COUPLING OF SYMPATHETIC AND SOMATIC MOTOR OUTFLOWS FROM THE SPINAL-CORD IN A PERFUSED PREPARATION OF ADULT-MOUSE IN-VITRO

1. The relationship between sympathetic and somatic motor outflows fro m thoraco-lumbar spinal cord was investigated in a novel arterially pe rfused trunk-hindquarters preparation of adult mouse. 2. Ongoing activ ity was present in both somatic motor (obturator, sciatic or femoral n erves) and sympathetic outflows (either renal nerve or abdominal sympa thetic chain). Sympathetic activity was rhythmic with bursts frequenci es of 0.6-2.2 Hz. No obvious rhythmic activity was found in the somati c motor outflow. There were periods during which sympathetic and somat ic motor activity were correlated. 3. Addition of NMDA (20-80 mu M) to the perfusate elicited repetitive burst discharges in the somatic mot or outflow which were sometimes rhythmic. The frequency of these burst discharges/rhythmic activity varied between preparations but in all c ases increased with increasing NMDA concentration. 4. NMDA induced bur st discharges in the sympathetic outflow. This bursting activity was o f the same frequency as the somatic motor outflow and the two were cou pled as revealed by correlation analysis. Periods of coupling persiste d for up to 3 min. 5. Administration of hexamethonium (300 mu M), to b lock sympathetic ganglionic transmission, had no effect on the somatic motor activity but severely attenuated sympathetic nerve discharge. 6 . The thoraco-sacral cord therefore has the neuronal machinery necessa ry for generating and coupling activity in somatic motor and sympathet ic outflows. Our findings indicate a dynamic control over the degree o f coupling. We discuss that the synchronization of these neural outflo ws reflects either coupling between two independent mechanisms or the presence of a common synaptic driver impinging on both somatic motor a nd sympathetic neurones.