Morphologies and projections of defined classes of neurons in the submucosa of the guinea‐pig small intestine

Abstract

Four types of neurons have previously been identified by neurochemical markers in the submucosal ganglia of the guinea-pig small intestine, and functional roles have been ascribed to each type. However, morphological differences among the classes have not been determined, and there is only partial information about their projections within the submucosa. In the present work, we used intracellular microelectrodes to fill neurons of each type with biocytin, which was then converted to a permanent dye, so that the shapes of the neurons could be determined and their projections within the submucosa could be followed. Cell bodies of noncholinergic secretomotor/ vasodilator neurons had Dogiel type I morphology. These neurons, which are vasoactive intestinal peptide immunoreactive, had single axons that ran through many ganglia without providing terminals around other neurons. Cholinergic secretomotor neurons with neuropeptide Y immunoreactivity had Stach type IV morphology, and cholinergic secretomotor/vasodilator neurons had stellate cell bodies. The axons of these two types ran short distances in the plexus and did not innervate other submucosal neurons. Neurons of the fourth type, intrinsic primary afferent neurons, had cell bodies with Dogiel type II morphology and their processes supplied networks of varicose processes around other nerve cells. It is concluded that each functionally defined type of submucosal neuron has a characteristic morphology and that intrinsic primary afferent neurons synapse with secretomotor neurons to form monosynaptic secretomotor reflex circuits. Anat Rec Part A 272A: 475-483, 2003.

Electrical stimulation of the mucosa evokes slow EPSPs mediated by NK1 tachykinin receptors and by P2Y1 purinoceptors in different myenteric neurons

“…One way this might occur is if inputs to myenteric AH neurons from submucosal AH neurons operate via NK1 receptors, while those inputs from other myenteric AH neurons operate via NK3 receptors. Both submucosal and myenteric AH neurons have projections to the mucosa and to each nerve plexus (12,13), and these connections may be important for the coordination of motility and secretion. Thus the pathway activated by electrical stimulation leading to the NK1-mediated slow EPSPs in our study could involve the activation of either or both of these classes of neurons.…”

Synaptic Transmission at Functionally Identified Synapses in the Enteric Nervous System: Roles for Both Ionotropic and Metabotropic Receptors

“…In guinea-pig ileum, there are 4 classes of neurons within the submucosa: AH/Dogiel type II neurons, cholinergic secretomotor neurons that are immunoreactive for neuropeptide Y, non-cholinergic secretomotor neurons immunoreactive for vasoactive intestinal peptide (VIP) and cholinergic vasodilator neurons immunoreactive for calretinin (for details see [32]). …”

“…Extensive studies of the guinea-pig ileum have identified nearly all these different classes of enteric neurons by their characteristic neurochemistries or chemical codes (for detailed reviews see [16,17,32]). Such studies indicate that there are at least 20 neurochemically and functionally distinct classes of enteric neurons in this part of the guinea-pig gastrointestinal tract (see Table 1 of [16]).…”

Alterations to enteric neural signaling underlie secretory abnormalities of the ileum in experimental colitis in the guinea pig

“…Having identified an abnormality involving the neural control of secretion, in the absence of a corresponding defect in epithelial responsiveness, we investigated the neurophysiological properties of the submucosal plexus. We focused primarily on enteric S neurons, since these have been established as the secretomotor neurons of the guinea pig ileum (18). In S neurons, input resistance, resting membrane potential, rheobase, and the number and width of action potentials were largely unchanged in TNBS-treated animals ( Table 2).…”