Chapter 10 Some properties of the sympathoinhibition from the caudal ventrolateral medulla oblongata in the cat

Abstract

Publisher Summary Neurons in the caudal ventrolateral medulla oblongata (CVLM) play an important role in the control of sympathetic activity. The excitation of these neurons by small injections of excitatory amino acids causes an inhibition of sympathetic activity and a fall in arterial blood pressure. This chapter presents a study that clarifies the question that whether the sympathoinhibition from CVLM is because of post-synaptic inhibition or the disfacilitation of sympathetic preganglionic neurons (SPNs) by first studying the spinal pathway of this inhibitory response. If its pathway in the spinal cord could be dissociated from the descending pathway of sympathoexcitatory neurons in rostral ventrolateral medulla (RVLM) that runs in the dorso- and ventrolateral funiculus of the spinal cord, this would be strong evidence against the disfacilitation of SPNs. Because more direct evidence for either disfacilitation or post-synaptic inhibition should be provided by intracellular recordings of SPNs, this question has also been addressed by recording SPNs intracellularly and studying the effects of glutamate injections into CVLM on their membrane potential. It has also been studied if noradrenaline acting on α 2 -adrenergic receptors is involved as a transmitter in this inhibition and if this sympathoinhibition involves an afferent projection from the CVLM to the hypothalamus or cerebellum.