Inhibitory effects of forskolin and papaverine on nerve conduction partially blocked by tetrodotoxin in the frog sciatic nerve

Rat hippocampal slices were exposed briefly (12-15 min) to AlF4- (10 mmol/l NaF, 10 mumol/l AlCl3). The effect on synaptic transmission in area CAl was measured using extracellular electrodes placed in the stratum pyramidale and stratum radiatum. During fluoride exposure, both spike and EPSP amplitude fell to very low levels. Upon washout, spike amplitude recovered beyond control values, and in half of the preparations a prolonged enhancement of spike amplitude (greater than 2 h) occurred. Similar modulation of EPSP slope indicated that these charges were primarily synaptic. If Al3+ was omitted from the F(-)-containing saline, enhancement of spike amplitude, when observed, was brief (20-30 min) and no enhancement of EPSP slope was seen. Omission of Ca2+ from the AlF(4-)-containing saline also abolished any long-lasting enhancement of synaptic transmission, though population spike amplitude in most slices showed a brief (20-30 min) stimulatory response. In preparations in which LTP had previously been saturated, synaptic transmission was not enhanced by exposure to AlF4-. It is concluded that NaF/ACl3 exposure induces an LTP-like process by G-protein activation, which involves recruitment of processes involved in LTP, possibly including an enhancement of Ca(2+)-influx.

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