Axon terminals containing CGRP-immunoreactivity form synapses with CRF- and Met-enkephalin-immunopositive neurons in the laterodorsal division of thebed nucleus of the stria terminalis in the rat

The lateral division of the bed nucleus of the stria terminalis (BSTL) is a n important forebrain structure that relays information between limbic stru ctures and the hypothalamus. The BSTL displays a very dense calcitonin gene -related peptide-immunoreactive (-ir) fiber terminal network, and contains a substantial number of the corticotropin releasing factor (CRF)-ir neurons . Several Met-enkephalin-ir perikarya have also been observed in the BSTL. The distributions of CRF- and Met-enkephalin-ir neurons and that of the cal citonin gene-related peptide (CGRP)-ir axon terminals overlap within the BS TL, suggesting synaptic connections between CRF- and Metenkephalin-ir neuro ns and axon terminals immunoreactive For CGRP. Double staining immunohistoc hemistry revealed that CGRP-ir axon terminals were within close proximity t o dendrites or perikarya of corticotropin releasing factor and Met-enkephal in-ir neurons. When viewed at the electron microscopic level, axodendritic or axosomatic synapses between CGRP-ir fiber terminals and neurons immunore active for CRF and Met-enkephalin were detected. Most of the CRF-ir neurons project to brainstem centers, which modulate the physiological changes acc ompanying stress, whereas the Met-enkephalin-ir perikarya are most likely i nterneurons that often colocalize with GABA. The parabrachial nucleus, a vi tal autonomic center, is the primary source of CGRP-ir fiber terminals to t he BSTL. The synaptic contacts between the CGRP axon terminals and CRF- and Met-enkephalin-ir neurons underlie the importance of connections between a utonomic brainstem centers and BSTL, which can be fundamental in the modula tory control of endocrine, physiological and behavioral responses during st ress. (C) 2001 Elsevier science B.V. All rights reserved.