Mapping Fos-immunoreactive neurons activated by intra-oral infusion of quinine, sucrose or water throughout the brain of B6 mice

Fos immunohistochemistry was used to identify neurons in taste-related brain areas throughout the B6 mouse brain activated by intra-oral (IO) infusion of 3.0 mM quinine hydrochloride (Q), 1.0 M sucrose (S) or filtered water (W). IO infusion of Q and S elicited more Fos-immunoreactive (Fos-IR) neurons than W in the central medial (CM) and dorsomedial (DM) subareas of the parabrachial nucleus (PBN) and the central medial (CeM) amygdala (ps < 0.05). Infusion of Q led to more Fos expression than W in the central lateral (CL) PBN and the parvocellular reticular formation (PCRT; ps < 0.05). The only area where IO infusion of Q and S elicited a different number of Fos-IR neurons was the PCRT which responded more to Q (p < 0.05). Cluster analysis of the number of Fos-IR neurons in all 29 taste-related nuclei and subareas examined revealed that populations of neurons distributed among these brain regions respond best to Q, S or both Q and S. Specifically, the Q-best cluster included more posterior structures like the nucleus of the solitary tract, RT and most of the PBN. The S-best cluster included more anterior structures like the bed nucleus of the stria terminalis, nucleus accumbens and orbitofrontal cortex. And, the cluster of areas that responded better to Q and S than W included the amygdala, gustatory and piriform cortices and a few PBN subareas. Therefore, the data suggest that collections of neurons among taste-responsive brain areas are important for distinguishing Q and S from water as well as identifying the specific tastant.