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Electrophysiological properties and glucose responsiveness of guinea‐pig ventromedial hypothalamic neurones in vitro.
Author(s) -
Minami T,
Oomura Y,
Sugimori M
Publication year - 1986
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1986.sp016276
Subject(s) - hyperpolarization (physics) , electrophysiology , membrane potential , guinea pig , stimulation , chemistry , time constant , pulse (music) , resting potential , refractory period , biophysics , medicine , endocrinology , physics , biology , stereochemistry , biochemistry , engineering , optics , detector , nuclear magnetic resonance spectroscopy , electrical engineering
The membrane properties of neurones in the guinea‐pig ventromedial hypothalamic nucleus (v.m.h.) were studied in in vitro brain slice preparations. The average resting potential was ‐62.9 +/‐ 5.4 mV (mean +/‐ S.D.), input resistance was 155 +/‐ 58 M omega, and action potential amplitude was 69.9 +/‐ 6.3 mV. Three types of neurone were identified. The type A neurones were characterized by a short membrane time constant (7.3 +/‐ 2.0 ms) and a small after‐hyperpolarization (a.h.p.) (2.0 +/‐ 1.2 mV) with a short half decay time of 67 +/‐ 55 ms after stimulation with a long outward current pulse. Type B had a long time constant (18.8 +/‐ 5.7 ms) and a large a.h.p. (6.9 +/‐ 2.4 mV) with a medium half decay time of 203 +/‐ 90 ms. Type C was characterized by a long time constant (14.3 +/‐ 2.3 ms) and a large a.h.p. (6.5 +/‐ 1.5 mV) with a long half decay time of 478 +/‐ 230 ms. The slopes of the frequency‐current (f‐I) plots of the three types were different, particularly for the first spike interval. The slopes for the type A (414 +/‐ 102 impulses s‐1 nA‐1) and type B neurones (480 +/‐ 120 impulses s‐1 nA‐1) were steeper than that for the type C neurones (178 +/‐ 41 impulses s‐1 nA‐1). This difference is probably related to the relatively long first interval observed in the type C neurones. In all type B and a few type C neurones, when the membrane potential was hyperpolarized beyond‐‐65 mV the application of orthodromic or direct stimulation generated a burst of spikes, consisting of a low‐threshold response (l.t.r.) of low amplitude and superimposed high‐frequency spikes. At the original resting potential, outward current pulses produced a train of low‐frequency spikes. In type C neurones maintained in a depolarized state (about ‐50 mV), inward current pulses produced a specific delay of the return to the original membrane potential. This delayed return was thought to be generated by activation of a transient K+ (IA) conductance. Stimulation at the lateral edge of the v.m.h. produced excitatory post‐synaptic potentials (e.p.s.p.s) in type A neurones, e.p.s.p.s with l.t.r. in type B neurones and e.p.s.p.‐inhibitory post‐synaptic potential sequences in type C neurones. About 20% of v.m.h. neurones, particularly the type C cells, were depolarized by glucose application with an associated increase in the input membrane resistance.(ABSTRACT TRUNCATED AT 400 WORDS)