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.
Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA.
James F
JF
Peoples
Martin W
MW
Wessendorf
Tracy
T
Pierce
Elisabeth J
EJ
Van Bockstaele
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