Role of ventrolateral medulla in generating the 10-Hz rhythm in sympathetic nerve discharge

Susan M. Barman and Gerard L. Gebber
Am J Physiol Regul Integr Comp Physiol 293: R223–R233, 2007.

The main focus of this study is how inputs of selective and non-selective excitatory amino acid receptor antagonists affect the ventrolateral medulla (VLM) in generating a 10-Hz rhythm in sympathetic nerve discharge. Using urethane-anesthetized, baroreceptor-denervated cats, they would record the changes of frequency in both the right inferior cardiac and  left inferior cardiac nerves. After unilateral injections of bicuculline (GABA-A receptor antagonists) were giving 1 and 5 mm rostral to the obex in the VLM, they found it would completely remove or reduce the 10-Hz rhythm on both sides of the body. Similarly they did unilateral injections kynurenate, (nonselective excitatory amino acid receptor antagonist) but this time did the injections both caudal or rostral in the VLM. Results found that the 10-Hz frequency was reduced but not eliminated. This study shows that GABAerginc transmission is in some way necessary for this 10-Hz rhythm to occur in sympathetic nerve discharge and that both rostral and caudal GABAerginc neurons play a role. - ZAK