Action of neurotropin on rat hypothalamic neurons in tissue slices

Effects of T-588, a newly synthesized cognitive enhancer, on hippocampal CA1 neurons in rat brain tissue slices

The effects of a newly synthesized cognitive enhancer, (-)-R-alpha-[[2-(diethylamino) ethoxy] methyl] benzo [b] thiophene-5-methanol hydrochloride (T-588), on the membrane properties of hippocampal CA1 neurons were investigated in a rat brain slice preparation. T-588 produced a slow and long-lasting depolarization of CA1 neurons with an increase in membrane resistance; this action showed close similarity to that of acetylcholine (ACh). However, the action of T-588 was not affected by atropine, tetrodotoxin or DL-2-amino-5-phosphonovalerate, while the action of ACh was blocked by atropine. The estimated reversal potential of this T-588 effect was near -90 mV which is the reversal potential of potassium ions in CA1 neurons. In the whole-cell voltage-clamp study, T-588 produced a reversible block of the outward potassium current in CA1 neurons. T-588 did not block the afterhyperpolarization evoked by an intracellular current injection, while ACh suppressed it. These results suggest that T-588 has a direct effect on CA1 neurons independent of its cholinergic activity, resulting from blockade of a conductance carried predominantly by potassium ions.

Electrophysiological study of neurotropin-induced responses in guinea pig hypothalamic neurons

To investigate the direct actions of neurotropin (NSP, a nonproteinaceous extract from inflamed skin of rabbits which is in therapeutic use), intracellular recordings were made from neurons of the ventromedial hypothalamic nucleus (VMH) and lateral hypothalamic area (LHA) in slices of guinea pig brain. In the VMH, NSP, applied by perfusion (0.1-3.0 NU/ml), caused dose-dependent depolarization in 29 of 48 neurons (60%) tested. No change in membrane resistance was observed during the depolarization, which hypothesized that the NSP-induced depolarization might be mediated through the inactivation of the Na-K pump. The NSP-induced depolarization persisted even after the elimination of synaptic activity by perfusion with Ca(2+)-free and high Mg2+ Ringer solution. NSP hyperpolarized the cell membrane of three neurons (6%) while two neurons (4%) showed biphasic responses; transient depolarization followed by long-lasting hyperpolarization. Membrane potential of the remaining 14 neurons was not changed by application of NSP. Of 14 LHA neurons tested for NSP effects, eight (57%) were depolarized, three (21%) were hyperpolarized, and one showed a biphasic response. The present results suggest that NSP significantly modulates hypothalamic neuron activity, and the central modulation of autonomic functions by NSP might be mediated through hypothalamic neurons.