Periaqueductal gray lesions do not affect grooming, induced electrically in the hypothalamic paraventricular area in...

Electrical stimulation inducing behavioral responses from the hypothalamus seems to activate systems involved in the execution phase of the behaviour rather than in the introductory or decision-making phase. However, the pathways involved are not fully understood. Projections originating from hypothalamic areas involved in specific behavioral responses are rather complex. The periaqueductal gray (PAG) has been proposed to be an essential output station of hypothalamic behavioral mechanisms. Here we report that lesions of the periaqueductal gray area have no effect on grooming responses evoked by electrical stimulation of the hypothalamic paraventricular area. Neither threshold current intensities needed to evoke grooming, nor latencies were affected 7 or 14 days after lesioning. The lesions caused severe behavioural deficits. Animals did not drink or eat spontaneously, had problems with motor coordination and sometimes showed strong defensive reactions upon touch. However, their grooming responses induced by hypothalamic stimulation were not changed. The PAG may have a modulatory role on grooming behaviour; however, this modulatory effect apparently is overruled during electrical stimulation of the hypothalamus.