TYROSINE HYDROXYLASE-LIKE IMMUNOREACTIVITY IN PREVIOUSLY DESCRIBED CATECHOLAMINE-CONTAINING NEURONS IN THE VENTRAL NERVE CORD OF RHODNIUS-PROLIXUS

Tyrosine hydroxylase is the rate-limiting enzyme in catecholamine biosynthesis in vertebrates, but its use in catecholaminergic neurones in insectsis problematic. The present study examines the distribution of tyrosine hydroxylase-like immunoreactive neurones in wholemount preparations of the ventral nerve cord of fifth-instar Rhodnius prolixus, and compares these neurones to previously described catecholamine-containing neurones. It has been found that virtually all of the catecholamine-containing neurones in Rhodnius are also positive for tyrosine hydroxylase-like immunoreactivity. It seems logical to assume that tyrosine hydroxylase is indeed used in the catecholamine pathway in this insect, and that tyrosine hydroxylase-like immunohistochemistry is a sensitive, reproducible and powerful tool for the routine mapping of catecholaminergic neurones in insects. Analysis of the ganglia of the ventral nerve cord with HPLC and electrochemical detection reveals the presence of the catecholamines dopamine and nor-epinephrine, with dopamine values being greater. A number of the tyrosine hydroxylase-like immunoreactive, catecholamine-containing, neurones are large identifiable neurones with distinctive branching patterns. They therefore afford preparations which can be used to address the question as to the physiological function of catecholamines in insects, and which can be used for HPLC analysis of microdissected cells. © 1990.