The hypothalamus contains catecholaminergic neurons marked by the expression of tyrosine hydroxylase (TH). As multiple chemical messengers coexist in each neuron, we determined if hypothalamic TH-immunoreactive (ir) neurons express vesicular glutamate or GABA transporters. We used Cre/loxP recombination to express enhanced GFP (EGFP) in neurons expressing the vesicular glutamate (vGLUT2) or GABA transporter (vGAT), then determined whether TH-ir neurons colocalized with native EGFPVglut2- or EGFPVgat-fluorescence, respectively. EGFPVglut2 neurons were not TH-ir. However, discrete TH-ir signals colocalized with EGFPVgat neurons, which we validated by in situ hybridization for Vgat mRNA. To contextualize the observed pattern of colocalization between TH-ir and EGFPVgat, we first performed Nissl-based parcellation and plane-of-section analysis, and then mapped the distribution of TH-ir EGFPVgat neurons onto atlas templates from the Allen Reference Atlas (ARA) for the mouse brain. TH-ir EGFPVgat neurons were distributed throughout the rostrocaudal extent of the hypothalamus. Within the ARA ontology of gray matter regions, TH-ir neurons localized primarily to the periventricular hypothalamic zone, periventricular hypothalamic region, and lateral hypothalamic zone. There was a strong presence of EGFPVgat fluorescence in TH-ir neurons across all brain regions, but the most striking colocalization was found in a circumscribed portion of the zona incerta (ZI)—a region assigned to the hypothalamus in the ARA—where every TH-ir neuron expressed EGFPVgat. Neurochemical characterization of these ZI neurons revealed that they display immunoreactivity for dopamine but not dopamine β-hydroxylase. Collectively, these findings indicate the existence of a novel mouse hypothalamic population that may signal through the release of GABA and/or dopamine.

, , , , , ,
Journal of Comparative Neurology
Department of Neuroscience

Negishi, K. (Kenichiro), Payant, M.A. (Mikayla A.), Schumacker, K.S. (Kayla S.), Wittmann, G. (Gabor), Butler, R.M. (Rebecca M.), Lechan, R.M. (Ronald M.), … Chee, M. (2020). Distributions of hypothalamic neuron populations coexpressing tyrosine hydroxylase and the vesicular GABA transporter in the mouse. Journal of Comparative Neurology. doi:10.1002/cne.24857