Haimin Zhang; Jianping Zhang & Maoyun Yuan

Parvalbumin (PV)-positive interneurons play a critical role in modulating cognitive processes. The orexin system is also implicated in the regulation of cognitive function. To provide morphological evidence regarding the neural connection between PV and orexin neurons and their involvement in cognitive function regulation in cognitive function-related brain regions, a double-label immunohistochemical staining for PV and orexin was employed to investigate overlapping distributions of PV and orexin immunoreactivity in these brain regions of the mouse. Somata of PV and orexin neurons were co-localized exclusively in the lateral hypothalamic area (LH), where their fibers were also closely intermingled. In other regions, there were different degrees of contact and overlap between PV neurons and fiber projections of orexin neurons. Within the frontal lobe and temporal lobe, slight-to-moderate density overlap was observed in the orbitofrontal cortex (OFC), medial prefrontal cortex (mPFC), temporal association cortex (TeA) and perirhinal cortex (PRh), while overlap was relatively sparse in the medial entorhinal cortex (MEnt). Low density overlap was detected in the caudate putamen (CPu). Within the basal forebrain (BF), the accumbens nucleus (Acb), medial septal nucleus (MS), nucleus of the vertical limb of the diagonal band (VDB), nucleus of the horizontal limb of the diagonal band (HDB), ventral pallidum (VP), substantia innominata (SI) and magnocellular preoptic nucleus (MCPO) had different degrees of overlap. Slightly overlapping distributions were noted in the field CA1 of hippocampus (CA1) and dentate gyrus (DG) of the hippocampus (HPC). Low density overlap was found in the basolateral amygdaloid nucleus, anterior part (BLA) and central amygdaloid nucleus (Ce) of the amygdala. Within the diencephalon, varying degrees of contact and overlap were observed in the reuniens thalamic nucleus (Re), anterior hypothalamic area (AHA), mediodorsal thalamic nucleus (MD), paraventricular thalamic nucleus (PVT) and zona incerta (ZI). Within the brainstem, in the periaqueductal gray (PAG) and latero-dorsal tegmental nucleus (LDTg), a large number of intermingled orexin fibers and PV branched fine fibers were detected, and overlap was also observed in the ventral tegmental area (VTA). Overall, somata of PV and orexin neurons were co- localized substantially in LH. PV neurons and the fiber projections of orexin neurons were contacted and intermingled to varying degrees in other brain regions implicated in cognitive function regulation. These findings provide morphological evidence supporting a co- regulatory role for the PV and orexin systems in modulating cognitive function.

KEY WORDS: Parvalbumin Orexin; Cognitive function; Memory; Immunohistochemistry.

ZHANG, H.; ZHANG, J. & YUAN, M. Overlapping distributions of parvalbumin and orexin immunoreactivity in mouse brain regions associated with cognitive function. Int. J. Morphol., 44(1):291-303, 2026.