ELECTROTONIC COUPLING BETWEEN RAT SYMPATHETIC PREGANGLIONIC NEURONS IN-VITRO

1. Using the whole-cell recording technique in rat-spinal cord slices we have shown that 26% of sympathetic preganglionic neurones (SPNs) sh ow spontaneous membrane potential oscillations. These oscillations con sist of trains of biphasic waves, which we have termed spikelets becau se of their similarity to truncated action potentials. 2. The spikelet s were inhibited by TTX and anaesthetics such as alpha-chloralose but not by the intracellular application of lidocaine N-ethyl bromide (QX- 314). 3. By stimulating the ventral roots we have demonstrated the pre sence of short-latency depolarizations (SLDs) in oscillating neurones. These SLDs have a similar waveform to the spontaneous spikelets, and also show the ability to override the frequency of occurrence of the s pontaneous spikelets. These observations suggest that the spikelets re sult from electrotonic coupling between the oscillating SPNs. 4. SLDs were also observed in a population of non-oscillating, electrotonicall y coupled, quiescent SPNs. It was possible to induce oscillations in t hese neurones by the injection of depolarizing current (in the presenc e of QX-314), suggesting that these neurones are also gap-junction cou pled. 5. Simultaneous whole-cell recordings were obtained from twenty- three pairs of SPNs. Two pairs displayed both spontaneous, synchronize d oscillations and action potentials. Electrotonic coupling was confir med by the detection of membrane polarization in both neurones in resp onse to current injected into one neurone. In a further two pairs of q uiescent SPNs, injection of depolarizing current pulses into one neuro ne induced action potential discharge in that neurone and a depolariza tion and oscillations in the other neurone. 6. The ability of groups o f electrotonically coupled SPNs to generate spontaneous discharges wit hin the spinal cord provides a novel mechanism for the integration and synchronization of information within the sympathetic nervous system.