Evaluation of head motility and posture in cats with horizontal torticollis

Unilateral electrolytic lesions and injections of 6-hydroxydopamine (6-OHDA) and 5,7-dihydroxytryptamine (5,7-DHT) were made in structures and pathways linked to the striatopallidal system of cats. The effects of such lesions on horizontal head symmetry and head motility were measured in restrained cats by electrogoniometry. Analysis of electrogoniometric recordings provided (i) an index of head symmetry, (ii) net time-course patterns of head turning in degrees per minute, and (iii) time-course patterns of head motility, measured in number of head movements per minute. All lesions except the electrolytic lesion of the superior colliculus induced an enduring horizontal head asymmetry. Electrolytic, 5,7-DHT, and 6-OHDA lesions made in the medial forebrain bundle induced a nearly total head asymmetry (95 to 98%). Cats in which an electrolytic lesion was made in the substantia nigra reticulata (SNR) also displayed an important head asymmetry (80%). For all lesions except the SNR lesions the direction of the induced head asymmetry was ipsilateral. In 6-OHDA-lesion cats a marked and consistent decrease head motility was also observed. The combined evaluation of head posture and head movements indicated that according to the lesion, head symmetry and head motility are disturbed in different manners. The results further emphasized the complementary contribution of the caudate and SNR in regulation of head symmetry and indicated the advantages of the electrogoniometric method for selectively measuring head posture and movements.