The nucleus tegmenti pedunculopontinus and circling behaviour in the rat

Lesioning the rat's substantia nigra (SN) with kainic acid (0.8 microgram) or by electrocoagulation (1 mA for 6 sec) significantly lowered GABA and glutamate decarboxylase levels at the treatment site, but not in the nucleus tegmenti pedunculopontinus (PPN), suggesting nigro-PPN fibres do not synthesize or store GABA. Stereotaxic injection of one PPN with muscimol (40 ng), picrotoxin (40 ng) or tetanus toxin (30 mouse LD50 doses) had little or no effect on the animals' behaviour; kainate caused ipsilateral body flexion, sporadic ipsiversive circling and contraversive barrel-rolling. These behavioural abnormalities disappeared after 7 days when histology confirmed virtually complete loss of PPN perikarya, intense gliosis and some demyelination of passing axons. Impairing PPN transmission with kainate (chronically) or muscimol (acutely) caused weak apomorphine-induced contraversive rotation, but did not modify the robust nigral muscimol-evoked contraversive asymmetry. While we do not exclude a role of PPN in motor control, these data suggest that nigro-PPN neurones are neither GABAergic nor mediators of central dopaminergic function.