Generation of rhythmic patterns in the absence of descending commands is an essential and powerful trait of many motor networks. Cyclic rhythmic discharges of motoneurons in repeated motor activities like locomotion, mastication and respiration require underlying circuits of neurons, which are called central pattern generators (CPG). This study examined the possible roles of Ih cation channels in the pyloric network of the stomatogastric nervous system, a rhythmically active network of motoneurons that controls movements of the lobster foregut. Of specific interest were the H-current�s involvement in maintaining firing properties, the distribution of Ih channels within the stomatogastric ganglion, and a potential role for Ih in regulation of synaptic strength. I was able to confirm a homeostatic interaction of Ih with A-type potassium channels, where the over-expression of the IA shal gene after RNA injection evoked a compensatory increase of Ih in different motoneuron types. I observed an additional, non-Ih component of the hyperpolarization activated current, which was more likely to occur in shal-RNA and gfp-RNA injected neurons, compared to untreated neurons. Further, I showed that the homeostatic response of Ih increase is unidirectional; overexpression of the Ih protein PIIH did not lead to an increase of IA. In an immunocytochemical study, I found high concentrations of Ih protein localized in the fine neuropil of the stomatogastric ganglion, an area which is rich in synaptic contacts. Finally, I demonstrate a potential role for Ih in regulating synaptic transmission, for which I found evidence in electrophysiological experiments, where the amplitude of inhibitory postsynaptic potentials decreased with increasing activation of Ih
