Functional role of hypothalamic D1 and D2 receptors in organization of some forms of behavior of the common frog Rana temporaria

Abstract

Dopamine is one of the most ancient, widely spread neurotransmitters. It performs a great number of neuromodulator effects in the vertebrates CNS. For the last few years there considerably increases an interest in study of functional role of this neurotransmitter in regulation of various forms of behavior of poikilothermal vertebrates. The present work deals with study of the role of the dopaminergic system, specifically of the hypothalamic dopaminergic system in providing some behavioral frog reactions. We studied behavior of the animals in the “open field” before and after administration to them of antagonists of D1 (SCH 23390) and D2 (haloperidol) receptors as well as of animals with destroyed anterior and posterior parts of hypothalamus. Administration of SCH 23390 to intact frogs caused a statistically significant decrease in the number of exploratory reactions and goal-oriented jumps, whereas haloperidol only moderately increased the number of the above reactions. Destruction of the posterior part of hypothalamus suppressed essentially all kinds of activity, while destruction of the anterior part inhibited them completely. Antagonist of D12 and D2 receptors of dopamine little changed the initial motor and emotional activity of the operated animals. The obtained data are discussed in terms of evolutionary origin of D1 and D2 receptors in vertebrates and allow concluding that D1 and D2 receptors of hypothalamic dopamine of the common frog are located predominantly in the anterior hypothalamic areas and that their effect on behavior can be mediated and is associated with other brain neurotransmitter systems in such brain structures as lateral hypothalamus, locus coereleus, and striatum that provide different aspects of wakefulness of amphibians.