Showing papers by "Pavel M. Balaban published in 1993"

Long-term sensitization and environmental conditioning in terrestrial snails.

Abstract: The hypothesis that a long-term increase of behavioural responses in snails (over a period of days) might be due to environmental conditioning was examined. Training consisted of delivering electric shocks non-contingently with test stimuli twice per day for 5 days to freely moving snails on a ball floating in water. After training, a significant difference in amplitude of a withdrawal reaction to tactile test stimulation appeared between shocked and control snails. Responses were significantly facilitated in shocked animals for up to 12 days after training, but only if the animals were tested in the environment used for training. Testing of the same groups of animals crawling freely on the glass lid of a tank in which they lived between experimental sessions revealed no difference in responses to the same stimuli between shocked and control snails. Injection of the neurotoxin 5,7-dihydroxytryptamine, which selectively impairs serotonergic cells, eliminated the differences between shocked and control animals. Changing the pH of the water in which the ball floated, by addition of citric acid, led to a significant selective increase of responsiveness in snails sensitized in this environment relative to the responsiveness of the same snails with normal water in the tank. The results suggest that the long-term sensitization of withdrawal reactions observed is at least in part a manifestation of an associative process, namely environmental conditioning.

Positive and negative brain zones in the snail.

Abstract: Fine wire electrodes were surgically implanted in two regions of the brain of the snail Helix aspersa. To receive electrical stimulation of the brain, a tethered snail was required to displace the end of a rod. Self-stimulation delivered to the parietal ganglion resulted in non-repetition of the operant response, whereas self-stimulation delivered to the mesocerebrum resulted in an increase in response frequency. The reinforcing effect of local extracellular stimulation of two brain zones was investigated in a semi-intact preparation of a closely related species with an identical cellular map (H. lucorum). It was found that mesocerebral stimulation increased the frequency of the reinforced spontaneous movement, but decreased the frequency of the same movement if its absence was reinforced. These results allow us to attribute positive reinforcing effects to this brain area, which is involved in the control of sexual behaviour. Different results were obtained by contingent stimulation of the rostral part of the parietal ganglia, where giant cells controlling avoidance behaviour are located. Stimulation of this zone resulted in a decrease in the frequency of the ongoing spontaneous movements. These findings make possible intracellular investigations of the mechanisms of positive and negative reinforcement.

Serotonergic input on identified command neurons in Helix.

Abstract: In Helix, serotonin evokes long-lasting alteration of activity of withdrawal triggering neurons. Cell bodies of these neurones are surrounded by a dense network of serotonin-containing fibres without any synaptic membrane specializations, which confirm the suggestion on the non-synaptic, modulatory action of serotonin on the withdrawal command elements.

The neurochemical basis of backward inhibition in a defense reaction reflex arc.

Abstract: An investigation was carried out on a preparation of the isolated nervous system of the edible snail of the mechanism of habituation in the network of defense behavior neurons. It was established that the intracellular activation of one of the systems of the defense behavior command neurons, as in the case of the application of the neuropeptide FMRF-amide, leads to a decrease in the amplitude of the postsynaptic potentials in the remaining neurons of this class. An inference is reached, when account is taken of the presence of endogenous FMRF-amide in the defense behavior command neurons, regarding the possibility of active inhibition of the behavioral response to an appropriate stimulus through this neurochemical mechanism of the backward connection. The possible interrelationships with other modulating systems and the significance of such an association in the organization of behavior are discussed.