Intrinsic Properties of Deep Dorsal Horn Neurons in the L6-S1 Spinal Cord
of the Intact Rat.
Jiang, Minchun, Corey L. Cleland and G.F. Gebhart.
Department of Pharmacology, University of Iowa, Iowa City, IA 52242.
APStracts 2:0190N, 1995.
SUMMARY AND CONCLUSIONS
1. Stable intracellular recordings were obtained from neurons (n=62) in the
L6-S1 deep dorsal horn of the spinal cord in pentobarbital anesthetized,
intact rats (n=26). All neurons responded to natural mechanical stimuli and/or
electrical stimulation of peripheral afferents. 2. Intracellular penetrations
were maintained for 30 minutes to 2 hours. Action potentials occurred
spontaneously in most neurons (n=50) and could be evoked in the remainder
(n=12) by depolarizing current passage. The mean resting membrane potential
was -60.9 mv, mean action potential height amplitude was 75.2 mv, mean half
width of the action potentials was 0.33 ms, mean input resistance was 38 MW
and the mean time constant was 9.1 ms. 3. Action potentials were followed by
afterpotentials comprised of at least three components: a fast
afterhyperpolarization (fAHP), slow afterhyperpolarization (sAHP) and an
afterdepolarization (ADP). Most neurons (n=40) exhibited all three
afterpotentials, though some displayed only a fAHP and an ADP (n=10) or a fAHP
and a sAHP (n=12). The duration and magnitude of the afterpotentials varied
widely among neurons. 4. Steady-state current-voltage relations were
investigated in 14 neurons with depolarizing and hyperpolarizing current
pulses. In these 14 neurons, five exhibited inward rectification, three had
outward rectification and the remaining six showed a predominantly linear
change of membrane potential to current injection. In addition, several
neurons (n=9) exhibited a post-inhibitory rebound that was sometimes (n=4)
accompanied by a "sag" in voltage during the preceding hyperpolarizing current
step. 5. Four patterns of spike-frequency adaptation occurred during step
depolarizing current passage. The firing of most neurons gradually decreased
with a simple, approximately exponential time course (n=21), some decreased
with both a fast and a slow time course (n=8), several incremented in rate
(n=3), and one showed a complex combination of multiple decrementing and
incrementing adaptations. Time constants, magnitude of adaptation and the
slopes of the steady-state current-voltage varied widely. 6. Oscillations in
membrane potential and firing rate occurred in three neurons. The oscillations
arose from endogenous mechanisms in at least one neuron because manipulation
of membrane potentials altered the frequency of oscillation; a depolarizing
current increased the period of oscillation and eventually produced tonic
firing and a hyperpolarizing current increased the frequency of oscillation
and eventually terminated firing. 7. The results demonstrate that neurons in
the L6 - S1 region of dorsal horn exhibit a diversity of cellular mechanisms
that may significantly modulate normal somatosensory and visceral input.
Received 26 August 1995; accepted in final form 21 June 1995.
APS Manuscript Number J538-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.