tnrnflrfamide and crustacean-cardioactive-peptide

Neurons in the central pattern-generating circuits in the crustacean stomatogastric ganglion (STG) release neurotransmitter both as a graded function of presynaptic membrane potential that persists in TTX and in response to action potentials. In the STG of the male crab

Topics: Action Potentials; Animals; Brachyura; Central Pattern Generators; Ganglia, Invertebrate; Male; Muscarinic Agonists; Neuropeptides; Neurotransmitter Agents; Oligopeptides; Oxotremorine; Pylorus; Pyrrolidonecarboxylic Acid; Sodium Channel Blockers; Synaptic Transmission; Tetrodotoxin

Six neuromodulators [proctolin, Cancer borealis tachykinin-related peptide Ia, crustacean cardioactive peptide (CCAP), red pigment-concentrating hormone, TNRNFLRFamide, and pilocarpine] converge onto the same voltage-dependent inward current in stomatogastric ganglion (STG) neurons of the crab C. borealis. We show here that each of these modulators acts on a distinct subset of pyloric network neurons in the STG. To ask whether the differences in cell targets could account for their differential effects on the pyloric rhythm, we systematically compared the motor patterns produced by proctolin and CCAP. The motor patterns produced in proctolin and CCAP differed quantitatively in a number of ways. Proctolin and CCAP both act on the lateral pyloric neuron and the inferior cardiac neuron. Proctolin additionally acts on the pyloric dilator (PD) neurons, the pyloric (PY) neurons, and the ventricular dilator neuron. Using the dynamic clamp, we introduced an artificial peptide-elicited current into the PD and PY neurons, in the presence of CCAP, and converted the CCAP rhythm into a rhythm that was statistically similar to that seen in proctolin. This suggests that the differences in the network effects of these two modulators can primarily be attributed to the known differential distributions of their receptors onto distinct subsets of neurons, despite the fact that they activate the same current.

Topics: Animals; Brachyura; Digestive System; Dose-Response Relationship, Drug; Ganglia, Invertebrate; Membrane Potentials; Nerve Net; Nervous System Physiological Phenomena; Neurons; Neuropeptides; Neurotransmitter Agents; Oligopeptides; Patch-Clamp Techniques; Periodicity; Pilocarpine; Pyrrolidonecarboxylic Acid; Tachykinins

The stomatogastric ganglion of the crab, Cancer borealis, is modulated by >20 different substances, including numerous neuropeptides. One of these peptides, proctolin, activates an inward current that shows strong outward rectification (Golowasch and Marder, 1992). Decreasing the extracellular Ca(2+) concentration linearizes the current-voltage curve of the proctolin-induced current. We used voltage clamp to study the currents evoked by proctolin and five additional modulators [C. borealis tachykinin-related peptide Ia (CabTRP Ia), crustacean cardioactive peptide, red pigment-concentrating hormone, TNRNFLRFamide, and the muscarinic agonist pilocarpine] in stomatogastric ganglion neurons, both in the intact ganglion and in dissociated cell culture. Subtraction currents yielded proctolin-like current-voltage relationships for all six substances, and the current-voltage curves of all six substances showed linearization in low external Ca(2+). The lateral pyloric neuron responded to all six modulators, but the ventricular dilator neuron only responded to a subset of them. Bath application of saturating concentrations of proctolin occluded the response to CabTRP and vice versa. N-(6-Aminohexyl)-5-chloro-1-napthalensulfonamide, a calmodulin inhibitor, increased the amplitude and altered the voltage dependence of the responses elicited by CabTRP and proctolin. Together, these data indicate that all six substances converge onto the same voltage-dependent current, although they activate different receptors. Therefore, differential network responses evoked by these substances may primarily depend on the receptor distribution on network neurons.

Topics: Animals; Biological Clocks; Brachyura; Calmodulin; Cells, Cultured; Drug Synergism; Ganglia, Invertebrate; In Vitro Techniques; Invertebrate Hormones; Ion Channels; Neurons; Neuropeptides; Oligopeptides; Patch-Clamp Techniques; Pyrrolidonecarboxylic Acid; Second Messenger Systems