COLOCALIZATION OF TYROSINE-HYDROXYLASE AND FOS IN THE MALE SYRIAN-HAMSTER BRAIN FOLLOWING DIFFERENT STATES OF AROUSAL

Tn an investigation of the role that central tyrosine hydroxylase- (TH ) containing neurons play in copulation in the male Syrian hamster, th e induction of Fos protein was used as an index of neuronal activation . With a double immunoperoxidase technique, the activation of TH neuro ns was compared in hamsters from three experimental groups: (1) mated in a new cage; (2) handled controls placed into a new cage, and (3) un handled controls. Although mating selectively induces Fos production i n the medial amygdaloid nucleus (Me), more than half of the TH neurons in Me (a region outside of the classical catecholamine systems) expre ssed Fos equally in all of the experimental groups. In the paraventric ular hypothalamic nucleus (PVN), TH neurons were activated equivalentl y in mated and handled control animals compared to unhandled controls. TH neurons in the nucleus of the solitary tract (NST) were also activ ated in handled control animals, and mating further enhanced the level of Fos immunostaining in these neurons above both groups of nonmated animals. Although not quantified, co-localization of Fos and TH was al so observed in all experimental groups in the olfactory bulbs and the interfascicular nucleus, and in the horizontal limb of the diagonal ba nd of Broca and the cerebral cortex, regions which contain TH neurons but are not part of the classically described TH cell groups. Few, if any, TH neurons in other catecholaminergic brain regions, such as the substantia nigra and locus coeruleus, produced Fos in any of the exper imental groups. These results suggest that TH neurons in the PVN and N ST may be activated during different states of arousal, and that noncl assical TH neurons in the amygdala produce high levels of Fos even in unstimulated animals. (C) 1994 John Wiley and Sons, Inc.