Differential expression of AMPA receptor subunits in dopamine neurons of the rat brain: a double immunocytochemical study

We have examined the distribution of dopamine neurons expressing alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunits (glutamate receptors 1, 2/3 and 4) in the A8-A15 regions of the rat brain using double immunofluorescence. The distribution of glutamate receptor 1- or 2/3-like immunoreactive neurons completely overlapped that of tyrosine hydroxylase-like immunoreactive neurons in dopamine cell groups in the retrorubral field (A8), the substantia nigra (A9), the ventral tegmental area and the nucleus raphe linealis (A10), and the rostral hypothalamic periventricular nucleus (A14, A15). In the caudal hypothalamic periventricular nucleus (A11), arcuate nucleus (A12) and zona incerta (A13), the distribution was partially overlapping. Neurons double-labeled for tyrosine hydroxylase and glutamate receptor 1 or 2/3 immunoreactivities were, however, exclusively found in certain dopamine cell regions: in areas A14-A15, 85-88% of tyrosine hydroxylase-containing neurons expressed glutamate receptor 1 and 22-25% expressed glutamate receptor 2/3, while in areas A8-A10, 20-43% expressed glutamate receptor 1 and 63-84% expressed glutamate receptor 2/3. In contrast, the double-labeled neurons were hardly detected in the A11-A13 regions. No tyrosine hydroxylase-positive neurons displayed glutamate receptor 4 immunoreactivity, though a partially overlapping distribution of tyrosine hydroxylase- and glutamate receptor 4-immunopositive neurons was also seen in regions A8-10, A11 and A13. The present study has demonstrated the morphological evidence for direct modulation of dopamine neurons via AMPA receptors in rat mesencephalon and hypothalamus. This distribution may provide the basis for a selective dopamine neuron loss in neurodegenerative disorders, such as Parkinson's disease.

Hydrogen peroxide mediates activation of nuclear factor of activated T cells (NFAT) by nickel subsulfide

Nickel compounds induce cell transformation in cell culture models and tumor formation in experimental animals. However, the molecular mechanisms by which nickel compounds induce tumors are not yet well understood. The present study found that exposure of cells to either Ni(3)S(2) or NiCl(2) could result in specific transactivation of nuclear factor of activated T cells (NFAT), although it did not show any activation of p53 or AP-1. Furthermore, nickel compounds were also able to cause generation of reactive oxygen species (ROS). The scavenging of nickel-induced H(2)O(2) with N-acety-L-cyteine (a general antioxidant) or catalase, or the chelation of nickel with deferoxamine, resulted in inhibition of NFAT activation. In contrast, pretreatment of cells with sodium formate (an .OH radical scavenger) or superoxide dismutase (an O(-.)(2) radical scavenger) did not show any inhibitory effects. These results demonstrate that nickel compounds are able to induce NFAT activation, and that the mechanism of NFAT activation seems to be mediated by the generation of H(2)O(2) by these metal compounds. This study should help us understand the signal transduction pathways involved in carcinogenic effects of these nickel compounds.

Quantitative evaluation of synaptophysin-like immunoreactive nerve terminals or varicosities in anterior pituitary of normal and adrenalectomized rats

Our previous studies have demonstrated the presence of substantial amounts of peptidergic nerve fibres in the anterior pituitary of monkeys, dogs and rats. The nerve fibres increase in number following adrenalectomy and ovariectomy. Furthermore, typical synapses between nerve fibres and anterior pituitary glandular cells have been demonstrated in the dog and rat, strongly suggesting the existence of some direct neural regulation. However, it is difficult to evaluate the functional importance of synapses or nerve terminals in general, unless quantitative data can be provided. The present study therefore aimed to quantify the number of terminals or varicosities in the anterior pituitary of the rat and its changes following adrenalectomy. Nerve terminals or varicosities were identified by their synaptophysin (SYN)-like immunoreactivity. Under the light microscope, SYN-like immunoreactivity appeared mainly as dots, mostly among glandular cells, and some were found distributed along blood vessels. SYN-like immunoreactive dots were found under the electron microscope to be localized in the nerve terminals or varicosities. Synapse-like contracts between the nerve terminals or varicosities and the glandular cells could be identified. The number of SYN-like immunoreactive nerve terminals or varicosities was then counted under the light microscope. There were as many as 12424.2 +/- 2941.5 and 20700.4 +/- 6128 (mean +/- SD) nerve terminals or varicosities per anterior pituitary of normal and adrenalectomized rats, respectively. The increase in number following adrenalectomy was statistically significant. It is concluded that nerve fibres may play an important role in the regulation of the anterior pituitary.

Increase in cytochrome oxidase activity in regenerating nerve fibers of hemitransected spinal cord in the rat

We explored the possibility of cytochrome oxidase (CO) involvement in spinal cord regeneration in adult rats. The spinal cord was hemitransected at T9. After one month's survival, the animals were deeply anesthetized and perfused. The spinal cord segments including the lesion site were removed and sectioned horizontally for CO histochemistry. Under light microscope, a substantial number of CO-reactive nerve fibers and boutons were identified in the lateral funiculus adjacent to the lesion site. Under electron microscope, moderately to highly CO-reactive mitochondria could be seen within nerve fibers and boutons. Synaptic contacts were identified among them. The increase in CO activity in nerve fibers and boutons may indicate their high-energy demand for synaptic and spontaneous activity following spinal cord hemisection.

Distribution and colocalization of neurotransmitters and receptors in the pre-Bötzinger complex of rats

The pre-Bötzinger complex (PBC), thought to be the center of respiratory rhythm generation, is a cell column ventrolateral to the nucleus ambiguus. The present study analyzed its cellular and neurochemical composition in adult rats. PBC neurons were mainly oval, fusiform, or multipolar in shape and small to medium in size. Neurokinin-1 receptor, a marker of the PBC, was present in the plasma membrane of mostly medium and small neurons and their associated processes and boutons. Among neurons immunoreactive for different neurotransmitter or receptor candidates, various numbers were colocalized with neurokinin-1 receptor. The highest ratio was with nitric oxide synthase (52.72%), and the lowest was with glycine receptors (31.93%). Glutamic acid decarboxylase- and glycine transporter 2-immunoreactive boutons, as well as GABA(A) receptor-immunoreactive plasma membrane processes and boutons, were also identified in the PBC. PBC neurons exhibited different levels of cytochrome oxidase activity, indicating their various energy demands. Our results suggest that synaptic interactions within the PBC of adult rats involve a variety of neurotransmitter and receptor types and that nitric oxide may play an important role in addition to glutamate, GABA, glycine, and neurokinin.

Vanadium-induced nuclear factor of activated T cells activation through hydrogen peroxide

The present study investigated the role of reactive oxygen species (ROS) in activation of nuclear factor of activated T cells (NFAT), a pivotal transcription factor responsible for regulation of cytokines, by vanadium in mouse embryo fibroblast PW cells or mouse epidermal Cl 41 cells. Exposure of cells to vanadium led to the transactivation of NFAT in a time- and dose-dependent manner. Scavenging of vanadium-induced H(2)O(2) with N-acety-L-cyteine (a general antioxidant) or catalase (a specific H(2)O(2) inhibitor) or the chelation of vanadate with deferoxamine, resulted in inhibition of NFAT activation. In contrast, an increase in H(2)O(2) generation by the addition of superoxide dismutase or NADPH enhanced vanadium-induced NFAT activation. This vanadate-mediated H(2)O(2) generation was verified by both electron spin resonance and fluorescence staining assay. These results demonstrate that H(2)O(2) plays an important role in vanadium-induced NFAT transactivation in two different cell types. Furthermore, pretreatment of cells with nifedipine, a calcium channel blocker, inhibited vanadium-induced NFAT activation, whereas and ionomycin, two calcium ionophores, had synergistic effects with vanadium for NFAT induction. Incubation of cells with cyclosporin A (CsA), a pharmacological inhibitor of the phosphatase calcineurin, blocked vanadium-induced NFAT activation. All data show that vanadium induces NFAT activation not only through a calcium-dependent and CsA-sensitive pathway but also involved H(2)O(2) generation, suggesting that H(2)O(2) may be involved in activation of calcium-calcineurin pathways for NFAT activation caused by vanadium exposure.

Cholinergic neurons expressing neuromedin K receptor (NK3) in the basal forebrain of the rat: a double immunofluorescence study

By using a double immunofluorescence method we have examined the distribution of cholinergic neurons expressing neuromedin K receptor (NK3) in the rat brain and spinal cord. The distribution of neuromedin K receptor-like immunoreactive neurons completely overlapped with that of choline acetyltransferase-positive neurons in certain regions of the basal forebrain, e.g. the medial septal nucleus, nucleus of the diagonal band of Broca, magnocellular preoptic nucleus and substantia innominata. Partially overlapping distributions of neuromedin K receptor-like immunoreactive and choline acetyltransferase-positive neurons were found in the basal nucleus of Meynert, globus pallidus, ventral pallidum of the forebrain, tegmental nuclei of the pons and dorsal motor nucleus of the vagus. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities, however, were found predominantly in the medial septal nucleus, nucleus of the diagonal band of Broca and magnocellular preoptic nucleus of the basal forebrain: 66-80% of these choline acetyltransferase-positive neurons displayed neuromedin K receptor-like immunoreactivity. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities were hardly detected in other aforementioned regions of the forebrain, brainstem and spinal cord. The present study has provided morphological evidence for direct physiological modulation or regulation of cholinergic neurons by tachykinins through the neuromedin K receptor in the basal forebrain of rats.

Involvement of Erks activation in cadmium-induced AP-1 transactivation in vitro and in vivo

Cadmium is a potent and effective carcinogen in rodents and has recently been accepted by IARC (International Agency for Research on Cancer) as a category I carcinogen. Cadmium-induced up-regulation of intracellular signaling pathways leading to increased mitogenesis is thought to be a major mechanism for the carcinogenic activity following chronic cadmium exposure. In the present study, we found that exposure of cells to cadmium induced significant activation of AP-1 and all three members of the MAP kinase family in mouse epidermal JB6 cells. The induction of AP-1 activity by cadmium appears to involve activation of Erks, since the induction of AP-1 activity by cadmium was blocked by pretreatment of cells with PD98058. Interestingly, the induction of AP-1 by cadmium was greatly enhanced by the chemical tumor promoter, TPA and the growth factor EGF, but not by ultraviolet C radiation. In vivo studies demonstrated that cadmium could also induce transactivation of AP-1 in AP-1-luciferase report transgenic mice. Considering the role of AP-1 activation in tumor promotion, the results presented in this study provide a possible molecular mechanism for cadmium-induced carcinogenesis.

Transactivation of RARE and GRE in the cellular response to arsenic

Arsenic compounds are a somewhat unique class of metals, which have been considered as both carcinogens and chemotherapeutic agents for cancers. Tumor promotion effects of arsenic are believed to be associated with its transactivational activities on transcription factors, such as AP-1 and NFkappaB, while the induction of cell apoptosis and differentiation by arsenic is considered to be a mechanism for the chemotherapeutic effects of arsenic. Here, we found that exposure of cells to arsenite and arsenate leads to transactivation of retinoic acid response elements (RARE) and glucocorticoid response elements (GRE) in mouse epidermal JB6 cells. These inductions occur in a time-dependent manner. Furthermore, induction of RARE activity by arsenic was synergistically enhanced by co-treatment of cells with retinoic acid, while GRE activation by arsenic was not affected by combined treatment of cells with fluocinolone acetonide (FA). In consideration of the important role of RARE and GRE in induction of cell differentiation, we speculate that transactivation of RARE and GRE by arsenic may be involved in its induction of cell differentiation and anti-cancer activities in addition to its induction of apoptosis.

Arsenic-induced NFkappaB transactivation through Erks- and JNKs-dependent pathways in mouse epidermal JB6 cells

Tumor promoting effects of arsenic are believed to be associated with its transactivation activity on transcription factors, such as AP-1 and NFkappaB. However, the results from different groups studying the effects of arsenic on NFkappaB activation are contradictory in different cell models. Since arsenic is a strong skin carcinogen, we have investigated the activation of NFkappaB by arsenic in a mouse skin epidermal cell line, JB6 cells. Exposure of cells to arsenite or arsenate led to NFkappaB transactivation in mouse epidermal JB6 NFkappaB-luciferase reporter stable transfectants, C141 NFkappaB mass1. This induction of NFkappaB activity by arsenic was dose- and time-dependent. The transactivation of NFkappaB by arsenic appeared to be through activation of Erks and JNKs pathways because increased NFkappaB activity by arsenic could be dramatically inhibited by either pre-treatment of cells with PD98059 or overexpression of dominant negative JNK1. That Erks activation is required for arsenic-induced NFkappaB transactivation was further supported by the findings that arsenic-induced NFkappaB transactivation was impaired in JB6 30.7b cells, which were deficient in Erks.

Evidence of direct neural regulation of the anterior hypophysis reproductive functions

It is generally acknowledged that the anterior hypophysis is not directly regulated by neural elements. Our studies in the past decade, however, have demonstrated otherwise. The anterior pituitary gland has been found to be actually under neural-humoral dual regulation. The present article outlines the main data that have led us to this conclusion. Evidence that is related to direct neural regulation of the reproductive functions of the anterior hypophysis is provided in great detail. Thus, synapses have been demonstrated between the nerve fibers innervating the anterior pituitary gland and the gonadotropes and lactotropes. Furthermore, there is ultrastructural evidence indicating that synaptic activities may induce secretion of the gland cells. Hormone manipulation study shows that following ovariectomy there is a significant increase of nerve fibers in the anterior pituitary gland, which is related to plasma estrogen level.

Adrenergic sensitivity of neurons with non-periodic firing activity in rat injured dorsal root ganglion

In this study, we compared the sensitivity of non-periodically and periodically active neurons in chronically compressed dorsal root ganglion in rats to norepinephrine and sympathetic stimulation. Forty-nine of 58 (84.5%) neurons with non-periodic activity showed responses to norepinephrine, whereas only five of 48 (10.4%) neurons with periodic activity displayed any response. The dose-response relationship of norepinephrine to the irregular burst pattern neurons shifted towards the left significantly compared to that of the periodic activity neurons. Responses to norepinephrine became apparent in eight neurons after their periodic firing activity was transformed into the non-periodic firing activity through the increase in Ca(2+). Changes in the time-response curves indicate a higher sensitivity of irregular burst pattern neurons to sympathetic stimulation than the periodic activity neurons. Finally, deterministic dynamics contained within the interburst interval series for non-periodic activity were identified. From these results, we suggest that the non-periodic activity neurons have a higher adrenergic sensitivity than those displaying periodic activity, and that this sensitivity may depend on the deterministic chaos within its firing dynamic system.

Retinal dopaminergic neurons (A17) expressing neuromedin K receptor (NK(3)): a double immunocytochemical study in the rat

By using a double immunofluorescence method we examined the distribution of dopaminergic neurons (A17) expressing neuromedin K receptor (NKR, NK(3)) in the rat retina. The distribution of NKR-like immunoreactive (-LI) neurons partially overlapped that of tyrosine hydroxylase (TH)-LI neurons in the inner retina of section and flat-mount preparation. Neurons showing both TH- and NKR-like immunoreactivities were found in the retina (A17): 100% of these TH-LI neurons displayed NKR-like immunoreactivity, and they constituted about 3.5% of total NKR-LI neurons. The majority of double-labeled neurons with TH- and NKR-like immunoreactivities were distributed in the proximal inner nuclear layer and the upper part of inner plexiform layer of the retina, and characterized with appearance of amacrine cells. The present study has provided morphological evidence for direct physiological modulation of dopaminergic neurons by tachykinins through NKR in the rat retina (A17).

Intracerebroventricular injection of senktide-induced Fos expression in vasopressin-containing hypothalamic neurons in the rat

Intracerebroventricular injection of senktide, a selective agonist for neurokinin B receptor (NK3), induced Fos expression in many neurons of the rat hypothalamus. Fos-positive neurons were predominantly present in the supraoptic and paraventricular hypothalamic nuclei, and some of them were seen in the lateral preoptic area, lateral hypothalamic area, arcuate nucleus, perifornical region, posterior hypothalamic area, circular nucleus, and along relatively large blood vessels (lateral hypothalamic perivascular nucleus) in the anterior hypothalamus. A double labeling study was performed to examine if vasopressin-containing neurons in the hypothalamus could be activated by the treatment. Neurons with both Fos-like immunoreactivity (-LI) and vasopressin-LI were found in the paraventricular nucleus, supraoptic nucleus, circular nucleus and lateral hypothalamic perivascular nucleus. In the supraoptic nucleus, about 87% of vasopressin-containing neurons exhibited Fos-LI, which corresponded to about 64% of Fos-positive neurons in the nucleus. In the paraventricular nucleus, about 80% of vasopressin-like immunoreactive neurons exhibited Fos-LI, which constituted about 51% of the total population of Fos-positive neurons in the region. The results suggest that NK3 receptor may be involved in the modulation of release of vasopressin from the hypothalamus in the rat.

Evidence for the medullary visceral zone as a neural station of neuroimmunomodulation

The aim of the present study was to test the possibility that the catecholaminergic projectional pathway from the vagus nerve to the medullary visceral zone (MVZ) thence to the paraventricular nucleus of hypothalamus (PVN) was involved in the cytokine-to-brain communication. A triple labeling method in which WGA-HRP retrograde tracing was combined with anti-Fos and -TH immunohistochemical staining was used. WGA-HRP was stereotaxically injected into unilateral PVN in the rat, after a survival of 48 h, animals received intraperitoneal injection of lipopolysaccharide (LPS). The distribution of the HRP retrogradely labeled neurons, Fos protein positive and catecholaminergic neurons (tyrosine hydroxylase as marker) in the MVZ was observed. Subdiaphragmatic vagotomy (SDV) and sham surgery were also used to observe the different Fos expression in the MVZ after intraperitoneal administration of lipopolysaccharide (LPS) or pyrogen-free saline (NS). Under light microscope, seven types of positively stained neurons could be distinguished within the MVZ, namely neurons single-labeled with Fos, HRP or TH, respectively; neurons double-labeled with Fos/TH, Fos/HRP or HRP/TH separately; and neurons triple-labeled with Fos, HRP and TH staining. Intraperitoneal LPS caused lots of robust Fos expression within the MVZ in the sham surgery groups and this response in the MVZ was markedly inhibited in the vagotomized rats. The results suggested that some catecholaminergic neurons in the MVZ could send projections to the PVN and this pathway might be involved in the relay of peripheral immune information via vagus nerve. MVZ was a neural relay station in the immune-to-brain communication and might play a significant role in the neuroimmunomodulation via vagus-MVZ-PVN pathway.

Expression and changes of HSP70 in the rat forebrain subjected to gamma knife (100Gy) irradiation targeted on the caudate putamen and survived for different times

Forebrain heat shock protein 70 (HSP70) immunohistochemical reactivity was investigated in rats subjected to gamma knife irradiation focusing on the right caudate putamen nucleus. The forebrain sections of all experimental animals were processed with anti-HSP70 antiserum and then by avidin-biotin peroxidase complex immunohistochemistry after gamma ray irradiation with a dose of 100Gy and they each survived for different times (from 30 min to 30 days). Some neurons, glial cells, and endothelial cells were HSP70-like immunoreactivity (HSP70-LI) positive. HSP70-LI was mainly distributed in the target area of irradiation, as well as in non-target regions, e.g. the cortex, hippocampus, and hypothalamus, etc. The expression and change of HSP70-LI from 3 h to 30 days after irradiation followed the following rules: (1) Within 3 to 24 h, the dilated vessels with HSP70-LI endothelial cells were found at first, and a few lightly stained HSP70-LI neurons and glias were observed in the target and non-target regions; (2) In 3-7 days, darkly stained HSP70-LI neurons and glias were apparently increased and formed an expression peak. From 14 to 30 days, HSP70-LI cells were distinctly decreased and became weakly stained or negative. These results suggested that although the irradiation target of the gamma knife was localized, the response to irradiation occurred extensively.

Time-dependent astroglial changes after gamma knife radiosurgery in the rat forebrain

OBJECTIVE

Using an experimental rat model and a clinically relevant treatment dose, we performed gamma knife radiosurgery to define the hyperacute radiation effects in normal rat forebrain, the time dependence of the astrocytic reaction, and the participation of astrocytes in the healing process after single-dose gamma radiation injuries.

METHODS

Seventy-one rats underwent radiosurgical treatment (4-mm collimator) of the caudate-putamen nucleus (single-fraction maximal dose of 100 Gy) and were killed at times ranging from 3 hours to 90 days. Serial cryostat brain sections were processed with the immunohistochemical avidin-biotin complex technique, using anti-glial fibrillary acidic protein as the primary antibody (to identify astrocytes).

RESULTS

Vascular changes, including endothelial hyperplasia and vessel wall thickening, were identified as the earliest postradiation manifestations and continued throughout the observation period. Astrocytes reacted to the radiation injury with hyperplasia and hypertrophy. At earlier time points (3-24 h), proliferation was the predominant reaction. The expression of glial fibrillary acidic protein in the proliferating and hypertrophic astrocytes formed an initial peak in the adjacent corpus callosum 3 days after radiosurgery and peaked within the target site between 14 and 30 days. Astrocytic proliferation and hypertrophy were also observed in distant cortices (frontal, parietal, insular, and piriform cortices) and in the hippocampus. No necrosis was observed less than 30 days after irradiation. By Day 90, necrotic lesions with a mean diameter of 4 mm were identified, with glial scar at their peripheries. Astrocytic morphological features varied according to the distance from the necrosis. The irradiated side contained more glial fibrillary acidic protein-containing cells than did the nonirradiated contralateral side.

CONCLUSION

During the early phase after radiation, vasculopathy was the first morphological change and may serve as the initiating factor for subsequent changes. Reactive astrocytes appeared not only at the target site but also in the surrounding regions; the severity of injury was determined by the distance from the target.

Suppression of adrenocorticotropic hormone release by stimulation of the nerve fibres in the anterior pituitary

With the recent revelation of considerable peptidergic innervation of the anterior pituitary in several mammalian species, including man, it becomes imperative to elucidate the physiological significance of such a morphological entity. We addressed this issue by employing an anterior pituitary slice in vitro superfusion system coupled with electrical field stimulation. Anterior pituitary slices of 0.8 mm were perfused with Krebs-Ringer bicarbonate-bovine serum albumin buffer in a superfusion chamber for 30 min before electrical field stimulation. A square current of 30 mA, 10 Hz and 0.5 ms was then applied for 10 min. The perfusate was collected every 10 min and measured for adrenocorticotropic hormone (ACTH) by radio-immunoassay. It was found that under the experimental condition the basal release of ACTH was suppressed by electrical field stimulation of the nerve fibres in the anterior pituitary. Furthermore, vasopressin was added as a secretagogue. The suppression of ACTH by electrical field stimulation became even more marked. This is the first physiological evidence of the effect of stimulation of the nerve fibres innervating the anterior pituitary on its secretory activity.

[Alteration of sensitivity of supraoptic nucleus neurons to cytokine in the hypothalamic slices from the rat after lipopolysaccharide injection]

Using the whole cell patch clamp technique, the effects of interleukin 1beta (IL-1beta) and IL-2 on the membrane potential and spontaneous discharges in the supraoptic nucleus (SON) neurons from the rat hypothalamic slices in vitro were examined to determine the changes in sensitivity of supraoptic nucleus neurons to cytokine. The results obtained are as follows. IL-1beta (100 U/ml) hyperpolarized the SON neurons from the control rats (n=15) and the rats 9 d after i.p. lipopolysaccharide (LPS) (n=20), and decreased the rate of their spontaneous discharges. When 100 U/ml IL-2 was perfused, most SON neurons (n=14) from the control rats were hyperpolarized and the spontaneous firing decreased, but the rest (n=3) remained unchanged. When IL-2 (100 U/ml) was applied, 19 neurons out of the 45 SON neurons from the rats 9 days after i.p. LPS were depolarized accompanied with an increase of the discharges, 16 did not show significant changes in both membrane potential and spontaneous discharges, the rest 10 were hyperpolarized and their discharges were suppressed. These results show that the sensitivity of part of SON neurons from the immuned rat to cytokine IL-2 was altered, suggesting that IL-2 may be involved in modulation of the activity of SON neurons and thus play a role in modulation of the immune response.

Activity of p44/42 MAP kinase in the caudal subnucleus of trigeminal spinal nucleus is increased following perioral noxious stimulation in the mouse

The extracellular signal-regulated protein kinase-1 and -2 (ERK1 and ERK2), also referred to as the p44/42 mitogen-activated protein kinase (p44/42 MAP kinase), plays an essential role in neuronal signal transduction, but its function involved in nociceptive response has not been deeply studied yet. Here we report immunohistochemical evidence that p44/42 MAPK might be critical in nociceptive response. We found that after formalin was injected into the perioral skin of the upper lip of mice, the number of activated p44/42 MAPK-like immunoreactive neurons was significantly increased in the laminae I and II of the caudal subnucleus of the trigeminal spinal nucleus (Sp5C). The positive neurons and fibers were mostly concentrated in the middle portion of Sp5C dorsoventrally, where the afferent fibers innervating the skin of the upper lip are terminated. The reactive products were localized in perikarya, dendrites, nuclei, and diffusely in the neuropil. The present result suggests that p44/42 MAPK may be important in the transmission and modulation of noxious information in Sp5C.

Selective modulation of excitatory transmission by mu-opioid receptor activation in rat supraoptic neurons

Opioid peptides have profound inhibitory effects on the production of oxytocin and vasopressin, but their direct effects on magnocellular neuroendocrine neurons appear to be relatively weak. We tested whether a presynaptic mechanism is involved in this inhibition. The effects of mu-opioid receptor agonist D-Ala(2), N-CH(3)-Phe(4), Gly(5)-ol-enkephalin (DAGO) on excitatory and inhibitory transmission were studied in supraoptic nucleus (SON) neurons from rat hypothalamic slices using whole cell recording. DAGO reduced the amplitude of evoked glutamatergic excitatory postsynaptic currents (EPSCs) in a dose-dependent manner. In the presence of tetrodotoxin (TTX) to block spike activity, DAGO also reduced the frequency of spontaneous miniature EPSCs without altering their amplitude distribution, rising time, or decaying time constant. The above effects of DAGO were reversed by wash out, or by addition of opioid receptor antagonist naloxone or selective mu-antagonist Cys(2)-Tyr(3)-Orn(5)-Pen(7)-NH(2) (CTOP). In contrast, DAGO had no significant effect on the evoked and spontaneous miniature GABAergic inhibitory postsynaptic currents (IPSCs) in most SON neurons. A direct membrane hyperpolarization of SON neurons was not detected in the presence of DAGO. These results indicate that mu-opioid receptor activation selectively inhibits excitatory activity in SON neurons via a presynaptic mechanism.

Evidence for direct neural regulation of the mammalian anterior pituitary

1. The mammalian anterior pituitary was not known to be directly regulated by nervous elements until recently. Although it is generally acknowledged that there are a small number of nerve fibres in the anterior pituitary, they are considered to be autonomic in nature and are not directly involved in the regulation of the activities of the gland cells. 2. A growing body of evidence has been accumulated in the past decade, mainly from our laboratory, indicating that the anterior pituitary can be directly regulated by nerve fibres innervating it. The present article reviews the evidence for the hypothesis that there is neural-humoral dual regulation of the mammalian anterior pituitary. 3. Human, macaque monkey, dog and rat anterior pituitaries have been used for immunocytochemical studies at light and electron microscopic levels. Studies of the changes in the nerve fibres in the anterior pituitary following adrenalectomy or ovariectomy have been conducted on rats. The effects of electrical stimulation of the nerve fibres in the anterior pituitary on adrenocorticotropic hormone (ACTH) secretion have also been studied. 4. There are substantial amounts of nerve fibres in the anterior pituitary. They are in close proximity to the gland cells, including forming synapses. The number of nerve terminals are large. Adrenalectomy or ovariectomy induces an active response of the nerve fibres and electrical stimulation of the nerve fibres changes ACTH secretion. 5. It has been concluded that the anterior pituitary can be directly regulated by the innervating nerve fibres.

Primary afferent fibers of the pelvic nerve terminate in the gracile nucleus of the rat

After injection of horseradish peroxidase (HRP) into the pelvic nerve of the rat, a small number of HRP-labeled axon terminals were found in the gracile nucleus. Double labeling experiments were also performed: Fluoro-Gold (FG) was injected into the pelvic nerve, while cholera toxin B subunit (CTb) was injected into the gracile nucleus or dorsal faciculus at the fifth and sixth cervical cord segments ipsilateral to the FG injection. About 5% of FG-labeled neurons were labeled with CTb in the L6-, S1- and S2-dorsal root ganglia ipsilateral to the tracer injection. The results suggest that some primary afferent information from pelvic visceral organs may be directly conveyed to gracile nucleus by the primary afferent neurons.

Direct projections from the medial preoptic area to spinally-projecting neurons in Barrington's nucleus: an electron microscope study in the rat

Direct projections from the medial preoptic area (MPO) to the pontine micturition center neurons directly projecting to the lumbosacral spinal cord were revealed electron microscopically in the rat by a double labeling method. Biotinylated dextran amine (BDA) was injected into the MPO and horseradish peroxidase (HRP) was injected into the lumbosacral cord segments. At light microscopic level, BDA-labeled presumptive axon terminals completely overlapped with HRP-labeled neurons in Barrington's nucleus. Electron microscopic observation showed that some BDA-labeled axon terminals made synaptic contacts with dendrites of HRP-labeled neurons in Barrington's nucleus. The present results indicated that the MPO may be involved in the modulation of the pontine micturition reflex in the rat.