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K Yamanouchi - One of the best experts on this subject based on the ideXlab platform.
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effect of direct application of estrogen aimed at lateral septum or Dorsal Raphe Nucleus on lordosis behavior regional and sexual differences in rats
Neuroendocrinology, 1999Co-Authors: Motoyasu Satou, K YamanouchiAbstract:The role of estrogen in lordosis-inhibiting systems in the lateral septum or the Dorsal Raphe Nucleus was investigated in female and male rats. Ovariectomized rats received implantation of 22-gauge gu
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lordosis inhibiting effect of progesterone in female rats with lesions in septum preoptic area or Dorsal Raphe Nucleus
Physiology & Behavior, 1996Co-Authors: Motoyasu Satou, K YamanouchiAbstract:Radiofrequency lesions in the septum (SL), the preoptic area (POAL), or the Dorsal Raphe Nucleus (DRL) were made in ovariectomized rats. In a control group of 16 females, ovariectomy, but no brain surgery, was performed. All animals except half of the control rats received injections of 5 mg progesterone (P) 1 h prior to the injection of 5 micrograms/kg b.w. of estradiol benzoate (EB). Instead of 5 mg P, oil was administered to half of the controls. Forty-four hours after EB, all females received 0.5 mg P. A sexual behavior test was performed 4 h after the last injection of P. The result was that oil-treated control rats showed high lordosis quotient (LQ) and soliciting behavior. In contrast, low scores of LQ and no soliciting behavior were observed in all of the 5 mg P-treated rats, even if the SL, POAL, or DRL was made. These results suggest that the septum, the preoptic area, and the Dorsal Raphe Nucleus are not essential for the female sexual behavior-inhibiting mechanisms of progesterone.
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INHIBITORY EFFECT OF BACLOFEN ON LORDOSIS IN FEMALE AND MALE RATS WITH Dorsal Raphe Nucleus LESION OR SEPTAL CUT
Neuroendocrinology, 1996Co-Authors: M Kakeyama, K YamanouchiAbstract:The inhibitory effect of baclofen, a GABAβ receptor agonist, on lordosis was examined in female and male rats with Dorsal Raphe Nucleus lesions (DRL) or cut of the septal fibers (ARD). Both female and
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Two types of lordosis-inhibiting systems in male rats: Dorsal Raphe Nucleus lesions and septal cuts
Physiology & behavior, 1994Co-Authors: M Kakeyama, K YamanouchiAbstract:Abstract To examine the functional relationships between the Dorsal Raphe Nucleus and the septum in the inhibitory regulation of feminine sexual behavior in male rats, castrated male rats received destruction of the Dorsal Raphe Nucleus (DRL), interruption of the septal outputs (ARD), or both DRL and ARD (DRL + ARD). All animals were treated with estradiol by using Silastic tubes, and feminine sexual behavior was observed every other day for 10 days. Most castrated control male rats did not show lordosis throughout the tests. In contrast, all of the males with DRL alone or ARD alone displayed lordosis, but the lordosis quotients (LQ) in these groups were lower than those of the female control group. On the other hand, DRL + ARD males showed higher LQs than the DRL or the ARD males, being comparable to control females. Thus, two types of strong inhibitory influence exist in the Dorsal Raphe Nucleus and the septum, and resist the facilitation of feminine sexual behavior by estrogen in male rats. Furthermore, these inhibitory systems operate independently, because an additive effect of DRL and ARD in facilitating lordosis was clearly observed in DRL + ARD males.
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Female sexual behaviors in male rats with Dorsal Raphe Nucleus lesions: treatment with p-chlorophenylalanine.
Brain research bulletin, 1993Co-Authors: M Kakeyama, K YamanouchiAbstract:The effects of the serotonin-synthesis inhibitor, p-chlorophenylalanine (PCPA) on female sexual behaviors were examined in male rats with or without lesions (DRL) of the Dorsal Raphe Nucleus, which contains a large number of serotonergic cell bodies. Estrogen-primed castrated males without brain surgery (control) showed extremely low levels of lordosis compared with females. On the other hand, DRL males displayed lordosis response more frequently than control males, but the lordosis quotient (LQ) in this group was lower than that in females. As well as DRL males, all PCPA-treated males showed lordosis, the mean LQ being comparable to the DRL group. Thus, the destruction of the Dorsal Raphe Nucleus or the deprivation of serotonin by PCPA treatment facilitates manifestation of lordosis behavior in male rats. However, synergistic effect of DRL and PCPA treatments on female sexual behaviors have not been observed. The mean LQ in PCPA-treated male rats with DRL was almost the same as in DRL males or PCPA-treated males. These results suggest that the possible site of action of PCPA in regulating female sexual behavior in male rats is the serotonergic neurons in the Dorsal Raphe Nucleus. Furthermore, the lordosis-facilitating effect of DRL is due to destruction of the serotonergic cell bodies in the Dorsal Raphe Nucleus.
Yasumitsu Nakai - One of the best experts on this subject based on the ideXlab platform.
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An electron microscopic observation of the vesicular acetylcholine transporter-immunoreactive fibers in the rat Dorsal Raphe Nucleus.
Brain research bulletin, 1998Co-Authors: Qing-ping Wang, Jian-lian Guan, Hidehiko Ochiai, Yasumitsu NakaiAbstract:By using immunocytochemistry with an antibody directed against the vesicular acetylcholine transporter, many cholinergic neuronal processes were found to be immunopositive in the Dorsal Raphe Nucleus. At the electron microscopic level, most of these processes were found to be axons. The immunopositive axon terminals made synapses on immunonegative dendrites and their spines whereas rare synapses were found between the immunopositive axon terminals and the immunonegative neuronal perikarya. Occasionally, the dendrites postsynaptic to an immunopositive axon terminal also received a synapse from an immunonegative axon terminal. The synapses made by the immunopositive axon terminals were usually symmetric and had a short active zone. Fewer immunostained dendrites were found, and they usually received asymmetric synapses from nonimmunostained axon terminals. The existence of cholinergic axon terminals and the synapses made by these terminals support the physiological data indicating that acetylcholine plays a role in the pain inhibition system in the Dorsal Raphe Nucleus.
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Ultrastructural localization of delta-1 opioid receptor in the Dorsal Raphe Nucleus of the rat.
Synapse (New York N.Y.), 1997Co-Authors: Qing-ping Wang, Jian-lian Guan, Hidehiko Ochiai, Yasumitsu NakaiAbstract:The ultrastructural localization of delta-1 opioid receptor in the rat Dorsal Raphe Nucleus was studied by the preembedding avidin-biotin-peroxidase complex technique. With application of a low concentration of the first antiserum in incubation and control of short-time reaction to 3,3'-diaminobenzidine, the immunoreaction seemed to be faint at the light microscopic level. At the electron microscopic level, however, delta-1 opioid receptor immunoreaction products were found to be localized specifically on the postsynaptic membrane of dendrites, dense-cored vesicles, and the surface of the small, clear vesicles in axon terminals with strong immunoreactivity. Of the total 659 immunopositive profiles observed, up to 62.4% (411/659) were dendrites, whereas 33.8% (223/659) were axon terminals. The immunostained myelinated axons and perikarya were relatively rare, with the frequencies 0.8% (5/659) and 3.0% (20/659), respectively. Most of the immunopositive dendrites (338/411, 82.2%) were immunostained only at the postsynaptic membranes. Other immunoreactive dendrites showed their immunoreaction products also in some other contents besides the postsynaptic membranes (44/411, 10.7%) or only in those contents but not the postsynaptic membranes (25/411, 6.1%). Only four dendrites showed their immunoreactive results only at the membrane not related to synapse (4/267, 1.0%). No dendrite was found immunostained in all the contents. About half of the immunopositive axon terminals (125/223, 56.1%) were found to make synapse with nonimmunoreactive dendrites (76/223, 34.1%) or immunoreactive dendrites (49/223, 22.0%), while only one was found to make contact with immunoreactive perikarya. The present study showed that delta-1 opioid receptor in the Dorsal Raphe Nucleus is mostly localized on postsynaptic membrane; the main function of the delta-1 receptor in the Dorsal Raphe Nucleus is to receive signals from the opioid-containing axon terminals through synapses.
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Immunoelectron microscopy of β-endorphinergic synaptic innervation of nitric oxide synthase immunoreactive neurons in the Dorsal Raphe Nucleus
Brain research, 1995Co-Authors: Qing-ping Wang, Yasumitsu NakaiAbstract:On the basis of the comparing of the distribution of β-endorphin-like immunoreactive neuronal fibers and nitric oxide synthase-like immunoreactive neurons in the Dorsal Raphe Nucleus, the synapses between the two immunocytochemically identified neurons were studied with a modified DAB-silver-gold intensification double immunostaining technique at the electron microscopic level. Although both of them can be found in the medioDorsal and medioventral parts of the Dorsal Raphe Nucleus, the synapses between them could only be found in the medioDorsal part. The majority of the β-endorphin-like immunoreactive neuronal fibers contained many dense-cored vesicles. The synapses made by β-endorphin-like immunoreactive neuronal axon terminals on nitric oxide synthase-like immunoreactive neurons were both symmetrical and asymmetrical with the former predominant, especially in the axo-dendritic ones. β-Endorphin-like immunoreactive perikarya could only be found in the ventrobasal hypothalamus. These findings suggest the possibility that the β-endorphin- producing neurons in the ventrobasal hypothalamus could influence nitric oxide synthase-containing neurons in the Dorsal Raphe Nucleus by synaptic relations.
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Distribution and synaptic relations of NOS neurons in the Dorsal Raphe Nucleus: A comparison to 5-HT neurons
Brain research bulletin, 1995Co-Authors: Qing-ping Wang, Jian-lian Guan, Yasumitsu NakaiAbstract:Abstract Anti-nitric oxide synthase antibody was used to study the distribution, cytowchhecture, and synaptic relations of nitric oxide synthase-like immunoreactive neurons in the whole rostral-caudel length of the Dorsal Raphe Nucleus of the rat and compared them with serotonergic neurons. Results showed that the distribution of the nitric oxide synthase in the Dorsal Raphe Nucleus was similar to that of the serotonergic neurons at the rostral part of the Dorsal Raphe Nucleus, including the medioDorsal and the medioventral cell groups, and changed at the middle and caudal parts of the Dorsal Raphe Nucleus. The cytoarchitecture of the nitric oxide synthase-like immunoreactive neurons in the medioventrai cell group of the Dorsal Raphe Nucleus was similar to that of the serotonergic neurons. Similar to the serotonergic neurons there, nitric oxide synthase-like immunoroactive neurons also received synapses from axon terminals that contained round, or flattened vesicles, or both kinds. Different to the serotonergic neurons, the few nitric oxide synthase-like immunoroactive axon terminals that were in this area formed synapses.
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Synaptic relations of neurotensinergic neurons in the Dorsal Raphe Nucleus
Peptides, 1995Co-Authors: Qing-ping Wang, Jian-lian Guan, Yasumitsu NakaiAbstract:Abstract The ultrastructure and synaptic relations of neurotensinergic neurons in the rat Dorsal Raphe Nucleus (DRN) were examined. The neurotensin-like immunoreactive (NT-LI) neurons in the DRN were fusiform or spherical. The NT-LI perikarya could only be detected in colchicine-treated animals whereas the immunoreactive axon terminals could only be found in the anirnals not treated with colchicine. Although many NT-LI dendrites received synapses from nonimmunoreactive axon terminals, the NT-LI perikarya received few synapses. NT-LI axon terminals also made synapses on nonimmunoreactive dendrites. Occasionally, synapses were found between the NT-LI axon terminals and NT-LI dendrites in the cases in which the animals were not treated with colchicine.
K Semba - One of the best experts on this subject based on the ideXlab platform.
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A direct retinal projection to the Dorsal Raphe Nucleus in the rat.
Brain research, 1994Co-Authors: H Shen, K SembaAbstract:A direct projection from the retina to the Dorsal Raphe Nucleus at the pontomesencephalic junction was demonstrated with both antero- and retrograde tracing techniques in the rat. Following intravitreous injections of choleratoxin subunit B (CTB), horseradish peroxidase (HRP) and CTB-conjugated HRP, varicose fibers were labeled in the lateral region of the Dorsal Raphe Nucleus, predominantly contralateral to the injection. Many of these labeled fibers were intermingled with serotonin-immunoreactive neurons, but some fibers were also found further laterally, beyond the boundary of Dorsal Raphe Nucleus but within the periaqueductal gray. Following injections of the retrograde tracers Fluoro-Gold and CTB into the Dorsal Raphe Nucleus and adjacent periaqueductal gray (without contamination of previously known targets of retinal projections), a small population of ganglion cells was labeled in the retina. These data provide evidence for the existence of a direct retinal projection to the lateral region of the Dorsal Raphe Nucleus and the adjacent mesopontine periaqueductal gray in the rat. This projection may have a role in sensorimotor coordination and the regulation of circadian rhythm as well as sleep and wakefulness.
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A direct retinal projection to the Dorsal Raphe Nucleus in the rat
Brain Research, 1994Co-Authors: H Shen, K SembaAbstract:Abstract A direct from the retina to the Dorsal Raphe Nucleus at the pontomesencephalic junction was demonstrated with both antero- and retrograde tracing techniques in the rat. Following intravitreous injections of choleratoxic subunit B (CTB), horseradish peroxidase (HRP) and CTB-conjugated HRP, varicose fibers were labeled in the lateral region of the Dorsal Raphe Nucleus, predominatly contralateral to the injection. Many of these labeled fibers were intermingled with serotonin-immunoreactive neurons, but some fibers were also found further laterally, beyond the boundary of Dorsal Raphe Nucleus but within the periaqueductal gray. Following injections of the retrograde tracers Flouoro-Gold and CTB into Dorsal Raphe Nucleus and adjacent periaqueductal gray (without contamination of previously known targets of retinal projections), a small population of ganglion cells was labeled in the retina. These data provide evidence for the existence of a direct retinal projection to the lateral region of the Dorsal Raphe Nucleus and the adjacent mesopontine periaqueductal gray in the rat. This projection may have a role in sensorimotor coordination and the regulation of circadian rhythm as well as sleep and wakefulness.
Qing-ping Wang - One of the best experts on this subject based on the ideXlab platform.
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the orexinergic synaptic innervation of serotonin and orexin 1 receptor containing neurons in the Dorsal Raphe Nucleus
Regulatory Peptides, 2005Co-Authors: Qing-ping Wang, Jian-lian Guan, Yoshimasa Koyama, Kazumi Takahashi, Yukihiko Kayama, Seiji ShiodaAbstract:Orexin/hypocretin has been well demonstrated to excite the serotonergic neurons in the Dorsal Raphe Nucleus (DRN). We studied the morphological relationships between orexin-containing axon terminals and serotonin- as well as orexin-receptor-containing neurons in the Dorsal Raphe Nucleus. Using immunohistochemical techniques at the light microscopic level, orexin A (OXA)-like immunoreactive neuronal fibers in the DRN were found to make close contact with serotonergic neurons, while some of the serotonergic neurons also expressed the orexin 1 receptor (OX1R). At the electron microscopic level, double-immunostaining experiments showed that the orexin A-like immunoreactive fibers were present mostly as axon terminals that made synapses on the serotonin- and orexin 1-receptor-containing neurons. While only axodendritic synapses between orexin A-containing axon terminals and serotonergic neurons were detected, the synapses made by orexin A-containing axon terminals on the orexin 1-receptor-containing neurons were both axodendritic and axosomatic. The present study suggests that excitation effect of orexin A on Dorsal Raphe serotonergic neurons is via synaptic communication through orexin 1 receptor.
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Electron microscopic examination of the orexin immunoreactivity in the Dorsal Raphe Nucleus.
Peptides, 2003Co-Authors: Qing-ping Wang, Jian-lian Guan, Takashi Matsuoka, Yumi Hirayana, Seiji ShiodaAbstract:The ultrastructure and the synaptic relationships of the orexin-A-like immunoreactive fibers in the Dorsal Raphe Nucleus were examined with an immunoelectron microscopic method. At the electron microscopic level, most of the immunoreactive fibers, a varicosity appearance at the light microscopic level, were found as axon terminals. The large dense-cored vesicles contained in the immunoreactive axon terminals were the most intensely immunostained organellae. These axon terminals were often found to make synapses. While the axo-dendritic synapses were usually asymmetric in appearance, the axo-somatic synapses were symmetric. Orexin-A-like immunoreactive processes with no synaptic vesicles were also found. These processes often received asymmetric synapses. With less frequency, the synapses were found between the orexin-like immunoreactive processes. The results suggest that the orexin peptides are stored in the large dense-cored vesicles; the orexin-containing fibers may have influences on the physiological activities of the Dorsal Raphe Nucleus through direct synaptic relationships.
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Immunoelectron microscopic study of β-endorphinergic synaptic innervation of GABAergic neurons in the Dorsal Raphe Nucleus
Synapse (New York N.Y.), 2001Co-Authors: Qing-ping Wang, Jian-lian Guan, Seiji ShiodaAbstract:Using a preembedding double immunoreactive technique by immunostaining with antirat β-endorphin and antisynthetic glutamic acid decarboxylase antisera sequentially, the synaptic relationships between β-endorphinergic neuronal fibers and GABAergic neurons in the Dorsal Raphe Nucleus of the rat were examined at the ultrastructural level. Although both β-endorphin-like immunoreactive fibers and glutamic acid decarboxylase-like immunoreactive neurons can be found in the medioDorsal and medioventral parts of the Dorsal Raphe Nucleus, the synapses between them were found only in the medioDorsal part. Most of the β-endorphin-like immunoreactive neuronal fibers contained many dense-cored vesicles. The synapses made by β-endorphin-like immunoreactive neuronal axon terminals on glutamic acid decarboxylase-like immunoreactive neurons were both symmetrical and asymmetrical, with the latter predominant, especially in the axo-dendritic synapses. Perikarya with β-endorphin-like immunoreactivity were found only in the ventrobasal hypothalamus. These findings suggest the possibility that the β-endorphin-producing neurons in the ventrobasal hypothalamus could influence GABAergic neurons in the Dorsal Raphe Nucleus directly by synaptic relationships. Synapse 42:234–241, 2001. © 2001 Wiley-Liss, Inc.
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An electron microscopic observation of the vesicular acetylcholine transporter-immunoreactive fibers in the rat Dorsal Raphe Nucleus.
Brain research bulletin, 1998Co-Authors: Qing-ping Wang, Jian-lian Guan, Hidehiko Ochiai, Yasumitsu NakaiAbstract:By using immunocytochemistry with an antibody directed against the vesicular acetylcholine transporter, many cholinergic neuronal processes were found to be immunopositive in the Dorsal Raphe Nucleus. At the electron microscopic level, most of these processes were found to be axons. The immunopositive axon terminals made synapses on immunonegative dendrites and their spines whereas rare synapses were found between the immunopositive axon terminals and the immunonegative neuronal perikarya. Occasionally, the dendrites postsynaptic to an immunopositive axon terminal also received a synapse from an immunonegative axon terminal. The synapses made by the immunopositive axon terminals were usually symmetric and had a short active zone. Fewer immunostained dendrites were found, and they usually received asymmetric synapses from nonimmunostained axon terminals. The existence of cholinergic axon terminals and the synapses made by these terminals support the physiological data indicating that acetylcholine plays a role in the pain inhibition system in the Dorsal Raphe Nucleus.
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Ultrastructural localization of delta-1 opioid receptor in the Dorsal Raphe Nucleus of the rat.
Synapse (New York N.Y.), 1997Co-Authors: Qing-ping Wang, Jian-lian Guan, Hidehiko Ochiai, Yasumitsu NakaiAbstract:The ultrastructural localization of delta-1 opioid receptor in the rat Dorsal Raphe Nucleus was studied by the preembedding avidin-biotin-peroxidase complex technique. With application of a low concentration of the first antiserum in incubation and control of short-time reaction to 3,3'-diaminobenzidine, the immunoreaction seemed to be faint at the light microscopic level. At the electron microscopic level, however, delta-1 opioid receptor immunoreaction products were found to be localized specifically on the postsynaptic membrane of dendrites, dense-cored vesicles, and the surface of the small, clear vesicles in axon terminals with strong immunoreactivity. Of the total 659 immunopositive profiles observed, up to 62.4% (411/659) were dendrites, whereas 33.8% (223/659) were axon terminals. The immunostained myelinated axons and perikarya were relatively rare, with the frequencies 0.8% (5/659) and 3.0% (20/659), respectively. Most of the immunopositive dendrites (338/411, 82.2%) were immunostained only at the postsynaptic membranes. Other immunoreactive dendrites showed their immunoreaction products also in some other contents besides the postsynaptic membranes (44/411, 10.7%) or only in those contents but not the postsynaptic membranes (25/411, 6.1%). Only four dendrites showed their immunoreactive results only at the membrane not related to synapse (4/267, 1.0%). No dendrite was found immunostained in all the contents. About half of the immunopositive axon terminals (125/223, 56.1%) were found to make synapse with nonimmunoreactive dendrites (76/223, 34.1%) or immunoreactive dendrites (49/223, 22.0%), while only one was found to make contact with immunoreactive perikarya. The present study showed that delta-1 opioid receptor in the Dorsal Raphe Nucleus is mostly localized on postsynaptic membrane; the main function of the delta-1 receptor in the Dorsal Raphe Nucleus is to receive signals from the opioid-containing axon terminals through synapses.
N. Mizuno - One of the best experts on this subject based on the ideXlab platform.
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direct projections from the midbrain periaqueductal gray and the Dorsal Raphe Nucleus to the trigeminal sensory complex in the rat
Neuroscience, 1993Co-Authors: Masahiko Takada, Yasuhide Shinonaga, N. MizunoAbstract:Abstract It is well known that analgesia can be produced by stimulation of the midbrain periaqueductal gray and Dorsal Raphe Nucleus. This stimulation-produced analgesia may operate, at least partly, through direct projections to nociceptors in the primary sensory nuclei. In the present study, direct projections from the midbrain periaqueductal gray and Dorsal Raphe Nucleus to the trigeminal sensory complex were studied in the rat. After injection of Phaseolus vulgaris leucoagglutinin into the periaqueductal gray or Dorsal Raphe Nucleus, terminal labeling was found in the principal sensory trigeminal Nucleus and the oral, interpolar and caudal subnuclei of the spinal trigeminal Nucleus, bilaterally with an ipsilateral predominance. The terminal labeling was prominent in the ventrolateral parts of the trigeminal sensory complex; it was particularly marked in the principal sensory trigeminal Nucleus and laminae I and III of the caudal subNucleus of the spinal trigeminal Nucleus. After injection of cholera toxin B subunit into the principal sensory trigeminal Nucleus or one of the subnuclei of the spinal trigeminal Nucleus, retrogradely labeled cells were seen in the periaqueductal gray and Dorsal Raphe Nucleus, bilaterally with an ipsilateral dominance. In the periaqueductal gray they were most often seen in the ventrolateral and dorsolateral subdivisions, but no particular topographic organization was detected in the distribution of retrogradely labeled neurons in the periaqueductal gray and Dorsal Raphe Nucleus after tracer injection into each subdivision of the trigeminal sensory complex. After injections of Fast Blue and Diamidino Yellow, respectively, into the principal sensory trigeminal Nucleus and the caudal subNucleus of the spinal trigeminal Nucleus on one side of the brain, a number of doubly labeled neurons were found in the periaqueductal gray and Dorsal Raphe Nucleus, bilaterally with an ipsilateral dominance. The results indicate that a considerable number of neurons in the periaqueductal gray and Dorsal Raphe Nucleus send projection fibers to the trigeminal sensory complex, and that some of them send their axons to both the principal sensory trigeminal Nucleus and the caudal subdivision of the spinal trigeminal Nucleus by way of axon collaterals. These projections may subserve suppression of the activity of nociceptive neurons in the trigeminal system.
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Serotoninergic projections from the Dorsal Raphe Nucleus to the Nucleus submedius in the rat and cat
Neuroscience, 1993Co-Authors: S Matsuzaki, Hironobu Tokuno, Mikiko Takada, Y Q Li, N. MizunoAbstract:The Nucleus submedius in the medial thalamus has been known to receive spinothalamic and trigeminothalamic fibers, and to contain neurons which can be activated by noxious stimuli. These previous findings suggest that the Nucleus submedius may be involved in the processing and relay of pain-related information. In the present study, we immunohistochemically observed in the rat and cat that the Nucleus submedius was distributed with a considerable amount of serotoninergic fibers. After iontophoretic injection of cholera toxin B subunit into the Nucleus submedius, the sequential double-antigen immunofluorescence histochemistry for retrogradely transported cholera toxin B subunit and serotonin revealed that the serotoninergic fibers to the Nucleus submedius arose mainly from the Dorsal Raphe Nucleus, and additionally from the ventrolateral and medial parts of the midbrain periaqueductal gray. The direct projections from the Dorsal Raphe Nucleus to the Nucleus submedius were confirmed by anterograde axonal tracing after iontophoretic injection of Phaseolus vulgaris-leucoagglutinin into the Dorsal Raphe Nucleus. The disappearance of almost all serotoninergic fibers in the Nucleus submedius was also observed after destruction of the Dorsal Raphe Nucleus. The fluorescent retrograde double-labeling with Diamidino Yellow and Fast Blue further revealed that some neurons in the Dorsal Raphe Nucleus projecting directly to the Nucleus submedius sent their axon collaterals to the ventrolateral orbital region of the cerebral cortex, Nucleus accumbens, amygdala, Nucleus Raphe magnus, caudal spinal trigeminal Nucleus, or spinal cord. The possible roles of the serotoninergic projections from the Dorsal Raphe Nucleus to the Nucleus submedius in pain control and/or the olfactolimbic functions are discussed. ?? 1993.