Molecular architecture of excitatory and inhibitory neurons in the first gustatory relay

Abstract

Taste perception is a major determinant of food intake and is dynamically modulated by hunger and satiety signals across species. While the peripheral and cortical representations of taste sensory stimuli are well characterized, far less is known about how metabolic state shapes taste processing in subcortical structures such as the brainstem. The rostral nucleus of the solitary tract (rNTS) is the first central relay for gustatory input, yet how fasting remodels transcriptional programs in rNTS neurons remains poorly defined. To address this gap, we performed cell-type-specific bulk nuclear RNA sequencing of molecularly defined excitatory (Vglut2+) and inhibitory (Vgat+) rNTS neurons. We combined Cre-dependent Sun1-sfGFP nuclear tagging with fluorescence-activated nuclear sorting to profile each population in ad libitum-fed and 24-hour-fasted mice. The two populations were transcriptionally distinct and differed in their baseline complement of hunger- and metabolic-sensing genes. Fasting elicited a transcriptional response that was largely restricted to excitatory, Vglut2+, rNTS neurons, while the inhibitory population was minimally affected. In excitatory neurons, fasting reduced the expression of Gabrd, the {delta} subunit of the GABAA receptor that mediates extrasynaptic tonic inhibition, while leaving synaptic GABAA subunits and the glutamatergic or GABAergic neurotransmission machinery unchanged. RNAscope in situ hybridization confirmed Gabrd expression in Vglut2+ rNTS neurons and showed that Gabrd is also expressed in the non-Vglut2+ population; the cell-type specificity of the fasting response therefore reflects differential regulation of a shared gene rather than its restricted expression. Our results identify a cell-type-specific, state-dependent transcriptional signature in which fasting downregulates a mediator of tonic GABAergic inhibition in excitatory rNTS neurons, providing a candidate substrate for the metabolic modulation of taste processing within the brainstem. HighlightsO_LIExcitatory and inhibitory rNTS neurons are intermingled, not spatially segregated, in rNTS C_LIO_LIVglut2+ and Vgat+ rNTS nuclear transcriptomes are distinct at baseline C_LIO_LIFasting reshapes the Vglut2+ transcriptome but leaves Vgat+ neurons largely unchanged C_LIO_LIFasting downregulates Gabrd, a mediator of tonic inhibition, in Vglut2+ neurons C_LI