Electrical stimulation of the brain stem in freely moving rats: II. Effects on hippocampal and neocortical electrical activity, and relations to behavior

Abstract

Hippocampal and neocortical slow-wave activity and behavior were recorded in freely moving rats during electrical stimulation (100 pulses/s) of sites throughout the brain stem. Stimulation at many sites (including nucleus cuneiformis; subnucleus compactus; nucleus reticularis oralis, caudalis, and medial gigantocellularis; the pontine central gray; adjacent to the midbrain central gray; centralis superior of the raphe; locus ceruleus) produced hippocampal rhythmical slow activity (RSA; theta) and neocortical low-voltage fast activity (LVFA) during behavioral immobility, especially after treatment with chlorpromazine. At slightly higher currents stimulation at most sites elicited behaviors such as walking, circling, or running, and concomitant RSA and LVFA. Atropine sulfate abolished the RSA and LVFA elicited during immobility by stimulation at most sites. The RSA and LVFA which accompanied centrally elicited locomotion was not abolished by atropine. However, exceptions to the rule that RSA and LVFA occurring during immobility are selectively abolished by atropine were provided by sites in the region of the subnucleus compactus and the nucleus of the posterior commissure. Stimulation in or near the subnucleus compactus produced primarily atropine-resistant RSA whereas stimulation in or near the nucleus of the posterior commissure produced primarily atropine-resistant LVFA. These effects could be obtained while the rats stood totally immobile. In general, the results support the idea that a diffuse ascending system from the brain stem is capable of producing two pharmacologically distinct forms of RSA and LVFA. This neurochemical specificity may be established above the brain stem. The RSA and LVFA which appear during immobility are probably dependent on cholinergic synapses. The neurotransmitter(s) required for the production of atropineresistant (movement-related) RSA and/or LVFA is unknown. It is suggested that the monoamines (noradrenaline, dopamine, and serotonin) are not critically important for the appearance of RSA or LVFA.