Bay K 8644 induces a reversible spasticity-like syndrome in rats

The dihydropyridine Bay K 8644 exerts a positive modulation of Ca²⁺ channels. Administration of Bay K 8644 3–5 mg/kg i.p. to rats induces within 15 min a severe spasticity syndrome consisting of stiff tail, arched back, stretching and twisting of forelimbs and hindlegs and backwards motility and rolling over. The syndrome was effectively antagonized by nifedipine 3–30 mg/kg but not by the other Ca²⁺ channel blockers flunarizine, diltiazem and verapamil. Diltiazem even enhanced the spasticity. Diazepam 10–30 mg/kg i.p. completely blocked the spasticity whereas the other muscle relaxants (−)-baclofen and the β-carboline ZK 93423 were completely inactive. These findings with Bay K 8644 suggest that spasticity may be caused by changed Ca²⁺ homeostasis.