Effects of l-amphetamine on the central neurons of the snail

Effects of 2,3-Butanedione Monoxime on Induction of Action Potential Bursts in Central Snail Neurons: Direct and Indirect Modulations of Ionic Currents

The effects of 2,3-butanedione monoxime (BDM) on induction of action potential bursts were studied pharmacologically on the RP4 central neuron of giant African snail (Achatina fulica Ferussac). The effect of okadaic acid on the neuron was also tested. The RP4 neuron showed a spontaneous firing of action potential. Okadaic acid (1 micromol/l) did not alter the frequency of spontaneous action potential while BDM (3 mmol/l) reversibly elicited bursts of potential (BoP) of the RP4 neuron. The BoP elicited by BDM (3 mmol/l) were reversed 20 min after incubation with diazoxide (500 micromol/l) while the BoP were not altered in preparations treated with okadaic acid and BDM. The BDM-elicited BoP were not inhibited after administration with (a) hexamethonium (100 micromol/l), (b) atropine (1 mmol/l), (c) d-tubocurarine (100 micromol/l), (d) prazosin (100 micromol/l), (e) propranolol (100 micromol/l), (f) calcium-free solution, (g) high K(+) (12 mmol/l) or (h) with high Mg(2+) (30 mmol/l) solutions. The BDM-elicited BoP were inhibited by pretreatment with KT-5720 (10 micromol/l) or H89 (10 micromol/l), the protein kinase A inhibitors. However, the BoP were not affected after application of chelerythrine (10 micromol/l) or Ro 31-8220 (10 micromol/l), the protein kinase C inhibitors. Voltage-clamped studies revealed that BDM elicited a negative slope resistance (NSR) at membrane potentials between -50 and -10 mV. The NSR was not detectable at the same membrane potential in control RP4 neuron. It is suggested that the BoP elicited by BDM were not due to (1) the synaptic effects of neurotransmitters; (2) the activation of cholinergic, adrenergic receptors, or (3) phosphatase activity of the neuron. The BDM-elicited BoP were dependent on the protein kinase A related cAMP in the neuron and the delayed outward K(+) current may contribute to the BDM-elicited BoP.

Burst firing of action potentials in central snail neurons elicited by d-amphetamine: effect of anticonvulsants

The effect of anticonvulsants on the burst firing of action potentials in snail central neuron elicited by d-amphetamine was studied in the identified RP4 neuron of the African snail, Achatina fulica Ferussac. Oscillation of membrane potential and burst firing of action potentials were elicited by d-amphetamine in a concentration-dependent manner. Voltage clamped studies revealed that d-amphetamine elicited a negative slope resistance (NSR) in steady-state I-V curve between - 40 and - 10 mV. The burst firing of action potentials was alleviated following extracellular application of phenytoin, but was not affected after ethosuximide, carbamazepine, and valproic acid. The NSR elicited by d-amphetamine was blocked by phenytoin. However, the NSR was not altered if carbamazepine was added. These results suggest that of the four anticonvulsants tested, only phenytoin could alleviate the burst firing of action potentials elicited by d-amphetamine in snail neuron.