Striatal somatotopy and motor responses evoked by acute electrical stimulation of the posterior striatum in rats.

ABSTRACT

INTRODUCTION/OBJECTIVES: Previous experiments suggest that the striatal sensorimotor territory in rats is located in its dorsolateral region, along the rostrocaudal axis, unlike what has been observed in primates. In the present study, electrical stimulation was performed to investigate the degree of participation of the posterior striatum in its motor territory, its somatotopic organization, and the motor responses evoked by stimulation. METHODS: Twenty-five rats were submitted to stereotactic stimulation of the posterior striatum under general anesthesia, receiving consecutively four different current intensities. The motor responses observed in the different body parts were registered for later comparison. We considered as threshold the smallest of these current intensities able to evoke a motor response. RESULTS: The observed motor responses were qualitatively different for each segment forepaws ipsilateral, adduction, and contralateral abduction; hindpaws ipsilateral, flexion, and contralateral, extension/abduction; trunk, rotation/flexion; and tail, rotation/elevation. High-frequency, small-amplitude distal tremor occurred in the ipsilateral forepaw in 95% of the animals. Progressively larger current intensities were necessary for the induction of motor response in the forepaws, hindpaws, and trunk/tail, in that order. CONCLUSIONS: The results allowed us to infer the following posterior striatal somatotopic organization forepaws, posterolaterally, being the contralateral medial to the ipsilateral; trunk/tail, anteromedially; and hindpaws, in an intermediate position, being the contralateral posterior to the ipsilateral. It is suggested that the tremor and the other observed motor responses derive from the excitation of striatal projection neurons and that the striatum may play an important role in the genesis of essential tremor.