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

Abstract

Gwynne RM, Bornstein JC. Electrical stimulation of the mucosa evokes slow EPSPs mediated by NK1 tachykinin receptors and by P2Y1 purinoceptors in different myenteric neurons. Am J Physiol Gastrointest Liver Physiol 297: G179 -G186, 2009. First published April 30, 2009 doi:10.1152/ajpgi.90700.2008.-Slow excitatory postsynaptic potentials (EPSPs) in enteric neurons arise from diverse sources, but which neurotransmitters mediate specific types of slow EPSPs is unclear. We investigated transmitters and receptors mediating slow EPSPs in myenteric neurons evoked by electrical stimulation of the mucosa in guinea pig small intestine. Segments of ileum or jejunum were dissected to allow access to the myenteric plexus adjacent to intact mucosa, in vitro. AH and S neurons were impaled with conventional intracellular electrodes. Trains of stimuli delivered to the mucosa evoked slow EPSPs in AH neurons that were blocked or depressed by the neurokinin-1 (NK1) tachykinin antagonist SR140333 (100 nM) in 10 of 11 neurons; the NK3 tachykinin receptor antagonist SR142801 (100 nM) had no effect on slow EPSPs in seven of nine AH neurons. Single pulses to the mucosa evoked fast EPSPs and slow depolarizations in S neurons. The depolarizations were divided into intermediate (durations 300 -900 ms) or slow (durations 1.3-9 s) EPSPs. The slow EPSPs were blocked by pyridoxal phosphate-6-axophenyl-2-4-disulfonic acid (30 M, N ϭ 3) or the specific P2Y1 antagonist MRS 2179 (10 M, N ϭ 6) and were predominantly in anally projecting S neurons that were immunoreactive for nitric oxide synthase (NOS). In contrast, intermediate EPSPs were predominantly evoked in NOS-negative neurons; these were abolished by MRS 2179 (N ϭ 8). Thus activation of pathways running from the mucosa excites three different types of slow EPSP in myenteric neurons, which are mediated by either a tachykinin (NK1, AH neurons) or a purine nucleotide (P2Y1, S neurons). AH neurons; S neurons; ATP; neurokinin-1 THE NEURAL PATHWAYS CONTROLLING intestinal motility are contained within the myenteric plexus of the enteric nervous system (ENS). These pathways are activated by various stimuli such as the presence of nutrients in the lumen (16,19) and distension of the gut wall to adapt motility according to conditions within the lumen (for review see Ref. 5). Studies of the guinea pig ileum have identified at least 15 classes of myenteric neurons that can be distinguished by their morphologies, neurochemical codes, and functions. These include one or more populations of intrinsic sensory (or primary afferent) neurons, orally directed (ascending) and anally directed (descending) interneurons, and excitatory and inhibitory motor neurons supplying the circular and longitudinal muscle layers (9). However, the diversity of the ENS is such that the functions of some classes cannot always be clearly defined. For example, there are recent reports that some interneurons in the myenteric plexus of the guinea pig distal colon respond directly to stretch (39, 40). Furthermore, under some conditi...

Purinergic and nitrergic neuromuscular transmission mediates spontaneous neuronal activity in the rat colon

“…In the present paper, we demonstrate that ATP or a related purine acting on P2Y 1 receptor is probably the transmitter involved in this response. It is important to note that, in the presence of MRS-2500, L-NNA was still able to cause smooth muscle depolarization, suggesting that prejunctional P2Y 1 receptors that might mediate sEPSP (15) are not involved in NO release.…”

The roles of purinergic signaling during gastrointestinal inflammation

“…In the submucosal plexus, purinergic fast EPSPs are rarely observed in the small or large intestines [32,33]. Tachykinins, acetylcholine, and serotonin are the primary mediators of slow EPSPs in the ENS, but purinergic slow EPSPs mediated by P2Y 1 receptors have been reported in myenteric [34,35 ] and submucosal [32,36] ganglia. Neurotransmission from enteric and sympathetic neurons to enteric glial cells involves purinergic activation of P2Y 1 and P2Y 4 receptors [37–39], and is regulated by ectonucleotidases [16,37].…”

Transmission to Interneurons Is via Slow Excitatory Synaptic Potentials Mediated by P2Y1 Receptors during Descending Inhibition in Guinea-Pig Ileum

“…In 8 cases, the axon could be followed through several ganglia before either fading or reaching the end of the preparation. In 7 of these cells, the axon produced varicose side branches in one or more ganglia (Figure 2B), indicating that it was an interneuron [12], [13]. Immunoreactivity for NOS was examined for 6 of these neurons and all were immunoreactive for this enzyme (Figure 2B).…”

“…Furthermore, these slow EPSPs were found to be the result of synaptic transmission from descending interneurons with cell bodies close to the distension sensitive sensory neurons. In a second series of experiments, we showed that individual electrical stimuli applied focally to the mucosa evoked P2Y 1 mediated slow EPSPs in the same population of descending interneurons [13]. The question remains whether the slow EPSPs evoked by distension are mediated by P2Y receptors and if blocking these receptors will modify descending inhibition.…”