Cyclic nucleotides in the rat brain in the dynamics of hypothalamic self-stimulation

The content of cyclic nucleotides was measured in the brain structures of rats performing hypothalamic self-stimulation. Changes of the cAMP content were shown to possess a specific pattern corresponding to the features of self-stimulation. An increasing self-stimulation frequency (SSF) was followed by the maximum increase in the above index in the sensorimotor cortex; a stable SSF was accompanied by activation of the cAMP-dependent mechanisms of the septum, hypothalamus, and posterior hypophysis, while a decreasing SSF correlated with suppression of these processes in the septum, hypothalamus, and anterior hypophysis. Changes in the cAMP phosphodiesterase activity were less intensive and did not depend on the cGMP level. Changes in the cGMP content were nonspecific and unidirectional: this index increased, with the maximum at the stable self-stimulation mode. The ratio of cyclic nucleotides shifted toward cAMP when the SSF increased, and towards cGMP when the SSF decreased, while at a stable frequency their content was equal to the control level. The changes in the cyclic nucleotide contents were non-reciprocal (except an inverse correlation between their contents in the hypothalamus observed when the SSF dropped).