Effect of deltorphin on behavior and hippocampal electrical activity in rabbits.

To clarify the role of delta-opioid receptors on modulation of hippocampal electrical activity and behavior, deltorphin (DT), a naturally occurring heptapeptide that selectively binds to delta-opioid receptors, was intravenously (IV) administered to rabbits. For this purpose, at 8-day intervals, the effects of IV administration of normal saline and IV infusion of synthetic DT (1 mg/kg b.wt. for 2 min) on the spontaneous behavior in neutral environment, both in absence of any external stimulus and after the introduction of a stuffed predator, were examined in seven adult male rabbits, on separate and successive occasions. During each session of experimental procedure, hippocampal EEG was also recorded by telemetry. Behavioral activity showed an increase in alert and reactive immobility after the peptide injection in comparison with that observed during control period (saline administration). Under DT treatment the frequency of hippocampal electrical activity decreased, and a reduction in rhythmicity of electrical pattern was also observed in presence of stressful stimulus. These findings show that DT may affect neural and behavioral elements related to the control of attentional and emotional processes, suggesting a modulating role of delta-opioid receptors.

Effect of dermorphin on behavior and hippocampal electrical activity in rabbits.

Dermorphin, a naturally occurring heptapeptide that selectively binds to mu-opioid receptors, was injected intravenously 0.4 mg/kg in male rabbits. Eight days before injection the spontaneous behavior of the animals was observed in a neutral environment in the absence of external stimuli. At the same time, hippocampal EEG was recorded by telemetry. After dermorphin injection, the same experimental procedure was repeated. Behavior showed a strong increase in quiet immobility and a concomitant reduction in voluntary activities as compared to control periods. Treatment did not affect either the pattern or the frequency of hippocampal electrical activity.

Self-directed behaviour and hippocampal electrical activity in rabbits living in a semi-natural environment.

Rabbits living in a semi-natural environment show a variety of behavioural elements related to voluntary or automatic movements. The aim of the present experiment was to study the hippocampal electrical correlates of self-directed activities occurring during spontaneous behaviour and emotional responses (the presence of a second rabbit of the same sex: intruder). Behaviour was divided into two broad categories. One included autocleaning elements such as scratching, shaking, washing and self-grooming. The other was characterized by consummatory activities: eating and drinking. Hippocampal activity was recorded by telemetry and the EEG periods related to specific behavioural elements were selected and analyzed. The electrical parameters were different for the various behavioural elements, for example rhythmic and irregular EEG patterns were recorded in different percentages during autocleaning and consummatory activities. Differences were also observed in the frequency peak distributions of power spectra. Confrontations influenced the occurrence of self directed behavioural elements and modified the pattern and frequency of hippocampal EEG during autocleaning activities. Results show that environmental variations can affect automatic behaviours and influence the mechanisms of hippocampal function.