Impulse transmission in the myenteric plexus‐longitudinal muscle preparation of the guinea‐pig ileum

Abstract

Summary1. In a preparation consisting of the myenteric plexus and the longitudinal muscle layer removed from a segment of guinea-pig ileum, spontaneous action potentials occurred which were unaffected by tetrodotoxin but suppressed by Mn2+ and were therefore myogenic. 2. A single current pulse of 0-1 ms duration evoked a response consisting of an early action potential followed after a delay of about 200 ms by a complex of biphasic spikes. The first action potential was conducted for no more than 15 mm and the second complex for 30-70 mm.3. Since the first action potential was unaffected by hyoscine or Mn2" but abolished by tetrodotoxin, it was due to excitation of nerve fibres. The later complex of spikes was suppressed by hyoscine and Mn2+ and therefore due to excitation of smooth muscle. It was also inhibited by adrenaline or morphine, compounds which depress acetylcholine release. The evoked smooth muscle response was followed by absence of spontaneous electrical activity for 2-4 seconds. 4. The nerves travelling in a longitudinal direction had a mean maximum conduction velocity of 0 65 m/s, an absolute refractory period of 2-8 ms and a relative refractory period of about 20 ms. 5. The conduction velocity of the smooth muscle response evoked by stimulation of the nerve with a single pulse was 0-16 m/second. After a single pulse the muscle was inexcitable for 0-7-1 3 s; the delay of transmission from nerve to muscle was 210 ms. When instead of a single pulse a train of two-five pulses at 20 ms intervals was applied, the size, conduction distance and con-

Two types of neurones lacking synaptic input in the submucous plexus of guinea‐pig small intestine.

“…In addition to sensory neurones and excitatory and inhibitory effector neurones, A. SURPRENANT some proposals concerning the neural circuitry involved in the peristaltic reflex also require the presence of continuously active interneurones which synapse onto other excitatory interneurones or onto inhibitory motor neurones (Hirst, 1979;Wood, 1981). When extracellular recordings have been made from neurones of the myenteric or submucosal plexus spontaneous action potentials have been recorded from the majority of cells (Wood, 1970;Kosterlitz & Lydon, 1971;Ohkawa & Prosser, 1972;Sato, Takayanage & Takagi, 1973;North & Williams, 1977). However, most of the spontaneous spikes which occur during extracellular recordings appear to be the result of mechanical deformation of the neurone or its processes, caused by the recording electrode (North & Williams, 1977).…”

“…When extracellular recordings have been made from neurones of the myenteric or submucosal plexus spontaneous action potentials have been recorded from the majority of cells (Wood, 1970;Kosterlitz & Lydon, 1971;Ohkawa & Prosser, 1972;Sato, Takayanage & Takagi, 1973;North & Williams, 1977). However, most of the spontaneous spikes which occur during extracellular recordings appear to be the result of mechanical deformation of the neurone or its processes, caused by the recording electrode (North & Williams, 1977).…”

Intracellular recording from the myenteric plexus of the guinea‐pig ileum

“…Several electrophysiological attempts have been made to elucidate this S. NISHI AND R. A. NORTH role (Yokoyama, 1966(Yokoyama, , 1971Wood, 1970;Kosterlitz & Lydon, 1971;Ohkawa & Prosser, 1972); however, the continual movement of the intestinal smooth muscle, the small size of the individual ganglia (about 0-1 by 1-0 mm) and the high sensitivity of the cells to mechanical damage have frustrated efforts to record intracellularly from myenteric plexus neurones. Only one short report has appeared of successful intracellular recording (Hirst, Holman, Prosser & Spence, 1972); this was from ganglion cells of the guinea-pig duodenum in the presence of sufficient isoprenaline to inhibit spontaneous muscle movement.…”

How far from the stimulation site in myenteric plexus-longitudinal muscle preparations the neurogenic cholinergic contraction can be evoked?

“…Measuring the distance between local gut distension or focal neurogenic stimulation at one side and junction potentials of smooth muscle or neuronal firing at the other side gave the value of about 15 mm length for the descending inhibitory pathway in the guinea-pig ileum (Hirst and McKirdy, 1974). The excitatory pathways as judged from extracellular recordings from fiber tracts within the plexus were considered to conduct for shorter distances in the longitudinal direction (Biilhring and Tomita, 1967;Kosterlitz and Lydon, 1971;Yokoyama r al., 1977). Kosterlitz and Lydon (1971) did not record compound nerve action potential further than 12 mm from the stimulation site in the absence of any ganglion-blocldng drug; the participation of a chain of intercalated neurons could not be excluded.…”