systolic function at 14, 28, and 365 days. At 660 days, 50 cGy simGCRsim-IR mice exhibited preserved LV systolic function with altered LV size and mass. At this timepoint, the simGCRsim-IR mice had elevated levels of cardiac fibrosis, inflammation, and hypertrophy markers Tgfβ1, Mcp1, Mmp9, and βmhc, suggesting that space-type IR may induce the cardiac remodeling processes that are commonly associated with diastolic dysfunction. IR groups showing statistical significance were modeled to calculate the Relative Biological Effectiveness (RBE) and Radiation Effects Ratio (RER). The observed dose-response shape did not indicate a lower threshold at these IR doses. A single full-body IR at doses of 100–200 cGy for γ-IR, and 50–100 cGy for simGCRsim-IR decreases the global LV systolic function in WT mice as early as 14 and 28 days after exposure, and at 660 days post IR. Interestingly, there is an intermediate time point (365 days) where the impairment in LV function is observed. These findings do not exclude the possibility of increased acute or degenerative cardiovascular disease risks at lower doses of space-type IR, and/or when combined with other space travel-associated stressors such as microgravity.

The space radiation (IR) environment contains high charge and energy (HZE) nuclei emitted from galactic cosmic rays with the ability to overcome current shielding strategies, posing increased IR-induced cardiovascular disease risks for astronauts on prolonged space missions. Little is known about the effect of 5-ion simplified galactic cosmic ray simulation (simGCRsim) exposure on left ventricular (LV) function. Three-month-old, age-matched male Apolipoprotein E (ApoE) null mice were irradiated with 137Cs gamma (γ; 100, 200, and 400 cGy) and simGCRsim (50, 100, 150 cGy all at 500 MeV/nucleon (n)). LV function was assessed using transthoracic echocardiography at early/acute (14 and 28 days) and late/degenerative (365, 440, and 660 days) times post-irradiation. As early as 14 and 28-days post IR, LV systolic function was reduced in both IR groups across all doses. At 14 days post-IR, 150 cGy simGCRsim-IR mice had decreased diastolic wall strain (DWS), suggesting increased myocardial stiffness. This was also observed later in 100 cGy γ-IR mice at 28 days. At later stages, a significant decrease in LV systolic function was observed in the 400 cGy γ-IR mice. Otherwise, there was no difference in the LV systolic function or structure at the remaining time points across the IR groups. We evaluated the expression of genes involved in hemodynamic stress, cardiac remodeling, inflammation, and calcium handling in LVs harvested 28 days post-IR. At 28 days post-IR, there is increased expression of Bnp and Ncx in both IR groups at the lowest doses, suggesting impaired function contributes to hemodynamic stress and altered calcium handling. The expression of Gals3 and β-Mhc were increased in simGCRsim and γ-IR mice respectively, suggesting there may be IR-specific cardiac remodeling. IR groups were modeled to calculate the Relative Biological Effectiveness (RBE) and Radiation Effects Ratio (RER). No lower threshold was determined using the observed dose-response curves. These findings do not exclude the possibility of the existence of a lower IR threshold or the presence of IR-induced cardiovascular disease (CVD) when combined with additional space travel stressors, e.g., microgravity.

OBJECTIVE:In schizophrenia, somatostatin (SST) and parvalbumin (PV) mRNA levels are lower in the dorsolateral prefrontal cortex (DLPFC), but it remains unclear whether these findings reflect lower transcript levels per neuron, fewer neurons, or both. Distinguishing among these alternatives has implications for understanding the pathogenesis of, and developing new treatments for, DLPFC dysfunction in schizophrenia.METHODS:To identify SST and PV neurons in postmortem human DLPFC, the authors used fluorescent in situ hybridization to label cells expressing two transcripts not altered in schizophrenia: vesicular GABA transporter (VGAT; a marker of all GABA neurons) and SOX6 (a marker of only SST and PV neurons). In cortical layers 2 and 4, where SST and PV neurons, respectively, are differentially enriched, levels of SST and PV mRNA per neuron and the relative densities of SST-, PV-, and VGAT/SOX6-positive neurons were quantified.RESULTS:In individuals with schizophrenia, mRNA levels per positive neuron were markedly and significantly lower for SST in both layers (effect sizes >1.48) and for PV only in layer 4 (effect size=1.14) relative to matched unaffected individuals. In contrast, the relative densities of all SST-, PV-, or VGAT/SOX6-positive neurons were unaltered in schizophrenia.CONCLUSIONS:Novel multiplex fluorescent in situ hybridization techniques permit definitive distinction between cellular levels of transcripts and the presence of neurons expressing those transcripts. In schizophrenia, pronounced SST and PV mRNA deficits are attributable to lower levels of each transcript per neuron, not fewer neurons, arguing against death or abnormal migration of these neurons. Instead, these neurons appear to be functionally altered and thus amenable to therapeutic interventions.

In schizophrenia, GABA neurons expressing the neuropeptide somatostatin (SST) are markedly affected in the dorsolateral prefrontal cortex (DLPFC). Cortical SST neurons comprise a heterogenous group of neurons, and the subtype(s) that are affected in schizophrenia are unknown. One SST subtype, distinguished by the expression of chondrolectin (CHODL), resides primarily in the subcortical white matter (sWM), contains high levels of neuropeptide Y (NPY) and nitric oxide synthase 1 (NOS1) and regulates neurovascular coupling (NVC). In addition, CHODL-SST neurons are the near-exclusive subtype of SST neuron found in the striatum. Here, we investigated this SST neuron subtype in these two brain regions in schizophrenia.

Human genetics strongly support the involvement of synaptopathy in psychiatric disorders. However, trans-scale causality linking synapse pathology to behavioral changes is lacking. To address this question, we examined the effects of synaptic inputs on dendrites, cells, and behaviors of mice with knockdown of SETD1A and DISC1, which are validated animal models of schizophrenia. Both models exhibited an overrepresentation of extra-large (XL) synapses, which evoked supralinear dendritic and somatic integration, resulting in increased neuronal firing. The probability of XL spines correlated negatively with working memory, and the optical prevention of XL spine generation restored working memory impairment. Furthermore, XL synapses were more abundant in the postmortem brains of patients with schizophrenia than in those of matched controls. Our findings suggest that working memory performance, a pivotal aspect of psychiatric symptoms, is shaped by distorted dendritic and somatic integration via XL spines.

Importance Individuals with schizophrenia (SZ) exhibit pronounced deficits in somatostatin (SST) messenger RNA (mRNA) levels in the dorsolateral prefrontal cortex (DLPFC). Molecularly distinct subtypes of SST neurons, located in the superficial and deep zones of the DLPFC, are thought to contribute to different functional processes of this region; understanding the specificity of SST alterations in SZ across these zones could inform the functional consequences of those alterations, including cognitive impairments characteristic of SZ.Objective To quantify mRNA levels of SST and related neuropeptides in the DLPFC in individuals with SZ, bipolar disorder (BPD), or major depressive disorder (MDD) and unaffected comparison individuals.Design, Setting, and Participants This case-control study, conducted from January 20, 2020, to March 30, 2022, used postmortem brain tissue specimens previously obtained from individuals with SZ, MDD, or BPD and unaffected individuals from a community population through 2 medical examiners' offices. Demographic, clinical, and educational information was ascertained through psychological autopsies.Exposures Diagnosis of SZ, BPD, or MDD.Main Outcome and Measures The main outcome was levels of SST and related neuropeptide mRNA in 2 DLPFC zones, examined using laser microdissection and quantitative polymerase chain reaction or fluorescent in situ hybridization (FISH). Findings were compared using educational attainment as a proxy measure of premorbid cognition.Results A total of 200 postmortem brain specimens were studied, including 65 from unaffected comparison individuals (42 [65%] male; mean [SD] age, 49.2 [14.1] years); 54 from individuals with SZ (37 [69%] male; mean [SD] age, 47.5 [13.3] years); 42 from individuals with MDD (24 [57%] male; mean [SD] age, 45.6 [12.1] years); and 39 from individuals with BPD (23 [59%] male; mean (SD) age, 46.2 [12.5] years). Compared with unaffected individuals, levels of SST mRNA were lower in both superficial (Cohen d, 0.68; 95% CI, 0.23-1.13; P = .004) and deep (Cohen d, 0.60; 95% CI, 0.16-1.04; P = .02) DLPFC zones in individuals with SZ; findings were confirmed using FISH. Levels of SST were lower only in the superficial zone in the group with MDD (Cohen d, 0.58; 95% CI, 0.14-1.02; P = .12), but the difference was not significant; SST levels were not lower in either zone in the BPD group. Levels of neuropeptide Y and tachykinin 1 showed similar patterns. Neuropeptide alterations in the superficial, but not deep, zone were associated with lower educational attainment only in the group with SZ (superficial: adjusted odds ratio, 1.71 [95% CI, 1.11-2.69]; P = .02; deep: adjusted odds ratio, 1.08 [95% CI, 0.64-1.84]; P = .77).Conclusions and Relevance The findings revealed diagnosis-specific patterns of molecular alterations in SST neurons in the DLPFC, suggesting that distinct disease processes are reflected in the differential vulnerability of SST neurons in individuals with SZ, MDD, and BPD. In SZ, alterations specifically in the superficial zone may be associated with cognitive dysfunction.