Multisite optical recording of excitability in the enteric nervous system

Free cytosolic Ca2+ recordings from myenteric neurones in multilayer intestinal preparations

The ability to simultaneously monitor different myenteric neurones in a multilayer preparation may enhance our understanding of the enteric nervous system. Longitudinal muscle myenteric plexus preparations were mounted in recording chambers with a coverslip base and loaded with Indo-1-AM. cytosolic Ca2+ concentration ([Ca2+]i); changes were recorded at room temperature with a confocal microscope. In addition to mechanical (pressure-ring) and pharmacological (nifedipine) reduction of muscle contractions, purpose-designed software was developed to reposition regions of interest and avoid artefacts. Confocal scanning permitted optical selection of single cell layers. High K+ depolarization, used to distinguish between excitable and nonexcitable cells, caused a synchronous [Ca2+]i rise in 84.3% of the ganglion cells. Acetylcholine, substance P and serotonin (all at 10(-5) mol L(-1)) induced transient [Ca2+]i changes in subpopulations of myenteric neurones (45.1%, 42.9 and 21.9%, respectively). In addition to immediate responses to agonists, delayed [Ca2+]i changes were also recorded, suggesting the presence of both directly activated and synaptically driven neurones. Functionally identified neurones and other cells in close apposition to the ganglia (interstitial cells of Cajal) could also be studied. This study demonstrates the potential of optical Ca2+ recordings to monitor spread of activity in myenteric neurones and to study their interaction with non-neuronal targets.

Enteric pathways in the stomach

This report summarises the characteristics of target specific projection and neurochemical coding patterns of motor and interneuronal pathways in the gastric enteric nervous system (ENS) which are involved in the innervation of the mucosa, the circular and the longitudinal muscle. The pathways were identified by retrograde tracing and further characterised by optical and intracellular recordings of the synaptic activation of muscle motor neurones, and by recordings of pathway-specific muscle responses. All motor pathways had polarised projections consisting of ascending cholinergic and descending nitrergic populations. Thus, both muscle layers were innervated by excitatory and inhibitory motor neurones. Their projections indicated the presence of intrinsic circuits that mediate excitatory and inhibitory components of a peristaltic reflex and/or are involved in reflex mediated changes in gastric tone. Although polarised projections were also identified for interneuronal pathways, a substantial proportion of descending interneurones was cholinergic. Interneurones and longitudinal muscle motor pathways had longitudinal projection preferences whereas circular muscle motor pathways had circumferential projection preferences. Target-specific coding was primarily revealed for cholinergic populations; ChAT/ENK/+/-SP neurones projected to the muscle layers, ChAT/NPY/+/-VIP projected to the mucosa and ChAT/+/-SP/+/-5-HT/+/-Calret/+/-Calb were interneurones. Muscle strip recordings revealed the functional significance of ascending excitatory and descending inhibitory pathways to the circular muscle and the prominent influence of ascending and descending cholinergic interneurones which activated excitatory and inhibitory circular muscle motor neurones through nicotinic synapses. It is concluded that enteric pathways in the stomach have region specific features which reflect structural and functional adaptation of the gastric ENS.