CONTRIBUTION OF BED NUCLEUS OF THE STRIA TERMINALIS TO THE CARDIOVASCULAR-RESPONSES ELICITED BY STIMULATION OF THE AMYGDALA

Anatomical and physiological studies were done in the rat to investiga te the possibility that the cardiovascular responses elicited by stimu lation of central nucleus of the amygdala (ACe) were mediated via proj ections to bed nucleus of the stria terminalis (BST). In the first ser ies, to determine the distribution of neurons in ACe that projected to the cardiovascular region of BST, the retrograde tracer Fluorogold (F G) or rhodamine latex micro-beads (Rd) were injected into BST. FG and Rd injections that overlapped the cardiovascular region of BST resulte d in retrogradely labelled neurons throughout the amygdala. In ACe, re trogradely labelled neurons were observed primarily in the lateral sub division of the rostral ACe compared to the caudal ACe. The medial sub division of ACe was found to have very few retrogradely labelled neuro ns. In the second series, the effect of either blocking synaptic trans mission in BST with CoCl2, chemical lesions of BST with ibotenic acid (IBO), or electrolytic lesions of BST on the depressor response elicit ed by either electrical or chemical stimulation of ACe was investigate d in the chloralose-anesthetized, artificially ventilated and paralyse d rat. Microinjections of CoCl2 into BST significantly attenuated the depressor responses to stimulation of the rostral components of the la teral subnucleus of ACe, but not those to stimulation of the caudal an d medial components of ACe. Microinjections of IBO into BST or electro lytic lesions of BST resulted in similar effects on the depressor resp onses to ACe stimulation. Taken together, these data indicate that neu rons within the rostral components of the lateral subnucleus of ACe pr oject to the cardiovascular region of BST and mediate in part the depr essor responses to stimulation of the rostral ACe. On the other hand, the depressor responses elicited from the caudal ACe are not mediated through BST. These results suggest that at least two independent pathw ays originate in the ACe that influence the circulation.