R-Type Ca2+ channels couple to inhibitory neurotransmission to the longitudinal muscle in the guinea-pig ileum.

NEW FINDINGS: What is the central question of this study? Subtypes of enteric neurons are coded by the neurotransmitters they synthesize, but it is not known whether enteric neuron subtypes might also be coded by other proteins, including calcium channel subtypes controlling neurotransmitter release. What is the main finding and its importance? Our data indicate that guinea-pig ileum myenteric neuron subtypes may be coded by calcium channel subtypes. We found that R-type calcium channels are expressed by inhibitory but not excitatory longitudinal muscle motoneurons. R-Type calcium channels are also not expressed by circular muscle inhibitory motoneurons. Calcium channel subtype-selective antagonists could be used to target subtypes of neurons to treat gastrointestinal motility disorders. There is evidence that R-type Ca2+ channels contribute to synaptic transmission in the myenteric plexus. It is unknown whether R-type Ca2+ channels contribute to neuromuscular transmission. We measured the effects of the nitric oxide synthase inhibitor nitro-l-arginine (NLA), Ca2+ channel blockers and apamin (SK channel blocker) on neurogenic relaxations and contractions of the guinea-pig ileum longitudinal muscle-myenteric plexus (LMMP) in vitro. We used intracellular recordings to measure inhibitory junction potentials. Immunohistochemical techniques localized R-type Ca2+ channel protein in the LMMP and circular muscle. Cadmium chloride (pan-Ca2+ channel blocker) blocked and NLA and NiCl2 (R-type Ca2+ channel blocker) reduced neurogenic relaxations in a non-additive manner. Nickel chloride did not alter neurogenic cholinergic contractions, but it potentiated neurogenic non-cholinergic contractions. Relaxations were inhibited by apamin, NiCl2 and NLA and were blocked by combined application of these drugs. Relaxations were reduced by NiCl2 or ω-conotoxin (N-type Ca2+ channel blocker) and were blocked by combined application of these drugs. Longitudinal muscle inhibitory junction potentials were inhibited by NiCl2 but not MRS 2179 (P2Y1 receptor antagonist). Circular muscle inhibitory junction potentials were blocked by apamin, MRS 2179, ω-conotoxin and CdCl2 but not NiCl2 . We conclude that neuronal R-type Ca2+ channels contribute to inhibitory neurotransmission to longitudinal muscle but less so or not all in the circular muscle of the guinea-pig ileum.

Upregulation of L-type calcium channels in colonic inhibitory motoneurons of P/Q-type calcium channel-deficient mice.

Enteric inhibitory motoneurons use nitric oxide and a purine neurotransmitter to relax gastrointestinal smooth muscle. Enteric P/Q-type Ca2+ channels contribute to excitatory neuromuscular transmission; their contribution to inhibitory transmission is less clear. We used the colon from tottering mice (tg/tg, loss of function mutation in the α1A pore-forming subunit of P/Q-type Ca2+ channels) to test the hypothesis that P/Q-type Ca2+ channels contribute to inhibitory neuromuscular transmission and colonic propulsive motility. Fecal pellet output in vivo and the colonic migrating motor complex (ex vivo) were measured. Neurogenic circular muscle relaxations and inhibitory junction potentials (IJPs) were also measured ex vivo. Colonic propulsive motility in vivo and ex vivo was impaired in tg/tg mice. IJPs were either unchanged or somewhat larger in tissues from tg/tg compared with wild-type (WT) mice. Nifedipine (L-type Ca2+ channel antagonist) inhibited IJPs by 35 and 14% in tissues from tg/tg and WT mice, respectively. The contribution of N- and R-type channels to neuromuscular transmission was larger in tissues from tg/tg compared with WT mice. The resting membrane potential of circular muscle cells was similar in tissues from tg/tg and WT mice. Neurogenic relaxations of circular muscle from tg/tg and WT mice were similar. These results demonstrate that a functional deficit in P/Q-type channels does not alter propulsive colonic motility. Myenteric neuron L-type Ca2+ channel function increases to compensate for loss of functional P/Q-type Ca2+ channels. This compensation maintains inhibitory neuromuscular transmission and normal colonic motility.

Bridge to neuroscience workshop: An effective educational tool to introduce principles of neuroscience to Hispanics students.

Neuroscience as a discipline is rarely covered in educational institutions in Puerto Rico. In an effort to overcome this deficit we developed the Bridge to Neuroscience Workshop (BNW), a full-day hands-on workshop in neuroscience education. BNW was conceived as an auxiliary component of a parent recruitment program called Bridge to the PhD in Neuroscience Program (BPNP). The objectives of BNW are to identify promising students for BPNP, and to increase awareness of neuroscience as a discipline and a career option. BNW introduces basic concepts in neuroscience using a variety of educational techniques, including mini-lectures, interactive discussions, case studies, experimentation, and a sheep brain dissection. Since its inception in 2011 BNW has undergone a series of transformations that continue to improve upon an already successful and influential educational program for underrepresented minorities. As of Fall 2018, we have presented 21 workshops, impacting 200 high school and 424 undergraduate students. BNW has been offered at University of Puerto Rico (UPR)-Arecibo, UPR-Cayey, UPR-Humacao, Pontificia Universidad Católica de Ponce, and Universidad Interamericana de Puerto Rico-Arecibo. A pre-and post evaluation was given to evaluate material comprehension and thus measure effectiveness of our one-day interactive workshop. Our results suggest that both high school and undergraduate students have little prior knowledge of neuroscience, and that participation in BNW improves not only understanding, but also enthusiasm for the discipline. Currently, our assessment has only been able to evaluate short-term effects (e.g. comprehension and learning). Therefore, our current focus is developing methods capable of determining how participation in BNW impacts future academic and career decisions.