ABSTRACT The study of gustatory pathways from the periphery to the brain offers valuable insights into the neural mechanisms underlying taste processing and foraging choices, particularly in ecologically and economically relevant species such as the honey bee, Apis mellifera . While the neural substrates of other sensory modalities in bees, notably olfaction and vision, have been thoroughly characterized, the organization principles of gustatory pathways in the primary gustatory center (the subesophageal zone, SEZ) and brain of this species remain largely unexplored. Using anterograde mass staining with dextran‐coupled fluorescent tracers applied into the main gustatory appendages (antennae, mouthparts, and foreleg tarsi), we identified the projection areas of their sensory afferents within the SEZ. Our results show that sensory circuits are confined to specific, distinct regions of the SEZ, suggesting the presence of somatotopic “maps” corresponding to the different appendages. Overlaps between projections, reflecting potential information exchange between appendicular domains in the SEZ, were most evident among inputs originating from similar appendages (e.g., between mouthparts—proboscis and mandibles) and were limited between domains of different appendages (e.g., antennae and mouthparts). We also confirm the subesophageal‐calycal tract (SCT) as the main output of the SEZ. Combined retrograde staining of the SCT and anterograde staining of taste appendages revealed that SCT dendrites overlap specifically with sensory input from the maxillae in the SEZ. The functional significance of these findings is discussed in the context of gustatory information processing during bee feeding behavior, and the results are considered within a comparative framework across insect taxa.
ABSTRACT The superior colliculus (SC) is extensively connected with cortical and subcortical nuclei to facilitate a range of cognitive and sensorimotor functions. Efferent projections from the SC vary by originating layer and topographic location. The present study identifies an additional determinant of efferent connectivity: released neurotransmitter. We show that long‐range GABAergic and glutamatergic projection neurons produce distinct connectivity patterns in the mouse diencephalon, midbrain, and hindbrain. Targets strongly innervated by inhibitory vGAT+ neurons included the lateral dorsal, reuniens, anterior pretectal, and red nuclei, as well as the inferior colliculus. Targets of weaker vGAT+ innervation included the lateral habenula, ventral anterior–lateral complex, and reticular nucleus. In contrast, strongly innervated targets of excitatory vGlut2+ projections included the ventral medial, parafascicular, and tegmental reticular nuclei, whereas weaker innervation was present in the central medial intralaminar nucleus as well as in several contralateral thalamic and hindbrain nuclei. In shared efferent targets, vGAT+ and vGlut2+ projections often innervated different subregions or differed in cross‐hemispheric connections, notably in the zona incerta, periaqueductal gray, and lateral posterior, pedunculopontine, pontine reticular, and tegmental reticular nuclei. These results collectively demonstrate an additional dimension of complexity in SC efferent connectivity in mice. Inhibitory projections may facilitate SC‐mediated functions through a number of mechanisms independently of, or in concert with, excitatory projections. Future work examining the functional roles of SC long‐range inhibition stands to elucidate these mechanisms and their contributions to behavior.
ABSTRACT The inner ears of teleosts are structurally diverse, reflecting the crucial role of audition in sound detection, balance, and social communication within each species’ ecological niche. However, very little is known about the inner ear morphology of large pelagic teleosts. This study investigates the functional morphology of the inner ears of southern bluefin tuna Thunnus maccoyii , using scanning electron microscopy and magnetic resonance imaging, and examines the auditory sensory epithelia (maculae) of the three otolithic end organs (saccule, lagena, and utricle). The results show the inner ears of T. maccoyii are enveloped in compact otic capsules, cartilage‐like semicircular canals, and an interaural angle (35° from the midline) between the left and right saccules. The hair cell types are found to be heterogeneously distributed, where hair cell types with longer kinocilia lie along the periphery of the maculae, while the hair cell type with shorter kinocilium lies along the center of the maculae. Six groups of hair cells with opposing orientations are found in the saccular macula, where each opposing orientation group is innervated by separate rami of the VIIIth cranial nerve. The mean hair cell densities of the saccule, lagena, and utricle are 20,400, 39,300, and 36,400 mm −2 , respectively. The lagenar and utricular maculae are only partially covered by the overlying otolith. These findings contribute to the understanding of morphological adaptations of inner ears in pelagic teleosts and highlight the need for further research on structure‐function relationships in the auditory system of these species.
ABSTRACT Having the life cycle divided into a larval and an adult stage, each dwelling in a separate habitat, is advantageous since it prevents competition for resources and separates development and reproduction into different stages. In holometabolous insects, larval life is characterized by intense feeding, growth, and molting, whereas the adults constitute the reproductive and highly mobile stage. This review discusses how this switch in lifestyle is reflected in the neuroendocrine system and peptidergic signaling. Neuropeptides and peptide hormones (collectively NPHs) are important regulators of most aspects of development and daily life physiology and behavior. Thus, it is of interest to understand to what extent peptidergic neurons and NPHs signaling change as the behavior and physiology alters and diversifies after metamorphosis. Focusing on larvae and adults of Drosophila melanogaster , I discuss changes in signaling in peptidergic systems. As an example, the complement of neurosecretory cells and their NPHs remain largely the same over metamorphosis, yet their functional roles change to a large extent. In larvae, many NPHs are mainly associated with regulation of development and growth, whereas in adults they regulate reproduction and complex behavior. Common to the two stages, NPHs regulate feeding, metabolism, excretion, and avoidance behavior. Other peptidergic systems, such as components of the biological clock increase drastically in complexity, both in terms of neuron types and NPHs. In summary, NPH signaling is highly flexible and individual NPHs serve multiple functions, many of which are stage specific. This review provides comprehensive descriptions of structure and function of major peptidergic systems in larvae and adults.
ABSTRACT Aging is associated with progressive alterations in cortical circuits that compromise cognitive function. Somatostatin‐positive (SST+) Martinotti interneurons, which regulate pyramidal cell activity in the medial prefrontal cortex (mPFC), are particularly relevant for inhibitory control, yet their age‐related vulnerability remains poorly understood. Here, we examined GFP‐labeled SST+ interneurons in mice at 3, 9, and 16 months of age, focusing on neuronal density, dendritic arborization, and expression of NMDA receptor subunits GluN1 and GluN2B. Our findings reveal a significant decline in SST+ interneuron density in aged male mice, whereas female mice displayed an increase in dendritic arborization with age. Analysis of NMDA receptor puncta showed a reduction in GluN1 and GluN2B density with increased puncta size in older animals. Together, these findings reveal age‐ and sex‐dependent structural and molecular remodeling of SST+ interneurons in the mPFC.
