Cellular properties of lateral spinal nucleus neurons in the rat L-6-S-1 spinal cord

Conventional intracellular recordings were made from 26 lateral spinal nucl eus (LSN) neurons in slices of L-6-S-1 spinal cord from 10- to 15-day-old r ats. At rest, LSN neurons did not fire spontaneous action potentials. With injection of a positive current pulse, action potentials had an amplitude o f 72 +/- 7 (SD) mV and duration at half-peak height of 0.75 +/- 0.22 ms. Ac tion potentials were followed by an afterpotential. Most LSN neurons (13/17 ) exhibited only an afterhyperpolarization (AHP); four neurons exhibited bo th a fast and a slow AHP separated by an afterdepolarization (ADP). For LSN neurons that exhibited only an AHP, a slow ADP could be identified during bath application of apamin (100 mM). Four of 11 LSN neurons show ed a posti nhibitory rebound (PIR). Two types of PIR were noted, one with high thresho ld and low amplitude and the other with low threshold and high amplitude. T he PIR with high amplitude was partially blocked in 0 mM Ca2+/high Mg2+ (10 mM) recording solution. Repetitive firing properties were examined in 17 L SN neurons. On the basis of the ratio of the slopes between initial instant aneous firing and steady-state firing frequencies, neurons with low spike f requency adaptation (SFA, 8/17) and high SFA (4/17) were identified. In add ition, 2/17 LSN neurons exhibited biphasic repetitive firing patterns, whic h were composed of a fast SFA, delayed excitation, and low SFA; another two neurons showed only delayed excitation. Plateau potentials also were found in two LSN neurons. Dorsal root stimulation revealed that most LSN neurons (12/13) had polysynaptic postsynaptic potentials (PSP); only one neuron ex hibited a monosynaptic PSP. Electrical stimulation of the dorsal root evoke d prolonged discharges in low SFA neurons and a short discharge in high SFA neurons. Intrinsic properties were modulated by bath application of substa nce P (SP). Membrane potentials were depolarized in all eight LSN neurons t ested, and membrane resistance was either increased (n = 3) or decreased (n = 2). Both instantaneous firing and steady-state firing were facilitated b y SP. In addition, oscillation of membrane potentials were induced in three LSN neurons. These results demonstrate that LSN neurons exhibit a variety of intrinsic properties, which may significantly contribute to sensory proc essing, including nociceptive processing.