The C-type natriuretic peptide receptor is the predominant natriuretic peptide receptor mRNA expressed in rat hypothalamus

The natriuretic peptide receptors (NPR) are membrane-bound guanylate cyclases with extracellular binding domains specific for particular members of the natriuretic peptide family. NPR-A binds atrial natriuretic peptide (ANP) with high affinity, whereas the NPR-B appears to be specific for C-type natriuretic peptide (CNP). Previous data indicating extensive overlap between localization of ANP and CNP in hypothalamic neuroendocrine circuits suggest the importance of determining whether specificity of natriuretic peptide action may be conferred via receptor type present on target cells. To address this issue, we used in situ hybridization histochemistry to localize NPR-A and NPR-B mRNA in the hypothalamus. NPR-A mRNA was not found in substantial abundance in any hypothalamic nucleus; however, detectable NPR-A signal was observed in other brain regions, including the subfornical organ and medial habenula. In contrast, NPR-B mRNA was expressed throughout the hypothalamus, including neurons of the magnocellular and parvocellular paraventricular, the arcuate, and the supraoptic nuclei. Expression was also seen in other nuclei essential to neuroendocrine control, including the median preoptic, anteroventral periventricular, tuberomammilary, ventromedial and suprachiasmatic nuclei. NPR-B mRNA was also observed in the neural lobe of the pituitary gland, suggesting expression by pituicytes. The results suggest that NPR-B is the primary natriuretic peptide receptor in hypothalamus, and by inference indicate that CNP is the primary active natriuretic peptide in neuroendocrine regulation.

Case report: transverse colon volvulus in a patient with Clostridium difficile pseudomembranous colitis

Sixty-eight cases of transverse colon volvulus have been reported in the literature. The authors report the first case of transverse colon volvulus in association with Clostridium difficile pseudomembranous colitis, with a review of the available literature. It is possible that the acute inflammation of the colonic mucosa, which occurred from the pseudomembranous colitis in this patient, contributed to the development of volvulus. Further studies are needed to explore the role of mucosal inflammation in the occurrence of volvulus.

Distribution of mRNA for the GABA transporter GAT-1 in the rat brain: evidence that GABA uptake is not limited to presynaptic neurons

Cells containing mRNA for the gamma-aminobutyric acid (GABA) transporter GAT-1 were identified in rat brain by in situ hybridisation. They were found in most of the known locations of GABAergic neurons, as defined by the distribution of mRNA for glutamic acid decarboxylase, the synthetic enzyme for GABA. Within the cerebellum there was substantial labelling of basket and stellate cells in the molecular layer, and of Golgi cells but no others in the granule cell layer. Many Purkinje cells were unlabelled while others, particularly in the hemispheres, were moderately labelled. Many of the Purkinje cells negative for GAT-1 mRNA had adjacent intensely labelled small cells whose size and position corresponded to Bergmann glia. Numerical comparison of cells labelling for GAT-1 mRNA and the mRNAs for the two known isoforms of glutamic acid decarboxylase were made on serial sections of cerebral cortex. Cells positive for GAT-1 mRNA were more numerous, indicating that expression of the transporter is not just limited to GABAergic cells and we suggest that it may also be expressed postsynaptically by some non-GABAergic neurons.

Estrous cycle-associated axosomatic synaptic plasticity upon estrogen receptive neurons in the rat preoptic area

This study examined the hypothesis that synaptic relationships change on a daily basis in the anterior preoptic area of the intact, cycling female rat. Specifically, the anteroventral periventricular nucleus (AVPv) was chosen for analysis due to its abundant estrogen- and progesterone-receptive neurons and its critical role in the control of gonadotropin secretion. Ultrastructural analysis revealed that in the 24 h between proestrus and estrus, there was a 39% increase in axosomatic synapses upon AVPv neurons. In the subsequent 24 h to metestrus, the number of synapses decreased by 22%. Additional data showed that ovariectomy resulted in more axosomatic synapses in the AVPv relative to proestrus (46%) and metestrus (35%). Another component of the study investigated synaptic relationships on estrogen receptor-immunoreactive (ER-ir) and non-ER-ir neurons across the estrous cycle. ER-ir neurons received significantly more synaptic input at proestrus and estrus than did non-ER-ir neurons. At metestrus and following ovariectomy, no significant differences were present. The present study indicates that estrous cycle-associated synaptic plasticity occurs in the AVPv and lends further support to the critical role of this nucleus in regulation of gonadotropin secretion. Moreover, it provides the first evidence that ER- and non-ER-ir neurons are differentially innervated.

Colocalization of natriuretic peptide and estrogen receptor immunoreactivities in preoptic nuclei in the female rat

Estrogen is known to play an important role in regulating reproductive function in female rats through actions exerted at the preoptic area, a part of the brain that is markedly sexually dimorphic and which contains abundant estrogen receptors. A critical question to our understanding of estrogen's action on the brain is to identify the types of neurons that contain estrogen receptors (ER). Previous studies have shown that atrial natriuretic peptide (ANP) is in abundance in the preoptic area, and that ANP and other natriuretic peptides are capable of regulating gonadotropin secretion. In an effort to determine whether ERs are present in natriuretic peptide-immunoreactive (NP-ir) neurons in the preoptic area of the rat, double label immunocytochemistry was performed. Since ER-ir, as demonstrated with antibody H222 is known to be localized predominantly in cell nuclei, while NP-ir is present in the cytoplasm, single cells can be double labeled. Diaminobenzidine tetrahydrochloride was used for localization of NP-ir neurons, while nickel-enhanced diaminobenzidine tetrahydrochloride was used for localization of ER-ir. The results revealed that many nuclei throughout the preoptic area contained neurons that were ER-ir or NP-ir and that a substantial number were double labeled. Cell counts in selected preoptic nuclei and components, including the anteroventral periventricular nucleus, periventricular preoptic nucleus, medial part of the medial preoptic nucleus, and central part of the medial preoptic nucleus revealed that 13.6%, 11.1%, 13.5%, and 24.4%, respectively, of the NP-ir neurons in these nuclei also contained ER-ir. Collectively, a total of 14.9% of the NP-ir neurons in these nuclei also contained ER-ir.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of C-type natriuretic peptide mRNA in rat hypothalamus

Central or peripheral administration of C-type natriuretic peptide (CNP) affects numerous neuroendocrine systems, including the hypothalamo-pituitary-gonadal, hypothalamo-pituitary-adrenocortical and hypothalamo-neurohypophysial axes. The present report characterizes the distribution of CNP mRNA in hypothalamus, providing the first definition of CNP-containing neuroendocrine circuits. In situ hybridization histochemical analysis revealed high expression of CNP mRNA in the anteroventral periventricular nucleus (AVPv) and in hypothalamic arcuate nucleus (ARC). Hybridization signals of significantly lower intensity were seen in the medial, median and periventricular preoptic area, the supraoptic, dorsomedial, ventral premammillary and lateral mammillary nuclei and in the posterior hypothalamic area. A few scattered CNP mRNA containing cells were visualized in the medial parvocellular paraventricular nucleus, posterior magnocellular paraventricular nucleus and lateral hypothalamic area. In the AVPv and ARC the pattern of CNP mRNA distribution paralleled that of ANP mRNA. The results indicate a distribution of CNP mRNA associated with key neuroendocrine systems, and underscores the potential importance of this novel natriuretic peptide in neuroendocrine regulation.

Further Evidence that Most Luteinizing Hormone-Releasing Hormone Neurons are not Directly Estrogen-Responsive: Simultaneous Localization of Luteinizing Hormone-Releasing Hormone and Estrogen Receptor Immunoreactivity in the Guinea-Pig Brain

Gonadotropin secretion from the pituitary is regulated in large part by steroid action on the brain. An important question concerns whether luteinizing hormone-releasing hormone (LHRH) neurons themselves transduce steroid signals, or whether, alternatively, steroid-sensitive interneuronal populations regulate their activity. A previous study in the rat employing steroid autoradiography combined with LHRH immunocytochemistry revealed that only an exceedingly small percentage of LHRH-immunoreactive (ir) neurons was estrogen concentrating. This study has examined the relationship of estrogen receptive and LHRH-ir cells in the male and female guinea-pig brain with double label immunocytochemistry. Since estrogen receptor-ir, as demonstrated with antibody H222, is known to be confined predominantly to the cell nucleus, whereas LHRH-ir is localized mainly in the cytoplasm, single cells can be double-labeled. Diaminobenzidine tetrahydrochloride was used for localization of LHRH-ir while nickel-enhanced diaminobenzidine tetrahydrochloride was used for localization of estrogen receptor-ir. The results revealed that there were many brain nuclei that contained both LHRH and estrogen receptor-positive cells, including the preventricular periventricular nucleus, the anterior subcompact nucleus of the medial preoptic nucleus (MPNa), the remainder of the medial preoptic nucleus, the retrochiasmatic area, and the anterior, dorsomedial, ventrolateral and arcuate nuclei. However, of a total of 2,604 LHRH-ir cells that were examined, we observed only 5 double-labeled cells (<0.2%). The double-labeled cells were not restricted to a single nucleus; they were present in the MPNa, the retrochiasmatic area and the arcuate nucleus. Moreover, at the light microscopic level, LHRH cells quite frequently appeared to be apposed to estrogen receptor-positive cells (8.8% in the female), especially in the MPNa. These results lend further support to the notion that estrogen-mediated regulation of the LHRH system is achieved primarily through estrogen receptive interneurons. However, due to the existence of LHRH-LHRH synaptic interactions, the possibility also exists that a small population of estrogen-sensitive LHRH neurons could contribute to generalized activation of the LHRH system.

Estrogen receptive neurons in the preoptic area of the rat are postsynaptic targets of a sexually dimorphic enkephalinergic fiber plexus

The periventricular preoptic area (pePOA) is a sexually dimorphic component of the rat forebrain that contains a sexually dimorphic Met-enkephalin immunoreactive (ENK-ir) fiber plexus. This plexus is especially dense in the female while only scattered ENK-ir fibers are present in the pePOA of the male. Abundant estrogen receptive neurons are located in the pePOA of both the female and male. This experiment was conducted to determine if estrogen receptive neurons in the pePOA are postsynaptic targets of ENK-ir terminals. Double label ultrastructural localization of estrogen receptor (ER)-ir neurons and ENK-ir fibers was performed using the chromogens 3,3',5,5'-tetramethylbenzidine (TMB) and diaminobenzidine tetrahydrochloride (DAB), respectively. TMB-stained ER-ir neurons contained electron dense crystalline spicules located predominantly in their nuclei. Flocculent DAB reaction product was distributed over membraneous structures in ENK-ir fibers and terminals. Numerous ER-ir neurons were present in the pePOA of the male and female. In females, many ENK-ir terminals, both synaptic and non-synaptic, contacted the perikarya of ER-ir neurons. In contrast, many fewer ENK-ir terminals made contact on ER-ir neurons in the male. Thus, these results provide morphological evidence that ENK-ir neurons can regulate ER-ir neurons in the pePOA. Moreover, because expression of the ENK-ir pePOA fiber plexus is estrogen-sensitive in the female, these results suggest strongly that estrogen may regulate these neurons both pre- and postsynaptically. Finally, these results provide additional evidence for the involvement of the sexually dimorphic pePOA ENK-ir fibers plexus in the control of estrogen-mediated function in the female.

Estrogen receptor-immunoreactive glia, endothelia, and ependyma in guinea pig preoptic area and median eminence: electron microscopy

The presence of estrogen receptors (ERs) in nonneural cells in brain, including glia, ependyma, and endothelia, has not previously been documented with electron microscopy. This study employed immunocytochemistry to investigate whether ER immunoreactivity (ER-ir) is present in glial, ependymal, or endothelial cells in the medial preoptic area (POA) and median eminence (ME) in the brain of gonadally intact female guinea pigs. Tissue sections through these regions were immunostained with monoclonal antibody H222 for ER localization using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogen. ER-ir cells were identified ultrastructurally by the presence of distinct spicule-like TMB crystals in nuclei. While neurons constituted the clear majority of ER-immunopositive cells, labeled astrocytes, ependyma, and endothelia were also present. Distinct intranuclear TMB crystals were present in astrocytes at the anterior pole of the POA within the preventricular periventricular nucleus, anterior compact subnucleus of the medial preoptic nucleus (MPNa), and organum vasculosum of the lamina terminalis, indicating ER-ir. In the MPNa, cell counts performed at the ultrastructural level revealed that 9.6% (15 of 156) of the astrocytes were ER-ir. To further explore the relationship of ERs with astrocytes, ER/glial fibrillary acidic protein (GFAP) double labeling experiments were performed using TMB and diaminobenzidine tetrahydrochloride for ER and GFAP localization, respectively. These studies verified the presence of ERs in astrocytes at the anterior pole of the POA and demonstrated the presence of ERs in GFAP-ir cells in the ME. Cell counts at the ME showed that 23 of 50 (46%) GFAP-ir cells were ER-ir. ER-ir was also present in scattered ependymal cells lining the third ventricle at the POA and overlying the ME. Typically, approximately four to eight ER-ir ependymal cells were present around the perimeter of the third ventricle, although occasionally small aggregations of greater numbers of labeled cells were observed. Both common ependyma and cells morphologically identified as tanycytes were ER-ir. Some endothelial cells and vascular smooth muscle cells also contained ERs. While approximately 11% of the vessels were lined by ER-ir cells in sections through the MPNa and preventricular periventricular nucleus, approximately 15% of the vessels were labeled in the organum vasculosum of the lamina terminalis. In the ME a greater percentage (59%) of the vessels contained ER-ir endothelial cells. Collectively, these results indicate that in addition to regulating the activity of neurons, estrogen may affect brain function through effects exerted on astrocytes, ependymal cells, and endothelial cells.

Experimental oral foreign body reactions: vegetable materials

Foreign bodies and tissue reactions to foreign materials are commonly encountered in the oral cavity. Exogenous materials most commonly causing foreign body reactions are metallic in origin (usually amalgam). Of the nonmetallic materials seen during biopsies, suture materials and vegetable matter are most often observed. Since many foodstuff foreign materials are unidentifiable histologically, common vegetables were experimentally implanted subcutaneously in rats to assess local host responses and to characterize the nature of these materials microscopically. The histologic characteristics of these vegetable foreign body reactions are detailed herein. The implanted materials correspond to reactions seen in human subjects.

Ultrastructural evidence for luteinizing hormone-releasing hormone neuronal control of estrogen responsive neurons in the preoptic area

Both estrogen receptor (ER) immunoreactive (ir) and LHRH-ir neurons and processes are present in the preoptic area of the guinea pig. This experiment was conducted to determine if LHRH-ir terminals interact synaptically with ER-ir cells. A light microscopic dual chromogen immunocytochemical technique employing diaminobenzidine (DAB) and nickel-enhanced DAB for LHRH and ER localization, respectively, revealed that many varicose LHRH-ir fibers coursed in close proximity to ER-ir cells in the anterior part of the preoptic area at the preventricular periventricular nucleus (Pep), suggesting the likelihood of synaptic interactions. Ultrastructural analysis was performed using DAB and 3,3',5,5'-tetramethylbenzidine (TMB) for LHRH and ER localization, respectively. DAB labeling in LHRH-ir neurons appeared as a dense flocculent product dispersed throughout the cytoplasm. TMB stained ER-ir neurons contained electron dense crystalline spicules located predominantly in their nuclei. Numerous TMB labeled ER-ir neurons were present in the Pep, and occasionally occurred in clusters, closely apposed to one another. Many LHRH-ir terminals made synaptic contact or were apposed to unlabeled dendrites, while fewer contacted perikarya. Most significantly, ER-ir neurons showing clear evidence of intranuclear TMB crystals received synaptic input from LHRH-ir terminals. In addition, LHRH-ir terminals lacking synaptic specializations were also in direct apposition to ER-ir perikarya. These results provide morphological evidence that LHRH-ir neurons can regulate ER-ir neurons in the preoptic area. Since LHRH-ir cells are thought to be regulated by estrogen responsive neurons, interaction of LHRH terminals with ER-ir cells may represent a regulatory feedback circuit between the two systems.

Experimental oral foreign body reactions. Commonly employed dental materials

Foreign bodies and tissue reactions to foreign materials are commonly encountered in the oral cavity. The more common lesions include apical deposition of endodontic materials, mucosal amalgam and graphite tattoos, myospherulosis, oil granulomas, and traumatically introduced dental materials and instruments. Since many foreign materials are unidentifiable histologically, commonly used dental materials were experimentally implanted subcutaneously in rats to assess local host responses and characterize the nature of these materials microscopically. The histologic characteristics of these foreign body reactions are detailed herein. The implanted materials corresponded to reactions seen in human subjects.