No abstract

SUMMARY1. The membrane effects of substance P on neurones of isolated inferior mesenteric ganglia and the underlying ionic mechanisms were investigated by means of intracellular recording techniques.2. When applied to the neurones by superfusion, substance P (0 5 /M) caused a membrane depolarization; in a few neurones, the depolarization was preceded by a small hyperpolarization. Substance P effects were not altered in a low Ca2+/high Mg2+ solution or in a solution containing D-tubocurarine and atropine.3. When the membrane potential was clamped manually at the resting level between -50 and -60 mV, substance P caused, in about an equal number of neurones, a slight to moderate decrease and also increase of membrane resistance; a brief increase occurred prior to the decrease of membrane resistance.4. In neurones with high resting membrane potential (>-70 mV), substance P elicited a large depolarization accompanied by a marked increase in membrane resistance; the latter was probably due to anomalous rectification.5. Conditioning hyperpolarization of the membrane close to the level of EK increased and decreased substance P-induced depolarization in eleven and two neurones, respectively. 6. Substitution of external Na+ with an equimolar amount of either sucrose or Tris buffer markedly attenuated the depolarizing effect of substance P.7. The substance P-induced depolarization was diminished in a high K+ (10 mM) solution, and it could be augmented when membrane was hyperpolarized to EK. On the other hand, the effect of substance P was not appreciably affected in a low Clsolution. 8. It is concluded that substance P depolarizes the sympathetic neurones by increasing and decreasing membrane permeability to Na+ and K+, respectively, and that the concomitant membrane resistance change depends on interaction of GNa activation and GK inactivation.9. The possibility that substance P is the transmitter mediating the non-cholinergic slow excitatory potential elicited by repetitive preganglionic stimulation in the neurones of the inferior mesenteric ganglia is suggested.

SUMMARY1. Long-lasting potentiation of transmitter release induced by repetitive presynaptic activities in bull-frog sympathetic ganglia was studied by recording intracellularly fast excitatory post-synaptic potentials (fast e.p.s.p.s).2. Following a brief period of post-tetanic potentiation or depression (less than 10 min), the amplitude of the fast e.p.s.p. was potentiated for a period between several tens of minutes and more than 2 h in response to tetanic stimulation of the preganglionic nerve in twenty-one out of twenty-eight cells.3. Quantal analysis revealed that this long-term potentiation of the fast e.p.s.p. (l.t.p.) was accompanied by an increase in quantal content m (in nine out oftwenty-one cells), quantal size (four cells) or both (eight cells).4. The increased quantal content (presynaptic l.t.p.) declined exponentially (ten cells) or decayed gradually to a certain enhanced level which lasted several hours. In contrast, the increased quantal size grew with a relatively long latency (10-25 min) and remained relatively constant for at least 2 h.5. The magnitude of presynaptic l.t.p. increased with increased duration of the presynaptic tetanus (33 Hz) from 2 to 5 s. No l.t.p. was elicited by a 1-s tetanus, whereas the time course appears to be independent of the tetanus duration and the magnitude of l.t.p.6. There was a positive correlation between the magnitude of presynaptic l.t.p. and the pre-tetanic quantal content up to m = 3, but the former deviated from linear regression when the value of the latter exceeded 3. No l.t.p. occurred when quantal content was less than 0 5. 7. A tetanus (33 Hz, 10 s) applied in Ca2+-free solution elicited no presynaptic l.t.p., while the same tetanus in normal Ringer solution produced a large presynaptic l.t.p.8. Presynaptic l.t.p. was enhanced in magnitude at low temperature (8-10 'C). 9. These results demonstrate the existence of a use-dependent, long-term potentiation of transmitter release in bull-frog sympathetic ganglia. Several possible mechanisms are discussed in terms of Ca2+-buffering mechanisms of the presynaptic nerve terminals.

SUMMARY1. The mechanism of a long-term potentiation of transmitter release (pre-LTP) induced by a tetanic stimulation (33 Hz for 1-30 s) applied to the preganglionic nerve was examined by intracellularly recording the fast excitatory postsynaptic potentials (fast EPSPs) in bull-frog sympathetic ganglia.2. Short-term facilitation induced by paired pulses was decreased during the course of pre-LTP; the extent of reduction paralleled with the magnitude of pre-LTP.3. The frequency of miniature EPSPs increased after tetanic stimulation that produced the pre-LTP.4. The Ca2" ionophore, A23187, increased both the amplitude and quantal content of fast EPSPs and frequency of miniature EPSPs while it decreased short-term facilitation.5. A Ca2" chelating agent, Quin-2, loaded as acetoxymethyl ester, reduced the amplitude and quantal content of fast EPSPs and short-term facilitation, and blocked the generation of pre-LTP.6. Activators of protein kinase C, phorbol 12,13-dibutyrate and 1-oleoyl-2-acetylrac-glycerol, and its inhibitors, H-7 and staurosporine, did not block the generation of pre-LTP, while the activators enhanced transmitter release.7. Inhibitors of calmodulin, trifluoperazine and W-7, blocked the generation of pre-LTP, whereas the amplitude and quantal content of fast EPSPs were not influenced.8. These results suggest that the pre-LTP results from a sustained rise in the basal level of intraterminal Ca2' and an activation of the Ca2+-calmodulin-dependent process in the preganglionic nerve terminals.