Glial responses during evoked behaviors in the leech

Glial cells can respond with membrane potential changes during electrically stimulated neuronal activity (Kuffler, Proc R Soc Lond B 168:1-21, 1967; Orkand, Oxford University Press, 1995). Their role in contributing to, or controlling, neural circuits underlying behaviors, however, is completely unknown. We have used semi-intact preparations of the leech Hirudo medicinalis, where behaviors can be elicited and monitored (Kristan et al., J Neurobiol 27:380-389, 1995), to record membrane responses of identified glial cells during whole-body shortening and during fictive swimming. Giant glial cells are located in the neuropil of segmental ganglia, where neuronal axons and dendrites establish numerous synaptic contacts (Coggeshall and Fawcett, J Neurophysiol 27:229-289, 1964). We report here that these glial cells hyperpolarize when the whole-body-shortening response is evoked but not during fictive swimming. To our knowledge, this is the first report that associates a specific behavior with glial cell responses.