Detection of corticotropin-releasing hormone receptor 1 immunoreactivity in cholinergic, dopaminergic and noradrenergic neurons of the murine basal forebrain and brainstem nuclei--potential implication for arousal and attention.

Corticotropin-releasing hormone (CRH) interacts with noradrenergic, dopaminergic and cholinergic systems of the brain, and these interactions are thought to be of relevance for the stress response, anxiety-related behavior, and cognitive function. CRH mediates its central effects through two high-affinity membrane receptors, CRH receptor subtypes 1 and 2. It is however unclear at present whether cholinergic or catecholaminergic cells express these receptors themselves or whether the effects of CRH are indirectly mediated through interaction with other neurotransmitter systems. Therefore, this study investigated whether choline acetyltransferase immunoreactive neurons of the murine basal forebrain and brainstem nuclei, and tyrosine hydroxylase immunoreactive neurons located within the locus coeruleus, ventral tegmental area and substantia nigra co-express CRH receptor 1, employing a double-immunocytochemical procedure. Using an antibody against the C-terminus of the CRH type 1 receptor (CRH-R1), CRH-R1-like immunoreactivity was found in all cholinergic basal forebrain nuclei except the nucleus basalis magnocellularis. In particular, the diagonal band of Broca (vertical and horizontal limbs) showed a high degree of co-localization of CRH-R1 immunoreactivity and choline acetyltransferase immunoreactivity (both limbs >90%). A less intense immunoreactivity but still high rate of co-localization was detected in the cholinergic neurons of the medial septum (80%), while lowest co-localization was observed in choline acetyltransferase immunoreactive neurons of the substantia innominata (58%). An intermediate degree of co-localization (75%) was seen in the brainstem pedunculopontine tegmental nucleus, while the other major brainstem cholinergic nucleus, the laterodorsal tegmental nucleus, showed an even higher degree of choline acetyltransferase immunoreactivity-positive cells also immunoreactive for CRH-R1 (92%). All catecholaminergic structures studied displayed a pattern of CRH-R1 immunoreactivity strongly overlapping the pattern of tyrosine hydroxylase immunoreactivity. The intensity of the CRH-R1 signal was relatively low within the ventral tegmental area and the substantia nigra pars compacta, while the CRH-R1 signal was very intense and detected in almost all of the neurons of the locus coeruleus. These results clearly demonstrate that the cholinergic and catecholaminergic systems provide direct anatomical substrates for CRH action through the CRH-R1. These findings are of particular relevance for understanding the action of recently developed CRH-R1 antagonistic drugs which may offer a new therapeutic approach to treat stress-related disorders such as anxiety and depression and their concomitant alterations in arousal and cognitive functions.