The effect of calcium ions on the responses to motoneurons to substance P and eledoisin-related peptide in the toad and rat spinal cord.
The effects of changes in the external calcium ion concentration [Ca2+]0 on segmental reflexes and the responses of motoneurons to bath applied agonists have been studied in the toad and rat spinal cords in vitro. Reducing [Ca2+]0 enhanced polysynaptic reflexes in the toad, with maximal discharges occurring at 0.3 mM. Monosynaptic reflexes in the rat were reduced by lowering [Ca2+]0. Responses of toad motoneurons to substance P and eledoisin-related peptide were enhanced by lowering [Ca2+]0, maximum responses occurring at 0.3 mM. Lowering [Ca2+]0 also enhanced responses to L-glutamate but the effect was smaller and less consistent. This effect of Ca2+ was abolished by the addition of tetrodotoxin to the bathing solution. Toad motoneuron responses to gamma-aminobutyrate and glycine were not affected by alterations in [Ca2+]0. Rat motoneuron responses to substance P and eledoisin-related peptide were also enhanced by reductions in [Ca2+]0 but the effect was more pronounced in younger (less than 5 days post partum) than older (5-10 days post partum) animals. These results are consistent with the idea that motoneuron responses to peptides in normal solutions result from activation of receptors on both motoneurons and interneurons: enhancement of the responses by lowering [Ca2+]0 results from the potentiation of the transynaptic component.
D000818:Animals; D000831:Animals, Newborn; D002024:Bufo marinus; D002118:Calcium / Q000494:pharmacology*; D004600:Eledoisin / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D051381:Rats; D012018:Reflex / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects*; D013373:Substance P / Q000037:antagonists & inhibitors*
D018377:Neurotransmitter Agents; C019092:substance P analog(eledoisin related peptide); D013373:Substance P; D004600:Eledoisin; D002118:Calcium