Journal of neurophysiology
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Activation of metabotropic glutamate receptors (mGluRs) has diverse effects on the functioning of vertebrate synapses. The cellular mechanisms that underlie these changes, however, are largely unknown. The role of presynaptic mGluRs in modulating Ca(2+) dynamics and regulating neurotransmitter release was investigated at the vestibulospinal-reticulospinal (VS-RS) synapse in the lamprey brain stem. ⋯ These results demonstrate the presence of presynaptic Group I mGluRs at the VS-RS synapse. Activation of these receptors leads to a rise in [Ca(2+)](i) and enhances the spontaneous and evoked release of glutamate. Taken together, these studies highlight the importance of synaptic activation of these facilitatory autoreceptors in both short-term plasticity and synaptic transmission.
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Mammalian vestibular organs have two types of hair cell, type I and type II, which differ morphologically and electrophysiologically. Type I hair cells alone express an outwardly rectifying current, I(K, L), which activates at relatively negative voltages. We used whole cell and patch configurations to study I(K,L) in hair cells isolated from the sensory epithelia of rat semicircular canals. ⋯ Ca(2+)-dependent NO synthase is reported to be in hair cells and nerve terminals in the vestibular epithelium. Excitatory input to vestibular organs may lead, through Ca(2+) influx, to NO production and inhibition of I(K,L). The resulting increase in R(m) would augment the receptor potential, a form of positive feedback.