An electrophysiological study of the projections of motor neurones that mediate non-cholinergic excitation in the circular muscle of the guinea-pig small intestine

Isolated segments of the guinea pig small intestine were used to examine the transmitter circuitry of the neural pathways subserving the ascending enteric reflex (AER) contraction of the circular muscle. Inflation of an intraluminal balloon provided the distension stimulus for the AER. The ascending contraction was reduced to 5% of its original amplitude by atropine and to 10% by hexamethonium, which indicates that cholinergic interneurons and cholinergic motor neurons constitute the main AER pathway. However, in the continued presence of atropine or hexamethonium for 60 min, the AER recovered to approximately 30% of its original amplitude. The atropine-resistant AER was blocked by hexamethonium and the tachykinin antagonist spantide [( D-Arg1,D-Trp7,9, Leu11]-substance P) suggesting that it involved cholinergic interneurons and tachykinin-utilizing motor neurons. The hexamethonium-resistant AER was abolished by atropine but left unaffected by spantide, suggesting the participation of as yet unidentified interneurons and cholinergic motor neurons. These findings demonstrate that the AER is mediated by multiple neural pathways with different transmitters and that adaptive interactions between these pathways take place after blockade of one of its neurotransmitters systems.

Download Full-text

Mechanisms underlying nutrient-induced segmentation in isolated guinea pig small intestine

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00441.2006 ◽

2007 ◽

Vol 292 (4) ◽

pp. G1162-G1172 ◽

Cited By ~ 34

Author(s):

R. M. Gwynne ◽

J. C. Bornstein

Keyword(s):

Small Intestine ◽

Guinea Pig ◽

Motor Neurons ◽

Slow Wave ◽

Neural Circuit ◽

Circular Muscle ◽

Decanoic Acid ◽

Slow Waves ◽

Longitudinal Position

Mechanisms underlying nutrient-induced segmentation within the gut are not well understood. We have shown that decanoic acid and some amino acids induce neurally dependent segmentation in guinea pig small intestine in vitro. This study examined the neural mechanisms underlying segmentation in the circular muscle and whether the timing of segmentation contractions also depends on slow waves. Decanoic acid (1 mM) was infused into the lumen of guinea pig duodenum and jejunum. Video imaging was used to monitor intestinal diameter as a function of both longitudinal position and time. Circular muscle electrical activity was recorded by using suction electrodes. Recordings from sites of segmenting contractions showed they are always associated with excitatory junction potentials leading to action potentials. Recordings from sites oral and anal to segmenting contractions revealed inhibitory junction potentials that were time locked to those contractions. Slow waves were never observed underlying segmenting contractions. In paralyzed preparations, intracellular recording revealed that slow-wave frequency was highly consistent at 19.5 (SD 1.4) cycles per minute (c/min) in duodenum and 16.6 (SD 1.1) c/min in jejunum. By contrast, the frequencies of segmenting contractions varied widely (duodenum: 3.6–28.8 c/min, median 10.8 c/min; jejunum: 3.0–27.0 c/min, median 7.8 c/min) and sometimes exceeded slow-wave frequencies for that region. Thus nutrient-induced segmentation contractions in guinea pig small intestine do not depend on slow-wave activity. Rather they result from a neural circuit producing rhythmic localized activity in excitatory motor neurons, while simultaneously activating surrounding inhibitory motor neurons.

Download Full-text

An intracellular study of myenteric neurons in the mouse colon

Journal of Neurophysiology ◽

10.1152/jn.1986.55.6.1395 ◽

1986 ◽

Vol 55 (6) ◽

pp. 1395-1406 ◽

Cited By ~ 51

Author(s):

K. Furukawa ◽

G. S. Taylor ◽

R. A. Bywater

Keyword(s):

Small Intestine ◽

Guinea Pig ◽

Nerve Stimulation ◽

Circular Muscle ◽

Input Resistance ◽

Synaptic Activity ◽

Myenteric Neurons ◽

Mouse Colon ◽

Long Latency ◽

Wide Range

Intracellular recordings have been made in vitro from the myenteric neurons of the distal colon of normal littermates of the piebald-lethal mouse. Out of a total of 90 neurons, 82 were classified as S/type 1 cells and 8 as AH/type 2 cells. Seventy-eight out of 82 S cells showed spontaneous fast excitatory postsynaptic potentials (EPSPs) sensitive to d-tubocurarine (dTC, 280 microM), and 22 S cells showed spontaneous action potentials (APs). Six S cells and 1 AH cell showed spontaneous nonnicotinic slow depolarizations associated with an increase in the input resistance of the cells; during the spontaneous slow depolarization in the S cells there was an increase in the frequency of nicotinic fast EPSPs and APs. Three S cells showed spontaneously occurring regular oscillations of the membrane potential (approximately mV in amplitude and approximately 4/min). Transmural nerve stimulation produced fast EPSPs with a wide range of latencies (3 ms to 20 s) in S cells; the fast EPSPs were blocked by dTC (280 microM) or solutions containing low Ca2+ (0.25 mM) and high Mg2+ (12 mM) but not by atropine (ATR, 14 microM). Single or repetitive transmural stimulation produced slow EPSPs in 24 S cells and 3 AH cells; these were not blocked by dTC (280 microM) nor ATR (14 microM). During the slow EPSPs there was an increase in the input resistance of the cells. In those S cells that showed slow EPSPs there were many long-latency fast EPSPs; long-latency fast EPSPs were also observed in 11 other S cells that did not show a slow EPSP following repetitive transmural nerve stimulation. Long-latency fast EPSPs may be related to the firing of other neurons during their slow EPSPs. The myenteric neurons in the mouse colon have similar properties to the myenteric neurons in the guinea pig small intestine. However, the colonic myenteric neurons show more ongoing synaptic activity and more prolonged activity after nerve stimulation than myenteric neurons in the guinea pig small intestine. This activity may be due to regional differences, species differences, or preparation differences (in this study the myenteric plexus was adherent to the underlying circular muscle layer).

Download Full-text

Occurrence of FMRF amide-like immunoreactive nerve fibers in guinea pig small intestine.

Journal of Histochemistry & Cytochemistry ◽

10.1177/37.9.2768811 ◽

1989 ◽

Vol 37 (9) ◽

pp. 1427-1433 ◽

Cited By ~ 3

Author(s):

E Fehér ◽

G Burnstock

Keyword(s):

Small Intestine ◽

Guinea Pig ◽

Pancreatic Polypeptide ◽

Circular Muscle ◽

Muscle Layer ◽

Nerve Fibers ◽

Circular Muscle Layer ◽

Fmrf Amide ◽

Granular Vesicles ◽

Large Granular Vesicles

We investigated the distribution of FMRF amide-like immunoreactivity in the small intestine of the guinea pig. Immunoreactive nerve fibers were found mainly in the myenteric and submucous plexuses and in the inner circular muscle layer. The labeled processes contained variable proportions of small clear vesicles 30-40 nm in diameter and large granular vesicles 80-120 nm in diameter. The large granular vesicles showed heavy immunoreactivity. The antisera against FMRF amide crossreact with peptides belonging to the pancreatic polypeptide family; it has therefore been suggested that the FMRF amide immunoreactivity demonstrated in the small intestine is caused by a peptide that is biosynthetically related to, but not necessarily a member of, the pancreatic polypeptide family.

Download Full-text