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Biomedical subjects

H F Urbanski

Publications and source records attributed to H F Urbanski.

At least 37 records · Page 2Linked to original sources
PubMed1997

Lesions in the anterior bed nucleus of the stria terminalis in Syrian hamsters block short-photoperiod-induced testicular regression.

To elucidate the neural circuitry involved in the photoperiodic control of seasonal reproduction, adult male Syrian hamsters, previously housed under long photoperiods (LD; 14 h of light per day), received sham or bilateral radiofrequency-current lesions directed towards one of three anterior-to-posterior levels of the bed nucleus of the stria terminalis (BNST; far anterior, anterior, posterior). They were then transferred to a short photoperiod (SD; 6 h of light per day) for 12 wk, and their testicular weights and plasma FSH, LH, and testosterone concentrations were determined. All of these parameters became markedly inhibited in the sham-lesioned SD controls and also in the far anterior and posterior BNST lesioned groups. In contrast, this inhibitory response to SD was completely abolished in 8 of 14 animals that had received anterior BNST lesions; only in these 8 animals did the lesion encompass the lateral aspect of the anterior BNST. In a second experiment, hamsters that had previously been exposed to SD for 12 wk in order to induce testicular regression were lesioned in the anterior BNST and for the next 4 weeks were either exposed to LD or further maintained in SD. However, in neither case did the anterior BNST lesions perturb the normal photoperiodic response. Paired testes weights and plasma FSH, LH, and testosterone concentrations at 4 wk did not differ significantly (p > 0.05) between the lesioned animals and their respective sham-lesioned LD and SD controls, which, respectively, showed recrudescence of the reproductive axis or remained in a regressed condition. Taken together, the results suggest that lateral aspects of the anterior BNST contain a cell group that is critical for perception of the SD neuro-inhibitory signal; obliteration of this cell group interrupts the transmission of the inhibitory signal to the reproductive axis but does not directly stimulate it.

Animals↗
PubMed1997

A second form of gonadotropin-releasing hormone (GnRH) with characteristics of chicken GnRH-II is present in the primate brain.

The primate brain was thought to contain only the GnRH known as mammalian GnRH (mGnRH). This study investigates whether a second form of GnRH exists within the primate brain. We found that brain extracts from adult stumptail and rhesus monkeys contained two forms of GnRH that were similar to mGnRH and chicken GnRH-II (cGnRH-II) based on the elution position of the peptides from HPLC and on cross-reactivity with antisera that are specific to mammalian or chicken GnRH-II in RIAs. The fetal brain of rhesus monkeys also contained mGnRH and a cGnRH-II-like peptide by the same criteria. Immunocytochemistry with a cGnRH-II-specific antiserum in adult and fetal rhesus monkeys showed immunopositive neurons generally scattered in the periaqueductal region of the midbrain, with a few positive cells in the posterior basal hypothalamus. Neurons immunopositive for cGnRH-II were fewer in number and smaller in size, with less defined nuclei and thinner neurites compared with those for mGnRH. Administration of synthetic cGnRH-II to adult rhesus monkeys resulted in a significant increase in the plasma LH concentration during the luteal phase of the menstrual cycle, but not during the midfollicular phase. We conclude that the primate brain contains mGnRH and a cGnRH-II-like molecule, although the function of the latter is unknown.

Aging↗
PubMed1996

Distribution of NMDA and AMPA receptors in the cerebellar cortex of rhesus macaques.

The distribution of glutamate receptors in the cerebellar cortex of the rhesus macaque was examined by light microscopic immunocytochemistry using an antibody specific to the N-methyl-D-aspartate (NMDA) R1 receptor subunit (i.e. NMDAR1) as well as antibodies specific to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subunits (i.e. GluR1, GluR2/3, and GluR4). NMDAR1 immunolabeling was most prevalent in the Purkinje cell perikarya and dendrities, but was also significant in the stellate and basket cells of the granular layer and Golgi cells of the molecular layer. On the other hand, GluRl and GluR4 immunolabeling was concentrated principally in the processes of the Bergmann glia located in the vicinity of the Purkinje cell perikarya. Although GluR2/3 immunolabeling also occurred in these Bergmann glia processes as well as in the Bergmann fibers, it was more pronounced in the Purkinje cell perikarya and dendrites; additionally, significant GluR2/3 labeling was evident in the stellate and basket cells of the molecular layer and medium-size soma of the granular layer (most likely Golgi cells). In situ hybridization histochemistry (ISHH), using cRNA probes to NMDAR1. GluR1.GluR2, and GluR3, showed glutamate receptor mRNA distribution patterns consistent with those disclosed in the immunocytochemical study. Furthermore, the ISHH findings suggest that the positive immunocytochemical labeling of Purkinje cells with the GluR2/3 antibody is most likely due to the gene expression of both GluR2 and GluR3 AMPA receptor subtypes. Taken together, the results are potentially important for the elucidation of mechanisms that control aspects of cerebellar function, such as long-term depression.

Animals↗
PubMed1995

Lesions in the bed nucleus of the stria terminalis, but not in the lateral septum, inhibit short-photoperiod-induced testicular regression in Syrian hamsters.

The transfer of adult male hamsters from long days (LD) to short days (SD) (i.e. < 12 h of light per day) typically results in marked testicular regression and a decline in plasma testosterone concentrations. To help disclose key brain regions responsible for mediating this photoperiodic response male hamsters received either chemical (i.e. N-methyl-D-aspartate; NMDA) or radiofrequency current lesions in the bed nucleus of the stria terminalis (BNST), and were then exposed to SD for 15 or 12 weeks, respectively. Although body weights were similar between sham-lesioned controls and the NMDA-lesioned hamsters, the latter showed a significant attenuation of testicular regression; additionally, their plasma testosterone concentrations remained at typical LD levels. When radiofrequency current-lesioned hamsters were transferred from LD to SD they also failed to show significant signs of testicular regression, nor a decline in plasma testosterone concentrations, nor a complete arrest of spermatogenesis. In contrast, sham-lesioned controls or hamsters that were lesioned dorsally to the BNST at a site primarily involving the lateral septum all showed the expected degree of testicular regression, a decline in plasma testosterone concentrations, and complete arrest of spermatogenesis; body weights were similar in all of the experimental group. Taken together, these findings suggest that the BNST, a brain area traditionally not associated with reproductive function, may play an important role in mediating photoperiodic information to the neural circuits that control the reproductive axis.

Animals↗
PubMed1995

Effects of N-methyl-D-aspartate (NMDA) on seasonal cycles of reproduction, body weight and pelage colour in the male Siberian hamster.

Siberian hamsters (Phodopus sungorus) transferred from stimulatory photoperiods (long days: LD) to inhibitory photoperiods (short days: SD) undergo testicular regression within 8 weeks. This reproductive response to photoperiod was blocked by systemic daily treatment with the glutamatergic agonist N-methyl-D-aspartate (NMDA: 20 mg/kg BW, sc). This powerful effect of NMDA demonstrates the potential for endogenous glutamate to regulate reproductive function. The overall aim of the subsequent studies was to investigate the site and mechanism of action of this glutamatergic agonist in order to identify potential mechanisms through which endogenous glutamate might act. To investigate whether the effect of systemic NMDA was via an effect on the circadian timing system, alterations in gonadal regression and recrudescence, seasonal coat changes (pelage) and body weight (BW) were examined. It would be predicted that long-term cycles of all these seasonal parameters would be affected if the action of NMDA were to perturb the transduction of photoperiodic information. Daily treatments with NMDA, which initially maintained reproductive function in hamsters exposed to SD, did not influence the time course of subsequent testicular recrudescence, nor did they influence long-term cycles of pelage and BW. Moreover, treatment with NMDA induced a dose-dependent increase in serum concentrations of LH within 15 min of systemic injection. These data are consistent with the hypothesis that systemic NMDA exerts it reproductive effects not via an action on the circadian system, but via an action on secretion of GnRH. To investigate potential central sites of action of glutamate, induction of the immediate early gene c-fos, an acute marker of cellular response, was evaluated immunocytochemically (ICC) in brain areas after treatment with NMDA. Although dual-label ICC studies revealed that NMDA did not induce c-fos within GnRH neurons, NMDA did induce c-fos in many cells in the region of the organum vasculosum of the lamina terminalis (OVLT), an area containing a large number of GnRH perikarya, and in the arcuate nucleus, a region close to GnRH secretory terminals in the median eminence. The lack of c-fos induction of GnRH cells argues against a direct effect of NMDA on GnRH neurons. Thus, we examined immunocytochemically the distribution of the common NMDAR1 glutamate receptor subunit to evaluate further the potential sites of glutamatergic action. As expected, NMDAR1-ir was widespread in perikarya throughout the brain, including the region of the OVLT and the arcuate nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗
PubMed1994

Diurnal expression of Fos in luteinizing hormone-releasing hormone neurons of Syrian hamsters.

The aim of the present study was two-fold: first, to examine the temporal relationship between increased expression of Fos in LHRH neurons of proestrous hamsters and increased plasma levels of LH, FSH, estradiol-17 beta (E2), and progesterone (P4); and second, to establish whether male hamsters, like females, also show diurnal variations in the number of LHRH neurons expressing Fos. Blood samples were collected from proestrous females at 0900 n, 1200 h, 1500 h, and 1800 h and also from males at 0300 h, 0900 h, 1500 h, and 2100 h. RIA of the plasma revealed significant peaks of LH, FSH, and E2 at 1500 h, and of P4 at 1800 h in the females; a significant but smaller peak of LH also occurred at 1500 h in the males. Double-label immunocytochemistry, using antibodies directed against amino acids 127-152 of the human Fos protein and against LHRH, showed that female hamsters expressed Fos in fewer than 10% of their LHRH neurons during the morning and at noon of proestrus but in approximately 41% of these neurons during the late afternoon (1800 h). In contrast, no expression of Fos occurred in LHRH neurons of male hamsters at any time of the day. The finding that the females showed an increase in the number of LHRH neurons expressing Fos after, and not before, the initiation of the preovulatory gonadotropin surge is significant because it does not readily support the hypothesis that this expression of immediate-early genes is in some way associated with the induction of the surge. Instead, the results are consistent with the view that expression of Fos in LHRH neurons reflects either the activation of a mechanism responsible for terminating the surge or, alternatively, the activation of a compensatory mechanism responsible for replenishing depleted neuropeptide stocks.

Animals↗
PubMed1994

N-methyl-D-aspartate receptor gene expression in the hamster hypothalamus and in immortalized luteinizing hormone-releasing hormone neurones.

Although the excitatory amino acid (EAA) receptor agonist N-methyl-D-aspartate (NMDA) can exert profound stimulatory effects on the neuroendocrine reproductive axis of Syrian hamsters, the exact relationship between NMDA receptors and LHRH neurones is unclear. In the present study, in situ hybridization histochemistry was performed on sections of hamster brain using an 35S-labelled riboprobe to the EAA receptor gene, NMDAR1. A high content of NMDA receptor mRNA was detected not only in brain areas classically associated with specific NMDA binding (for example, hippocampus and cerebral cortex) but also in the hypothalamus, in particular the ventromedial-arcuate area; diffuse hybridization of the riboprobe also occurred in the medial-septal area and diagonal band of Broca, regions of the hamster brain in which the LHRH neuronal perikarya are primarily located. In a separate experiment, RNA was extracted from immortalized LHRH neurones (GT1-1 and GT1-7 cells) and used for northern analysis with a 32P-labelled NMDAR1 riboprobe. Clear-cut hybridization occurred with RNA bands of approximately 4.2 and 4.4 kb from the two LHRH neuronal subtypes. These findings suggest that at least some of the stimulatory action of EAAs on LHRH secretion is likely to be exerted directly at the level of the LHRH neurones rather than being mediated through interneurones. Furthermore, the demonstration of abundant NMDA receptor gene expression within hypothalamic areas that lie outside the blood-brain barrier adds plausibility to the concern that EAAs of dietary origin, such as monosodium glutamate, have the capacity to perturb the normal secretory activity of neuroendocrine circuits of the hypothalamus.

Animals↗
PubMed1993

Maturational changes in gonadotrophin secretion: the LH response to realimentation and a nocturnal increment in LH secretion of feed-restricted prepubertal gilts.

Potential maturational changes in patterns of LH secretion during feed restriction and the LH response to realimentation were examined. Ten sets of four growth-matched littermate gilts were fed ad libitum, to reach either 55, 65, 75 or 85 kg target body weights (one littermate per weight). Gilts were then maintenance fed for 8 days (days 1-8), and to appetite on day 9, and kept in a 9 h light (07:00-16:00 h):15 h dark photoperiod. Blood samples were obtained every 10 min from 07:00 to 16:00 h, and from 16:00 to 24:00 h on day 8 to evaluate any nocturnal rise in LH, and from 07:00 to 16:00 h on day 9 to evaluate the LH response to realimentation. Radioimmunoassays for LH, FSH, melatonin and oestradiol were performed on selected plasma samples. In all three sampling periods, LH and FSH secretion decreased as gilt weight increased, in a quadratic manner. During feed restriction, daytime LH, but not FSH, secretion was lower than at nighttime, irrespective of weight. Daytime LH secretion increased in response to realimentation, irrespective of weight. Plasma oestradiol concentrations were increased by feed restriction and decreased by realimentation but showed little relationship to gilt weight. No consistent relationship was established between plasma melatonin concentrations and ambient illumination. In conclusion, LH secretion exhibits a diurnal rhythm during feed restriction in the prepubertal gilt and, in a similar way to FSH, decreases as puberty is approached. The plane of nutrition influences circulating oestrogen concentrations. The increase of LH secretion following realimentation is not influenced by maturation over the prepubertal period.

Animals↗
PubMed1993

Influence of N-methyl-D-aspartate on the reproductive axis of male Syrian hamsters.

The influence of excitatory amino acids (EAAs) on reproductive neuroendocrine function was investigated in adult male Syrian hamsters of the LSH/Ss Lak strain. Before the study, the animals were maintained in a sexually regressed condition, under short days (SD) and subsequently were either transferred to long days (LD) or kept under SD, for a further 4 weeks. In the former group, photostimulation produced a predictable elevation in the hypophysial contents and serum concentrations of FSH and LH. This was accompanied by an increase in testicular size, an elevation in serum testosterone levels and an increase in spermatogenic activity; the SD hamsters remained sexually quiescent throughout the study. In contrast, SD hamsters that were given daily injections of the EAA agonist, N-methyl-D,L-aspartate (NMA; 50 mg/kg body weight, s.c.), showed stimulatory responses that were generally even more pronounced than those shown by the LD group. Surprisingly, an identical NMA treatment paradigm failed to cause a similar activation of the reproductive axis in LD hamsters that were given daily afternoon injections of melatonin (25 micrograms, s.c.), even though the inhibitory effect of this melatonin treatment is generally regarded as being comparable with that produced by exposure to SD. Although EAAs can acutely stimulate the neurocircuitry that controls LH-releasing hormone secretion, the present findings suggest that EAAs might also exert a long-term stimulatory action by acting further upstream in the photoneuroendocrine pathway.

Animals↗
PubMed1992

Maturation of the hypothalamo-pituitary-gonadal axis of male Syrian hamsters.

Light-microscope immunocytochemistry (ICC) was used to investigate postnatal changes in the morphology of LHRH neurons in the brains of male Syrian hamsters and to relate these changes to more overt maturational developments within the hypothalamo-pituitary-gonadal axis. The animals were maintained under long-day photoperiods (14L:10D), and groups of 6-7 were killed at 10-day intervals from Day 15 to Day 65. Their brains were fixed with 4% paraformaldehyde, sectioned sagittally with a vibratome (75 microns), and processed for ICC using monoclonal LHRH antibody HU4H. Throughout the study period, the hamsters showed a progressive increase in plasma gonadotropin levels, closely followed by an increase in testicular weight and plasma testosterone levels. Histology of the testes revealed that spermatogenesis was already qualitatively completed by Day 35 and quantitative aspects were established by Day 45. Within the brain, LHRH neuronal perikarya were distributed primarily in the medial septal-preoptic area and the diagonal band of Broca; morphologically, these immunopositive neurons were either monopolar or bipolar. The total number of LHRH neurons detected in the areas examined was approximately 440 throughout the developmental period, and the relative proportions of monopolar and bipolar subtypes (86% and 14%, respectively) remained unchanged. In contrast, the area of the perikarya, as determined by autoimage analysis, showed a highly significant age-related increase, both for the monopolar and bipolar neurons. It is suggested that these developmental changes in the LHRH neurons reflect an increase in LHRH synthesis and may, therefore, provide a neuroendocrine trigger for the onset of puberty.

Animals↗
PubMed1992

Photoperiodic modulation of luteinizing hormone secretion in orchidectomized Syrian hamsters and the influence of excitatory amino acids.

The effect of N-methyl-D,L-aspartate (NMA) on LH secretion was investigated in Syrian hamsters of the LSH/Ss Lak strain, maintained under either long days (14 h of light, 10 h of darkness) or short days (6 h of light, 18 h of darkness). After 6 weeks of photoperiodic treatment, the animals were orchidectomized. Ten days later, 10-min blood samples were remotely collected from each animal, using surgically implanted intraatrial catheters, and individual pulsatile LH release profiles were subsequently determined by RIA. At the end of the 4-h sampling period, NMA was administered iv (30 mg/kg BW), and the LH response was determined in the next three plasma samples. Hamsters maintained under long days had very high mean plasma LH levels (453 +/- 46 ng/ml) and displayed episodic release patterns characterized by high amplitude pulses. In marked contrast, hamsters that were maintained under short days had significantly (P less than 0.001) lower mean plasma LH levels (90 +/- 12 ng/ml) and showed a significantly (P less than 0.001) lower mean pulse amplitude. The interpulse interval was similar in both of the groups, with LH peaks occurring, on the average, once every 65 min. When challenged with NMA, the long-day hamsters showed only a 37% increase in mean plasma LH levels, which was not statistically significant. In contrast, the short-day hamsters showed a highly significant (P less than 0.01) increase of 294%. Interestingly, the mean plasma LH levels after NMA administration were the same in the two photoperiodic groups despite a marked difference in the plasma levels that preceded the administration. These findings demonstrate that short days can inhibit the neuroendocrine activity of the hamster's reproductive axis independently of gonadal influences. They also suggest that the LHRH neurons have an intrinsic capacity to secrete very high levels of the neuropeptide, regardless of the photoperiod. Taken together, the results support the hypothesis that the breeding season in the hamster is regulated by a gonad-independent mechanism involving a photoperiodic modulation of neuroexcitatory inputs to the LHRH neurons.

Amino Acids↗
PubMed1991

Monoclonal antibodies to luteinizing hormone-releasing hormone: production, characterization, and immunocytochemical application.

Luteinizing hormone-releasing hormone (LHRH) was conjugated to bovine thyroglobulin and used to immunize a BALB/c mouse. Spleen lymphocytes were subsequently fused to SP2/0 myeloma cells and two of the resulting hybridoma clones were found to produce high titer antibodies to LHRH (HU4H and HU11B); both belonged to the IgG1 subclass. Characterization of the monoclonal antibodies revealed that HU4H and HU11B have conformational and sequential specificity to LHRH, respectively, and that neither one shows significant immunoactivity with pro-LHRH. The value of these antibodies in immunocytochemical applications is demonstrated by their ability to cause intense specific staining of LHRH neuronal cell bodies and fibers in brain sections from several mammalian species.

Amino Acid Sequence↗
PubMed1991

Immunocytochemical investigation of luteinizing hormone-releasing hormone neurons in Syrian hamsters maintained under long or short days.

Light-microscope immunocytochemistry was used to investigate the LHRH system of adult male Syrian hamsters. Half of the animals were transferred from long to short photoperiods (14L:10D to 6L:18D) for 10 wk, causing plasma gonadotropin levels and the testes to revert to a prepubertal condition. In spite of the marked differences in the reproductive axis between the two groups of hamsters, the number of immunopositive LHRH neurons observed in the preoptic-medial septal area and diagonal band of Broca was approximately 400 in both cases; of these, 87-91% were monopolar and 9-13% were bipolar, regardless of whether the brains were sectioned in a coronal or sagittal plane. These results, therefore, fail to support the hypothesis that photoperiodic changes in the number of LHRH neurons play a major role in controlling the seasonal regression and recrudescence of the reproductive system in the hamster. However, morphometric analysis of the perikarya using an IBAS 2000 automatic image analyzer revealed a photoperiod-related difference. Surprisingly, the perikarya of both monopolar and bipolar LHRH neurons were significantly larger in hamsters that had been maintained on short days, as opposed to long days. These findings, therefore, are in harmony with the view that the inhibitory effect of short days on the reproductive axis is mediated through a suppression of LHRH secretion, which in turn is reflected as an increase in the net content of LHRH within the brain.

Animals↗
PubMed1990

Involvement of transforming growth factor alpha in the release of luteinizing hormone-releasing hormone from the developing female hypothalamus.

Little is known about the presence of trophic factors in the hypothalamus and the role they may play in regulating the functional development of hypothalamic neurons. We have investigated the ability of epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha) to affect the release of luteinizing hormone-releasing hormone (LHRH), the neuropeptide that controls reproductive development. We have also determined whether the genes encoding EGF and TGF-alpha are expressed in the prepubertal female hypothalamus. Northern blot analysis of poly(A)+ RNA utilizing a single-stranded EGF cDNA probe failed to reveal the presence of EGF mRNA in either the hypothalamus or the cerebral cortex at any age studied (fetal day 18 to postnatal day 36). In contrast, both a complementary RNA probe and a double-stranded TGF-alpha cDNA recognized in these regions a 4.5-kilobase (kb) mRNA species identical to TGF-alpha mRNA. The abundance of TGF-alpha mRNA was 3-4 times greater in the hypothalamus than in the cerebral cortex. Both EGF and TGF-alpha (2-100 ng/ml) elicited a dose-related increase in LHRH release from the median eminence of juvenile rats in vitro. They also enhanced prostaglandin E2 (PGE2) release. The transforming growth factors TGF-beta 1 and -beta 2 were ineffective. Only a high dose of basic fibroblast growth factor was able to increase LHRH and PGE2 release. Blockade of the EGF receptor transduction mechanism with RG 50864, a selective inhibitor of EGF receptor tyrosine kinase activity, prevented the effect of both EGF and TGF-alpha on LHRH and PGE2 release but failed to inhibit the stimulatory effect of PGE2 on LHRH release. Inhibition of prostaglandin synthesis abolished the effect of TGF-alpha on LHRH, indicating that PGE2 mediates TGF-alpha-induced LHRH release. The results indicate that the effect of EGF and TGF-alpha on LHRH release is mediated by the EGF/TGF-alpha receptor and suggest that TGF-alpha rather than EGF may be the physiological ligand for this interaction. Since in the central nervous system most EGF/TGF-alpha receptors are located on glial cells, the results also raise the possibility that--at the median eminence--TGF-alpha action may involve a glial-neuronal interaction, a mechanism by which the trophic factor first stimulates PGE2 release from glial cells, and then PGE2 elicits LHRH from the neuronal terminals.

Aging↗
PubMed1990

A role for N-methyl-D-aspartate (NMDA) receptors in the control of LH secretion and initiation of female puberty.

The physiological role of N-methyl-D-aspartate (NMDA) receptors in controlling LH secretion and the initiation of puberty was investigated using two specific antagonists, MK-801 and DL-2-amino-5-phosphono valeric acid (AP-5). Single daily sc injections of MK-801 (0.1-0.2 mg/kg BW), a noncompetitive NMDA receptor antagonist, given to prepubertal rats significantly delayed but did not prevent the timing of puberty, as determined by the age at vaginal opening and first ovulation. Infusion of MK-801 (5 micrograms/h) via osmotic minipumps for 4 days inhibited the postovariectomy rise of LH secretion in prepubertal rats. Both MK-801 (0.2 mg/kg BW, sc) and AP-5 (4 x 30 mg, iv), a competitive NMDA receptor antagonist, blocked the estradiol-induced LH surge in prepubertal ovariectomized rats. These results demonstrate that blockade of NMDA receptors can prevent the development of enhanced LH secretion in female rats undergoing sexual maturation. Moreover, they support the view that activation of NMDA receptors significantly contributes to the physiological initiation of the pubertal process.

2-Amino-5-phosphonovalerate↗
PubMed1990

A role for N-methyl-D-aspartate receptors in the control of seasonal breeding.

The neuroendocrine basis for short-day induced testicular regression was studied in Syrian hamsters of the LSH/Ss Lak strain. Adult animals were maintained either under long or short days (14:10D or 6L:18D, respectively) and given single, daily ip injections of N-methyl-D-aspartate (NMDA) (25 mg/kg BW); control animals received injections of saline. As expected, the testes of the short-day controls had completely regressed to a prepubertal condition within 6 weeks, a change that was associated with significantly reduced mean plasma gonadotropin levels. In contrast, the NMDA-treated hamsters from both the long-day and short-day groups, as well as the long-day controls, all maintained large testes and elevated plasma gonadotropin levels, although plasma luteinizing hormone (LH) was partially suppressed in the short-day group. In a second experiment which lasted 2 weeks, short-day hamsters with completely regressed testes were either transferred to long days, maintained further on short days, or maintained on short days and given a daily ip injection of NMDA (25 mg/kg BW). The short-term exposure to long days caused an expected increase in plasma and pituitary concentrations of follicle-stimulating hormone, pituitary LH, and testicular weight. Similar, but even more marked, changes were observed in the short-day hamsters that were treated with NMDA, including significant increases in plasma LH and serum testosterone concentrations. Moreover, histological examination revealed that the recrudescing testes from this latter group already contained mature spermatocytes and in some individuals even spermatozoa. These results demonstrate that NMDA receptors may play a pivotal role in both the termination and onset of the breeding season in photoperiodic species.

Animals↗
PubMed1990

Influence of photoperiod and 6-methoxybenzoxazolinone on the reproductive axis of inbred LSH/Ss Lak male hamsters.

Adult male Syrian hamsters of the inbred LSH/Ss Lak strain were maintained under a 14L:10D light cycle until 13 weeks of age. At this point, they were implanted s.c. with elastomer capsules that were either empty or packed with 30-40 mg of 6-methoxybenzoxazolinone (6-MBOA), a compound found naturally in some monocotyledonous plants; half of the animals from each treatment group were then kept in long days (14L:10D) or transferred to short days (9L:15D). Testicular size was measured and blood samples collected from each hamster immediately before capsule implantation and again 2, 4, 6 and 8 weeks later. Within just 2 weeks of exposure to short days the mean plasma levels of LH and FSH had significantly declined, in both the control and 6-MBOA-treated animals, and were basal within 4 weeks. Testicular size closely followed these gonadotrophin changes; within 4-6 weeks the testes from all of the short-day hamsters had completely regressed to a prepubertal size. At the end of the experiment, at Week 8, the animals were killed and various components of the hypothalamo-pituitary-testicular axis were compared between the treatment groups. The pituitary content of FSH and LH, testicular weight, mean serum level of testosterone, but not hypothalamic LHRH content or pituitary gland weight, were considerably lower in the short-day than in the long-day hamsters, regardless of whether or not they had been chronically treated with 6-MBOA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗