Functional and structural mapping of inhibitory neurons in the rat stomach muscle

Abstract

Functional gastrointestinal disorders such as gastroparesis and achalasia can be caused by changes in the stomach’s intrinsic neural circuitry, the enteric nervous system. We used electrophysiological, immunohistochemistry and lesion techniques to map the function and structure of this circuitry, to aid in novel neuromodulation therapies to treat these debilitating disorders. It is expected that a single enteric neuron innervates multiple smooth muscle cells, and that an increased stimulus recruits more axons, evoking a summated response at the autonomic neuromuscular junction. Strips of muscle from different stomach regions of rats were taken for in vitro intracellular electrophysiology recordings from the circular muscle layer. Both inhibitory and excitatory neuromuscular junction potentials (JP) were measured. Inhibitory transmission was antagonised by a combination of nitric oxide synthase inhibitors and purine receptor antagonists and excitatory transmission was substantially reduced by muscarinic block. The relative amplitudes of excitatory and inhibitory JPs were quantified across all regions of the stomach, in most cases the relative amplitude was halved 9 millimetres (mm) circumferentially from the stimulation site. In the antrum, the whole circumference can be affected simultaneously. Innervation effectiveness at all distances was graded with stimulus strength. Suggesting each individual smooth muscle cell received multiple neuronal inputs. However, the relative amplitudes varied depending on the stomach region. Localisation studies show that the numbers of inhibitory and excitatory neurons are similar however the distribution of myenteric ganglia within the stomach were uneven from the lesser to greater curvature. This potentially influences the relative JP amplitudes recorded from different regions. Response amplitudes recorded closest to the lesser curvature were smaller when compared to the site further circumferentially. Furthermore, our results indicate that this may not be the only factor leading to the variabilities in innervation. Lesion and immunohistochemistry studies indicate that axons of inhibitory and excitatory neurons branch and extend circumferentially and the innervation fields of several neurons overlap. Our electrophysiology shows that the degree of influence of excitatory neurons on the smooth muscle cell varies dependent on the region recorded. We conclude that inhibitory and excitatory neural influences extend around the gastric circumference and the effectiveness of inhibitory and excitatory influences can be graded by the recruitment of different numbers of motor neuron nerve terminals. This study was supported by NIH (SPARC) grant, The Virtual Stomach (OT2OD030538), Principal Investigators Leo Cheng (University of Auckland) and Zhongming Liu (University of Michigan) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.