Postnatal development of protein gene product 9.5 and calcitonin gene-related peptide immunoreactive nerve fibres in rat temporomandibular joint disc

Protein gene product 9.5 (PGP 9.5), an immunohistochemical marker of whole nerve fibres, and calcitonin gene-related peptide (CGRP), a marker of thin nerve fibres, were used to elucidate the postnatal development of nerve fibres in rat temporomandibular joint (TMJ) disc. At birth, PGP 9.5-immunoreactive nerve fibres exhibited running towards the central area of the disc, invading by approximately 95 m from the disc attachment. The nerve fibres existing inside the disc became longer during postnatal development. The number of nerve fibres in the disc increased in a progressive manner up to 40 days after birth. CGRP-immunoreactive nerve fibres also presented changes essentially similar to those of PGP 9.5-immunoreactive nerve fibres. However, the proportion of CGRP-immunoreactive nerve fibres to PGP 9.5-immunoreactive ones was approximately 80%, and remained constant up to 40 days after birth. In conclusion, the distribution and the number of nerve fibres are variable during postnatal development, although the ratio of thin nerve fibres remains invariable. It is emphasized that these changes of innervation in the TMJ are associated with the development of masticatory function.