The Overlapping of Parvalbumin and Orexin Immunoreactivity in Mice Brain Regions Mediating Depressive Behaviors

There is a significant correlation between regulatory functions of orexin system and depressive symptoms.Parvalbumin (PV) interneurons, the main subtype of inhibitory g-aminobutyric acid (GABA) interneurons, are involved in the regulation of depression-like behaviors too.To provide several lines of evidence regarding neural connection between two types of neurons in the depression associated nuclei, a double-label immunohistochemical staining technique was employed to reveal overlap between PV and orexin immunoreactivity in the mouse brain.Medial prefrontal cortex (mPFC) mainly consists of the cingulate cortex, area 1 (Cg1), prelimbic cortex (PrL) and infralimbic cortex (IL), in which regions contained similar obvious overlap between orexin fibers and PV somas with axons.In the basal forebrain (BF), overlap was observed in the lateral septal nucleus, ventral part (LSV), the nucleus accumbens shell (AcbSh), bed nucleus of the stria terminalis, ventral division (BSTV), ventral pallidum (VP), central amygdaloid nucleus (Ce).In the diencephalon, besides the lateral hypothalamic area (LH) and dorsomedial hypothalamic nucleus (DM), in which two regions contained overlap between orexin positive perikarya with fibers and PV immunoreactivity, different densities of orexin and PV fibers were closely intermingled in the paraventricular hypothalamic nucleus (PVN), paraventricular thalamic nucleus (PVT), arcuate hypothalamic nucleus (Arc).In the brainstem, densities of intermixed orexin and PV fibers were from high to low in the dorsal raphe nucleus (DR), laterodorsal tegmental nucleus (LDTg), periaqueductal gray (PAG), lateral parabrachial nucleus (LPB), median raphe nucleus (MnR), and orexin buttons were embedded within PV fibers, as for the ventral tegmental area (VTA), overlap was observed between PV somas with axons and orexin fibers.Hence, PV and orexin neurons and its projections jointly target several brain regions involved in regulating depression, which provides anatomic evidence supporting coordinated PV/orexin actions within these brain regions.