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The Sites of Origin of Brain Stem Neurotensin and Serotonin Projections to the Rodent Nucleus Raphe Magnus'

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The Sites of Origin of Brain Stem Neurotensin and Serotonin Projections to the Rodent Nucleus Raphe Magnus' 0270.6474/82/0207-0829$02.00/0 The Journal of Neuroscience Copyright 0 Society for Neuroscience Vol. 2, No. 7, pp. 829-842 Printed in U.S.A. July 1982 THE SITES OF ORIGIN OF BRAIN STEM NEUROTENSIN AND SEROTONIN PROJECTIONS TO THE RODENT NUCLEUS RAPHE MAGNUS’ ALVIN J. BEITZ” Department of Anatomy, University of South Carolina, Columbia, South Carolina 29208 Received December 4, 1981: Revised February 22, 1982; Accepted February 22, 1982 Abstract The combined horseradish peroxidase retrograde transport-peroxidase-antiperoxidase immuno- histochemical procedure was utilized in the present study to ascertain the sites of origin of serotonin and neurotensin projections to the rodent nucleus raphe magnus. The major serotonin inputs to the raphe magnus arise from the B-8 and B-9 groups of Dahlstrom and Fuxe (Dahlstrom, A., and K. Fuxe (1964) Acta Physiol. Stand. Suppl. 232 62: l-55), the nucleus reticularis paragigantocellularis, and the nucleus reticularis gigantocellularis pars (Y. Neurotensinergic projections to the raphe magnus originate predominantly from the periaqueductal gray, the nucleus solitarius, the dorsal and ventral parabrachial nuclei, and the nucleus cuneiformis. The periaqueductal gray and the nucleus paragigantocellularis were found to provide both a neurotensin and a serotonin projection to this raphe nucleus. The present results indicate that several brain stem nuclei, which have been implicated previously in endogenous analgesia mechanisms, provide serotonergic and neurotensi- nergic input to the nucleus raphe magnus. Reynolds (1969) and Mayer and Liebeskind (1974) jection is the critical link in the analgesia produced by were among the first investigators to demonstrate that PAG stimulation (Fields and Basbaum, 1978). potent analgesia could be produced by electrical brain Although the raphe-spinal system may play a role in stimulation in freely moving animals. Most of the early PAG stimulation-produced analgesia, the role of the studies of centrally induced analgesia focused on the NRM in exogenous opiate action in still far from clear. midbrain periaqueductal gray (PAG) from which stimu- Although systemic administration of opiates has been lation-produced analgesia was best elicited. Subsequent shown by some investigators to increase the discharge studies have demonstrated that stimulation of the med- rate of raphe magnus neurons (Deakin et al., 1977; Oleson ullary nucleus raphe magnus (NRM), a source of sero- et al., 1978), most investigators interpret these results as tonin neurons, also produces potent analgesia (Fields and indicating that raphe neurons are activated indirectly Basbaum, 1978; Oliveras et al., 1979). Moreover, it has from the PAG (Fields and Basbaum, 1978). For instance, been shown that stimulation of the PAG alters the activ- Proudfit (1981) has demonstrated recently that raphe ity of cells in the NRM (Pomeroy and Behbehani, 1979) magnus neurons are not involved directly in mediating and that lesions of the NRM produce a pronounced the antinociceptive actions of opiates. In contrast Dick- decrease in nociceptive threshold (Proudfit, 1981). Both enson and co-workers (1979) reported that the rodent the analgesic action of opiates and electrical stimulation NRM is sensitive to the microinjection of opiates and of the PAG are blocked by lesion of the dorsolateral part that naloxone can reverse the analgesic action of NRM of the spinal cord (Basbaum et al., 1977). Since (I) the stimulation. PAG sends very few direct projections to the spinal cord Although some controversy exists, the majority of stud- and (2) a PAG-NRM projection was demonstrated ies to date would suggest that opiates administered sys- (Ruda, 1976; Gallager and Pert, 1978; Abols and Bas- temically do not act at the level of the raphe. It is baum, 1981), it was proposed that the raphe-spinal pro- probable that opiate compounds act at other CNS sites which, in turn, influence the NRM as indicated above. The present investigation is part of an ongoing study ’ This work was supported by Grant BNS 7906486 from the National Science Foundation and, in part, by Grant I ROl NS17401-01 from the designed to elucidate the origin of several neurotrans- National Institutes of Health. mitter and neuropeptide inputs to the NRM. This report ‘Present address: Department of Veterinary Biology, School of deals with the brain stem origin of serotonergic and Vet,erinary Medicine, University of Minnesota, St. Paul, MN 5.5108. neurotensin projections to the NRM and the results are 829 830 Beitz Vol. 2, No. 7, July 1982 correlated with the known distribution of opiate recep- against NT was purchased from Immuno Nuclear Corp. tors and with the location of brain nuclei which have (Stillwater, MN). Sections were incubated from 12 to 36 been implicated as part of the endogenous analgesia hr in either 5-HT antiserum (1:3000 to 15000) or NT system. antiserum (1:lOOO) diluted in a PBS/Triton X-100 solu- tion. After the immunocytochemical staining procedures, Materials and Methods sections were incubated in the DAB solution without The combined retrograde HRP histochemical and im- prior incubation in CoC12to yield a brown reaction prod- munocytochemical procedure developed by Bowker and uct in immunoreactive cells. Immunocytochemical spec- co-workers (1981) was employed with slight modification ificity was established by incubating the tissue with in order to determine the distribution of serotonin (5- diluted 5-HT antisera preabsorbed with 100 pg of 5-HT/ HT)- and neurotensin (NT)-immunoreactive cell bodies ml of antisera or with diluted NT antisera preabsorbed which project to the NRM. Eighteen adult Sprague- with 100 pg of NT/ml of antisera. These immunohisto- Dawley rats were injected stereotaxically with horserad- chemical controls were negative. ish peroxidase (HRP) by means of either iontophoretic Double labeled neurons which contained either 5-HT- or pressure injections. Iontophoretic injections of HRP or NT-like immunoreactivity and HRP-reactive granules were delivered via a glass micropipette filled with a 13% were identified by the presence of both black and brown solution of HRP in 0.05 M Tris buffer (pH 7.6). The reaction product within their cytoplasm. The HRP re- driving force for the microelectrophoretic injections was action product consisted of black punctate granules supplied by a 1%PA positive current delivered by a which were present in the cell soma and extended into constant current source (Midgard Electronics) at a pulse the dendritic processes (Fig. 1A). The PAP reaction rate of 7 set on, 7 set off for a duration of 20 to 40 min. product, on the other hand, appeared as a homogeneous Pressure injections (ranging from 0.1 to 2.0 ~1) of a 40% light brown coloration which occurred throughout the solution of HRP were delivered directly from either a l- cell cytoplasm, exclusive of the nucleus (Fig. IA). Single or a lo-a.1 syringe. After 24 to 72 hr, the animals were labeled neurons were easily identified by the presence of treated with colchicine (60 pg in 6 ~1 of NaCl) injected either a black granular reaction product (HRP-labeled intraventricularly. The animals were perfused 24 to 48 hr cell) or a brown reaction product (immunoreactive cell) later with warm physiological saline followed by 1000 ml throughout the neuronal cytoplasm (Fig. 1, B and C). of cold 3.5 to 3.8% paraformaldehyde solution in 0.1 M Small iontophoretic injections of HRP were made into sodium phosphate buffer or by 1000 ml of 3.5% paraform- the raphe magnus in two animals and the brain sections aldehyde, 0.1% glutaraldehyde. In either case, the fixative then were processed with the tetramethylbenzidine was followed by 1000 ml of a phosphate-buffered sucrose (TMB) procedure routinely used in our laboratory (Beitz, solution (30%). The brains were removed and 40-pm 1982). Because the TMB procedure is more sensitive sections were cut on a freezing microtome. Brain stem than the DAB-cobalt chloride method used in the above sections were subsequently incubated for 5 min in a 0.5% combined retrograde transport-immunohistochemical CoCl? solution in 0.1 M Tris buffer prior to incubation in experiments (see Mesulam and Rosene, 1979), these two 0.025% diaminobenzidine (DAB) containing 0.01% HaOa. cases were used to chart the total brain stem input to the Incubation of tissue sections in CoClz prior to the DAB NRM. In addition, control injections of the tracer enzyme reaction yields a black reaction product in the retro- were made into the nucleus reticularis gigantocellularis gradely labeled neurons. (NRG), the inferior olive, and the area immediately In some cases, the heavy metal intensification proce- dorsal to the NRM. The brain tissue from these control dure of Adams (1981) was utilized in the DAB-HRP cases also was processed with the TMB method and was reaction instead of prior treatment of CoC12. With this compared to the two NRM injections. This was done to method, both nickel ammonium sulfate and cobalt chlo- ascertain, if any of the labeling that occurred in our ride were added directly to the DAB solution. This double label experiments was due to spread of the enzyme method is much simpler and faster than the cobalt chlo- and subsequent uptake by axonal endings outside of the ride procedure and has the added advantage of providing NRM. a more sensitive substrate for detecting HRP. One dis- advantage of the heavy metal intensification procedure Results is that it often results in the presence of a black precipi- tate over the tissue section. Although some of this pre- Description of injection sites cipitate is lost during subsequent processing of the tissue Both the iontophoretic injections and the 0.2~~1pres- for immunohistochemistry, it can be eliminated by bub- sure injections of HRP resulted in the confinement of the bling nitrogen gas through the phosphate buffer that is dense core of black reaction product to the vicinity of the used to make the DAB solution.
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