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Amine Modulation of I_h in a Small Neural Network

¹Department of Psychology, Ithaca College; and ²Department of Neurobiology and Behavior, Cornell University, Ithaca, New York

Submitted 26 April 2005; accepted in final form 26 August 2006

We studied the functional role and modulation of the hyperpolarization-activated inward current (I_h) in the pyloric network of the lobster stomatogastric ganglion. In isolated neurons, I_h is a small current with a hyperpolarized voltage of half-activation (V_Act) and a slow time constant of activation (_Act). Bath application of dopamine (DA), octopamine (OCT), or serotonin (5HT) modified I_h in selected synaptically isolated pyloric neurons. DA significantly enhanced I_h in the anterior burster (AB) neuron by depolarizing its V_Act, accelerating its _Act, and enhancing its maximal conductance (g_max). DA more weakly enhanced I_h in the pyloric constrictor (PY) and ventricular dilator (VD) neurons. OCT weakly depolarized V_Act and accelerated _Act in the VD and inferior cardiac (IC) neurons. 5HT depolarized V_Act in the IC neuron. Under control conditions with intact modulatory inputs from other ganglia, the pyloric rhythm cycles strongly at about 1–2 Hz. Bath application of the I_h blocker cesium (Cs⁺) caused a mean increase in the period of 8%, although this effect was highly variable. When Cs⁺ was applied to an isolated ganglion where the pyloric rhythm had been activated only by DA, the cycle period was consistently increased by 13.5%, with no other strong changes in rhythm parameters. These results suggest that I_h regulates the pyloric rhythm by accelerating AB pacemaker frequency, but that this effect can vary with the modulatory conditions.

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