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 inhibitor and the octadecaneuropeptide (ODN). This paper reports the distribution of ODN-related peptides, investigated for the first time by immunocytochemistry, in different brain and pituitary regions of the Atlantic hagfish, Myxine glutinosa. Immunoreactive ODN-like material was found in the telencephalon at the level of bundles of different olfactory nerve fibres. Moreover, at the level of the pallium, immunoreactive multipolar neurons were observed in the pars parvocellularis of the stratum griseum superficialis. Similar immunopositive nerve cell bodies were found in the nucleus medialis of the central prosencephalic complex. In the mesencephalon, few immunoreactive neurons lining and contacting the mesencephalic ventricle were detected; such nerve cells could be involved in the regulation of cerebrospinal fluid homeostasis. Dorsally in the mesencephalon, numerous ODN-containing cell bodies were present in the area praetectalis. The rhomboencephalon was immunostained only in the octavolateral area and in the nucleus motorius magnocellularis of the trigeminal nerve. Furthermore, ODN immunoreactivity was also 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 neuromodulators in sensory pathways, such as olfactory and visual. Finally, ODN-like substances were localized in discrete populations of adenohypophysial cells and in tanycytes lining the neurohypophyseal walls, suggesting for endozepines a paracrine and/or endocrine control of pituitary hormones release and a neurohormone role respectively. These results could give new insights into the chemioarchitecture of the brain of myxinoids.