NEURITE EXTENSION OF DEVELOPING NORADRENERGIC NEURONS IS IMPAIRED IN GENETICALLY EPILEPSY-PRONE RATS (GEPR-3S) - AN IN-VITRO STUDY ON THE LOCUS-COERULEUS

A primary determinant of seizure susceptibility and severity in geneti cally epilepsy-prone rats (GEPRs), is a generalized deficiency in the central noradrenergic system of these animals. In particular? this def iciency includes reduced numbers of norepinephrine (NE) synaptic termi nals in several brain areas and distinctly fewer NE axons within the a uditory tectum. Two strains of GEPRs have been developed: GEPR-3s that have moderately severe clonic seizures and GEPR-9s that have severe t onic seizures culminating in complete hindlimb extension. Seizures in animals of each substrain are preceded by a brief episode of wild runn ing. The developmental profile of NE axonal growth in GEPRs compared t o control rats is not known, but may be causally related to NE deficie ncies in this seizure model. The present study compared developmental neurite extension of fetal NE neurons in vitro between GEPR-3s and Spr ague-Dawley control rats: the strain from which GEPR-3s were originall y derived. Neurite arborization of individual NE neurons was assessed by quantitative morphometry following immunocytochemical identificatio n of tyrosine hydroxylase (TH). Preliminary studies using explant and dispersed-cell cultures of control-rat tissues showed that optimal cul ture parameters to support neuritogenesis of LC neurons included the u se of dispersed-cell cultures, Pronectin-F substrate, day-14 gestation donor-tissue, no use of cytosine-arabinofuranoside (ARA-c, a glial mi totic inhibitor) and the presence of co-cultured tectal tissue. Compar ed to fetal control-rat NE neurons co-cultured with fetal control-rat tectum, NE neurons derived from fetal GEPR-3 LC in co-culture with GEP R-3 tectum exhibited only 30% of the neurite extension of control-rat LC neurons and GEPR-3 LC neurons bad a similarly deficient amount of b ranching. This study suggests, but does not prove, that deficiency in tectal NE in GEPR-3s involves a developmental deficiency in neurite ex tension from GEPR-3 LC neurons. Hypothetically, this deficiency may al so contribute to the well described NE deficiency in other regions of the adult GEPR brain. Supported by SIUSOM and UICOM-P. (C) 1998 Elsevi er Science B.V.