Modulation of locomotor activity induced by injections of carbachol into the tegmental pedunculopontine nucleus and adjacent areas in the rat

Abstract

The pedunculopontine nucleus (PPN) is a major component of the mesencephalic locomotor region. There is little known, however, about neurotransmitters in the PPN associated with locomotor activity. The purpose of the present study was to investigate a possible modulatory effect of the cholinergic system on locomotion. The effects of application of carbachol (CCh) into the PPN on locomotor activity of freely moving rats were studied. Unilateral injections of CCh into the PPN decreased spontaneous locomotor activity of rats. On the other hand, an increase in locomotor activity resulted from CCh injections into sites surrounding the PPN. These CCh-induced changes in locomotion were no longer observed after pretreatment of the PPN with atropine. Locomotor activity induced by injections of amphetamine into the nucleus accumbens was also reduced to control levels by ipsilateral injections of CCh into the PPN, whereas contralateral injections of CCh were ineffective. The results suggest that the muscarinic cholinergic system has a modulatory influence on locomotor activity presumably by affecting PPN cells involved in relaying locomotion-associated signals. The PPN receives signals from higher structures involved in initiation of locomotion while the muscarinic system seems to play a role in attenuation or inhibition of locomotor behaviour.