Differential responses of two identified neurons of the pond snail Lymnaea stagnalis to the convulsant drug pentylenetetrazol

The modulation effects of d-amphetamine and procaine on the spontaneously generated action potentials in the central neuron of snail, Achatina fulica Ferussac

The modulation effects of d-amphetamine and procaine on the spontaneously generated action potentials were studied on the RP1 central neuron of giant African snails (Achatina fulica Ferussac). Extra-cellular application of d-amphetamine or procaine reversibly elicited bursts of potential (BoP). Prazosin, propranolol, atropine or d-tubocurarine did not alter the BoP elicited by either d-amphetamine or procaine. KT-5720 or H89 (protein kinase A inhibitors) blocked d-amphetamine-elicited BoP, whereas they did not block the procaine-elicited BoP. U73122, neomycin (phospholipase C inhibitors) blocked the procaine-elicited BoP, whereas they did not block the d-amphetamine-elicited BoP in the same neuron. These results suggest that BoP elicited by d-amphetamine or procaine were associated with protein kinase A and phospholipase C activity in the neuron.

Blocking of the axon spikes by pentylenetetrazol in an identified neuron of the snail Helix lucorum, with consequent induction of epileptic activity in the cell body of the same neuron

In an isolated preparation which consists of the buccal ganglia and the salivary nerve of Helix lucorum, neuron B2 can be identified by simultaneously recording the soma spike intracellularly and the axon spike extracellularly from the peripheral salivary nerve. The convulsant drug pentylenetetrazol (PTZ) eliminates the axon spike of the neuron within 1-5 min after its application while epileptic activity is induced in the soma of the same neuron for hours. It is interesting that almost all nerve activity in the peripheral nerve is blocked by PTZ.

Characterization of an identified cerebrobuccal neuron containing the neuropeptide APGWamide (Ala-Pro-Gly-Trp-NH2) in the snail Lymnaea stagnalis

A bilaterally symmetrical pair of cerebrobuccal neurons in Lymnaea stagnalis shows immunoreactivity for the molluscan neuropeptide APGWamide. The neuron somata are whitish in colour and located on the ventral surface of each cerebral ganglion between the roots of the labial nerves. A single axon travels via the ipsilateral cerebrobuccal connective into the buccal ganglia, where it gives rise to fine neuritic branching. Based upon these characteristics, the neuron has been named the cerebrobuccal white cell (CBWC). In isolated CNS preparations, in the absence of feeding motor output, the CBWC is silent and receives few, low amplitude, synaptic inputs. During generation of fictive feeding, the CBWC bursts in phase with cycles of feeding motor output. Tonic or phasic stimulation of CBWC leads to initiation of rhythmic feeding motor output. However, evoked bursts of activity in CBWC, which mimic its normal burst pattern, cannot entrain the buccal rhythm, suggesting that CBWC is not itself a major component of the feeding central pattern generator (CPG). Strong stimulation of CBWC during ongoing feeding motor output leads to a reduction in frequency and/or intensity of the buccal rhythm. Bath application of synthetic APGWamide (10(-7)M-10(-4)M) to the isolated CNS can activate feeding motor output in quiescent preparations after a delay, but disrupts ongoing buccal rhythms. This study represents the first description of a peptidergic cerebrobuccal neuron in the well described gastropod feeding system and also provides new information about the role of a novel molluscan neuropeptide.

Inhibition of slow TTX-insensitive inward current by the anticonvulsant carbamazepine in an identified neuron of Lymnaea stagnalis

1. Pentylenetetrazol (PTZ), induces tonic depolarization and bursting activity in an identified neuron, B1, of Lymnaea stagnalis. This is due in part to activation of a slow, tetrodotoxin-insensitive inward sodium current. 2. Carbamazepine (CBZ) reversed the effect of PTZ on both membrane potential and inward current, after a delay of up to 5 min. CBZ alone had no effect on voltage or current responses. 3. These results suggest that CBZ blocks the slow sodium current, possibly via a decrease in intracellularly stored calcium ions.