Marina N, Taheri M, Gilbey MP. Generation of a physiological sympathetic motor rhythm in the rat following spinal application of 5-HT.
J Physiol 2006;
571:441-50. [PMID:
16396930 PMCID:
PMC1796786 DOI:
10.1113/jphysiol.2005.100677]
[Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2005] [Accepted: 01/04/2006] [Indexed: 11/08/2022] Open
Abstract
When applied in vitro to various CNS structures 5-HT and/or NMDA have been observed to generate rhythmic nervous activity. In contrast, reports of similar in vivo actions are relatively rare. Here we describe a physiological sympathetic motor rhythm regulating the thermoregulatory circulation of the rat tail (T-rhythm; 0.40-1.20 Hz) that can be elicited following intrathecal (i.t.) application of 5-HT to an in situ'isolated' spinal cord preparation (anaesthetized rats spinalized at T10-T11 and cauda equina cut). i.t. injections were delivered to L1 as sympathetic neuronal activity to the tail (SNAT) arises from preganglionic neurones at T11-L2. SNAT was abolished after spinal transection (n = 18) and it did not return spontaneously. The administration of 5-HT (250 nmol) generated rhythmic sympathetic discharges (n = 6). The mean frequency of the T-like rhythm during the highest level of activity was 0.88 +/- 0.04 Hz which was not significantly different from the T-rhythm frequency observed in intact animals (0.77 +/- 0.02 Hz; P > 0.05 n = 16). In contrast, NMDA (1 micromol) generated an irregular tonic activity, but it failed to generate a T-like rhythm (n = 9), even though the mean levels of activity were not significantly different to those produced by 5-HT. However, 5-HT (250 nmol) applied after NMDA generated a T-like rhythm (0.95 +/- 0.11 Hz, n = 6). Our observations support the idea that 5-HT released from rostral ventromedial medullary neurones, known to innervate sympathetic preganglionic neurones, can induce sympathetic rhythmic activity.
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