OBJECTIVE:Clozapine is underutilized in the management of treatment-resistant schizophrenia. To understand contributing factors, we analyzed the frequency and causes of clozapine discontinuations that occurred over a 15-year period in a clinical setting.METHOD:Data were extracted from computerized records and from mandatory termination reports for discontinuation events 1993-2007. The reasons for termination were analyzed.RESULTS:Over half of the patients (n = 183/320; 57%) had at least one discontinuation (median time 609 days). The two most common causes for discontinuation were non-adherence (35%) and side-effects (28%). Hematological side-effects accounted for 45% of all side-effect associated discontinuations; most such patients remained eligible for clozapine treatment, and a significant fraction remained on clozapine after rechallenge. Central nervous system side-effects accounted for 35% of side-effect induced discontinuations. General factors significantly associated with discontinuation were African American race, older age at initiation of clozapine and less improvement in psychiatric symptoms.CONCLUSION:In addition to anticipating and addressing causes of non-adherence, psychiatrists should consider clozapine rechallenge in eligible patients and implement measures to mitigate clozapine-associated sedation, seizures, and other side-effects. Future studies should particularly address why African American and older patients may be more likely to discontinue clozapine.

Using in vivo microdialysis, we examined whether tyrosine administration would potentiate the desipramine (DMI)-induced elevation of medial prefrontal cortex (MPFC) dopamine (DA) levels. DMI (10 or 20 mg/kg IP) increased MPFC DA levels but not DOPA accumulation. Tyrosine (12.5–100 μg/ml) administered by reverse microdialysis did not affect DMI-induced MPFC DA levels. The data support our hypothesis that DA synthesis must be significantly increased in order for administered tyrosine to increase extracellular DA levels.

Clozapine does not induce classical catalepsy. One explanation is that endogenous dopamine (DA) readily displaces clozapine from postsynaptic striatal DA receptors. If the latter were true, then depletion of striatal DA should permit clozapine to induce classical catalepsy. Rats received bilateral sham or 6-hydroxydopamine (6-OHDA) lesions of the striatum. Catalepsy using the bar test was assessed on days 21, 28 and 35 after i.p. vehicle, haloperidol (0.75 mg/kg) or clozapine (20 mg/kg). Brains were harvested on day 36 and striatal DA was assayed. A 97% depletion of striatal DA was associated with a significant increase in the duration of immobility after haloperidol or clozapine administration. Both in sham as well as in 6-OHDA lesioned animals, however, the duration of immobility was greater after haloperidol than after clozapine. Furthermore, clozapine-treated animals were hypotonic and did not show the classic rigidity of haloperidol catalepsy. While clozapine's low propensity to induce immobility in animals and extrapyramidal symptoms in man may depend in part on endogenous striatal DA, other mechanisms must also be involved.

It has been reported that tyrosine administration augments clozapine-induced dopamine (DA) release in the medial prefrontal cortex (MPFC). To characterize this effect and exclude possible confounds, we conducted a series of studies in which microdialysate collection started 24 h after probe implantation, a time at which most collected DA is thought to be impulse mediated. Tyrosine (25 or 50 mg/kg IP) administered 30 min after clozapine (10 mg/kg IP) augmented clozapine-induced MPFC but not striatal DA release. While tyrosine potentiation was also evident in both fasted animals and those with free access to food, the effective doses of tyrosine varied. We confirm that tyrosine administration can potentiate clozapine-induced MPFC DA release but note that the effect is not evident across all doses and conditions.

The beta-carboline FG-7142 exerts many stress-like effects in the adult rat, including the inhibition of locomotor exploration. However, comparable effects in immature animals have not been reported. Stress-like effects of FG-7142 are mediated via its inverse agonist actions on gamma-aminobutyric acid (GABA) receptors. GABA systems change considerably with development and GABA agonists such as diazepam have opposite behavioral actions in immature and adult rats. Accordingly, we compared FG-7142 effects on locomotor exploration in postweanling and adult rats. Postweanling male rats (24 days) and adult rats (90 days) received a single injection of vehicle or FG-7142 (15 mg/kg i.p.) and 15 min later were placed in photocell monitors for 1 h. Although postweanling animals traveled a smaller distance overall than adults, FG-7142 inhibited locomotor exploration to a similar degree in both groups. We conclude that FG-7142 exerts stress-like effects in postweanling rats and may be considered for use as a model of childhood stress.

Tyrosine uptake has been reported to differ across brain regions. However, such studies have typically been conducted over brief intervals and in anesthetized rats; anesthesia itself affects amino acid transport across the blood - brain barrier. To address these concerns, serum, brain tissue and in vivo microdialysate tyrosine levels were compared for 0 - 3 h after administration of tyrosine [0.138 - 1.10 mmol/kg intraperitoneally (i.p.)] to groups of awake rats. Serum and brain tissue tyrosine levels increased linearly with respect to dose. Basal tissue tyrosine levels varied significantly across brain regions [ medial prefrontal cortex ( MPFC), striatum, hypothalamus, and cerebellum], but the rate of tyrosine uptake was similar for hypothalamus, striatum and MPFC. For brain regions in which tyrosine levels in both microdialysate and tissue were assayed, namely MPFC and striatum, there was a high degree of correlation between tyrosine levels in tissue and in microdialysate. Increasing brain tyrosine levels had no effect on DA levels in MPFC microdialysate. We conclude that (i) regional differences in the response of dopamine neurons to systemic tyrosine administration cannot be attributed to pharmacokinetic factors; (ii) in vivo microdialysate provides an excellent index over time and across a wide range of tyrosine doses, of brain tissue tyrosine levels; and (iii) increases in brain tyrosine levels do not affect basal DA release in the MPFC.

R107474, 2-methyl-3-[2-(1,2,3,4-tetrahydrobenzo[4,5]furo[3,2-c]pyridin-2-yl)ethyl]-4H-pyrido[1,2-a]pyrimidin-4-one, was investigated using in vitro and in vivo receptor assays and proved to be a potent and relatively selective α2-adrenoceptor antagonist. Performed assays in vitro were inhibition of binding to a large number of neurotransmitter receptor sites, drug receptor binding sites, ion channel binding sites, peptide receptor binding sites, and the monoamine transporters in membrane preparations of brain tissue or of cells expressing the cloned human receptors. The compound has subnanomolar affinity for hα2A- and hα2C-adrenoceptors (Ki = 0.13 and 0.15 nM, respectively) and showed nanomolar affinity for the hα2B-adrenoceptors and 5-hydroxytryptamine7 (h5-HT7) receptors (Ki = 1 and 5 nM, respectively). R107474 interacted weakly (Ki values ranging between 81 and 920 nM) with dopamine-hD2L, -hD3 and -hD4, h5-HT1D-, h5-HT1F-, h5-HT2A-, h5-HT2C-, and h5-HT5A receptors. The compound, tested up to 10 μM, interacted only at micromolar concentrations or not at all with any of the other receptor or transporter binding sites tested in this study. In vivo α2A- and α2C-adrenoceptor occupancy was measured by ex vivo autoradiography 1 h after subcutaneous (sc) administration of R107474. It was found that R107474 occupies the α2A- and α2C-adrenoceptors with an ED50 (95% confidence limits) of 0.014 mg/kg sc (0.009–0.019) and 0.026 mg/kg sc (0.022–0.030), respectively. Radiolabeled 2-methyl-3-[2-([1-11C]-1,2,3,4-tetrahydrobenzo[4,5]furo[3,2-c]pyridin-2-yl)ethyl]-4H-pyrido[1,2-a]pyrimidin-4-one ([11C]R107474) was prepared and evaluated as a potential positron emission tomography (PET) ligand for studying central α2-adrenoceptors. [11C]R107474 was obtained via a Pictet–Spengler reaction with [11C]formaldehyde in 33 ± 4% overall decay-corrected radiochemical yield. The total synthesis time was 55 min and the specific activity was 24–28 GBq/μmol. The biodistribution of [11C]R107474 in rats revealed that the uptake of [11C]R107474 after in vivo intravenous administration is very rapid; in most tissues (including the brain) it reaches maximum concentration at 5 min after tracer injection. In agreement with the known distribution of α2-adrenoceptors in the brain, highest uptake of radioactivity was observed in septum (3.54 ± 0.52 ID/g, 5 min pi) and entorhinal cortex (1.57 ± 0.10 ID/g, 5 min pi). Tissue/cerebellum concentration ratios for septum (5.38 ± 0.45, 30 min pi) and entorhinal cortex (3.43 ± 0.24, 30 min pi) increased with time due to rapid uptake followed by a slow washout. In vivo blocking experiments using the non-selective α2-adrenoceptor antagonist mirtazapine demonstrated specific inhibition of [11C]R107474 binding in selective brain areas. The receptor binding profile of mirtazapine is reported and the selectivity of inhibition of binding is discussed. These results suggest that [11C]R107474 deserves further investigation as a potential radioligand for studying α2-adrenoceptors using PET.

A high-performance liquid chromatographic method for measuring neutral amino acids in rat sera, brain tissues, and perfusates was developed by using o-phthalaldehyde sulfite as a pre-column derivatization reagent. With the present method, it was possible to separate the neutral amino acids within a single run in 25 min, while the acidic amino acids were eluted near or at the solvent front. The recovery was above 88.8% with a relative standard deviation (RSD) below 4.2%. The within- and between-day assay reproducibility for the determination of rat serum amino acids showed RSDs below 1.35 and 7.61%, respectively. In the present study, the neutral amino acids were assayed with high sensitivity, accuracy and good reproducibility in a relatively short time and on a small sample size.

A method for selectively activating the dopaminergic field of the prefrontal cortex would be highly useful for studies of mesocortical dopamine systems. When a rat ('witness' rat) is exposed to a rat that is undergoing footshock, prefrontocortical dopamine metabolism is selectively increased in the witness rat. Since the anxiogenic beta-carboline FG 7142 mimics many of the effects of footshock, we hypothesized that exposure of a witness-rat to a rat treated with FG 7142 would also increase dopamine metabolism in the prefrontal cortex. We found that while as expected, FG 7142 itself increased prefrontal cortex dopamine metabolism, there was no significant change in dopamine metabolism in the witness rat. Thus exposure to a rat treated with FG 7142 does not selectively activate the mesocortical dopamine system.

Much of the current literature from both neuroimaging and post mortem studies points to a reduction in intracranial size and cerebrum in schizophrenia. Intriguingly, there is also evidence for reduced extracranial size in infants at high risk for schizophrenia, while studies in adults with schizophrenia which have assessed head size have been inconclusive. Using head measures of circumference, length and width derived from caliper examination in both coronal and saggital planes, we examined head size in 46 male controls (mean age 42 6 9 years; 20 Caucasian, 26 African American) and 44 patients (mean age 40 6 9 years; 18 Caucasian, 26 African American) with DSM-IV schizophrenia. In a linear regression model which entered race and diagnosis as independent factors and stature and elbow breadth as covariates, we found no evidence for reduced extracranial size in schizophrenia. These data suggest that the process(es) which underlie smaller brains in schizophrenia do not produce a corresponding reduction in head size.

Despite multiple lines of investigation the effect of neuroleptics on glutamate-mediated neurotransmission remains controversial. To study the effects of typical and atypical neuroleptics on selected parameters of glutamate-mediated neurotransmission, male Sprague-Dawley rats were randomly assigned to a 21-day oral treatment course with vehicle, haloperidol (HDL), or clozapine (CLZ). Coronal slices of rat brain were then incubated with tritiated ligands to measure NMDA, AMPA, and kainate receptor, and glutamate reuptake site density. Regions of interest included the frontal cortex, anterior cingulate cortex, dorsal striatum, ventral striatum, and the nucleus accumbens. CLZ increased the density of AMPA receptors significantly in the frontal and anterior cingulate cortices compared with normal controls. In the dorsal and ventral striatum, and nucleus accumbens as a whole, CLZ-treated rats had a higher AMPA receptor density compared with both the HDL- and vehicle-treated controls. Additionally, within the nucleus accumbens, CLZ-treated rats had a higher density of AMPA receptors compared with the HDL group in the core, and at trend level in the shell. There was a group by region interaction for NMDA receptor density, primarily reflecting the tendency of HDL treated rats to have high receptor densities in the frontal and anterior cingulate cortices. Kainate receptors and glutamate reuptake site densities did not differ significantly across groups. These results suggest a critical role for glutamate in the mediation of atypical antipsychotic drug action in anatomically-specific regions, and further encourage the investigation of glutamate neurotransmitter systems in schizophrenia. Published 1999 Wiley-Liss, Inc.

Neonatal excitotoxic hippocampal damage in the rat results in postpubertal onset of a variety of abnormal behaviors related to excessive dopaminergic transmission in the mesolimbic/nigrostriatal system, and thus may be considered an animal model of some aspects of schizophrenia. Because sensorimotor gating is impaired in adult patients with schizophrenia and in rats with experimentally induced mesolimbic dopamine hyperactivity, the present experiments investigated the effects of neonatal (postnatal day 7, PD7) ibotenic acid (3 µg) lesions of the ventral hippocampus (VH) on the amplitude and prepulse inhibition (PPI) of acoustic startle in prepubertal (PD35) and postpubertal (PD56) rats. Startle was elicited using 105 and 118-dB pulses alone or preceded by 4, 8, or 16 dB above-background prepulses in rats treated with vehicle or apomorphine (APO; 0.025 or 0.1 mg/kg SC). At PD35, PPI in VH-lesioned rats did not differ significantly from these measures in sham operated rats. Apomorphine significantly increased startle amplitude and reduced PPI in both sham operated and VH-lesioned rats at PD35. At PD56, startle amplitude in VH-lesioned rats was not significantly different from controls, but PPI was reduced significantly compared to controls. Ventral hippocampus lesioned rats also exhibited an exaggerated reduction in PPI after treatment with APO. These findings provide further evidence of postpubertal impairments that may be related to increased mesolimbic dopamine transmission and receptor sensitivity in rats with neonatal hippocampal damage, and provide further support for the fidelity of this animal model of schizophrenia.

Sensorimotor gating of the startle reflex is impaired in humans with schizophrenia and in rats after mesolimbic D2 dopamine receptor activation. The loss of startle gating after D2 activation in rats has been used as an animal model of impaired sensorimotor gating in schizophrenia, because the ability of antipsychotics to restore startle gating in D2-activated rats correlates significantly with antipsychotic clinical potency. Substantial evidence indicates that the pathophysiology of schizophrenia includes structural and functional deficits in prefrontal and temporal regions, particularly the dorsolateral prefrontal cortex and the hippocampus and parahippocampal gyrus. The present study assessed startle gating in adult rats after ibotenic acid lesions of the medial prefrontal cortex or ventral hippocampus. Medial prefrontal cortex lesioned rats exhibited normal startle amplitude and normal sensorimotor gating, as reflected by prepulse inhibition (PPI) of the startle reflex. Hippocampus lesioned rats exhibited elevated startle amplitude, and similar to rats with medial prefrontal cortex lesions, did not show significant changes in basal PPI. Low doses of the mixed dopamine agonist apomorphine did not significantly reduce PPI in sham lesioned rats, but significantly disrupted PPI in both medial prefrontal cortex- and ventral hippo-campus lesioned rats. These data are consistent with the hypothesis that cell damage in frontal and temporal cortex increases the sensitivity to the sensorimotor gating-disruptive effects of dopamine receptor activation.

Effects of prefrontal cortical or hippocampal excitotoxic lesions on behavioral parameters related to dopaminergic transmission in the basal ganglia were investigated in the rat. We examined haloperidol-induced catalepsy and apomorphine-induced stereotypic behaviors after ibotenic acid lesions of the medial prefrontal cortex (MPFC), dorsal (DH), or ventral hippocampus (VH) in adult rats. Haloperidol-induced (1 mg/kg) catalepsy was decreased in rats with either MPFC or VH but not DH lesions. While both DH and VH lesioned animals demonstrated a reduction in apomorphine-induced (0.75 mg/kg) stereotypic behaviors, the VH lesioned animals also showed an enhancement of locomotor activity. MPFC lesioned rats tended towards potentiation of stereotypic behaviors and reduced locomotion after apomorphine administration. These data indicate that loss of prefrontal cortical or hippocampal modulation leads to an enhancement of DA transmission within the basal ganglia, though the pattern of augmentation depends on the area lesioned.

The present study was undertaken to examine the effect of 5-HT2A receptor antagonists on MK-801 (5-methyl-10,11-dihydro-5H-dibenzo (a,d) cyclohepten-5,10-imine)-induced stereotypy and hyperlocomotion. MK-801 (0.1, 0.25 and 0.5 mg/kg) dose-dependently increased stereotypy and locomotion in mice. The 5-HT2A receptor antagonists, ketanserin (2.5, 5 and 10 mg/kg) and ritanserin (0.5, 1 and 2 mg/kg), dose-dependently blocked MK-801 (0.5 mg/kg)-induced hyperlocomotion. Only the higher dose (2 mg/kg) of seganserin could block locomotor activity. Similarly, ketanserin (2.5, 5 and 10 mg/kg), ritanserin (1 and 2 mg/kg) and seganserin (0.5, 1 and 2 mg/kg) dose-dependently blocked MK-801 (0.5 mg/kg)-induced stereotypy. The results suggest the involvement of 5-HT2A receptors in MK-801-induced stereotypy and hyperlocomotion. The lack of effect on spontaneous locomotion further suggests that 5-HT2A receptor antagonists will be less prone to induce psychomotor side-effects.

Ten patients, who underwent computerized tomography (CT) study during evaluation for first episode schizophreniform psychosis were restudied an average of 7 years later. Of the 10 patients, 7 were found to carry a diagnosis of schizophrenia at follow-up. In this subgroup, there was no significant change in the mean ventricular brain ratio measure of cerebral ventricular size between the index and follow-up scans. These findings are consistent with the hypothesis that ventricular enlargement is present at the onset of schizophrenia and does not progress with duration of illness or treatment.

The effects of excitotoxic damage to both the medial prefrontal cortex (MPFC) and the ventral hippocampus (VH) on behaviors related to mesolimbic/nigrostriatal dopamine (DA) transmission were investigated in the rat. Locomotor activity in a novel environment, after injection of saline, and after d-amphetamine was assessed 2 and 4 weeks after ibotenic acid lesion of both MPFC and VH in adult rats. In addition, stereotypic behaviors and locomotion after apomorphine were evaluated 8 weeks after the lesion. Locomotor activity was significantly enhanced in all testing conditions in lesioned rats as compared with sham-operated animals, while oral stereotypic behaviors elicited by apomorphine were attenuated possibly because they were eclipsed by excessive locomotion. These data indicate that coexisting lesions of the MPFC and VH in adult rats produce potent and long-lasting effects on behaviors believed to be dependent primarily on the mesolimbic DA system. The profile of changes resembles more closely that observed after excitotoxic lesions of the VH alone rather than that after separate MPFC lesion.