Spasmodic torticollis-like posture and caudate nucleus monoamine in cats: in vivo dialysis study

In order to study the monoamine mechanism in the caudate nucleus of experimental spasmodic torticollis, the left side of the ventromedial tegmentum (VMT) was electrically destroyed in cats, and in vivo brain dialysis in the caudate nucleus was performed for determining the changes in monoamines and their metabolites. Six out of 12 animals showed the torticollis-like posture in which the head became deviated towards the side of the lesion by rotating around the longitudinal axis. In 4 of these 6 cats, this posture continued for 3 d until brain dialysis was performed. The extracellular 5-HIAA level decreased compared to HVA level in the caudate nucleus of the lesion side. In the other 2 cats, the posture disappeared on the day after the lesion was induced and the change of 5-HIAA level was less prominent or within the range of the control group. The brain dialysis method was very useful for measuring the monoamine metabolite levels of the caudate nucleus while the experimental model was still alive and presenting the torticollis-like posture. These results suggest, although inconclusively, that decreased activity in the ipsilateral caudate nucleus serotonin neuron might play an important role in the manifestation of the torticollis-like posture in this animal model.