Biomedical subjects

P Popper

Publications and source records attributed to P Popper.

At least 37 records · Page 2Linked to original sources

PubMed1996

The role of apoptosis in sexual differentiation of the rat sexually dimorphic nucleus of the preoptic area.

The sexually dimorphic nucleus of the preoptic area (SDN-POA) in the rat hypothalamus is larger in volume in males than in females due to a larger number of cells in the nucleus. Although the SDN-POA, and its development, have been extensively studied, the actual mechanism of its sexual differentiation has not been established. The results of previous studies have not supported a role for gonadal steroids in the regulation of neurogenesis or the determination of the migratory pathway perinatally. In this study, the role of cell death in the development of the sexual dimorphism in the SDN-POA was investigated using in situ end-labeling to visualize fragmented DNA in apoptotic cells. In the experiments described here, the incidence of apoptosis was determined in part of the SDN-POA, the central division of the medial preoptic nucleus (MPNc), over the first 13 days postnatally in male and female rats. There was a sex difference in the incidence of apoptosis in the MPNc between postnatal days 7 and 10; the incidence was higher in females. The role of testosterone (T) in regulating the incidence of apoptosis in the developing MPNc was examined in neonatally castrated males following T or vehicle injection. Testosterone had a profound inhibitory effect on the incidence of apoptosis between days 6 and 10. In a control region within the lateral preoptic area, there was no sex difference in the incidence of apoptosis, nor was there an effect of T. Thus, the data indicate that the regulation of apoptosis by T is one mechanism involved in the sexual differentiation of the SDN-POA.

Animals↗

PubMed1996

Regulation of cholecystokinin receptors in the ventromedial nucleus of the hypothalamus: sex steroid hormone effects.

Quantitative autoradiography was used to analyze cholecystokinin receptor (CCK-R) binding in the ventromedial hypothalamic nucleus (VMH) of gonadectomized rats treated with estrogen or testosterone. In the rostral VMH, sex steroids did not affect binding levels. In the caudal VMH, in both gonadectomized male and female rats, the levels of CCK-R binding were decreased 24 h after injection of 50 micrograms of estrogen benzoate but were not changed after injection of 300 micrograms of testosterone propionate. We hypothesize that these changes in CCK-R binding in the VMH reflect ligand-induced down-regulation that result from an estrogen-facilitation of stimulated CCK release in the VMH.

Animals↗

PubMed1996

Distribution of calcitonin gene-related peptide immunoreactivity in vestibular efferent neurons of the chinchilla.

The distribution of calcitonin gene-related peptide immunoreactivity (CGRPi) within efferent vestibular neurons in the chinchilla was investigated using fluorescent retrograde labeling combined with immunohistochemistry. Efferent vestibular neurons were found bilaterally in clusters: dorsolateral (group E1) and medial (group E2) to the genu of CN VII, as well as ventromedial to the descending CN VII fibers in the parvicellular reticular formation (PCR). The percentage of retrogradely labeled cells containing CGRPi was 77.1 +/- 5.7 for group E1 neurons, 90.3 +/- 3.8 in the E2 region. Among the PCR efferents more then half of the neurons (61.4 +/- 19.9%) expressed CGRP peptide or message. The wide distribution of CGRP among vestibular efferent neurons suggests that CGRP plays an important role in vestibular efferent function. In addition, the differential distribution among the groups of vestibular efferent neurons suggests that efferent modulation of vestibular function is different between the E cell group efferent neurons and the PCR efferent neurons.

Animals↗

PubMed1996

Connexin 32 mRNA levels in the rat supraoptic nucleus: up-regulation prior to parturition and during lactation.

Toward the end of pregnancy, mammalian mothers undergo a cascade of hormonal, neural and somatic events that culminate in birth and lactation. Milk ejection, the final step in lactation, is regulated by high-frequency, synchronized firing of oxytocinergic neurons in the magnocellular nuclei of the hypothalamus. This synchronization of neural activity may be regulated by an increase in the cell-to-cell coupling of magnocellular neurons by connexins. Direct intercellular channels between neurons are formed by the connexin 32 protein. The present study examined the pattern of connexin 32 mRNA levels using semiquantitative in situ hybridization histochemistry with isotopically labeled cRNA probes complementary to connexin 32 and connexin 43, found in neurons/oligodendrocytes and astrocytes, respectively. Connexin 32 mRNA levels were relatively low in the supraoptic nucleus of virgin females and were dramatically up-regulated during late pregnancy. Immediately after birth, connexin 32 mRNA levels dropped and were similar to levels in virgins. On the 13th day of lactation when dye-coupling between magnocellular neurons is high, connexin 32 message levels were again very high. Levels of the astrocytic connexin 43 were no different in lactating and virgin animals. These results demonstrate that there are two peaks of connexin 32 expression, one immediately preceding parturition and one during lactation. So far, only the second peak of connexin 32 is known to be related to an increase in dye-coupling of magnocellular neurons in the supraoptic nucleus, suggesting that in this case, the elevation of connexin 32 message levels leads to the subsequent increase in intercellular coupling.

Animals↗

PubMed1996

Isolation and characterization of a novel oligodendrocyte-specific protein.

Myelin plays a critical role in nervous system function and alterations in myelin-specific proteins cause a variety of neurologic disorders. We isolated a novel cDNA from the CNS that shares little nucleotide sequence homology with previously reported genes but appears to encode a protein related to peripheral myelin protein-22 (PMP-22) based on its amino acid sequence, predicted structure, and cellular localization. PMP-22 is important in peripheral myelination and Schwann cell proliferation, and mutations in its gene cause diseases of peripheral nerves. The isolated cDNA is 1.8 kb in length with an open reading frame of 621 bp. Northern blot analysis detected hybridization of labeled cDNA with a single 2.1-kb transcript only in the CNS. In situ hybridization revealed expression of this cDNA in oligodendrocytes of brain and spinal cord as well as in oligodendrocyte-enriched cultures; therefore we have named it oligodendrocyte-specific protein (OSP) cDNA. An OSP-specific polyclonal antibody reacted with a single 22-kd protein present in CNS myelin and oligodendrocytes. Developmental expression of OSP mRNA in the spinal cord was similar to that of the mRNA for a major myelin protein, proteolipid protein (PLP), and similar to PMP-22 in peripheral nerves. Since OSP is localized to oligodendrocytes and myelin, has a similar structure with PMP-22, and has a developmental pattern of expression like other myelin proteins, it probably has an important role in CNS myelinogenesis.

Amino Acid Sequence↗

PubMed1995

Transient cerebral ischemia decreases calcium/calmodulin-dependent protein kinase II immunoreactivity, but not mRNA levels in the gerbil hippocampus.

During transient cerebral ischemia, intracellular calcium increases initiating a cascade of events which leads to the delayed death of neurons located in the hippocampus. Coupled to this calcium disturbance is the rapid decrease of calcium/calmodulin kinase II (CaM kinase) activity, a protein kinase critical to neuronal functioning. The present study correlated the increased locomotor activity following ischemic insult with alterations in CaM kinase mRNA levels and immunocytochemical labeling of alpha and beta CaM kinase subunits in the hippocampus. The protective effect of hypothermia was also compared with CaM kinase mRNA levels and immunoreactivity. Levels of CaM kinase message for either alpha or beta subunits was not altered in ischemic gerbils compared to sham or hypothermic ischemic conditions. Immunoreactivity for both the alpha and beta subunits was markedly reduced in the vulnerable CA1 region of ischemic animals compared to sham controls. Gerbils that underwent the ischemic insult while hypothermic showed no decrement in staining. CaM kinase-like immunoreactivity in the ischemia-resistant CA3 sector was not altered following ischemia. These data suggest that the loss of hippocampal CaM kinase immunoreactivity observed at 24 h following ischemia is not associated with a reduction in CaM kinase mRNA levels and support the notion that the rapid decline in CaM kinase activity following ischemic insult is a result of a posttranslational modification and/or translocation of the enzyme.

Animals↗

PubMed1995

Motoneurons dorsolateral to the central canal innervate perineal muscles in the Mongolian gerbil.

The Mongolian gerbil provides a model in which sexually dimorphic areas in the hypothalamus are correlated with sociosexual behaviors such as scent marking and male copulatory behavior. To extend this model, investigations were conducted to determine whether sexually dimorphic areas existed in the spinal cord that could be relevant to male sexual behavior. The focus of these investigations was the perineal muscles associated with the penis. Therefore, this research identified the spinal motoneurons that innervate the bulbocavernosus, levator ani, anal sphincter, and ischiocavernosus muscles of Mongolian gerbils. The motoneuron pool that innervates the bulbocavernosus, levator ani, and anal sphincter was designated the spinal nucleus of the bulbocavernosus (SNB), as for other species of rodents. The motoneuron pool innervating the ischiocavernosus was identified as the dorsolateral nucleus, again, to be consistent with the designation for other rodents. The motoneurons of the gerbil SNB were distributed dorsolateral to the central canal in the lumbosacral transition zone of the spinal column. These motoneurons are located in the region classically defined as area X of the spinal cord. The number of SNB motoneurons was sexually dimorphic, with male gerbils having about five times as many SNB motoneurons as do female gerbils. The size of SNB motoneurons was also sexually dimorphic. The SNB motoneurons of males were 1.5 times larger than the SNB motoneurons of females. The effects of adult castration on the male SNB were also studied. After castration, the size, but not the number, of SNB motoneurons in males was significantly decreased. This decrease was prevented by testosterone treatment. The percentage of calcitonin gene-related peptide (CGRP)-immunoreactive SNB motoneurons was also affected by adult castration. The percentage of CGRP-immunoreactive motoneurons was significantly decreased after adult castration. Again, this decrease was reversed by testosterone treatment. These findings suggest that the SNB of gerbils is sexually dimorphic and is sensitive to circulating levels of gonadal steroids. The unique placement of the SNB motoneurons suggests that an alternative laminar organizational scheme may be necessary for Mongolian gerbil.

Animals↗

PubMed1995

Expression of alpha 4 and beta 2 nicotinic acetylcholine receptor subunit mRNA and localization of alpha-bungarotoxin binding proteins in the rat vestibular periphery.

In situ hybridization histochemistry was used to map the distribution of alpha 2, alpha 3, alpha 4, and beta 2 nAChR subunit mRNAs throughout the peripheral vestibular system of the rat. The alpha 4 and beta 2 nAChR subunit genes were co-expressed by populations of primary afferent neurons within Scarpa's ganglion, while there was no expression of the alpha 2, alpha 3, alpha 4, or beta 2 nAChR subunit genes by type I or type II vestibular hair cells. alpha-bungarotoxin binding to nAChRs in the vestibular end-organs was primarily limited to the afferent chalices surrounding type I hair cells and the basal aspect of type II hair cells. These data suggest that nAChRs composed of alpha 4 and beta 2 subunits are localized on afferent chalices innervating the type I vestibular hair cells and that the direct cholinergic efferent innervation of the type II vestibular hair cells utilizes nAChR composed of other subunits.

Afferent Pathways↗

PubMed1994

Calcitonin gene-related peptide-like immunoreactivity in spinal motoneurons of the male mouse is affected by castration and genotype.

Calcitonin gene-related peptide (CGRP) is found in motoneurons of the mammalian spinal cord, including motoneurons of the androgen-dependent spinal nucleus of the bulbocavernosus (SNB) of the mouse. Motoneurons of the SNB innervate the bulbocavernosus (BC), a striated muscle involved in penile reflexes. CGRP is though to be a trophic factor produced by motoneurons to regulate the expression of the acetylcholine receptor at the neuromuscular junction. In rats, the number of SNB motoneurons containing CGRP is increased by gonadal steroids. This regulation appears to rely on an activity-dependent factor produced by the BC muscle. The purpose of the present study was to examine, using immunohistochemistry, the steroid dependence of CGRP in the SNB of male house mice. Genotypic differences in the steroid regulation of CGRP immunoreactivity were examined in three strains of mice that differ in their behavioral sensitivity to castration. The results demonstrate that castration reduces the number of CGRP-positive SNB motoneurons in mice. The magnitude of the change in CGRP in response to castration and the length of time required following castration to alter CGRP were dependent on genotype. Interestingly, the effect of castration in mice, to reduce the number of CGRP-immunoreactive SNB motoneurons, is opposite in direction from the increase in CGRP SNB motoneurons observed in rats observed following castration. These experiments suggest that androgens may alter neuromuscular junction function of mouse SNB by regulating the production of CGRP in a species-specific, genotypically dependent fashion.

Animals↗

PubMed1994

Cloning and sequencing of genomic DNA extracted from archival human temporal bone sections.

Cloning techniques allow the engineering and production of highly purified DNA. Further advances in molecular biology have provided the means to identify DNA sequences in a rapid fashion. Sequencing methods can identify mutations, deletions, polymorphisms, or confirm a known genetic sequence. The use of these techniques in clinical medicine has made it possible to accurately diagnose infectious diseases and determine the molecular etiology of many genetic disorders and malignancies. In this study, DNA extracted from archival, celloidin-embedded temporal bone sections has been cloned and sequenced using these techniques. We amplified, cloned, and sequenced varicella-zoster viral DNA extracted from archival temporal bone sections from patients who had herpes zoster oticus. The application of cloning and sequencing techniques to DNA extracted from archival temporal bones provides the methodology to study temporal bone pathology at the molecular level.

Base Sequence↗

PubMed1993

Distribution of calcitonin gene-related peptide mRNA and immunoreactivity in the rat central and peripheral vestibular system.

The distribution of calcitonin gene-related peptide (CGRP) mRNA and immunoreactivity (CGRPi) was examined in sections of brainstem and decalcified temporal bones to study the peptidergic innervation patterns in both the central and peripheral vestibular system. In the brainstem, neuron somata associated with the vestibular system and containing CGRP mRNA and CGRPi were found in both the dorsolateral and medial regions of the group E vestibular efferents as well as scattered throughout the caudal pontine reticular nucleus (CPR). The only labelled neuron somata containing CGRP mRNA and CGRPi in the temporal bone were found in the gustatory geniculate ganglion. Coarse CGRPi axons were traced ventrally from the dorsolateral and medial group E somata and dorsally from the CPR somata. CGRPi axons from the medial group E and CPR crossed the facial nerve ventral to the facial genu before entering the eighth nerve root. Immunoreactive axons projected from medial group E cells, beneath the ependyma of the fourth ventricle, to the contralateral brainstem. Unmyelinated CGRPi fibers passed among the primary afferent fibers in Scarpa's ganglion and continued through the subepithelial regions of the vestibular end-organs. Within the neurosensory epithelia of the maculae and cristae, the CGRPi axons ramified to produce numerous CGRPi terminals. An efferent neuromodulatory role of CGRP in the vestibular system is inferred from the wide distribution of CGRP mRNA and immunoreactivity found within efferent vestibular neurons.

Animals↗

PubMed1992

Long-lasting decreases of type II calmodulin kinase expression in kindled rat brains.

The kindling model of epilepsy is associated with long-lasting changes in type II calmodulin kinase (CaM kinase) activity and immunoreactivity. In order to determine the mechanism of these alterations, we measured gene expression of CaM kinase using in situ hybridization in septally kindled rat brains and paired controls using a 35S-labeled riboprobe for the beta subunit of the enzyme. We found CaM kinase mRNA concentrated in the hippocampus and other limbic structures. Kindling decreased hippocampal CaM kinase mRNA by 30% in CA1, 34% in CA2, 35% in CA3 41% in CA4, and 29% in the dentate gyrus. Hybridization was also decreased by 21% in the cerebral cortex but not in the lateral septum. These changes are similar in distribution and direction to those previously measured by immunohistochemistry. These data suggest that altered CaM kinase activity and immunoreactivity associated with kindling reflect long-lasting alterations in gene expression of this important synaptic protein, and provide further evidence for its possible importance in the kindling phenomenon.

Animals↗

PubMed1992

The role of target muscles in the expression of calcitonin gene-related peptide mRNA in the spinal nucleus of the bulbocavernosus.

Previous studies have shown that calcitonin gene-related peptide (CGRP) mRNA steady-state levels and CGRP immunoreactivity in motoneurons of the spinal nucleus of the bulbocavernosus (SNB) are inversely related to the gonadal steroid environment in male rats. Since both the SNB motoneurons and their target muscles, the bulbocavernosus and the levator ani, are steroid sensitive, gonadal steroids may act at either site to regulate CGRP expression. In the present study, we tested the hypothesis that gonadal steroids influence CGRP expression in SNB motoneurons through their effects on the bulbocavernosus and levator ani muscles. We determined the levels of alpha-CGRP mRNA and immunoreactive CGRP in SNB motoneurons of adult male rats following injection of the bulbocavernosus with muscle extracts from bulbocavernosus/levator ani of castrated rats, paralysis of the bulbocavernosus or pudendal nerve cuts. Following injection of the bulbocavernosus/levator ani with extracts from castrated rats, the level of CGRP expression and the number of SNB motoneurons with alpha-CGRP message were increased. These studies suggest that the bulbocavernosus/levator ani muscles from castrated rats produce a factor that increases levels of CGRP. Injections of extract prepared from the bulbocavernosus and levator ani muscles of gonadally intact rats did not change the expression of alpha-CGRP mRNA in the SNB. Paralysis of the bulbocavernosus/levator ani with a local anesthetic increased the number of SNB motoneurons expressing alpha-CGRP mRNA and CGRP immunoreactive neurons. To determine whether nerve damage accounted for the observed effects following injection of anesthetic, the pudendal nerves were cut bilaterally.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1992

Differential regulation of alpha-calcitonin gene-related peptide and preprocholecystokinin messenger RNA expression in alpha-motoneurons: effects of testosterone and inactivity induced factors.

alpha-Calcitonin gene-related peptide expression in alpha-motoneurons is regulated by spinal cord transection, axotomy and testosterone, but to date there are no studies which examine the regulation of cholecystokinin expression in motoneurons. In the present study, we compared the regulation of preprocholecystokinin and alpha-calcitonin gene-related peptide messenger RNA levels in motoneurons of the spinal nucleus of the bulbocavernosus. Previously, we demonstrated that manipulations which decrease activity in target muscles of the spinal nucleus of the bulbocavernosus motoneurons increase alpha-calcitonin gene-related peptide message and peptide levels in spinal nucleus of the bulbocavernosus motoneurons. This muscle-nerve interaction is mediated by a soluble factor which is increased by castration. We now report that decreasing plasma testosterone levels decreased preprocholecystokinin messenger RNA levels. Testosterone replacement at the time of castration restored preprocholecystokinin messenger RNA levels to intact values. Injections of crude extracts prepared from denervated bulbocavernosus/levator ani into the homologous muscles of gonadally intact rats increased the levels of alpha-calcitonin gene-related peptide messenger RNA in spinal nucleus of the bulbocavernosus motoneurons. The levels of preprocholecystokinin messenger RNA did not differ in rats injected with denervated bulbocavernosus/levator ani extract or buffer, both of which were significantly higher than in intact, untreated rats. The results of the present experiments imply that levels of preprocholecystokinin and alpha-calcitonin gene-related peptide messenger ribonucleic acid are differentially regulated in spinal nucleus of the bulbocavernosus motoneurons.

Animals↗

PubMed1991

Cell and molecular anatomy of nicotinic acetylcholine receptor subunits and calcitonin gene-related peptide in the rat vestibular system.

In this report we demonstrate the pattern of calcitonin gene-related peptide (CGRP) mRNA and immunoreactivity in the central and peripheral vestibular system of the rat, using a CGRP cRNA probe and a polyclonal CGRP antiserum. We present evidence that somata in all regions of efferent vestibular neurons contain CGRP based on the correspondence between in situ hybridization (mRNA) and immunohistochemistry (mRNA translation product). CGRP immunohistochemistry (CGRPi) and in situ hybridization confirm that CGRPi axons and terminals present in the vestibular neuroepithelium are efferent in origin. Immunoelectron microscopy revealed an extensive innervation of the afferent vestibular pathway by CGRPi terminals that was not limited to the primary afferent chalice, as previously reported by Tanaka et al. (Brain Res 1989;504:31-5). An efferent neuromodulatory role of CGRP can be inferred from the distribution of terminals found on the primary afferent fibers, and type I and type II hair cells. In addition, we present evidence that nicotinic acetylcholine receptor (nAChR) subunit mRNA is expressed by primary afferent cell bodies. On the basis of these data, a hypothetical molecular mechanism of vestibular efferent modulation of the primary afferent pathway is proposed.

Animals↗

PubMed1991

Molecular biology of the vestibular system.

Molecular biology of the vestibular system has been limited by a number of technical difficulties including fixation, decalcification of the temporal bone and the small size of specific structures relative to their surroundings. In situ hybridization histochemistry and immunoelectron microscopy allow the subcellular study of gene expression and gene products, respectively. We developed the methodologies necessary to apply these techniques to the central and peripheral vestibular systems. The central and temporal bone distributions of the neuropeptide calcitonin gene-related peptide (CGRP) mRNA and two genes coding for gap junction proteins, connexin C32 and C43 mRNA, were studied. The cellular distributions of these mRNAs are presented. In addition, examples of pre-embedding and postembedding immunoelectron microscopy are presented demonstrating the usefulness of these techniques in studying the subcellular localization of specific antigens. The ultrastructural innervation of the vestibular periphery by the efferent neuropeptide CGRP and ultrastructural evidence of glycoprotein secretion by the human endolymphatic sac is presented.

Animals↗

PubMed1990

Role of postnatal androgens in sexual differentiation of the lordosis-inhibiting effect of central injections of cholecystokinin.

The neuropeptide cholecystokinin (CCK) inhibits lordosis behavior when infused into the ventromedial nucleus of the hypothalamus (VMN) of female rats and has no effect when infused into the VMN of male rats. To test whether this sex difference develops under the control of perinatal steroids, male rats were castrated or given sham surgeries within 3 h of birth and female rats were injected with either 0 or 100 micrograms testosterone propionate on postnatal day 5. As adults, these rats were castrated as necessary, implanted with unilateral cannulae directed at the VMN, and tested for their ability to display female sexual behavior and to respond to CCK. Neonatal castration of males prevented defeminization of this response. When treated with 5 micrograms estradiol benzoate (EB), neonatally castrated males showed both lordosis behavior and a profound inhibition of that behavior after infusions of CCK. Neonatally castrated males did not display lordosis behavior when treated with 2 micrograms EB. Control males showed no lordosis behavior and, therefore, no response to CCK. Both doses of EB induced lordosis behavior in neonatally androgenized females. Significantly, these neonatally androgenized females were less responsive to CCK's inhibition of lordosis and were also anovulatory. These results imply that androgens alter the development of CCK responsive circuits as well as defeminize cyclic gonadotropin release. Levels of 125I-sCCK-8 binding in the VMN were correlated closely with an individual's ability to respond to sCCK-8. In summary, the inhibition of female sexual behavior caused by exogenously administered CCK in normal adult female rats appears to be controlled at least partially by levels of CCK receptors in the VMN and to differentiate under the control of perinatally present testosterone.

Androgens↗

PubMed1990

Steroid regulation of calcitonin gene-related peptide mRNA expression in motoneurons of the spinal nucleus of the bulbocavernosus.

Motoneurons express calcitonin gene-related peptide (CGRP). Previous studies have shown that CGRP immunoreactivity is regulated by testosterone in the androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB). In this research the effect of plasma levels of testosterone on the expression of alpha CGRP mRNA in the SNB motoneurons of adult male rats was studied with in situ hybridization. The number of motoneurons expressing alpha CGRP mRNA and the level of alpha CGRP mRNA expression was significantly higher in the SNB of castrated male rats than in the SNB of gonadally intact rats. Using a 5x background labeling criterion in castrated rats 88.1 +/- 4.5% while in intact rats 75.3 +/- 6.4% of SNB motoneurons expressed alpha CGRP mRNA. Testosterone replacement at the time of castration prevented the effect of castration on the expression of alpha CGRP mRNA in SNB motoneurons. In castrated rats, the increase in the number of SNB cells expressing CGRP was the result of increased steady state levels of alpha CGRP mRNA in all SNB neurons.

Animals↗