Sympathetic innervation of the suprasesamoidean region of the deep digital flexor tendon in the forelimbs of horses.
Authors: Beccati F, Pepe M, Pascucci L, Ceccarelli P, Chiaradia E, Mancini F, Mandara M T
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Sympathetic nerve fibres regulate blood flow and cellular function throughout equine tissues, yet their specific distribution within the deep digital flexor tendon—a structure critical to forelimb function and commonly affected by injury—remained poorly characterised. Beccati and colleagues used immunohistochemical staining to map sympathetic innervation patterns in the suprasesamoidean DDFT of 14 forelimbs, identifying tyrosine hydroxylase (sympathetic nerve marker) and alpha-1 adrenergic receptors (which mediate catecholamine effects) throughout the tissue. The researchers found that whilst sympathetic nerve terminals concentrated predominantly in blood vessel walls, both the tenocytes and fibrocartilage cells within the tendon itself expressed adrenergic receptors, indicating these cells can directly respond to circulating catecholamines independently of local nerve supply. This discovery of autocrine and paracrine catecholaminergic signalling pathways suggests that stress responses, systemic inflammation, and conditions affecting sympathetic tone may influence tendon cellular behaviour and healing capacity—a mechanism that could explain variable responses to injury and rehabilitation across different horses, and potentially inform management strategies during high-stress periods or in horses with dysautonomia.
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Practical Takeaways
- •Sympathetic nervous system activity may regulate blood flow and cellular function in the DDFT through vascular innervation, with potential implications for tendon healing and injury response
- •Understanding catecholaminergic signaling in tendon tissue may inform future therapeutic approaches to DDFT injuries, though clinical applications remain to be established
- •This anatomical knowledge provides foundational understanding of how stress responses and nerve function influence deep digital flexor tendon physiology
Key Findings
- •Sympathetic innervation in the suprasesamoidean DDFT region is predominantly localized to blood vessel walls rather than tendon tissue proper
- •Tenocytes and spindle cells of fibrocartilage express both tyrosine hydroxylase and alpha-1 adrenergic receptors
- •The dorsal fibrocartilage showed lesser degrees of sympathetic innervation compared to vascular structures
- •Evidence supports autocrine/paracrine catecholaminergic signaling mechanisms within equine tendon tissue