Abstract
The pedunculopontine tegmental nucleus (PPN) consists of cholinergic and non-cholinergic neurons located at the pontomesencephalic junction. The PPN is involved in the control of postural muscle tone via descending projections to the pontine reticular formation (PRF). Neuroanatomically the PPN receives GABAergic efferents from the substantia nigra pars reticulata (SNr), one of the basal ganglia output nuclei. Here we designed to test whether the GABAergic SNr-PPN projection contributes to the modulation of postural muscle tone. For this purpose intracellular recording was obtained from hindlimb motoneurons in decerebrate cats. Short train pulses of stimuli (3 pulses with 5 ms intervals, 30 μA) applied to the PPN induced a mixture of EPSPs and IPSPs. The EPSPs were induced within 30 ms and the IPSPs consisted of a peak latency of 40-50 ms with a duration of 40-50 ms. The late IPSPs were preferentially observed in both extensor and flexor motoneurons. Microinjection of atropine sulfate (10-20 mM/0.25 μl) into the PRF reduced the amplitude of the IPSPs. Conditioning stimuli applied to the SNr (30-60 μA and 100 Hz) alone did not alter input resistance of the motoneurons. However, it significantly reduced the amplitude of the IPSPs and amplified the EPSPs. Subsequent microinjection of bicuculline (5-10 mM/0.25 μl) into the PPN blocked the SNr effects. These results suggest that the GABAergic output from the basal ganglia controls postural muscle tone by modulating the activity of cholinergic PPN neurons projecting to the PRF. [J Physiol Sci. 2008;58 Suppl:S195]
