Possible collateral branches of periaqueductal gray axons which distribute to the nucleus raphe magnus, nucleus reticularis paragigantocellularis, nucleus reticularis gigantocellularis pars alpha and the spinal trigeminal nucleus were analyzed with the double fluorescent retrograde tracer technique. With the exception of a small number of double-labeled neurons observed in the periaqueductal gray following injections of fluorescent dyes into the nuclei reticularis paragigantocellularis and gigantocellularis pars alpha, no double-labeled cells were found in this midbrain region following injections of tracers into various combinations of the above 4 nuclear groups. The results of this investigation indicate that these 4 brainstem nuclei are innervated predominantly by separate neuronal populations within the periaqueductal gray.
Bibliographical noteFunding Information:
1 Abols, I. A. and Basbaum, A. I., Afferent connections of the rostral medulla of the cat: a neural substrate for mid-brain-medullary interactions in the modulation of pain, J. comp. Neurol., 201 (1981) 285-297. 2 Akaike, A., Shibata, T., Satoh, M. and Tagaki, H., Anal-gesia induced by microinjection of morphine into and elec-trical stimulation of nucleus reticularis paragigantocellula-ris of the rat medulla oblongata, Neuropharmacology, 17 (1978) 775-778. 3 AIheid, G. F. and Carlsen, J., Small injections of fluores-cent tracers by iontophoresis or chronic implantation of mi-cropipettes, Brain Research, 235 (1982) 174-178. 4 Andrezik, J. A., Chan-Palay, V. and Palay, S. L., The nu-cleus paragigantocellularis lateralis in rat. Conformation and cytology, Anat. Embryol., 161 (1981) 355-371. 5 Andrezik, J. A., Chan-Palay, V. and Palay, S. L., The nu-cleus paragigantocellularis lateralis in the rat. Demonstra-tion of afferents by retrograde transport of horseradish per-oxidase, Anat. Embryol., 161 (1981) 373-390. 6 Arendash, G. W. and GaUo, R. V., Serotonin involvement in the inhibition of episodic luteinizing hormone release during electrical stimulation of the midbrain dorsal raphe nucleus in ovariectomized rats, Endocrinology, 102 (1976) 1199-1206. 7 Azami, J., Llewelyn, M. B. and Roberts, M. H. T., The contribution of nucleus reticularis paragigantocellularis and nucleus raphe magnus to the analgesia produced by sys-temically administered morphine, investigated with the mi-croinjection technique, Pain, 12 (1982) 229-246. 8 Basbaum, A. I., Clanton, C. H. and Fields, H. L., Three bulbospinal pathways from the rostral medulla of the cat: an autoradiographic study of pain modulating systems, J. comp. Neurol., 178 (1978) 209-224. 9 Basbaum, A. I. and Fields, H. L., Endogenous pain control mechanisms. Review and hypothesis, Ann. Neurol., 4 (1978) 451-462. 10 Basbaum, A. I. and Fields, H. L., The origin of descending pathways in the spinal cord of the cat and rat: further stud-ies on the anatomy of pain modulation, J. comp. Neurol., 187 (1979) 513-532. 11 Behbehani, M. M. and Fields, H. L., Evidence that an ex-citatory connection between the periaqueductal gray and nucleus raphe magnus mediates stimulation produced anal-gesia, Brain Research, 170 (1979) 85-91. 12 Beitz, A. J., The sites of origin of brainstem neurotensin and serotonin projections to the rodent nucleus raphe mag-nus, J. Neurosci., 2 (1982)829-842. 13 Beitz, A. J., The nuclei of origin of brainstem serotonergic This work was supported by Research Grants BSN 8214873 from the National Science Foundation and DE06682 from the National Institute of Dental Research. The authors wish to thank Dr. George Leich-netz for providing us with a detailed protocol of the fluorescence technique used in this study and Drs. Alice Larson and Martin Wessendorf for their helpful comments during the preparation of this manuscript.
- nucleus reticularis paragigantocellularis
- periaqueductal gray
- raphe magnus
- spinal trigeminal nucleus