Distribution and immunohistochemical properties of autonomic neurons supplying the ovine hip joint capsule

Abstract

Combined retrograde tracing and double labelling immunohistochemistry were applied to study the distribution and chemical coding of autonomic neurons projecting to the ovine hip joint capsule. As revealed by retrograde tracing, fast blue-positive autonomic neurons supplying the lateral side of the hip joint capsule and the medial side of the hip joint capsule were located within the lumbar and sacral of the ipsilateral sympathetic chain ganglia and within the caudal mesenteric ganglion. Immunohistochemistry revealed that nearly all (sympathetic chain ganglia: 96% and caudal mesenteric ganglion: 98.8%) the neurons were adrenergic in nature (positive for dopamine β-hydroxylase). Many retrogradely labelled neurons also displayed immunoreactivity to neuropeptide Y (approximately 34% of fast blue-positive neurons within caudal mesenteric ganglion and sympathetic chain ganglia). Populations of Met-Enk⁺ (20%) and Leu-Enk⁺ (6%) neurons were present only in the sympathetic chain ganglia while within caudal mesenteric ganglion no enkephalinergic-labelled neurons were noted. Only a small population (2.2%) of hip joint capsule-projecting neurons were Gal-IR and they were observed only within the caudal mesenteric ganglion. No cholinergic neurons involved in the innervation of the hip joint capsule were found. However, fast blue-positive nerve cell bodies were surrounded by numerous cholinergic nerve fibres often forming basket-like formations. Single Gal⁺ nerve fibres were found in the intraganglionic connective tissue. Substance P-positive or calcitonin gene-related peptide-positive intraganglionic nerve terminals were very numerous and formed “baskets” surrounding fast blue-positive perikarya within sympathetic chain ganglias and caudal mesenteric ganglion.