Electrical stimulation reveals complex neuronal input and activation patterns in single myenteric guinea pig ganglia

Synaptic activation of putative sensory neurons by hexamethonium-sensitive nerve pathways in mouse colon

The gastrointestinal tract contains its own independent population of sensory neurons within the gut wall. These sensory neurons have been referred to as intrinsic primary afferent neurons (IPANs) and can be identified by immunoreactivity to calcitonin gene-related peptide (CGRP) in mice. A common feature of IPANs is a paucity of fast synaptic inputs observed during sharp microelectrode recordings. Whether this is observed using different recording techniques is of particular interest for understanding the physiology of these neurons and neural circuit modeling. Here, we imaged spontaneous and evoked activation of myenteric neurons in isolated whole preparations of mouse colon and correlated recordings with CGRP and nitric oxide synthase (NOS) immunoreactivity, post hoc. Calcium indicator fluo 4 was used for this purpose. Calcium responses were recorded in nerve cell bodies located 5-10 mm oral to transmural electrical nerve stimuli. A total of 618 recorded neurons were classified for CGRP or NOS immunoreactivity. Aboral electrical stimulation evoked short-latency calcium transients in the majority of myenteric neurons, including ~90% of CGRP-immunoreactive Dogiel type II neurons. Activation of Dogiel type II neurons had a time course consistent with fast synaptic transmission and was always abolished by hexamethonium (300 μM) and by low-calcium Krebs solution. The nicotinic receptor agonist 1,1-dimethyl-4-phenylpiperazinium iodide (during synaptic blockade) directly activated Dogiel type II neurons. The present study suggests that murine colonic Dogiel type II neurons receive prominent fast excitatory synaptic inputs from hexamethonium-sensitive neural pathways. NEW & NOTEWORTHY Myenteric neurons in isolated mouse colon were recorded using calcium imaging and then neurochemically defined. Short-latency calcium transients were detected in >90% of calcitonin gene-related peptide-immunoreactive neurons to electrical stimulation of hexamethonium-sensitive pathways. Putative sensory Dogiel type II calcitonin gene-related peptide-immunoreactive myenteric neurons may receive widespread fast synaptic inputs in mouse colon.

Technicalities of colonoscopy: endoscopic microscopy - where are we heading?

Confocal laser endomicroscopy (CLE) is a new endoscopic imaging tool enabling in vivo histology during ongoing endoscopy. Basically, three different patterns can be seen in the colon: normal, neoplastic and inflammatory mucosa. Several pilot studies have shown an excellent correlation with classical histology. However, what could be the future indications of CLE? (1) Differentiating neoplastic from inflammatory changes constitutes a promising diagnostic tool in screening for dysplasia in ulcerative colitis. This can help to further increase the efficacy of chromoendoscopy in dysplasia detection and reduce the number of biopsies. The possibility to differentiate sporadic adenoma from dysplasia-associated lesion or mass could have an immediate impact on patient management. (2) The diagnosis of collagenous colitis depends on multiple random biopsies. Case series have shown that CLE can guide the endoscopist to take more representative biopsies to make the diagnosis. Large prospective trials are needed to confirm this finding. (3) An interesting clinical application is graft-versus-host disease (GVHD). A pilot study showed that it was possible to predict the presence of GVHD in 14/19 patients with GVHD out of 35 patients who were referred for diarrhea after stem cell transplantation. (4) CLE for standard polyp surveillance is probably redundant since it will not change patient management at this stage. Moreover, it can currently not differentiate between classical hyperplastic and sessile serrated adenomas. (5) Future additional technological improvements of the system with faster Z-scanning, deeper light penetration and 3D reconstruction will help to improve the quality of CLE. Reports on in vivo molecular imaging and assessment of physiological changes provide a promising glance at the future possibilities of CLE imaging.

Prolonged IL-1beta exposure alters neurotransmitter and electrically induced Ca(2+) responses in the myenteric plexus

BACKGROUND Infection and inflammatory diseases of the gut results in profound changes of intestinal motor function. Acute administration of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) was shown to have excitatory and neuromodulatory roles in the myenteric plexus. Here we aimed to study the effect of prolonged IL-1beta incubation on the response of myenteric neurones to different stimuli. METHODS Longitudinal muscle myenteric plexus preparations (LMMP's) of the guinea pig jejunum were incubated for 24 h in medium with or without IL-1beta. After loading with Fluo-4, calcium imaging was used to visualize activation of neurones. The response to application of serotonin (5-HT), substance P (SP) and ATP or to electrical fibre tract stimulation (eFTS) was tested. Expression of nNOS, HuD, calbindin and calretinin was compared by immunohistochemistry. KEY RESULTS IL-1beta concentration-dependently influenced the neuronal responsiveness and duration of the [Ca(2+)](i) rises to 5-HT and ATP, while it also affected the Ca(2+)-transient amplitudes induced by 5-HT, ATP and SP. Ca(2+)-transients in response to eFTS were observed in significantly more neurones per ganglion after IL-1beta (10(-10) and 10(-11) mol L(-1)). Peak [Ca(2+)](i) rise after eFTS was concentration-dependently decreased by IL-1beta. The duration of the [Ca(2+)](i) rise after eFTS was prolonged after IL-1beta 10(-12) mol L(-1). IL-1beta (10(-9) mol L(-1)) incubation did not affect the number of nNOS, calretinin and calbindin expressing neurones, nor did it induce neuronal loss (HuD). CONCLUSIONS & INFERENCES In this study, IL-1beta differentially modulates the neuronal response to eFTS and neurotransmitter application in the myenteric plexus of guinea pigs. This cytokine could be implicated in the motility disturbances observed during gastrointestinal inflammation.

Dual purinergic synaptic transmission in the human enteric nervous system

Based on findings in rodents, we sought to test the hypothesis that purinergic modulation of synaptic transmission occurs in the human intestine. Time series analysis of intraneuronal free Ca(2+) levels in submucosal plexus (SMP) from Roux-en-Y specimens was done using Zeiss LSM laser-scanning confocal fluo-4 AM Ca(2+) imaging. A 3-s fiber tract stimulation (FTS) was used to elicit a synaptic Ca(2+) response. Short-circuit current (I(sc) = chloride secretion) was recorded in mucosa-SMP in flux chambers. A distension reflex or electrical field stimulation was used to study I(sc) responses. Ca(2+) imaging was done in 1,222 neurons responding to high-K(+) depolarization from 61 surgical cases. FTS evoked synaptic Ca(2+) responses in 62% of recorded neurons. FTS caused frequency-dependent Ca(2+) responses (0.1-100 Hz). FTS Ca(2+) responses were inhibited by Omega-conotoxin (70%), hexamethonium (50%), TTX, high Mg(2+)/low Ca(2+) (< or = 100%), or capsaicin (25%). A P2Y(1) receptor (P2Y(1)R) antagonist, MRS-2179 or PLC inhibitor U-73122, blocked FTS responses (75-90%). P2Y(1)R-immunoreactivity occurred in 39% of vasoactive intestinal peptide-positive neurons. The selective adenosine A(3) receptor (AdoA(3)R) agonist 2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide (2-Cl-IBMECA) caused concentration- and frequency-dependent inhibition of FTS Ca(2+) responses (IC(50) = 8.5 x 10(-8) M). The AdoA(3)R antagonist MRS-1220 augmented such Ca(2+) responses; 2-Cl-IBMECA competed with MRS-1220. Knockdown of AdoA(1)R with 8-cyclopentyl-3-N-(3-{[3-(4-fluorosulphonyl)benzoyl]-oxy}-propyl)-1-N-propyl-xanthine did not prevent 2-Cl-IBMECA effects. MRS-1220 caused 31% augmentation of TTX-sensitive distension I(sc) responses. The SMP from Roux-en-Y patients is a suitable model to study synaptic transmission in human enteric nervous system (huENS). The P2Y(1)/Galphaq/PLC/inositol 1,3,5-trisphosphate/Ca(2+) signaling pathway, N-type Ca(2+) channels, nicotinic receptors, and extrinsic nerves contribute to neurotransmission in huENS. Inhibitory AdoA(3)R inhibit nucleotide or cholinergic transmission in the huENS.

CRF-induced calcium signaling in guinea pig small intestine myenteric neurons involves CRF-1 receptors and activation of voltage-sensitive calcium channels

Corticotropin-releasing factor (CRF) is a 41-amino acid peptide with distinct effects on gastrointestinal motility involving both CRF-1 and CRF-2 receptor-mediated mechanisms that are generally claimed to be centrally mediated. Evidence for a direct peripheral effect is rather limited. Electrophysiological studies showed a cAMP-dependent prolonged depolarization of guinea pig myenteric neurons on application of CRF. The current study aimed to test the direct effect of CRF on myenteric neurons and to identify the receptor subtype and the possible mechanisms involved. Longitudinal muscle myenteric plexus preparations and myenteric neuron cultures of guinea pig small intestine were incubated with the calcium indicator Fluo-4. Confocal Ca(2+) imaging was used to visualize activation of neurons on application of CRF. All in situ experiments were performed in the presence of nicardipine 10(-6) M to reduce tissue movement. Images were analyzed using Scion image and a specifically developed macro to correct for residual minimal movements. A 75 mM K(+)-Krebs solution identified 1,076 neurons in 46 myenteric ganglia (16 animals). Administration of CRF 10(-6) M and CRF 10(-7) M during 30 s induced a Ca(2+) response in 22.4% of the myenteric neurons (n = 303). Responses were completely abolished in the presence of the nonselective CRF antagonist astressin (n = 55). The selective CRF-1 receptor antagonist CP 154,526 (n = 187) reduced the response significantly to 2.1%. Stresscopin, a CRF-2 receptor agonist, could not activate neurons at 10(-7) M, and its effect at 10(-6) M (15.3%, n = 59) was completely blocked by CP 154,526. TTX 10(-6) M (n = 70) could not block the CRF-induced Ca(2+) transients but reduced the amplitude of the signals significantly. Removal of extracellular Ca(2+) blocked all responses to CRF (n = 47). L-type channels did not contribute to the CRF-induced Ca(2+) transients. Blocking N- or P/Q-type Ca(2+) channels did not reduce the responses significantly. Combined L- and R-type Ca(2+) channel blocking (SNX-482 10(-8) M, n = 64) abolished nearly all responses in situ. Combined L-, N-, and P/Q-type channel blocking also significantly reduced the response to 8.6%. Immunohistochemical staining for CRF-1 receptors clearly labeled individual cell bodies in the ganglia, whereas the CRF-2 receptor staining was barely above background. CRF induces Ca(2+) transients in myenteric neurons via a CRF-1 receptor-dependent mechanism. These Ca(2+) transients highly depend on somatic calcium influx through voltage-operated Ca(2+) channels, in particular R-type channels. Action potential firing through voltage-sensitive sodium channels increases the amplitude of the Ca(2+) signals. Besides centrally mediated effects, CRF is likely to modulate gastrointestinal motility on the myenteric neuronal level.