Sympathetic preganglionic neurones in neonatal rat spinal cord in vitro: electrophysiological characteristics and the effects of selective excitatory amino acid receptor agonists.

Intracellular recordings were made from 52 lateral horn neurones in thin slices of neonatal rat thoracolumbar spinal cord. Of these neurones 12 were spontaneously active and the remainder silent. A number of these cells could be activated antidromically by stimulation of ventral roots. The conduction velocity of the antidromic potential was estimated to be 0.9-2 m/s which is within the range reported for axons of sympathetic preganglionic neurones (SPNs). The membrane properties of antidromically identified SPNs were similar to other lateral horn neurones included in this study and comparable to those reported for SPNs by others. Spontaneous burst firing was recorded in 3 neurones and activity in a further 5 neurones was characterized by the discharge of an action potential followed by an afterhyperpolarization potential (AHP) of peak amplitude 3-13 mV and duration 0.5-4 s. The AHP had an initial fast component (fAHP) which was sensitive to the potassium channel blocker tetraethylammonium (TEA), and a second slower component (sAHP) which was both sensitive to extracellular calcium and TEA. The effects of the selective excitatory amino acid receptor agonists N-methyl-D-aspartate (NMDA), kainate and quisqualate were investigated by superfusion of the agonists, at known concentrations (100 nM to 100 microM). These agonists induced concentration-dependent depolarizations which were primarily associated with a reduction in neuronal input resistance. NMDA-induced depolarizations were potentiated in the absence of magnesium.(ABSTRACT TRUNCATED AT 250 WORDS)