Electrophysiological analysis of the effects of L-Dopa on the reciprocal corticothalamic projections in the squirrel monkey

Abstract

SummaryEffects of i.p. administered L-Dopa was studied on the reciprocal corticothalamic projections in the squirrel monkey.1. Pendular rotation of the mediastinum produced electrocardiographic abnormalities and electrocorticograms which failed to show detectable spontaneous and evoked activities. Following administration of L-Dopa, persistent, high-amplitude, slow-wave bursts developed in the motor cortex. Increased unitary activity of medial thalamic neurons preceeded the development of neocortical spindle bursts. Diphasic (negative-positive) waves in medial thalamic nuclei were temporally linked to the neocortical slow-waves; such rhythmic activities in VL were not observed during motor cortical spindle bursts, 2. Low-frequency (8--10Hz) stimulation of the medial thalamus, which failed to elicit recruiting responses, triggered spindle bursts in the motor cortex in the untreated, comatose squirrel monkey. The electrographic properties of medial thalamus triggered bursts were essentially similar to those induced later by L-Dopa in the same comatose animals. 3. In the non-comatose animals, L-Dopa attenuated all short-latency components of corona radiata evoked potentials in the motor cortex, medial and ventrolateral thalamus. Concomitantly, orthodromically evoked longlatency recruiting responses were demonstrable in the motor cortex. The data indicate that one of the major effects of L-Dopa in the diencephalon is the disfacilitation of VL neurons which, in turn, disinhibit neurons in the medial thalamic nuclei.

Reafferent thalamo-?cortical? loops in the song system of oscine songbirds

“…More generally, our results help to extend the homologies drawn between avian and mammalian motor systems (see Karten, 1991 for a review). For example, the projections from RA to DLM and DMP, and from these regions to RA and HVC via lMAN and mMAN, are reminiscent of the projections from motor cortex to the ventral thalamus, and from the ventral thalamus to premotor and motor cortices (Frigyesi et al, 1972). These parallels may allow for more meaningful comparisons between avian and mammalian mechanisms of vocal communication.…”

“…Our demonstration of these novel thalamo-''cortical'' reafferent loops documents pathways by which information processed by the motor pathway can be directed back to the telencephalon. Our findings also bring the neuroanatomy of the song system in line with the organization of mammalian motor systems, which display prominent thalamo-cortical feedback pathways (Frigyesi et al, 1972). An additional finding is that DMP projects bilaterally to the right and left mMAN, providing a possible pathway for interhemispheric communication within the song system.…”

Auditory cortical projections to the cat inferior colliculus

“…In the motor cortex, for example, pyramidal neurons influence spinal motoneuronal discharge and exert an executive effect on the control of voluntary movement (Phillips and Porter, 1977). No analogous functional role exists for these sensory corticofugal projections, which are comparable in size and connectional divergence to their motor counterparts (Frigyesi et al, 1972).…”