Biomedical subjects

M J Gibson

Publications and source records attributed to M J Gibson.

At least 37 records · Page 2Linked to original sources

PubMed1997

Gonadotropin-releasing hormone axons target the median eminence: in vitro evidence for diffusible chemoattractive signals from the mediobasal hypothalamus.

The projection of GnRH neurons to the median eminence of the medial basal hypothalamus (MBH) is established early in development and is also seen when preoptic area-derived GnRH cell-containing grafts are placed in the third ventricle of hypogonadal mice. To further study the factors directing GnRH axonal targeting, we cultivated embryonic or postnatal day 1 preoptic area with a coexplant on collagen- and laminin-coated membranes in insert chambers. After 7 days of culture, GnRH-immunoreactive fibers extended significantly farther and in greater number onto the sector of membrane facing a MBH coexplant than in the opposite sector, but not toward coexplants of control tissue. Moreover, such effects were specific, as outgrowth of a general axonal population, immunoreactive for growth-associated protein 43 was not influenced by the presence of the MBH. Preferential GnRH outgrowth toward the MBH was established early and was maintained during 10 days of culture. The importance of substrate-derived guidance was also assessed with confocal microscopy. GnRH axons consistently traveled in the company of growth-associated protein 43-labeled axons, but only erratic associations were seen between GnRH and glial processes extending on the membrane. We suggest that although employing an axonal substrate, GnRH axons follow a diffusible chemoattractive signal(s) secreted by the MBH.

Animals↗

PubMed1996

FOS expression in grafted gonadotropin-releasing hormone neurons in hypogonadal mouse: mating and steroid induction.

We used FOS expression, widely accepted as a marker for neuronal activation, to evaluate physiologically induced activation of gonadotropin-releasing hormone (GnRH) neurons within intraventricular preoptic area grafts in hypogonadal (hpg) female mice. Hpg mice lack endogenous GnRH due to a mutated gene, but can respond to grafted GnRH neurons with reproductive development. The purpose of this study was to determine the degree to which the host brain regulates grafted GnRH neurons. FOS expression in grafted GnRH neurons was induced in progesterone-primed female mice paired with sexually active males. The degree of sexual activity did not affect the outcome, with 40.9 +/- 12.2% of the grafted GnRH cells expressing FOS when male partners performed intromissions, and 47.5 +/- 10.2% when they also ejaculated. There was little or no FOS expression in the grafts of unprimed hpg mice paired with sexually active males, in unpaired mice primed with progesterone or sequential estradiol benzoate and progesterone, or in controls. The pattern of FOS expression in the brains of the female hpg mice engaged in mating behavior was similar to that reported in other species, with moderate to high expression in the medial preoptic area, ventromedial nucleus, and medial amygdala in females paired with males that ejaculated. The present results support the hypothesis that host-derived activation of grafted GnRH neurons underlies aspects of reproductive responses seen in hpg mice with grafts, and further, that at least a portion of the host-graft connectivity is steroid sensitive.

Animals↗

PubMed1995

Neuromodulation of transplanted gonadotropin-releasing hormone neurons in male and female hypogonadal mice with preoptic area brain grafts.

Implantation of normal preoptic area (POA) tissue into the third ventricle of adult hypogonadal (HPG) mice provides a source of GnRH neurons that innervate the host median eminence and stimulate reproductive development in the sterile mutants. To further evaluate graft-host integration, the effects of N-methyl-D,L-aspartic acid (NMA) and opiate antagonists on LH secretion in HPG mice with POA transplants (HPG/POA) were tested. NMA challenges significantly stimulated LH secretion in 10 of 11 HPG/POA females. Only 5 of 12 HPG/POA males responded to the same treatment. Administration of the opiate antagonists naloxone or naloxone methiodide was ineffective in stimulating LH release in any mice, but opiate antagonist pretreatment significantly potentiated the LH secretory response to NMA in female, but not male, HPG/POA mice. A potential anatomical substrate for this facilitation may be the beta-endorphin-immunoreactive innervation of the POA grafts in all HPG/POA brains examined. beta-Endorphin fibers were also present in the median eminence in the vicinity of GnRH outgrowth from the grafts. However, similar innervation patterns in HPG/POA males that did not respond to opioid antagonism suggests that this is not sufficient. We tested whether the sex difference in HPG/POA responsivity to neuromodulation is related to the steroid milieu in the hosts. 17 beta-Estradiol (E2) treatment facilitated the LH secretory response of male HPG/POA to NMA challenges whether animals were castrated and given an E2 capsule prior to graft implantation or one week before testing two months after graft surgery. Intact or vehicle (sesame oil)-treated, castrated HPG/POA males rarely responded to NMA challenges, yet graft-derived GnRH innervation of the hosts' median eminence was comparable in all treatment groups. GnRH challenge testing indicated that pituitary sensitivity of the HPG/POA males was not significantly altered by E2 treatment, suggesting that estrogen acted centrally. These results indicate that the activity of grafted GnRH neurons may be modulated by endogenous opioids of host origin as well as by the hormonal milieu.

Animals↗

PubMed1995

Gonadotropin-releasing hormone (GnRH) neurons of the developing tectum of the mouse.

Using a modified immunocytochemistry protocol with enhanced sensitivity, we were able to visualize a population of neurons in the tectum of the developing mouse that contained GnRH-like immunoreactivity. In microscopic studies conducted using 100 microns sections cut in sagittal or horizontal planes, 10-20 lightly-stained neurons were first detected in the tectum at E13.75 (morning of plug = E0.5). The number of immunostained cells increased exponentially reaching a peak at E15.75 before decreasing in number. No positive neurons were seen in the tectum at PN20 or later. The GnRH cells were located medially along the dorso-ventral axis of the tectum in a region of the brain distinct from that containing GnRH neurons that migrate into the CNS from the olfactory placode. To determine the nature of the immunoreactivity, two approaches were used. Analysis of tissue from an hpg mutant strongly supports the hypothesis that these cells make mammalian GnRH. Immunocytochemical data suggest that although the precursor protein is synthesized, the cleaved and amidated decapeptide may be absent or be present at an undetectable level. Our results demonstrate that in addition to the GnRH neurons from the placade, a population of GnRH neurons exists in the mouse tectum. This population is developmentally regulated, appearing only during embryonic and early postnatal ages but not in the adult.

Aging↗

PubMed1994

Continuous gonadotropin-releasing hormone infusion stimulates dramatic gonadal development in hypogonadal female mice.

Adult hypogonadal (hpg) mice, lacking GnRH, have infantile reproductive systems and levels of pituitary gonadotropins that are lower than normal. The mutant mice respond to brain grafts containing GnRH neurons with gonadal development and increased production of gonadotropins. In view of the substantial literature regarding the nature and necessity of pulsatile GnRH stimulation of gonadotropins, we were not surprised in earlier studies to find that the majority of hpg mice with successful grafts have pulsatile LH secretion. It is not known, however, why LH pulsatility was undetectable in some animals with significant gonadal development. The present experiment was intended to determine the degree to which hpg mice respond to continuous infusion of GnRH via osmotic minipumps. Unexpectedly, female hpg mice exhibited dramatic ovarian and uterine growth after 15 or 30 days of continuous exposure to GnRH, with five- and eightfold increases in ovarian and uterine weights, respectively. Despite evidence of increased gonadotropin secretion in the treated hpg mice, pituitary stores of FSH and LH remained low. Similar treatment of normal female mice for 15 days also depleted pituitary concentrations of LH and FSH without significantly altering gonadal weights or plasma gonadotropin levels. It is clear from the present that inferences of pulsatile GnRH secretion based on stimulation of gonadal development in hpg mice should be made with caution.

Animals↗

PubMed1994

Opioidergic modulation of N-methyl-D,L-aspartic-acid-stimulated LH release in young adult but not older male mice.

Among the neuromodulators of the GnRH neuronal system are the endogenous opioid peptides and the excitatory amino acids. Although the opioid antagonist naloxone (NAL) induces LH secretion in many species, there are no reports of an effect of NAL on LH release in mice. Our previous studies demonstrated that the excitatory amino acid analog N-methyl-D,L-aspartic acid (NMA) stimulates LH release in mice and suggested that NMA-induced LH release is mediated via afferents to GnRH neurons. In the current study, the role of the endogenous opioid system in the regulation of LH release in adult male mice was assessed by testing whether this system is a component of the NMA-stimulated LH response. NAL, its quaternary derivative NAL methiodide (which remains outside of the blood-brain barrier) and saline (SAL) were administered alone and in combination with NMA via intravenous catheters. Although neither opioid antagonist stimulated LH release when administered alone, each significantly potentiated the LH response to NMA in young adult (10- to 14-week-old) male mice (p < 0.01) but not in older (10- to 16-month-old) male mice. The equivalent action of the two ipioid blockers suggested an action outside of the blood-brain barrier. To determine whether opioid blockade altered pituitary sensitivity to GnRH, a dose response for exogenously administered GnRH was first determined, and low and high doses of GnRH were tested in combination with NAL or SAL. Neither treatment was effective in altering the LH response to GnRH, indicating that the action of the opioid antagonists was at a suprapituitary location. (ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1993

Gonadotropin-releasing hormone (GnRH) neurons in the hypogonadal mouse elaborate normal projections despite their biosynthetic deficiency.

This study was undertaken to determine whether gonadotropin-releasing hormone (GnRH) neurons in the mutant hypogonadal (hpg) mouse can establish axonal connections with their target despite their failure to synthesize and secrete the GnRH neuropeptide. Normal and hpg males received intraperitoneal injections of the retrograde tracer Fluoro-Gold. This tracer does not cross the blood-brain-barrier and hence is taken up only by neurons in the central nervous system whose axons terminate on fenestrated capillaries, such as the capillaries of the median eminence. The brains of the injected animals were processed for in situ hybridization to visualize GnRH transcribing cells. In 3 hpg males 64.1 +/- 5.6% of GnRH transcribing cells contained Fluoro-Gold, while 55.8 +/- 6.4% of the cells in 3 normal males had Fluoro-Gold. Thus, we have demonstrated that secretory-deficient GnRH neurons can establish axonal connections with their primary secretory target, the median eminence. We conclude that the capability of GnRH neurons to recognize and interact with their target is not dependent upon their neurosecretory function.

Animals↗

PubMed1993

Biochemical differentiation and intercellular interactions of migratory gonadotropin-releasing hormone (GnRH) cells in the mouse.

GnRH cells are first detected in the olfactory placode of the mouse on Gestational Day 11.5 (E11.5). Between E12.5 and E15.5 they migrate across the nasal septum and by E16.5 attain their adult distribution within the forebrain. In the present study, we used immunocytochemistry at the light and electron microscopic level to study the biochemical and morphological differentiation of gonadotropin-releasing hormone (GnRH) neurons and the cellular associations that they make during this migratory process. On E12.5, when the majority of GnRH cells are still in the nasal septum, only 15% of the population can process the pro-GnRH precursor to the amidated decapeptide. Two days later (E14.5), when most of the cells have advanced into the forebrain, 79% contain mature GnRH. In keeping with these light microscopic observations, ultrastructural analysis reveals that on E12.5 GnRH immunologic reaction product is confined to the outer nuclear envelope and rough endoplasmic reticulum. By E14.5 these migratory cells in the nasal septum have more reaction product in the rough endoplasmic reticulum and some of the Golgi cisternae are also immunopositive. Neurosecretory granules, some of which are immunoreactive, also appear at this stage. We had anticipated that the expression of GAP-43 would coincide with axonal elongation and pathfinding in GnRH neurons. Instead, GAP-43 was expressed at the early migratory stage of GnRH cells and its expression declined rapidly after these neurons had entered the forebrain and commenced axonal outgrowth. Hence, on E12.5, 62.3% of GnRH cells in the nasal septum are immunopositive for GAP-43, while only 12.6% of the forebrain population at the same embryonic stages express the protein. Similarly, on E14.5 GAP-43 is expressed in 50.7% of the nasal septum GnRH cells but only 11.6% of cells in the E14.5 forebrain express this protein. While in the nasal septum, GnRH neurons migrate only within the confines of the olfactory and vomeronasal axonal fascicles. During this part of the migratory route, the cells maintain close membrane apposition with each other and with the axons and ensheathing glia of the nerve fascicles. Once in the forebrain, GnRH neurons no longer maintain these associations, nor do they follow any defined anatomical structure. These findings indicate that although GnRH cells express their unique neuropeptide early in their ontogeny, their differentiation continues and is coordinated with their migration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Intrahypothalamic injection of a cell line secreting gonadotropin-releasing hormone results in cellular differentiation and reversal of hypogonadism in mutant mice.

GT1 is an immortalized cell line that synthesizes and secretes the neurohormone gonadotropin-releasing hormone (GnRH). We have placed these cells into the brains of adult mutant hypogonadal (hpg) mice, which lack a functional GnRH gene, to determine whether such cells could differentiate in situ and support gonadal development. Immunocytochemical detection of GnRH revealed that these cells migrated widely in the central nervous system and elaborated axonal processes which on rare occasion projected to the normal target, the median eminence. Using a battery of antibodies, we demonstrated that these cells could cleave the GnRH precursor and that the amidated decapeptide as well as other cleavage products were present. The presence of biologically active material and its appropriate secretion were further documented by gonadal growth in both males and females. The morphological differentiation of the GT1 cells correlated with the density of cells injected. Those remaining within the injection site and/or forming a tumor retained a simple, rounded or fibroblastic appearance. Those cells that migrated into the host away from such tumors assumed the simple fusiform shape of normal GnRH neurons with dendrites extending from one or both poles. When cell density was drastically reduced a much more complex dendritic arbor was elaborated. These data suggest that such cell lines can be useful in reversing genetic defects and in studying such processes as GnRH neuronal migration, axonal targeting, and cytological differentiation.

Animals↗

PubMed1992

Brain grafts of migratory GnRH cells induce gonadal recovery in hypogonadal (hpg) mice.

Gonadotropin-releasing hormone (GnRH) neurons are derived from the olfactory placode and migrate into the CNS during embryogenesis. During this migration the GnRH neuronal population follows a very specific pathway through the nasal septum and forebrain with individual neurons 'stopping' at various points along the way. Following migration GnRH neurons elaborate axonal projections, the major one to the median eminence. The function of this neurosecretory connection can then be assessed by activation of the pituitary-gonadal axis. In previous experiments we had demonstrated that grafted post-migratory GnRH neurons could send axons to the median eminence and initiate gonadal development in hypogonadal (hpg) mice that lack GnRH. In the present experiment, grafts derived from the embryonic nasal septum, which contains the migratory population of GnRH neurons, were used to determine if the transplanted GnRH neurons could (1) continue their migration in the adult host brain, (2) elaborate axons to their normal target in the host and (3) stimulate the host pituitary-gonadal axis to induce gonadal development. Nasal tissue from normal mouse embryos was implanted into the preoptic area (n = 8), anterior hypothalamus (n = 3) or third ventricle (n = 1) of adult hpg males. Following survival of 10 days to 10 weeks, the distribution of GnRH immunoreactive elements was assessed and testicular weight recorded. Surviving GnRH neurons were few in number and were found within the graft (n = 3), the host brain (n = 2) or both (n = 1). Four grafts resulted in specific outgrowth of GnRH axons through the host parenchyma to the median eminence.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Application of a fluorescent dye to study connectivity between third ventricular preoptic area grafts and host hypothalamus.

The mutant hypogonadal (hpg) mouse lacks a functioning gene for the neurohormone gonadotropin releasing hormone (GnRH). Previous studies from our laboratory had indicated that the initiation and maintenance of reproductive function in these mice could be brought about by the implantation of normal fetal grafts into adult hosts. Testicular or ovarian growth and other indicators of normal neurosecretory output were always accompanied by survival of GnRH neurons and growth of GnRH axons into the host median eminence where such axons terminate on the hypophysial portal capillaries. To determine if other connections exist between graft and the host hypothalamus, small crystals of the carbocyanine dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI) were applied to either graft or host after fixation of the brain. Tissue sections were analyzed for retrograde and and anterograde movement of the dye. When crystals were placed on the graft, labeled axons were found in the host median eminence or in the host hypothalamus taking an arching trajectory toward the median eminence. Retrogradely labeled neurons in the host were few in number and largely confined to the host arcuate nucleus. With DiI crystals applied to the basal hypothalamus, labeled axons were distributed widely in the host but much sparser in the graft. Axons appeared to enter primarily at sites where the graft and host interface lacked an ependymal lining. Small numbers of retrogradely labeled neurons were also seen in the graft. Most were cells of very simple morphology and were distributed randomly in the graft. When double label experiments were carried out most DiI positive cells in the graft contained GnRH. These results indicate the connectivity between host hypothalamus and the third ventricular preoptic area grafts exists but is limited in nature.

Afferent Pathways↗

PubMed1992

Targeting of gonadotropin-releasing hormone axons from preoptic area grafts to the median eminence.

Implantation of normal GnRH neurons can reverse many of the reproductive deficiencies that characterize hypogonadal (hpg) mice. Since the GnRH axons follow a stereotyped trajectory to their target we investigated the possibility that host brain regions adjacent to the graft might provide signals that induced this directional growth. The role of the adenohypophysis in GnRH axonal outgrowth was studied in mice with co-grafts of fetal preoptic area (POA) and pituitary and in hypophysectomized hosts. When fetal pituitaries were grafted together with the POA, immunoreactive GnRH fibers did enter the glandular tissue but they also grew into the host median eminence. Surgical removal of the pituitary of hpg hosts prior to POA graft placement was also compatible with GnRH innervation of the host median eminence although in some individuals that innervation pattern was confined to the more caudal aspects. The results of these two experiments suggest that the anterior pituitary gland may be an attractive target for GnRH axons but that this tissue is not essential for directed GnRH axonal outgrowth to its target. To determine if the median eminence itself could direct the growth of GnRH axons, co-grafts of POA and a fetal medial basal hypothalamic (MBH) block, which was predominantly median eminence, were made. Immunocytochemistry showed that an intragraft mini-median eminence was formed with a highly organized and robust GnRH innervation. Ultrastructural analysis indicated that these axons terminated near fenestrated capillaries. However, even under these conditions some GnRH axons exited into the host median eminence. It now seems likely that a cellular component of the median eminence can provide a signal to attract GnRH axons. Whether this signal is produced by the specialized ependymal cells, by the endothelia, or by meningeal (pial) components must now be tested.

Animals↗

PubMed1992

Reversal of reproductive deficiency in the hpg male mouse by neonatal androgenization.

Some aspects of reproductive function in the GnRH-deficient hypogonadal (hpg) mutant mouse can be restored by transplanting normal fetal brain tissue containing GnRH cells into the central nervous system of adult hpg mice. However, hpg males showing physiological response to the graft fail to display sexual behavior and are infertile. We hypothesized that the reproductive deficit of these males is due to insufficient perinatal exposure to testicular androgens as a consequence of the GnRH deficiency. To test this hypothesis we androgenized hpg males by giving them neonatal injections of testosterone propionate (TP). Controls consisted of hpg males not androgenized neonatally and of normal males. All three groups received a TP implant in adulthood, and their copulatory behavior and reproductive capability were recorded. In addition, other hpg males, not androgenized neonatally, received fetal brain transplants containing GnRH neurons and were also tested for copulatory behavior and reproductive capability before and after receiving a TP implant. Three of 8 neonatally androgenized hpg males expressed the full repertoire of male sexual behavior, including intromission and ejaculation, and sired several litters. Three of 7 control hpg males that were not androgenized neonatally but received TP implants in adulthood also displayed mounting and intromission, but there was no evidence of ejaculation, and these males failed to impregnate normal females. Of the 8 hpg males that responded to a fetal transplant with testicular growth, only 1 displayed mounting behavior. However, when given a TP implant, 4 of 8 hpg males with grafts displayed mounting and intromissions.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗

PubMed1992

FOS expression in gonadotropin-releasing hormone neurons: enhancement by steroid treatment and mating.

Expression of the protooncoprotein FOS is now widely believed to be a marker for neuronal activation. In female rats, a steroid-induced LH surge is accompanied by an increase in FOS-positive GnRH neurons, especially in the region of the organum vasculosum of the lamina terminalis. The present study, conducted in mice, has examined the effects of both steroid hormone treatment and sexual behavior on the expression of FOS in GnRH neurons and their distribution in the central nervous system. Thirty-three ovariectomized mice, each bearing a sc priming capsule of 17 beta-estradiol, were divided into five groups, four of which were treated sequentially with estradiol benzoate (1 microgram) and progesterone (500 micrograms). In females maintained on 17 beta-estradiol only and killed between 1400-1530 h, only 1.3 +/- 0.7% of GnRH neurons contained FOS, while treatment with estradiol benzoate/progesterone increased FOS expression significantly to 31.7 +/- 8.5% in the same time period. In animals killed at 1530-1700 h, FOS expression declined in the absence of a male (13.8 +/- 2.2%) or when the male present in the cage displayed some sexual behavior but did not ejaculate (13.0 +/- 8.6%). Interestingly, the expression of FOS was maintained at a high level (42.3 +/- 11.4%) into the late afternoon in females paired with a reproductively successful (ejaculating) male. There was a positive correlation (r2 = 0.65; P < 0.01) between the level of LH and the number of FOS-positive GnRH neurons. Hence, the expression of FOS in GnRH neurons was enhanced by both a steroid regimen leading to a LH surge and an intense level of mating behavior. Mapping of the GnRH neurons indicates that in animals with the highest level of FOS expression, FOS-positive GnRH neurons were not confined to the region of the organum vasculosum of the lamina terminalis, but were found more widely distributed along the entire rostro-caudal axis of these cells.

Animals↗

PubMed1991

Norepinephrine neurons in mouse locus coeruleus express c-fos protein after N-methyl-D,L-aspartic acid (NMDA) treatment: relation to LH release.

In mouse, rat, and monkey, N-methyl-D,L-aspartic acid (NMDA) modulates gonadotropin releasing hormone (GnRH) release by an unknown mechanism. In previous studies we found that normal male mice consistently responded to NMDA administration with increased levels of plasma LH, as did most normal female mice and female hypogonadal mice with fetal preoptic area implants (HPG/POA). To investigate the mechanism of NMDA-induced GnRH release, immunocytochemistry of c-fos protein (FOS) was used for detection of neurons activated by NMDA administration. In both normal male and HPG/POA mice, FOS expression was unchanged in GnRH cells after NMDA administration. That neurosecretory cells can respond to NMDA was shown by the induction of FOS in many CRH (corticotropin-releasing hormone) cells in the paraventricular nucleus. Immunocytochemistry of beta-Endorphin, neuropeptide Y, tyrosine hydroxylase, an enzyme marker for catecholaminergic neurons, and glutamic acid decarboxylase, an enzyme marker for GABA neurons, was combined with that for FOS in normal male mice. Many noradrenergic (NA) neurons in the locus coeruleus (32-61%), and dopaminergic (DA) neurons in the mediobasal hypothalamus (15-31%) expressed FOS after NMDA administration while FOS was only rarely induced in neurons with the other neuromodulators tested. FOS was also induced in the locus coeruleus in male (43, 54%) and female (40, 55, 69%) HPG/POA mice. In contrast, few cells of the locus coeruleus expressed FOS in normal or HPG/POA mice after saline challenge. These results suggested that NMDA did not activate GnRH cells directly, but that NA neurons in the locus coeruleus were activated by NMDA and might be involved in stimulating GnRH release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Relationship of glia to GnRH axonal outgrowth from third ventricular grafts in hpg hosts.

The homozygous mutant hypogonadal (hpg) mouse lacks a functional gene for the neuropeptide gonadotropin releasing hormone (GnRH). The consequence of this defect is an infantile reproductive tract in adulthood. This condition can be reversed by the implantation of normal fetal preoptic area tissue that contains GnRH neurons. Reversal is always preceded by the outgrowth of GnRH axons into the host target tissue, the median eminence, by a stereotyped pathway. In the current experiments we investigated the cellular nature of the path taken by early emerging GnRH axons focusing on their relationship with astrocytic components and with the specialized ependymal population of this area, the tanycytes. In control tissue glial fibrillary acid protein (GFAP) immunoreactivity was confined to the exterior of cerebral blood vessels and glial limitans. Both GFAP and vimentin, another intermediate filament protein, marked the specialized ependymal cells of this region, the tanycytes. There was a robust reactive astrocytic response to the injury of transplantation in both the donor and host tissue within 5 days of implantation and the reactive astrocytes persisted for 60 days. These cells were GFAP-positive and were present in many areas of the host along the cannula tract and not confined to the area of GnRH axonal outgrowth. Vimentin, another intermediate filament, marked only the specialized ependymal cells of this region, the tanycytes, in both control and grafted tissue. Despite the profound reactive gliosis, GnRH axons were shown to exit the implant as early as 5 days after grafting suggesting that the gliotic process did not constitute a barrier to this phenomenon. At the light microscopic level, double label immunocytochemical studies did not reveal any specific association between GFAP or vimentin-positive cellular processes and these pioneer GnRH fibers. However, since normal GnRH axons had been reported to travel in tanycytic channels through the medial basal hypothalamus we reinvestigated the pattern of early emerging GnRH axons at the ultrastructural level. With this higher resolution, GnRH axons were found adjacent to glial elements along their entire traverse from the graft-host interface, through the host basal hypothalamus to their termination on the hypophysial portal capillaries. At the interface, GnRH-positive axons appeared to exit via glial channels similar to those described in other developing and regenerating systems. In the host, GnRH immunoreactive axonal profiles were surrounded by glial processes though the latter could not be further defined as tanycytic or astroglial. Other, immunonegative, axons were frequently seen in axonal bundles or fascicles and not necessarily in contact with glia.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Supracondylar fractures of the humerus in childhood: range of movement following the posterior approach to open reduction.

The posterior approach for open reduction of supracondylar fractures of the humerus has been condemned for causing decreased elbow movement. This study investigates this by comparing the range of movement in children treated by posterior open reduction and Kirschner wiring with those treated by closed reduction and immobilization. A total of 65 children with severely displaced supracondylar humeral fractures have been reviewed. There was some loss of movement in 66 per cent of the open reduction group and 42 per cent of the closed reduction group. The proportion losing more than 10 degrees of movement was the same in both groups. The difference between the two groups was due to the increased numbers in the open reduction group who lost less than 10 degrees of motion. Posterior open reduction of childhood supracondylar fractures is not associated with an important loss of elbow movement and need not be avoided on this account.

Adolescent↗

PubMed1991

Pulsatile luteinizing hormone secretion in normal female mice and in hypogonadal female mice with preoptic area implants.

Pulsatile LH secretion is driven by GnRH, the hypothalamic hormone that is lacking in the hypogonadal mutant mouse. Preoptic area grafts containing GnRH neurons correct many reproductive deficits in hypogonadal mice. In this study we evaluated the pattern of LH secretion in hypogonadal female mice with preoptic area grafts (hpg/POA) and in normal female mice. Normal females were ovariectomized at 10 weeks of age, and hpg/POA mice were ovariectomized 4 months after graft surgery. Three weeks later, all mice received intracardial catheters. The next day, sequential blood samples were obtained every 10 min for 4 h from the awake, freely moving mice. At ovariectomy, normal and hpg/POA ovarian weights were 8.6 +/- 0.9 and 7.1 +/- 1.2 mg, respectively. Significant LH pulses were detected in 9 of 10 normal mice and in 9 of 13 hpg/POA mice. Pulse frequency (normal, 0.86 +/- 0.13; hpg/POA, 0.61 +/- 0.13 pulse/h) and interpeak interval (normal, 81.7 +/- 20.3; hpg/POA, 93.2 +/- 24.0 min) were not significantly different (P greater than 0.2), but mean plasma LH levels (normal, 1.07 +/- 0.16 ng/ml; hpg/POA, 0.49 +/- 0.08 ng/ml; P less than 0.005) and mean LH pulse amplitude (normal, 1.92 +/- 0.53; hpg/POA, 0.63 +/- 0.28; P less than 0.05) were significantly lower in the hpg/POA mice. The lower mean LH level and LH pulse amplitude in ovariectomized hpg/POA mice are consistent with the inability of most of these mice to show increased LH secretion after castration. The findings indicate that preoptic area brain grafts are capable of supporting episodic LH release in the hypogonadal mouse and suggest the presence of a functional GnRH pulse generator in the majority of mice with grafts.

Animals↗