An Electrophysiological Study of Some Trigeminofacial Reflexes in Parkinson’s Disease before and after L-Dopam Administration

Abstract

The following problems were considered: (1) nature of the asynchronous response in the glabellar reflex (GR); (2) changes in the GR parameters induced by L-dopa; (3) changes induced by the drug in the masseter muscle silent period (SP); (4) meaning of the glabellar SP after synchronous and asynchronous reflex response; and (5) mode of suprasegmental control by the descending dopaminergic pathways. It is concluded that the synchronous response is probably multisynaptic, in view also of the changes induced by L-dopa in parameters of some GR components. The published data on the silent period in Parkinson’s disease were confirmed in the masseter muscle; some data on the SP after glabella tap are also reported. Lastly, it is supposed that the nigrostriatal dopaminergic pathways have two different actions over the segmental circuits of the facial reflexes: inhibitory over GR asynchronous response; facilitatory over the masseter and glabellar SP. Moreover, the facilitatory action could bias different systems of spinal inhibition over the peripheral afferences, which come from different receptorial structures.