Brainstem mechanisms subserving oesophageal peristalsis in the rat

Wang, Yu Tian (1992) Brainstem mechanisms subserving oesophageal peristalsis in the rat. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Functional organization and neurotransmitter mechanisms of the central oesophagomotor pathway from the subnucleus centralis of the nucleus tractus solitarii (NTSc) to the compact formation of the nucleus ambiguus (AMBc) were investigated in vivo in the anaesthetized rat and in vitro in a rat brainstem slice preparation. Techniques utilized included micropneumophoresis, extra- and intracellular recording, neuronal tracing and immunocytochemistry. -- Results from neuropharmacological investigations indicate solitarial GABA neurons exert a tonic inhibition of oesophageal premotor elements in the NTSc. Moreover, these GABAergic neurons are involved in pharyngoesophageal coupling of primary peristalsis as well as generation of secondary peristalsis. -- Activation of muscarinic cholinoceptors in the NTSc is necessary for generation of both fictive primary and secondary peristalsis. Such activation is functionally confined to ipsilateral AMBc motoneurons. The rat brainstem appears to lack excitatory commissural connections between the oesophagomotor circuits in each hemi-medulla. -- Results from in vivo and in vitro experiments demonstrate NTSc premotoneurons utilize an excitatory amino acid (EAA)-like substance, which activates N-methyl-D-aspartate (NMDA) and non-NMDA receptor subtypes on AMBc neurons. Activation of NMDA receptors is required for functional information transfer in this oesophagomotor pathway and, in turn, this system is dependent on the integrity of somatostatinergic input originating from the NTSc. -- Apart from solitarial input, NTSc-AMBc synaptic transmission is subject to modulation by nicotinic cholinoceptor-mediated input originating from the zona intermedialis reticularis parvicellularis (ZIRP). By augmenting the depolarizing response to glutamate and inhibiting nicotinic cholinoceptor-mediated excitation, somatostatin presumably plays a critical role in oesophagomotor control at the AMBc level. -- Taken together, the present work lends strong credence to the hypothesized role of the NTSc-AMBc projection as the common premotor substrate of oesophageal peristaltic control. NTSc premotoneurons are involved in initiating and organising the sequence of peristaltic activity, whereas AMBc motoneurons are intricately involved in modifying the final oesophagomotor output.

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