Parvalbumin-positive Neurons in the Mouse A8 Region were Lesser than those in the Rat

Abstract

Dopaminergic neurons play crucial roles in various physiological functions, such as reward, goal-directed behavior, memory formation, and pain sensation. One of the main dopaminergic cell groups in the brain is located in the retrorubral field (RRF, A8 region). A recent electrophysiological study using rats revealed that distinct neurons within the A8 region respond to the different degrees of the threat and aversive stimuli, and that the RRF is the origin of neural signals for threat and aversive outcomes. However, neurochemical characterization of the constituents of the A8 region is not enough. The aim of this study is to determine the neurochemical characteristics of these A8 neurons. To examine the neurochemical cellular organization of the A8 region, we performed immunohistochemistry for two GABAergic neuronal markers, parvalbumin (PV) and neuronal nitric oxide synthase (nNOS), in relation to tyrosine hydroxylase, a marker of dopaminergic neurons. We observed that the number of PV-positive neurons in the mouse A8 region was lesser than in rats. Moreover, nNOS-positive neurons were not detected within the A8 region in either species. These results indicate that the neurochemical organization of the A8 region was distinct between mice and rats. In addition, the cellular composition of the A8 dopaminergic cell group was distinct from other dopaminergic cell groups, such as the A9 and A10 region, in both mice and rats. Understanding these differences among species and cell groups is worth noting for translating the results obtained with distinct animal models into a clinical application.