The role of intramuscular interstitial cells of Cajal in gastric neurotransmission

The experiments described in this dissertation were performed to investigate the role of intramuscular interstitial cells of Cajal (ICC-IM) in motor neurotransmission in the murine stomach. Morphological studies demonstrated that ICC-IM within the gastric musculature were tightly interposed between enteric nerve terminals and smooth muscle cells suggesting their involvement in neurotransmission.; The functional importance of ICC-IM was investigated using W /WV and Sl/ Sld mutant mice which lack gastric ICC-IM. In the gastric fundus, loss of ICC-IM was associated with reduced membrane noise recorded from the circular smooth muscle layer and a marked attenuation of cholinergic and nitrergic postjunctional neural responses. Loss of postjunctional responses in mutant mice was not due to a reduction of smooth muscle responsiveness to exogenous neurotransmitters or a decreased density of enteric nerves. In the gastric antrum, loss of ICC-IM was associated with an inability to modulate slow wave frequency in response to intrinsic nerve stimulation, suggesting that neural regulation of slow wave frequency is normally mediated via an interaction between enteric nerves and ICC-IM.; Ultrastructural studies revealed membrane densification at regions of nerve-ICC-IM apposition suggesting the presence of organized sites of synaptic communication. Proteins implicated in synaptic transmission (synaptotagmin and SNAP25) were concentrated at nerve varicosities and located in close apposition to ICC-IM. In W/WV tissues synaptotagmin and SNAP25 were concentrated within nerve varicosities, demonstrating that trafficking of vesicle release machinery to nerve terminals can occur despite the absence of the postjunctional interstitial cell. Expression of the postsynaptic density protein PSD95 was reduced in W/ WV fundus tissues, supporting the hypothesis that ICC-IM express specialized postsynaptic apparatus involved in neurotransmission.; Membrane noise recorded from wildtype fundus was associated with an ongoing discharge of spontaneous transient depolarisations or 'unitary potentials'. Membrane noise was absent from W/WV fundus tissues, suggesting that ICC-IM generate unitary potentials. In wildtype fundus membrane noise had similar spectral density characteristics to unitary potential activity in the gastric antrum suggesting a common underlying mechanism in both regions. However, unlike the antrum, unitary potentials of the fundus were not suppressed by chloride channel antagonists and were largely voltage independent.; In conclusion, these experiments have examined the morphological and physiological properties of ICC-IM and demonstrated their critical importance in the transfer of neural signals to the musculature of the stomach.