Effects of ibotenate pedunculopontine tegmental nucleus lesions on exploratory behaviour in the open field.

The pedunculopontine tegmental nucleus (PPTg) as part of the mesencephalic locomotor region is discussed to be involved in motor activity. In this study, we examined whether the PPTg plays a role in exploratory behaviour. Therefore, we compared non-habituated motor behaviour of PPTg lesioned rats with sham lesioned rats under spontaneous, dizocilpine (MK-801) (0.1 and 0.16 mg/kg) and dl-amphetamine (1 and 2 mg/kg) conditions. In order to analyse exploratory behaviour only, session-times were limited to 5 min after placing the rats in an open field. The exploratory motor activity was compared to the motor activity obtained in rats habituated to the environment. PPTg lesions had no effect on spontaneous exploratory behaviour, but it intensified the enhanced motor activity induced by MK-801. However, PPTg lesions blocked the enhanced exploratory behaviour, i.e. horizontal activity, rearing and centre activity induced by amphetamine. These data indicate that the PPTg is involved in behaviour driven by the dopaminergic and glutamatergic systems, when the animals are in a particular motivational state, e.g. a state that increases motor activity for itself, like exploration. This is underlined by the finding that animals exploring their environment show a higher motor activity even after multiple sessions, than animals familiar to the environment.