SEXUAL MOTIVATION IN A PHARMACOLOGICAL MODEL OF NARCOLEPSY IN MALE RATS

Motivation determines the initiation, direction, and maintenance of goal-directed behaviours such as reproduction, and it seems to be modulated by the hypocretinergic/orexinergic system. Motivation consists of two components: the direction/focus and the activation/intensity. This study evaluates sexual motivation in a pharmacological model of narcolepsy induced in male rats, and their control mates.
Sixteen male rats implanted with electrodes for EEG recording received daily i.p. injections of DMSO (vehicle, N=8) or suvorexant-30mg/Kg (a dual hypocretinergic/orexinergic receptor antagonist, N=8) for 8 days. On the 8th day, each male was exposed for 25 minutes to a sexually receptive female, separated by a metal fence, 1.5 hours after treatment. The number of visits to the stimulus (direction), and the total time near the stimulus and the number of fence scales (intensity) were quantified. Besides, the relative power values of δ (1-3.5Hz), θ (3.5-7.8Hz), α (7.8-14Hz), β (14-30Hz) and γ (30-100Hz)-EEG bands were obtained from wakefulness episodes during the behavioural test, and the previous hour.
Suvorexant decreased the number of visits to the stimulus (p=0.0486), without affecting the total time near the stimulus (p=0.2889) and the number of fence scales (p=0.3952). In control animals, decreased θ- and increased δ-activities occurred in their cortical-EEG recordings during the behavioural test (p≤0.05). However, suvorexant promoted a higher θ-activity in motor (p=0.0150), somaesthetic (p=0.0317) and visual (p=0.0185) cortices during the test compared to controls. Therefore, only the directional component of motivation appears to be affected in the narcolepsy model, associated with changes in the θ and δ EEG-bands.