Effects of gamma-hydroxybutyrate on the performance of monkeys in a Go/No-go visual discrimination task

It has been suggested that monkeys, administered gamma-hydroxybutyrate (GHB), manifest a state resembling petit mal status. This implies that an animal would produce erroneous responses immediately prior to, and discontinue behaviors requiring any cognitive effort concurrently with, an episode of GHB-induced generalized 3 cps wave-spike bursts in the EEG. This prediction was not confirmed in the present study. Rhesus macaques (Macaca mulatta) were trained to perform in a visual discrimination Go/No-go test. Thereafter bipolar transcortical electrodes were implanted in the hemisphere contralateral to the preferred hand. All monkeys discontinued to lever-press for water reward when administered GHB (125 or 250 mg/kg, esophageal intubation) and exhibited signs of reduced postural control and somnolence punctuated by episodes of hypermotility about 40-50 min after GHB. However, the monkey's difficulties in completing the program were not associated with the development of generalized hypersynchronous EEG activity. While occasional wave-spike bursts did occur, they were poorly regulated, often 'focal' (i.e. developed only in isolated areas), and had a frequency of 1.5-2 cps. In this state, animals could be easily roused by sensory stimuli. All of them reacted with a characteristic aversive-aggressive display when confronted by a direct gaze. These effects are interpreted to be more consistent with characterization of GHB activity as that of a potent hypnotic rather than a convulsant agent.