A solitary cluster of parvalbumin-positive neurons - the PV1-nucleus - has been observed in the lateral hypothalamus of rodents. In the present study, we mapped the efferent connections of the rodent PV1-nucleus using non-specific antero- and retrograde tracers in rats, and chemoselective, Cre-dependent viral constructs in parvalbumin-Cre mice. In both species, the PV1-nucleus was found to project mainly to the periaqueductal grey matter (PAG), preponderantly ipsilateral. Indirectly in rats and directly in mice, a discrete, longitudinally- orientated cylindrical column of terminal fields (PV1-CTF) was identified ventrolateral to the aqueduct on the edge of the PAG. The PV1-CTF, which is particularly dense in the rostral portion, located in the supraoculomotor nucleus (Su3), is spatially interrupted over a short stretch at the level of the trochlear nucleus and abuts caudally on a second parvalbum in-positive (PV2) nucleus. The rostral and the caudal portions of the PV1-CTF consist of axonal endings that stem from scattered neurons throughout the PV1-nucleus. Minor terminal fields were identified in a crescentic column of the lateral PAG, as well as in the Edinger-Westphal-, the lateral habenular- and the laterodorsal tegmental nuclei. So far no obvious functions can be attributed to this small, circumscribed column ventrolateral to the aqueduct, the prime target of the PV1-nucleus.

A solitary, elongated cluster of parvalbumin-immunoreactive neurons has been previously observed in the rodent ventrolateral hypothalamus. However, the function of this so-called PV1 nucleus is unknown. In this article, we report the results of an unbiased, broad and in-depth molecular characterization of this small, compact group of neurons. The Allen Brain Atlas database of in situ hybridization was screened in order to identify genes expressed in the PV1-nucleus-containing area of the hypothalamus, and those that might be co-expressed with parvalbumin. Although GABA is the principal neurotransmitter in parvalbumin-expressing cells in various other brain areas, we found that PV1 neurons express the vesicular glutamate transporter (VGlut) VGlut2-encoding gene Slc17a6 and are negative for the glutamic acid decarboxylase 1 (GAD1) gene. These cells also express the mRNA for the neuropeptides Adcyap1 and possibly Nxph4, express several types of potassium and sodium channels, are under the control of the neurotransmitter acetylcholine, bear receptors for the glial-derived neurotrophic factor, and produce an extracellular matrix rich in osteopontin. The PV1 nucleus is thus composed of glutamatergic nerve cells, expressing some typical markers of long-axon, projecting neurons (e.g. VGlut2), but also co-expressing genes typical of short-axon GABA neurons (e.g. a variety of potassium channels). Hence, neurons of the PV1 nucleus combine physiological characteristics of interneurons with those of projection neurons.

A solitary cluster of parvalbumin-positive neurons-the PV1-nucleus-has been observed in the lateral hypothalamus of rodents. In the present study, we mapped the efferent connections of the rodent PV1-nucleus using non-specific antero-and retrograde tracers in rats, and chemoselective, Cre-dependent viral constructs in parvalbumin-Cre mice. In both species, the PV1-nucleus was found to project mainly to the periaqueductal grey matter (PAG), preponderantly ipsilateral. Indirectly in rats and directly in mice, a discrete, longitudinallyorientated cylindrical column of terminal fields (PV1-CTF) was identified ventrolateral to the aqueduct on the edge of the PAG. The PV1-CTF, which is particularly dense in the rostral portion, located in the supraoculomotor nucleus (Su3), is spatially interrupted over a short stretch at the level of the trochlear nucleus and abuts caudally on a second parvalbum in-positive (PV2) nucleus. The rostral and the caudal portions of the PV1-CTF consist of axonal endings that stem from scattered neurons throughout the PV1-nucleus. Minor terminal fields were identified in a crescentic column of the lateral PAG, as well as in the Edinger-Westphal-, the lateral habenularand the laterodorsal tegmental nuclei. So far no obvious functions can be attributed to this small, circumscribed column ventrolateral to the aqueduct, the prime target of the PV1-nucleus.

BackgroundThe role of microvascular endothelial cells in the brain is of importance in both healthy and diseased conditions. Various studies have reported heterogenicity in the phenotypical, morphological and molecular characteristics of endothelial cells in the different organs of the body. There is still not much known about the heterogenicity of the endothelial cells of the human brain microcirculation. This study was aimed at characterizing qualitatively the pattern of expression for endothelial cell markers for the microvessels within different regions of the brain.MethodsParaffin sections from different anatomical regions (precentral and postcentral gyrus, hippocampus, rhinal and visual cortex) of human formalin fixed brains (n=3) were stained immunohistochemically for endothelial cell markers, including CD31, claudin 5, von Willebrand Factor, E‐ selectin and P‐selectin.ResultsThe expression patterns of the markers was heterogenous in the different microvessels within the regions of the brain studied. The capillaries had the most positive expression among the different biomarkers especially for VWF and CD31 while the arterioles were most positive for the E‐Selectin marker. The density of of the stained microvessels were more in the white matter compared to the gray matter with the visual, rhinal and hippocampal regions showing high densities of the microvessels.ConclusionThe expression pattern of the different endothelial markers is heterogenous for the microvasculature within the different anatomical regions of the brain. This results indicate that the heterogenicity in microvascular endothelial cells contribute to functional differences in the different brain regions.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.