Either N- or P-type Calcium Channels Mediate GABA Release at Distinct Hippocampal Inhibitory Synapses (original) (raw)

Very few synapses allow direct access August Forel-Strasse 1 to presynaptic elements (Takahashi et al., 1996). The CH-8029 Zurich responses of cells to stimulation of a population of nerve Switzerland terminals, using either an extracellular electrode or an elevation of the external K ϩ concentration, have therefore usually been examined. Such techniques activate Summary large numbers of synapses of undetermined origin. These stimulation techniques are probably adequate Transmitter release at most central synapses depends when synapses are formed by a homogeneous populaon multiple types of calcium channels. Identification tion of neurons (e.g., Mintz et al., 1995), but they may of the channels mediating GABA release in hippocamlead to misleading results when a heterogeneous popupus is complicated by the heterogeneity of interneulation of presynaptic cells is involved. rons. Unitary IPSPs were recorded from pairs of inhibi-Hippocampal pyramidal cells receive inhibitory input tory and pyramidal cells in hippocampal slice cultures. from a diverse population of interneurons (Buckmaster The N-type channel antagonist-conotoxin MVIIA and Soltesz, 1996; Freund and Buzsá ki, 1996), and this is abolished IPSPs generated by interneurons in st. radireflected in the variable properties of inhibitory synaptic atum, whereas the P/Q-type antagonist-agatoxin responses. Spontaneous, action potential-independent IVA had no effect. In contrast,-agatoxin IVA abol-GABA release occurs primarily at perisomatic rather ished IPSPs generated by st. lucidum and st. oriens than dendritic synapses, suggesting release probability interneurons, but-conotoxin MVIIA had no effect. differs at these synapses (Soltesz et al., 1995). In addi-After unitary IPSPs were blocked by toxin, transmistion, GABA release from some but not all inhibitory synsion could not be restored by increasing presynaptic apses is inhibited by presynaptic GABA B autoreceptors calcium entry. The axons of the two types of interneuin the hippocampus (Lambert and Wilson, 1993; Pearce rons terminated within distinct strata of area CA3. et al., 1995), in part via an inhibition of presynaptic cal-Thus, GABA release onto pyramidal cells, unlike glutacium channels (Doze et al., 1995). Finally, evoked inhibimate release, is mediated entirely by either Nor tory synaptic responses are highly sensitive to the P-type calcium channels, depending on the presynap-N-type calcium current antagonist-conotoxin GVIA tic cell and the postsynaptic location of the synapse.