Immunoreactive endozepine-like peptides in the brain and pituitary of the Atlantic hagfish, Myxine glutinosa

Endozepines are a family of peptides capable of displacing benzodiazepines from their specific binding sites, to which belong the diazepam-binding inh ibitor and the octadecaneuropeptide (ODN). This paper reports the distribut ion of ODN-related peptides, investigated for the first time by immunocytoc hemistry, in different brain and pituitary regions of the Atlantic hagfish, Myxine glutinosa. Immunoreactive ODN-like material was found in the telenc ephalon at the level of bundles of different olfactory nerve fibres. Moreov er, at the level of the pallium, immunoreactive multipolar neurons were obs erved in the pars parvocellularis of the stratum griseum superficialis. Sim ilar immunopositive nerve cell bodies were found in the nucleus medialis of the central prosencephalic complex. In the mesencephalon, few immunoreacti ve neurons lining and contacting the mesencephalic ventricle were detected; such nerve cells could be involved in the regulation of cerebrospinal flui d homeostasis. Dorsally in the mesencephalon, numerous ODN-containing cell bodies were present in the area praetectalis. The rhomboencephalon was immu nostained only in the octavolateral area and in the nucleus motorius magnoc ellularis of the trigeminal nerve. Furthermore, ODN immunoreactivity was al so present in the nerve cells of ganglia of the ophthalmic division of the trigeminal nerve complex. The immunocytochemical patterns described here in the brain of M. glutinosa suggest an involvement of ODN-like peptides as n euromodulators in sensory pathways, such as olfactory and visual. Finally, ODN-like substances were localized in discrete populations of adenohypophys ial cells and in tanycytes lining the neurohypophyseal walls, suggesting fo r endozepines a paracrine and/or endocrine control of pituitary hormones re lease and a neurohormone role respectively. These results could give new in sights into the chemioarchitecture of the brain of myxinoids.