Search

Using an immunohistochemical procedure and optical densitometry, the distribution of neurons containing serotonin (5-HT) was investigated in the pedal ganglia of Megalobulimus abbreviatus after thermal "non-functional stimulus" (22 degrees C) and stressful thermal conditions (50 degrees C). The animals were sacrificed at different times (3 h, 6 h and 24 h) following these stimuli. In control animals, the results showed the location of these serotonergic immunoreactive elements (5HT-ir) in this ganglion to be similar to those shown in other studies, where the anterior region of ventral sections showed the largest number of 5HT-ir neurons. In the anterior neurons, significant differences (p < 0.01) were observed between the groups of animals stimulated at 50 degrees C and 22 degrees C and sacrificed after 6 h. In the medial neurons, significant differences (p < 0.05) were observed between the control group and the groups of animals stimulated at 50 degrees C and sacrificed after 6 and 24 h. Neuropilar area 1 showed differences (p < 0.01) in 5HT-ir between the control group and the groups of animals stimulated at 50 degrees C and sacrificed after 3 and 24 h. Neuropilar area 2 showed a significant difference (p < 0.05) between the groups of animals stimulated at 22 degrees C and sacrificed after 3 and 24 h. These results suggest the involvement of 5-HT in the nociceptive circuit of M. abbreviatus, mainly that of the medial neurons and neuropilar area 1, which showed increases in 5HT-ir after thermal aversive stimuli. These results could be helpful in drawing cellular homologies with other gastropods.

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.

The peptide FMRFamide (Phe-Met-Arg-Phe-NH(2)) is known to modulate the circadian pacemaker found in the eye of the marine snail Bulla gouldiana. In the present study, we investigated the cellular mechanisms underlying this modulation by examining the effects of FMRFamide on the membrane properties of the circadian pacemaker cells, known as basal retinal neurons in this preparation. Bath application of FMRFamide (0.1-1 microM) increased the membrane conductance, and hyperpolarized the membrane potential of these neurons. Next, perforated-patch recordings were used to demonstrate that FMRFamide reversibly increased the outward current amplitude due to an augmentation of a non-inactivating calcium-independent current. Reversal potential of the tail currents and its dependence on extracellular potassium concentration suggested potassium ions as the charge carrier for this current. The peptide-modulated outward current was blocked by 54% after bath application of the potassium channel blocker tetraethylammonium chloride and completely blocked by substituting cesium for intracellular potassium. Voltage dependence, activation kinetics and tail current kinetics of the FMRFamide-modulated current were consistent with values found for the delayed rectifier current.Overall, our data suggest that FMRFamide modulates a delayed rectifier potassium current and at least one other, less voltage-dependent conductance. This provides a mechanistic explanation for FMRFamide's ability to both shift the phase and attenuate light-induced phase shifts of the circadian pacemaker in B. gouldiana.

A study of the morphology and behaviour (cell adherence and spreading, in vitro phagocytosis and rosette formation) of blood cells of Planorbis corneus, revealed the presence of two cell types: the spreading haemocyte and the round haemocyte. Results obtained with vinblastine confirmed that these cell forms are distinct cell types and not different maturational stages of a single cell type.