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1 Psychology, Ithaca College, Ithaca, New York, United States; Neurobiology and Behavior, Cornell University, Ithaca, New York, United States
2 Psychology, Ithaca College, Ithaca, New York, United States
3 Neurobiology and Behavior, Cornell University, Ithaca, New York, United States
* To whom correspondence should be addressed. E-mail: peck{at}ithaca.edu.
We have studied the functional role and modulation of the hyperpolarization-activated inward current, Ih, in the pyloric network of the lobster stomatogastric ganglion. In isolated neurons, Ih is a small current with a hyperpolarized voltage of half activation (VAct) and a slow time constant of activation (
Act). Bath application of dopamine (DA), octopamine (OCT) or serotonin (5HT) modified Ih in selected synaptically isolated pyloric neurons. DA significantly enhanced Ih in the anterior burster (AB) neuron by depolarizing its VAct, accelerating its Act, and enhancing its maximal conductance (gmax). DA more weakly enhanced Ih in the pyloric constrictor (PY) and ventricular dilator (VD) neurons. OCT weakly depolarized VAct and accelerated Act in the VD and inferior cardiac (IC) neurons. 5HT depolarized VAct 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 Ih blocker, cesium (Cs+) caused a mean increase in the period of 8%, though this effect was highly variable. When Cs+ was applied to an isolated ganglion where the pyloric rhythm had been activated by DA, the cycle period was consistently increased by 13.5% with no other strong changes in rhythm parameters. These results suggest that Ih regulates the pyloric rhythm by accelerating AB pacemaker frequency, but that this effect can vary with the modulatory conditions.
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