Ultrastructure of endomorphin-1 immunoreactivity in the rat dorsal pontine tegmentum: evidence for preferential targeting of peptidergic neurons in Barrington's nucleus rather than catecholaminergic neurons in the peri-locus coeruleus.
Endomorphins are opioid tetrapeptides that have high affinity and selectivity for mu-opioid receptors (muORs). Light microscopic studies have shown that endomorphin-1 (EM-1) -containing fibers are distributed within the brainstem dorsal pontine tegmentum. Here, immunoelectron microscopy was conducted in the rat brainstem to identify potential cellular interactions between EM-1 and tyrosine hydroxylase (TH) -labeled cellular profiles in the locus coeruleus (LC) and peri-LC, an area known to contain extensive noradrenergic dendrites of LC neurons. Furthermore, sections through the rostral dorsal pons, from colchicine-treated rats, were processed for EM-1 and corticotropin releasing factor (CRF), a neuropeptide known to be present in neurons of Barrington's nucleus. EM-1 immunoreactivity was identified in unmyelinated axons, axon terminals, and occasionally in cellular profiles resembling glial processes. Within axon terminals, peroxidase labeling for EM-1 was enriched in large dense core vesicles. In sections processed for EM-1 and TH, approximately 10% of EM-1-containing axon terminals (n=269) targeted dendrites that exhibited immunogold-silver labeling for TH. In contrast, approximately 30% of EM-1-labeled axon terminals analyzed (n = 180) targeted CRF-containing somata and dendrites in Barrington's nucleus. Taken together, these data indicate that the modulation of nociceptive and autonomic function as well as stress and arousal responses attributed to EM-1 in the central nervous system may arise, in part, from direct actions on catecholaminergic neurons in the peri-LC. However, the increased frequency with which EM-1 axon terminals form synapses with CRF-containing profiles in Barrington's nucleus suggests a novel role for EM-1 in the modulation of functions associated with Barrington's nucleus neurons such as micturition control and pelvic visceral function.
Peoples
James F
JF
Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA.
Wessendorf
Martin W
MW
Pierce
Tracy
T
Van Bockstaele
Elisabeth J
EJ
D000818:Animals; D002450:Cell Communication / Q000502:physiology; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D007150:Immunohistochemistry; D008125:Locus Coeruleus / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D009457:Neuroglia / Q000378:metabolism / Q000648:ultrastructure; D009479:Neuropeptides / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D011149:Pons / Q000378:metabolism* / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000033:anatomy & histology / Q000378:metabolism*; D013312:Stress, Physiological / Q000378:metabolism; D009435:Synaptic Transmission / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D014554:Urination / Q000502:physiology
D009479:Neuropeptides; D009842:Oligopeptides; C105293:endomorphin 1; D003346:Corticotropin-Releasing Hormone; D014446:Tyrosine 3-Monooxygenase; D009638:Norepinephrine