BEHAVIORAL-CHANGES INDUCED BY GABA-RECEPTOR AGONISTS IN LYMNAEA-STAGNALIS L

1. GABA, the GABA(A) receptor agonist, muscimol, and the GABA(B) recep tor agonist, baclofen, were tested to study the involvement of the GAB A neurotransmitter system in control of behaviour in the freshwater pu lmonate snail, Lymnaea stagnalis L. Single injections of GABA (1-10 mu g/gbw) into the haemocoel of intact snails elicits a sequence of beha vioural changes subsequently affecting feeding, locomotion, escape rea ctions, male mating behaviour and respiration. 2. Both muscimol and ba clofen mimic distinct aspects of GABA action implying that the GABA ac tion is mediated by both types of receptors. 3. The modulatory actions of GABA, muscimol, and baclofen on feeding were manifested as opening of the mouth and triggering of specific radular movements (e.g., prot raction, retraction, rasping). 4. Baclofen (1-10 mu g/gbw) evoked the full erection of the penis for a time long enough for natural copulati on, while GABA itself caused only partial eversion of the preputium. M uscimol was less effective than GABA. The latency to penis eversion va ried in a dose-dependent manner. The data emphasize the participation of baclofen-sensitive receptors in control of reproduction. 5. GABA an d baclofen induced withdrawal of the head and anterior part of the foo t accompanied by arrest of locomotion and respiration could be conside red to be an escape reaction. 6. Muscimol (1-5 mu g/gbw) failed to eli cit withdrawal reactions but caused the loss of normal orientation and longitudinal contractions of the foot. 7. All the agents tested inhib ited locomotion in a dose-dependent manner, for a substantial period o f time. A decrease in total locomotor activity lead to the failure of animals to attach to the underlying surface, to have foot contractions and also to diminish locomotor velocity. 8. The majority of animals m aintained the stereotyped complex reactions of respiration, but with r estricted clockwise turning of the shell after drug treatment. 9. All the substances were shown to shift the background behavioural state ch aracterised by high BSSs to a state similar to ''rest'' which was awar ded a low BSS. It is concluded that the GABA neurotransmitter system c an play an important role in activation and coordination of neuronal e nsembles underlying behaviour and behaviour selection in Lymnaea stagn alis L.