Association of the pontine reticulospinal tract with velocity-dependent muscle tone changes after stroke in rats.

BACKGROUND

To investigate the regulatory role and the mechanism of the pontine reticulospinal tract (PRST) in velocity-dependent muscle tone changes following stroke.

MATERIAL: Seventy-four SD rats were divided into the following groups: normal, pontine reticular nucleus (PRN)-lesioned, stroke-induced spasticity, and stroke-induced spasticity with PRN lesion. Viral tracing identified the PRST's innervation zone in the anterior horn of spinal cord segments C5-C7 (referred to as the reticulospinal zone). After establishing stroke-induced spasticity and pontoreticular nucleus destruction models, neurological function was assessed using Zea-Longa scores and the modified Ashworth scale, while muscle tone was monitored with physiological recorders. Isometric muscle strength systems measured peak torque of the biceps brachii at different stretching speeds (5°/s, 10°/s, 20°/s). High-performance liquid chromatography detected glutamate concentration in the reticulospinal zone, while immunohistochemistry analyzed expression of glutamate AMPA receptor subtypes (GluR1-GluR4).

RESULTS

Compared with the normal group, the stroke spasticity group showed significantly elevated neurological function scores and muscle tone (P < 0.05). Pontine reticular nucleus destruction effectively reduced neurological function scores and muscle tone. Peak torque significantly increased in the stroke spasticity group during rapid stretching (20°/s), with a reduced increase following pontine reticular nucleus destruction. Glu concentration and GluR1/3/4 expression in the reticulospinal zone increased in the stroke group, while GluR2 decreased; pontine reticular nucleus destruction reversed this trend.

CONCLUSION

The functional integrity of the pontine reticulospinal tract is closely associated with the regulation of velocity-dependent muscle tone changes after stroke. Alterations in glutamatergic signaling and AMPA receptor subunit expression within the spinal reticulospinal zone may serve as key molecular correlates underlying this process.