162 Brain Research, 606 (1993) 162-166 © 1993 Elsevier Science Publishers B.V. All rights reserved 0006-8993/93/$06.00 BRES 25578 Contribution of caudal ventrolateral medulla to the cardiovascular responses elicited by activation of bed nucleus of the stria terminalis Sergio B. Giancola, Stefanie Roder and John Ciriello Department of Physiology, Health Science Centre, Universityof Western Ontario, London, Ontario (Canada) (Accepted 15 December 1992) Key words: Limbic system; Autonomic pathway; Rostral ventrolateral medulla; Brainstem; Arterial pressure; Cardiovascular regulation The contribution of caudal ventrolateral medulla (cVLM) to the mean arterial pressure (MAP) and heart rate (HR) responses elicited by microinjections of L-glutamate (GLU) into the cardiovascular responsive region of bed nucleus of the stria terminalis (BST) was investigated in the chloralose-anesthetized, paralysed and artificially ventilated rat. Unilateral injections of GLU into BST elicited decreases in MAP of - 25 _+ 3 mmHg (n = 10) and HR of - 13_+3 bpm (n = 10). These cardiovascular responses were not altered after a 100 nl microinjection of 0.9% NaCI into cVLM. However, the magnitudes of the decreases in MAP and HR were attenuated (- 11 _+3 mmHg and HR, - 4_+ 1 bpm, respectively) 5 min after a 100 nl microinjection of the reversible synaptic blocker cobalt chloride (CoCI 2) into cVLM. Restimulation of BST 40 rain after the 100 nl microinjection of CoC12 in cVLM elicited cardiovascular responses that were not significantly different in magnitude from those evoked before the microinjection of COC12 (MAP, -23_+ 4 mmHg; HR, - 12_+ 5 bpm). In an additional series of experiments (n = 3), restimulation of BST 1 h after an ipsilateral electrolytic lesion in cVLM elicited decreases in MAP ( - 11 _+ 2 mmHg) and HR (- 8 _+ 4 bpm) that were significantly smaller than those elicited prior to cVLM lesion. These data suggest that a component of the pathways originating in BST involved in mediating depressor responses and cardiac slowing relays in cVLM. Bed nucleus of the stria terminalis (BST) is a limbic, forebrain structure that has been implicated in behav- ioral 9, endocrine I and autonomic 9'mat functions be- cause of its anatomical relation with the amygdala 4'19. Recently, BST has also been suggested to play a role in cardiovascular regulation. Chemical stimulation of BST with the excitatory amino acid L-glutamate (GLU) has been shown to elicit changes in arterial pressure (AP) and heart rate (HR) 4'7. The cardiovascular responsive region in BST has been shown to be localized primarily to an area around the dorsolateral, lateral and ventro- lateral aspects of the anterior commissure. The cardiovascular responses elicited during activa- tion of BST are thought to be mediated by pathways from BST to the hypothalamus and to brainstem auto- nomic nuclei on the basis of previous anatomical stud- ies 12. However, few functional data supporting this suggestion are available. It has recently been shown that iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin into the cardiovascu- lar region of BST result in labelled fibers and pre- sumptive terminal boutons within the ipsilateral ven- trolateral medulla (VLM) 14. The densest projections from BST neurons were observed to the brainstem region containing the AI noradrenergic cell group. Electrical and chemical stimulation of this caudal VLM (cVLM) region have been shown to elicit decreases in arterial pressure and heart rate 2'13'24, cardiovascular responses similar to those observed during activation of BST neurons 4. Therefore, taken together, these data suggest that the cardiovascular responses elicited dur- ing stimulation of BST may be mediated by pathways to cVLM neurons. The present study was done to investigate the ef- fects of injecting the non-toxic, non-specific, reversible synaptic blocker cobalt chloride (COC12; ref. 3) or of electrolytic lesions in cVLM on the cardiovascular re- sponses elicited during stimulation of BST. Experiments were done in 13 adult, male Wistar rats (260-405 g) under ~-chloralose anesthesia (60 mg/kg, Correspondence: J. Ciriello, Department of Physiology, Health Science Centre, University of Western Ontario, London, Ontario N6A 5C1, Canada. Fax: (l) (519) 6613827.