Abnormal locomotor muscle recruitment activity is present in horses with shivering and Purkinje cell distal axonopathy.

This study investigates how abnormal muscle activity is related to shivering and specific brain cell damage in horses. They found that shivering horses showed unusually high muscle activity, especially in the biceps femoris and vastus lateralis muscles during backward walking, which is linked to the degeneration of their Purkinje brain cells.

Purpose and Objective

• The research was designed to explore the relationship between the shivering condition in horses and the degeneration of cerebellar Purkinje cells—a specific type of brain cell crucial for motor control.
• This study work aimed to analyze hindlimb muscle activity in horses with shivering, regard it against clinical scores, and examine horses for any signs of Purkinje cell degradation.

Methods

• The experiment included a control group of six horses and a shivering group of seven horses. The researchers assigned clinical scores to the hindlimb of these horses.
• They measured the muscular activity of individual muscles (Biceps femoris, vastus lateralis, tensor fasciae latae, and extensor digitorum longus) in the horses using surface electromyography (sEMG) as they moved forwards and backwards, as well as trotting.
• They compared the integrated and peak muscle activity between groups and matched them with clinical locomotor exam scores.
• The researchers examined the deep cerebellar nuclei (DCN), a region of the brain, of six of the seven shivering horses using a technique known as calbindin immunohistochemistry to identify Purkinje cell degeneration.

Results

• Compared to control horses, horses with shivering showed significant differences in their muscle activity during backward walking. Interestingly, their muscle activity pattern during backward walking was similar to their activity during trotting.
• For shivering horses, about a quarter of the stride in the biceps femoris and vastus lateralis muscles fell outside two standard deviations of mean control sEMG during backward walking.
• Locomotor exam scores were tied closely with peak and integrated EMG activity, demonstrating a high correlation.
• All the shivering horses that were examined showed calbindin-positive spheroids or signs of degeneration in their Purkinje axons in their DCN.

Conclusion

• The study concludes that shivering horses manifest significantly elevated muscle recruitment, notably in the biceps femoris and vastus lateralis muscles during backward walking. This abnormal behavior was associated with damage to the distal part of Purkinje cells.
• However, the researchers clarify that they focused specifically on the DCN for the neuropathological assessment, so other unidentified lesions might have also contributed to the abnormal muscle activity observed in shivering horses.