Activation and lateralization of sensorimotor field for perioral biting reflex by intranigral GABA agonist and by systemic apomorphine in the rat

Oral behaviour induced by intranigral muscimol is unaffected by haloperidol but abolished by large lesions of superior colliculus

It has been suggested that the GAbAergic striatonigral projection may form part of the efferent pathway responsible for the expression of dopamine-related oral behaviour. Consistent with this suggestion are reports that bilateral injection of the GABA agonist muscimol can produce stereotyped gnawing and biting. We report here two experiments on this effect: (1) A dose of the dopamine receptor blocker haloperidol (0.4 mg/kg), which effectively antagonised oral stereotypy induced by systemically administered apomorphine or intranigral carbachol, had no effect on either the latency or the intensity of the gnawing produced by intranigral muscimol (1 nM); (2) large lesions involving the superior colliculus which effectively suppressed the oral stereotypy induced by 8 mg/kg apomorphine completely abolished the gnawing induced by intranigral injection of muscimol. Collicular lesions suppressed both the gnawing which occurred spontaneously and that elicited by a perioral probe. These findings are consistent with the view that the substantia nigra is a relay station between the caudate nucleus and the superior colliculus in an efferent pathway mediating dopamine-related oral behaviour. In addition, they raise the possibility that such behaviour is produced by the sensitisation of a collicular-mediated perioral reflex.

Sensitization of the perioral biting reflex by intranigral GABA agonist after detelencephalization

Unilateral injection of 160 ng (0.4 microliter) of muscimol into the substantia nigra pars reticulata of rats elicits contraversive turning and simultaneously sensitizes the perioral biting reflex on the side of the face contralateral to the injected substantia nigra. Bilateral removal of the telencephalon eliminated neither the muscimol-induced behavior nor the peroral biting reflex.