CORTICOTROPIN-RELEASING FACTOR-CONTAINING AXON TERMINALS SYNAPSE ONTOCATECHOLAMINE DENDRITES AND MAY PRESYNAPTICALLY MODULATE OTHER AFFERENTS IN THE ROSTRAL POLE OF THE NUCLEUS LOCUS-COERULEUS IN THE RAT-BRAIN
Ej. Vanbockstaele et al., CORTICOTROPIN-RELEASING FACTOR-CONTAINING AXON TERMINALS SYNAPSE ONTOCATECHOLAMINE DENDRITES AND MAY PRESYNAPTICALLY MODULATE OTHER AFFERENTS IN THE ROSTRAL POLE OF THE NUCLEUS LOCUS-COERULEUS IN THE RAT-BRAIN, Journal of comparative neurology, 364(3), 1996, pp. 523-534
Physiological and immunohistochemical studies have suggested that cort
icotropin-releasing factor (CRF), the hypophysiotropic peptide that in
itiates endocrine responses to stress, may serve as a neurotransmitter
to activate noradrenergic neurons in the nucleus locus coeruleus (LC)
. We combined immunoperoxidase labeling for CRF and immunogold-silver
localization of the catecholamine-synthesizing enzyme tyrosine hydroxy
lase (TH) in single sections through the rat LC to determine potential
substrates for interactions between these two transmitters. Light mic
roscopic analysis indicated that CRF processes are dense and highly va
ricose in the rostral LC region in the vicinity of noradrenergic dendr
ites. Electron microscopy of this rostral region revealed that immunop
eroxidase labeling for CRF was mainly restricted to axons and axon ter
minals and was rarely seen in somata or dendrites. Axon terminals cont
aining CRF immunoreactivity varied in size, content of synaptic vesicl
es, and formation of synaptic specializations. The postsynaptic target
s of the CRF-labeled axon terminals consisted of both TH-labeled dendr
ites and dendrites lacking detectable TH-immunoreactivity. Of 113 CRF-
immunoreactive axon terminals, approximately 70% were in direct contac
t with TH-labeled and unlabeled dendrites. Of the CRF-labeled axon ter
minals forming synapses with TH-labeled and unlabeled dendrites, they
were either of the asymmetric (excitatory type; 19%) or symmetric (inh
ibitory type; 11%) variety or did not form identifiable contacts in th
e plane of section analyzed. Unlabeled axon terminals and glial proces
ses were also commonly located adjacent to the plasma membranes of CRF
-labeled axon terminals. These results provide the first direct ultras
tructural evidence that axon terminals containing CRF-immunoreactivity
1) directly contact catecholamine-containing dendrites within the ros
tral pole of the LC, 2) may presynaptically modulate other afferents,
and 3) are often enveloped by astrocytic processes. (C) 1996 Wiley-Lis
s, Inc.