Is the cuneiform nucleus a critical component of the mesencephalic locomotor region? An examination of the effects of excitotoxic lesions of the cuneiform nucleus on spontaneous and nucleus accumbens induced locomotion.

The cuneiform nucleus and the pedunculopontine tegmental nucleus have both been suggested as possible sites for the mesencephalic locomotor region (MLR), an area from which controlled stepping on a treadmill can be elicited following electrical or chemical stimulation in a decerebrate animal. It has been shown that excitotoxic lesions of the pedunculopontine tegmental nucleus impair neither spontaneous locomotion nor locomotion induced by stimulation of the nucleus accumbens. Excitotoxic lesions of the cuneiform nucleus have not previously been investigated. Rats received either bilateral ibotenate or sham lesions of the cuneiform nucleus combined with bilateral implantation of guide cannulae aimed at the nucleus accumbens. On recovery from surgery spontaneous locomotion was tested, followed by accumbens-stimulated locomotion. For nucleus accumbens stimulation, each rat received bilateral microinjection of each of three doses of d-amphetamine (10.0, 20.0 and 30.0 micrograms) and a vehicle only injection. Locomotor activity was recorded following the injection. In comparison to the sham-lesioned group, the ibotenate-lesioned group showed no differences in either spontaneous or amphetamine-induced locomotor activity. These results suggest that, like the pedunculopontine tegmental nucleus, the cuneiform nucleus is not involved in the direct mediation of spontaneous or accumbens-induced locomotion, and thus is very unlikely to be the anatomical substrate of the MLR. The role of the cuneiform nucleus in other types of behavioural control is discussed.