PubMed Health⌕ Search

Biomedical subjects

H F Urbanski

Publications and source records attributed to H F Urbanski.

At least 19 recordsLinked to original sources
PubMed2004

Effect of caloric restriction on the 24-hour plasma DHEAS and cortisol profiles of young and old male rhesus macaques.

Although dietary caloric restriction (CR) can retard aging in laboratory rats and mice, it is unclear whether CR can exert similar effects in long-lived species, such as primates. Therefore, we tested the effect of CR on plasma levels of dehydroepiandrosterone sulfate (DHEAS), a reliable endocrine marker of aging. The study included six young (approximately 10 years) and ten old (approximately 25 years) male rhesus macaques, approximately half of the animals in each age group having undergone >4 years of 30% CR. Hourly blood samples were collected remotely for 24 hours, through a vascular catheter, and assayed for DHEAS and cortisol. Both of these adrenal steroids showed a pronounced diurnal plasma pattern, with peaks occurring in late morning, but only DHEAS showed an aging-related decline. More importantly, there was no significant difference in plasma DHEAS concentrations between the CR animals and age-matched controls. These data fail to support the hypothesis that CR can attenuate the aging-related decline in plasma DHEAS concentrations, at least not when initiated after puberty.

Aging↗
PubMed2004

Effect of 17beta-estradiol on hypothalamic GnRH-II gene expression in the female rhesus macaque.

The hypothalamus of rhesus macaques expresses two molecular forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II). However, it is unclear whether these two neuropeptides play similar roles in the control of reproductive neuroendocrine function, especially in the context of positive and negative estrogen feedback. To address this issue, in situ hybridization histochemistry was used to compare the effect of 17beta-estradiol (E) on the expression of GnRH-I and GnRH-II mRNA in the medial basal hypothalamus (MBH) of adult female macaques. GnRH-I mRNA expression was found to be significantly (P<0.01) more abundant in ovariectomized (ovx) animals compared with ovariectomized E-treated (ovx+E) animals. In marked contrast, GnRH-II mRNA expression was found to be significantly (P<0.05) more abundant in ovx+E animals than in the ovx animals. To help elucidate how E exerts this stimulatory action on GnRH-II gene expression, hypothalamic sections were subsequently double labeled using a combination of immunohistochemisty for estrogen receptor (ER) -alpha or -beta and in situ hybridization histochemistry for GnRH-II. Approximately 50% of the GnRH-II positive cells in the MBH were found to express ERbeta, but none expressed ERalpha. Taken together, these data give credence to a novel pathway by which E may control the primate neuroendocrine reproductive axis, one that involves stimulation of GnRH-II release via an ERbeta-mediated mechanism.

Animals↗
PubMed2003

Expression and regulation of mPer1 in immortalized GnRH neurons.

Hypothalamic GnRH (gonadotropin-releasing hormone) neurons play a critical role in the initiation and maintenance of reproduction competence. Using the mouse GnRH neuronal cell line, GT1-7, we have characterized the expression of the gene mPer1, a recognized key element of the mammalian circadian clockwork. Both mPer1 transcripts and the 136 kDa mPER1 gene product could be detected in these cells. Immunocytochemical analysis also confirmed expression of mPER1 both in vitro and in vivo in GnRH neurons. Activation of cyclic AMP signalling pathways in vitro elevated GnRH secretion as well as mPer1 expression and nuclear mPER1 immunoreactivity. As mPER1 is known to feedback on transcriptional activities in many cell models, the data presented here point to a role for mPER1 in the regulation of gene expression in GnRH neurons, and thus in the control of neuroendocrine activities.

Animals↗
PubMed2001

Photoperiodic modulation of GnRH mRNA in the male Syrian hamster.

Male Syrian hamsters (Mesocricetus auratus) are seasonal breeders. They show marked testicular regression when exposed to short autumnal photoperiods, and then remain sexually quiescent for several months. By mid-winter, however, they show a loss in responsiveness to the inhibitory influence of short photoperiods and their testes begin to recrudesce. To shed light on the neuroendocrine mechanism responsible for mediating these reproductive changes, we examined the influence of photoperiod on the expression of GnRH mRNA in the hamster forebrain. Adult males were either exposed to short photoperiods (6L:18D) for 16 weeks or were maintained under long photoperiods (14L:10D); additional animals were exposed to short or long photoperiods for 22 weeks. As expected, exposure to short photoperiods for 12 weeks resulted in a marked decrease (P<0.01) in testicular mass and serum testosterone levels, but after 22 weeks these reproductive parameters were once again significantly elevated (P<0.01). In contrast, quantitative in situ hybridization histochemistry revealed no difference (P>0.05) between the GnRH mRNA levels of the short-photoperiod hamsters and their aged-matched long-photoperiod controls, although an age-related decrease (P<0.05) was evident in both photoperiod-treatment groups. These data emphasize that GnRH mRNA is highly expressed in hamsters even when their reproductive axis has been rendered sexually quiescent by exposure to short photoperiods, and that photoperiod-induced changes in GnRH secretion, rather than synthesis, are more likely to regulate the timing of the breeding season. On the other hand, the data indicate that GnRH mRNA levels show an aging-related decrease, regardless of photoperiod, suggesting that in the long term a decrease in GnRH gene expression may contribute to the reduced fertility of old hamsters.

Aging↗
PubMed2001

Immunoneutralisation of GnRH-I, without cross-reactivity to GnRH-II, in the development of a highly specific anti-fertility vaccine for clinical and veterinary use.

In recent years, several forms of gonadotrophin releasing hormone (GnRH) molecules have been isolated from primate brain. These molecules are very similar in sequence and this raises the question of whether previously developed neutralisation vaccines based on GnRH (now termed GnRH-I) would remove other forms of GnRH (namely GnRH-II) as well. As the function of these other molecules has not yet been clearly defined, potential health risks could exist by their ablation. In view of the high sequence homology between the molecules, this paper describes the production of highly specific polyclonal antibodies against GnRH-I and GnRH-II, with negligible cross-reactivity. The ultimate aim of this is to develop an anti-fertility vaccine which does not present any inappropriate side-effects, caused by neutralisation of a GnRH molecule which may or may not be directly involved in reproduction. Several formulations were investigated, based on analogues of the following molecules, conjugated to tetanus toxoid: 1. GnRH-I pGlu-His-Trp-Ser-Try-Gly-Leu-Arg-Pro-Gly-NH2 and 2. GnRH-II pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. The specificity of the antibodies produced was examined, together with effects on fertility and any inappropriate side-effects. Immunostaining of hypothalamic sections was carried out, using the generated antisera, to determine the regional distribution of GnRH-I and GnRH-II neurones, as well as to further evaluate the specificity of the antibodies.

Animals↗
PubMed2001

Leptin and puberty.

Leptin is thought to relay metabolic information to the hypothalamic-pituitary- gonadal axis and to participate in the neuroendocrine control of puberty. To help elucidate the underlying mechanism, Cheung et al. recently performed a diverse series of experiments, the results of which undermine the prevailing hypothesis that leptin acts as a metabolic trigger for the initiation of puberty. Instead, their results suggest that leptin is one of many permissive metabolic factors that allow pubertal development to proceed.

Animals↗
PubMed2001

A developmental increase in the expression of messenger ribonucleic acid encoding a second form of gonadotropin-releasing hormone in the rhesus macaque hypothalamus.

GnRH-I is thought to represent the primary neuroendocrine link between the brain and the reproductive axis. Recently, however, a second molecular form of this decapeptide (GnRH-II) was found to be highly expressed in the brains of humans and nonhuman primates. In this study, in situ hybridization was used to examine the regional expression of GnRH-II messenger ribonucleic acid in the hypothalamus of immature (0.6 yr) and adult (10-15 yr) male and female rhesus macaques (Macaca mulatta). Overall, no sex-related differences were observed. In all of the animals (n = 3 animals/group), intense hybridization of a monkey GnRH-II riboprobe was evident in the paraventricular nucleus and supraoptic nucleus and to a lesser extent in the suprachiasmatic nucleus, but no age- or sex-related differences were apparent. Intense hybridization of the riboprobe also occurred in the mediobasal hypothalamus, and this was markedly greater in the adults than in the immature animals. These data show that the expression of GnRH-II messenger ribonucleic acid increases developmentally in a key neuroendocrine center of the brain. Moreover, because GnRH-II can stimulate LH release in vivo, it is plausible that changes in its gene expression represent an important component of the mechanism by which the hypothalamus controls reproductive function.

Animals↗
PubMed2000

Distribution of estrogen receptor beta (ERbeta) mRNA in hypothalamus, midbrain and temporal lobe of spayed macaque: continued expression with hormone replacement.

This study used in situ hybridization (ISH) to examine the distribution of estrogen receptor beta (ERbeta) mRNA in hypothalamic, limbic, and midbrain regions of monkey brain and its regulation by estrogen (E) and progesterone (P). Monkey-specific ERbeta cDNAs were developed with human primers and reverse transcription and polymerase chain reaction (RT-PCR) using mRNA extracted from a rhesus monkey prostate gland. ERbeta 5' (262 bases) and 3' (205 bases) riboprobes were used in combination for ISH. Ovariectomized and hysterectomized (spayed) pigtail macaques (Macaca nemestrina; four per treatment group) were either untreated spayed-controls, treated with E (28 days), or treated with E plus P (14 days E+14 days E and P). Dense ERbeta hybridization signal was seen in the preoptic area, paraventricular nucleus, and ventromedial nucleus of the hypothalamus; the substantia nigra, caudal linear, dorsal raphe, and pontine nuclei of the midbrain; the dentate gyrus, CA1, CA2, CA3, CA4, and the prosubiculum/subiculum areas of the hippocampus. Expression in the suprachiasmatic region, supraoptic nucleus, arcuate nucleus, and amygdala was less intense. Image analysis of the dense areas showed no significant difference in the hybridization signal in individual regions of the hypothalamus, midbrain, or hippocampus between any of the treatment groups. However, P treatment decreased overall ERbeta signal in the hypothalamus and hippocampus when several different subregions were combined. The localization of ERbeta in monkey brain by ISH is in general agreement with that previously described in rodents. The presence of monkey ERbeta mRNA in brain regions that lack ERalpha should help to clarify the molecular mechanisms by which E acts in the central nervous system to influence hormone secretion, mood disorders, cognition, and neuroprotection.

Amygdala↗
PubMed2000

Two molecular forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed by two separate populations of cells in the rhesus macaque hypothalamus.

Gonadotropin-releasing hormone represents the primary neuroendocrine link between the brain and the reproductive axis, and at least two distinct molecular forms of this decapeptide (GnRH-I and GnRH-II) are known to be expressed in the forebrain of rhesus macaques (Macaca mulatta). Although the distribution pattern of the two corresponding mRNAs is largely dissimilar, their expression appears to show some overlap in specific regions of the hypothalamus; this raises the possibility that some cells express both molecular forms of GnRH. To resolve this issue, double-label histochemistry was performed on hypothalamic sections from six male rhesus macaques, using a monoclonal antibody to GnRH-I and a riboprobe to monkey GnRH-II mRNA. In total, more than 2000 GnRH neurons were examined but in no instance were GnRH-I peptide and GnRH-II mRNA found to be coexpressed. This finding emphasizes that GnRH-I and GnRH-II are synthesized by two distinct populations of hypothalamic neurons, and suggests that they may be regulated by different neuroendocrine pathways.

Animals↗
PubMed2000

Neuronal elements in the testis of the rhesus monkey: ontogeny, characterization and relationship to testicular cells.

Intrinsic neuron-like cells expressing the catecholamine-biosynthetic enzyme tyrosine hydroxylase (TH) were recently identified in the testis of the prepubertal rhesus monkey. In this study, we characterized the neuron-like nature of these cells and examined distribution and frequency of neuronal elements in the testes of monkeys during postnatal development, puberty and adulthood. Using immunohistochemical methods, we detected both nerve fibers and cell bodies, immunoreactive for the neuronal markers neurofilament 200 (NF-200) and synaptosomal associated protein of 25 kDa (SNAP-25), TH and neuropeptide Y (NPY) in perivascular locations, intermingled with interstitial cells and close to the wall of seminiferous tubules. Marked age-related differences in the numbers of these neuronal elements became apparent, when we quantified NF-200-immunoreactive neuronal elements. Thus, intrinsic neuron-like cell bodies were found only in the testes from immature animals (i.e. , until about 3 years of age). Conversely, nerve fibers, presumably representing mainly the extrinsic innervation, were observed at all ages although they became more prominent after the pubertal increase in LH and testosterone levels. Interestingly, another testicular cell type known to contain potent regulatory substances, mast cells, was found to be in close anatomical proximity to nerve fibers. The number of these cells, positively identified with an antibody to tryptase, increased significantly after puberty following the same pattern as nerve fibers. These results confirm that the testicular nervous system of the monkey is composed of two components, intrinsic nerve cells and extrinsic fibers, both of which are catecholaminergic and peptidergic in nature. Furthermore, both components show a marked degree of plasticity during development, especially around the time of puberty. The intratesticular locations of neuron-like cells and fibers suggest that catecholamines and neuropeptides are likely to have multiple sites of actions, and may affect Leydig cells, cells of the tubular wall and vascular cells directly and/or indirectly via intermediation of mast cells.

Age Factors↗
PubMed2000

Mitochondrial uncoupling protein 2 (UCP2) in the nonhuman primate brain and pituitary.

Energy dissipating mechanisms and their regulatory components represent key elements of metabolism and may offer novel targets in the treatment of metabolic disorders, such as obesity and diabetes. Recent studies have shown that a mitochondrial uncoupling protein (UCP2), which uncouples mitochondrial oxidation from phosphorylation, is expressed in the rodent brain by neurons that are known to regulate autonomic, metabolic, and endocrine processes. To help establish the relevance of these rodent data to primate physiology, we now examined UCP2 messenger RNA and peptide expressions in the brain and pituitary gland of nonhuman primates. In situ hybridization histochemistry showed that UCP2 messenger RNA is expressed in the paraventricular, supraoptic, suprachiasmatic, and arcuate nuclei of the primate hypothalamus and also in the anterior lobe of the pituitary gland. Immunocytochemistry revealed abundant UCP2 expression in cell bodies and axonal processes in the aforementioned nuclei as well as in other hypothalamic and brain stem regions and all parts of the pituitary gland. In the hypothalamus, UCP2 was coexpressed with neuropeptide Y, CRH, oxytocin, and vasopressin. In the pituitary, vasopressin and oxytocin-producing axonal processes in the posterior lobe and POMC cells in the intermediate and anterior lobes expressed UCP2. On the other hand, none of the GH-producing cells of the anterior pituitary was found to produce UCP2. The abundance and distribution pattern of UCP2 in the primate brain and pituitary suggest that this protein is evolutionary conserved and may relate to central autonomic, endocrine and metabolic regulation.

Animals↗
PubMed1999

Regional expression of mRNA encoding a second form of gonadotropin-releasing hormone in the macaque brain.

In mammals, reproduction is thought to be controlled by a single neuropeptide, gonadotropin-releasing hormone (GnRH-I), which regulates the synthesis and secretion of gonadotropins from the pituitary gland. However, another form of this decapeptide (GnRH-II), of unknown function, also exists in the brain of many vertebrate species, including humans; it is encoded by a different gene and its amino acid sequence is 70% identical to that of GnRH-I. Here we report the cloning of a GnRH-II cDNA from the rhesus macaque (Macaca mulatta), and show for the first time by in situ hybridization that GnRH-II mRNA is expressed in the primate midbrain, hippocampus and discrete nuclei of the hypothalamus, including the supraoptic, paraventricular, suprachiasmatic and arcuate. Because the regional distribution pattern of cells containing GnRH-II mRNA is largely dissimilar to that of cells containing GnRH-I mRNA, it is likely that these two cell populations receive distinct neuroendocrine inputs and thus regulate GnRH synthesis and release differently.

Amino Acid Sequence↗
PubMed1998

Regional distribution of glutamic acid decarboxylase (GAD65 and GAD67) mRNA in the hypothalamus of male rhesus macaques before and after puberty.

Glutamic acid decarboxylase (GAD) is the rate-limiting enzyme in the gamma-aminobutyric acid (GABA) biosynthetic pathway, and is coded for by two mRNAs, GAD65 and GAD67. Using in situ hybridization, we examine the distribution pattern of both GAD mRNAs in the hypothalamus and thalamus of prepubertal and adult male rhesus macaques. Qualitatively, GAD65 and GAD67 mRNAs showed a similar wide, but highly specific distribution pattern, supporting the view that GABAergic neurons play an important role in modulating neuroendocrine function. However, no quantitative difference in the intensity of hybridization signal was detected between prepubertal and adult animals in any of the hypothalamic or thalamic nuclei. Therefore, although GABAergic neurons are anatomically well-placed to control the secretion of gonadotropin-releasing hormone (GnRH) in primates, it is unlikely that the onset of puberty and the associated increase in GnRH secretion is triggered by a change in GAD gene transcription.

Animals↗
PubMed1998

Regional distribution of glutamate receptor mRNA in the monkey hippocampus and temporal cortex: influence of estradiol.

The distribution of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptor subunits was examined in the hippocampus and temporal cortex of adult ovariectomized female rhesus macaques, some of which received estradiol replacement. In situ hybridization revealed a generalized overlap of NR1, GluR1, and GluR2 subunit mRNAs, but no effect due to estradiol treatment. However, regional differences in expression were noted for each subunit.

Animals↗
PubMed1998

A biphasic developmental pattern of circulating leptin in the male rhesus macaque (Macaca mulatta).

To help elucidate the physiological role of leptin during somatic and sexual maturation, circulating concentrations of leptin were measured in 36 male rhesus monkeys of ages ranging from 0-20 yr. The body weight of these animals showed a steady increase of approximately 1 kg/yr during the first decade of life and reached a plateau at approximately 13 yr. In contrast, serum leptin concentrations showed a biphasic developmental pattern, which was highlighted by a strong negative correlation with body weight (r = -0.74, P < 0.001) before the onset of puberty (at approximately 3.5 yr) and by a strong positive correlation afterward (r = 0.77, P < 0.001). Overall, the developmental changes in serum leptin concentrations closely mimicked the expected developmental changes in serum testosterone concentrations (r = 0.62, P < 0.001), which were highly elevated at birth, fell to basal levels during the juvenile phase of development, and gradually rose again after the initiation of puberty. However, mean serum leptin concentrations during the peripubertal period itself (3-5 yr) were significantly lower (P < 0.01) than those observed during the first year of life or those observed in fully mature adults (i.e. > 7 yr) (3.5 +/- 0.3, 1.4 +/- 0.2, and 3.3 +/- 0.6 ng/ml, respectively). These data demonstrate that the role of leptin in energy homeostasis of primates is more than a simple linear relationship, being highly dependent upon the developmental age. Furthermore, the data do not support the hypothesis that leptin plays a major role in triggering the onset of puberty in primates, although the strong correlation between serum concentrations of leptin and testosterone suggests that the secretion of these two hormones may be causally linked.

Animals↗
PubMed1997

Distribution of glutamate receptor subunits in the primate temporal cortex and hippocampus.

The distribution of subunits for the N-methyl-D-aspartate (NR1, NR2A/B), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (GluR1, GluR2/3, GluR4) and low affinity kainate (GluR5/6/7) ionotropic glutamate receptors was examined by immunocytochemistry in the temporal cortex and hippocampus of the rhesus macaque (Macaca mulatta). Neurons expressing NR1, NR2A/B, GluR2/3, and GluR4 subunits were widely distributed in all of the cortical layers but the overall density of the GluR4-immunopositive neurons was very low. Neurons expressing the GluR1 subunit were found predominantly in cortical layers V and VI while those expressing the GluR5/6/7 subunits were concentrated in layer V and were readily distinguishable by the thick elongate shape of their primary apical dendrites. Subcellular differences in the immunostaining pattern were also noted between the different glutamate receptor subunits. NR1 and NR2A/B immunoreactivity was most pronounced in somatic and primary dendritic compartments and to a lesser extent in cortical and hippocampal molecular layers. GluR1 immunoreactivity was more intense than GluR2/3 in the hippocampal molecular layers whereas GluR4 was undetectable. GluR5/6/7 immunoreactivity was very intense in the dentate molecular layer, and the CA1 pyramidal cells had a subcellular distribution of GluR5/6/7 that was similar to the cortical neurons. Overall, the distribution patterns of the different glutamate receptor subunits was identical in animals that had been ovariectomized and in ovariectomized animals that had subsequently undergone estradiol or estradiol/progesterone hormone replacement. Taken together, these findings demonstrate a differential spatial arrangement of glutamate receptor subunits in the primate temporal cortex and hippocampus, which may have functional significance for the integration of excitatory inputs to these areas. Furthermore, they show that in adult macaques, sex steroids do not play a major role in determining the distribution patterns of these receptor subunits.

Animals↗
PubMed1997

Alpha-adrenergic receptor antagonism and N-methyl-D-aspartate (NMDA) induced luteinizing hormone release in female rhesus macaques.

The stimulatory influence of N-methyl-D-aspartate (NMDA), a glutamate receptor agonist, on LH secretion is well established in several mammalian species including the rhesus macaque. Although the mechanism of excitation appears to involve enhanced GnRH secretion, it is unclear whether the GnRH neurons respond directly to this excitation or whether stimulatory inter-neurons are involved. This study investigated the possibility that noradrenergic afferents play a major role in mediating the response of the primate hypothalamo-pituitary reproductive axis to NMDA. In situ hybridization histochemistry, using a cRNA probe coding for the NMDAR1 receptor subunit, revealed abundant mRNA in the locus coeruleus, a brain area rich in noradrenergic neurons. Furthermore, using double-label fluorescence immunocytochemistry, the tyrosine hydroxylase immunopositive neurons of the locus coeruleus showed immunoreactivity for the NMDAR1 receptor subunit protein. A second experiment examined whether prazosin, an alpha 1-adrenergic receptor antagonist, could attenuate NMDA-induced stimulation of LH release. Prazosin (either 1 or 5 mg/kg b.wt., i.v.) was administered to female rhesus macaques during the luteal phase of the menstrual cycle, 40 min before administration of NMDA (10 mg/kg b.wt., i.v.). Regardless of the prazosin pre-treatment, plasma LH concentrations showed a significant increase (P < 0.01) within 10 min of the administration of NMDA. Therefore, in spite of the evidence that at least some of the noradrenergic neurons of the primate hindbrain express the NMDAR1 receptor subunit, it is unlikely that noradrenergic inter-neuronal pathways alone play a major role in mediating the stimulatory action of NMDA on GnRH/LH secretion in primates. Indeed, because the GnRH neurons of the rhesus macaque are located diffusely in various regions of the hypothalamus and medial-septal/preoptic area, their net response to excitatory amino acids is likely to be more complicated, involving a combination of both stimulatory and inhibitory inter-neurons, and possibly also a direct interaction.

Adrenergic alpha-Antagonists↗