CUNEIFORM NUCLEUS STIMULATION-INDUCED SYMPATHOEXCITATION - ROLE OF ADRENOCEPTORS, EXCITATORY AMINO-ACID AND SEROTONIN RECEPTORS IN RAT SPINAL-CORD

Stimulation of the midbrain cuneiform nucleus has previously been show n to produce increases in arterial blood pressure and lumbar sympathet ic nerve activity. While this sympathoexcitatory effect is, in part, d ue to excitation of premotor sympathoexcitatory neurons in the rostral ventrolateral medulla, the specific spinal neurotransmitter systems r ecruited by cuneiform nucleus stimulation remains to be elucidated. In this study, mean arterial pressure, resting and cuneiform nucleus sti mulation-evoked lumbar sympathetic nerve activity were analysed follow ing intrathecal injections of an excitatory amino acid antagonist (kyn urenic acid), alpha(1)-adrenoceptor antagonist (prazosin) and a seroto nin receptor antagonist (methiothepin) in anesthetized, paralysed male Sprague-Dawley rats. Mean arterial pressure and resting sympathetic n erve discharge were decreased by all treatments (n = 6/group) compared to the vehicle control group. Intermittent electrical stimulation of the cuneiform nucleus produced a bimodal sympathoexcitatory response, of which the short latency peak was significantly attenuated (43% redu ction) by intrathecal kynurenate whereas the long latency peak was red uced by intrathecal prazosin (decrease of 21%) and methiothepin (38% a ttenuation). These results are consistent with the significant roles o f excitatory amino acid, alpha(1)-adrenergic and serotonin receptors i n modulating the activity of sympathetic vasomotor preganglionic neuro ns supplying the lumbar sympathetic nerve trunk, and suggest the exist ence of at least three neuronal groups and/or pathways associated with the sympathoexcitatory response to cuneiform nucleus stimulation.