9810524 Van BOCKSTAELE The brain nucleus locus coeruleus (LC) has been intensely investigated because it provides the neurotransmitter norepinephrine to all major levels of the brain and spinal cord. Neurons in the LC are the first norepinephrine- containing cell group to develop in the central nervous system. Numerous lines of research have shown that norepinephrine from the LC may be involved in regulating neuronal outgrowth in regions of the brain which receive norepinephrine innervation, such as cortical and limbic brain regions. Interestingly, the intrinsic physiological activity of LC neurons varies during development and may account for their involvement in these functions. Electrophysiological recordings from neonatal LC neurons in brain slices display oscillations in their membrane potentials which are synchronous throughout the entire nucleus. The frequency of oscillations increases from 0.3 Hz to 3 Hz until about three weeks of age when they disappear. The synchronous activity observed in neonatal LC neurons is thought to be the result of electrical coupling between LC cells. However, gap junction proteins, the anatomical substrate for electrical coupling, have not been demonstrated by electron microscopy nor has their existence been established at different periods of development in the LC. In addition, there have been no electrophysiological experiments that have examined the modulation of electrical coupling by compounds known to inhibit or stabilize gap junctions. The primary objective of our research is to unequivocally establish the existence of gap junction proteins that can couple LC neurons to each other or to glial cells at different stages of development. The methods include dual labeling immunocytochemistry at the electron microscopic level in young and adult rat brain using antibodies specific for the gap junction protein family, known as connexins, and for the norepinephrine synthesizing enzyme, tyrosine hydroxylase. Addition ally, electrophysiological recordings from individual LC neurons will be conducted in vitro and to test their responses to agents known to modulate gap junctions. Finally, individual LC neurons will be intracellularly filled and examined for dye coupling at both light and electron microscopic levels. Taken together, the anatomical and electrophysiological results obtained from this research will shed light on the functional architecture of LC in development and will thus lay the groundwork for future studies aimed at elucidating the role of the LC/norepinephrine system in regulating control of its postsynaptic targets.
