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R L Goodman

Publications and source records attributed to R L Goodman.

At least 19 recordsLinked to original sources
PubMed2006

Immunocytochemical colocalization of GABA-B receptor subunits in gonadotropin-releasing hormone neurons of the sheep.

GABA has been shown to play an important role in the control of gonadotropin-releasing hormone (GnRH) and luteinizing hormone secretion in many mammals. In sheep, seasonal differences in the ability of GABA-B receptor antagonists to alter pulsatile luteinizing hormone secretion have led to the hypothesis that this receptor subtype mediates the increased inhibitory effects of estradiol on GnRH and luteinizing hormone pulse frequency seen during the non-breeding season (anestrus). The aim of the present study was to use multiple-label immunocytochemistry to determine if ovine GnRH neurons contain the GABA-B receptor subunits R1 and/or R2, and to determine whether there are seasonal differences in the colocalization of these subunits in GnRH neurons. A majority of GnRH cells in the preoptic area, anterior hypothalamic area, and medial basal hypothalamus of both breeding season and anestrous ewes contained either GABA-B R1 or R2 subunits; a subset of GnRH neurons in breeding season (42%) and anestrous ewes (60%) contained both subunits. In contrast to colocalization within cell bodies, GnRH fibers in the median eminence did not colocalize GABA-B receptor subunits. Although the percentage of GnRH neurons expressing GABA-B receptor subunits tended to be higher in anestrus than in the breeding season, there were no significant seasonal differences in R1 and R2 subunit colocalization in GnRH cell bodies. Thus, while GABA may act directly on GnRH cell bodies via GABA-B receptors in the sheep, any role that GABA-B receptors may play in seasonal reproductive changes is likely mediated by other neurons afferent to GnRH cells.

Anestrus↗
PubMed2006

Colocalisation of dynorphin a and neurokinin B immunoreactivity in the arcuate nucleus and median eminence of the sheep.

Dynorphin A (DYN)-containing cells play a key role in conveying the negative feedback influence of progesterone upon pulsatile gonadotrophin-releasing hormone (GnRH) secretion in the ewe. A very high percentage of DYN cells in the arcuate nucleus express the progesterone receptor; another population of arcuate nucleus cells that also express steroid receptors in the sheep are those that express the tachykinin peptide, neurokinin B (NKB). Both DYN and NKB fibres have been shown to form close contacts with ovine GnRH cells. Therefore, the present study tested the hypothesis that neurones expressing NKB and DYN represent the same neuronal population in the arcuate nucleus. Confocal microscopic analysis of brain sections processed for dual immunofluorescence revealed that a large majority of DYN neurones in the arcuate nucleus were also immunoreactive for NKB. Likewise, a similar majority of NKB neurones in the arcuate nucleus were immunoreactive for DYN. By contrast, DYN cells in the preoptic area and anterior hypothalamus did not colocalise with NKB, nor did DYN cells in the paraventricular or supraoptic nuclei. Fibres that stained positively for both DYN and NKB were seen in the arcuate nucleus, where they formed close appositions with DYN/NKB-positive neurones, and in the external zone of the median eminence. Taken together with previous findings, these data suggest that a subpopulation of arcuate nucleus neurones coexpressing DYN and NKB mediate the negative feedback influence of progesterone on pulsatile GnRH secretion in the ewe and may also be involved in other feedback actions of gonadal steroids.

Animals↗
PubMed2005

Distribution of preprodynorphin mRNA and dynorphin-a immunoreactivity in the sheep preoptic area and hypothalamus.

Endogenous opioid peptides (EOP) are important modulators in a variety of neuroendocrine systems, including those mediating reproduction, energy balance, lactation, and stress. Recent work in the ewe has implicated the EOP, dynorphin (DYN), in the inhibitory effects of progesterone on pulsatile gonadotropin releasing hormone secretion. Although DYN is involved in a number of hypothalamic functions in the sheep, little is known regarding the localization of preprodynorphin (PPD) expression and its major product DYN A (1-17). In this study, we determined the distribution of PPD mRNA and DYN A-containing cell bodies in the brains of ovary-intact, luteal ewes. To detect PPD mRNA, an ovine PPD mRNA was subcloned by reverse transcription-polymerase chain reaction from sheep hypothalamus and used to create a (35)S-labeled riboprobe for in situ hybridization. Neurons that expressed PPD mRNA and DYN A immunoreactivity were widely distributed in the ovine preoptic area and hypothalamus. PPD mRNA-expressing cells were seen in the supraoptic nucleus, paraventricular nucleus, preoptic area, anterior hypothalamus area, bed nucleus of the stria terminalis, ventromedial nucleus (VMN), dorsomedial nucleus of the hypothalamus, and the arcuate nucleus. All of these regions also contained DYN A-positive cell bodies except for the VMN, raising the possibility that PPD is preferentially processed into other peptide products in the VMN. In summary, based on the expression of both mRNA and peptide, DYN cells are located in a number of key hypothalamic regions involved in the neuroendocrine control of homeostasis in sheep.

Animals↗
PubMed2002

Neuroendocrine control of pulsatile GnRH secretion during the ovarian cycle: evidence from the ewe.

This article reviews the neuroendocrine control of episodic GnRH secretion during the ovine oestrous cycle. There is general agreement that endogenous opioid peptides (EOPs) mediate the negative feedback action of progesterone on GnRH pulse frequency during the luteal phase of the ovarian cycle and recent preliminary data have implicated the dynorphin-kappa-receptor system in this effect of progesterone. Progesterone also acutely inhibits GnRH pulse frequency via a non-EOP mechanism, as naloxone does not block the rapid effects of this steroid. The effects of bicuculline, 3alpha-hydroxy-5alpha-pregnan-20-one and RU486 consistently indicated that the gamma-aminobutyric acid A (GABA-A) receptor is also not involved in the acute actions of progesterone. Thus, the neural system mediating this effect remains to be determined. Oestradiol has several actions on episodic GnRH secretion. The most well characterized action is inhibition of GnRH pulse amplitude, which is probably mediated by noradrenergic neurones. Oestradiol also increases the response to progesterone negative feedback, alters GnRH pulse shape and increases GnRH pulse frequency. The first two of these actions may involve EOPs, whereas the mechanisms underlying GnRH pulse frequency are currently unknown. Finally, there is also evidence that EOPs play a physiological role in synchronizing the firing of the GnRH neurones responsible for episodic release. Specifically, the effects of naloxone on the GnRH pulse shape lead to the hypothesis that EOP tone contributes to the termination of each GnRH pulse and prevents random firing of these GnRH neurones between pulses. Thus, it appears that EOPs play an important role in controlling several different aspects of pulsatile GnRH release during the ovine oestrous cycle.

Animals↗
PubMed2002

Seasonal plasticity in the brain: the use of large animal models for neuroanatomical research.

Seasonally breeding mammals display an annual cycle of fertility that is associated with both structural neuroplasticity and functional changes in the activity of the GnRH neurones in the brain. Sheep are valuable models for understanding the hormonal and environmental cues that regulate seasonal reproduction, as well as the brain circuitry that underlies this response. As a result of the large size of sheep, we can tightly correlate the anatomy of GnRH cells and their patterns of gene expression with direct measurements of their neurosecretory output. Tract tracing studies have begun to reveal the pathways by which seasonal changes in response to oestradiol negative feedback affect the function of the reproductive system. Electron microscopic studies have shown that synaptic inputs on to ovine GnRH cells undergo marked seasonal rearrangements that are independent of hormonal changes and may reflect the intrinsic seasonality of the brain. Recent work indicates that the polysialylated form of neural cell adhesion molecule (PSA-NCAM), a marker of neuroplasticity, is well positioned anatomically to contribute to seasonal structural and functional alterations. Applying state-of-the-art neuroanatomical techniques to this model has allowed us to delineate the neural pathways responsible for the seasonal shut down of reproduction in sheep, as well as to begin to uncover the cellular mechanisms underlying seasonal neuroplasticity in the adult mammalian brain.

Animals↗
PubMed2001

The relationship between radiation fields and regional lymph nodes in carcinoma of the breast.

PURPOSE: To examine the relationships between tangential, anterior, and posterior radiation fields and regional lymph nodes, including Levels I-III axillary and supraclavicular lymph nodes. METHODS AND MATERIALS: Fifty-five patients underwent computed tomography (CT) scanning in the supine treatment position, and radiation fields were developed to treat appropriate breast and lymphatic regions. After conventional fields had been selected, Levels I-III axillary and supraclavicular lymph nodes were identified on multiple CT slices performed at 3-5-mm intervals and their depths to the anterior skin surface and the anterior-posterior separations at multiple levels were measured. RESULTS: The mean depths of the Levels I-III axillary nodes were 4.6, 5.1, and 3.6 cm, respectively. The mean depth of the supraclavicular nodes was 3.9 cm. The mean anterior-posterior separations at these levels were 15.4, 15.2, 15.2, and 14.6 cm. The mean depths of the nodes, therefore, were well anterior to the midline. In the two-field treatment group, Level I axillary nodes appeared in the tangential portals in 9/9 patients, either alone or with other lymph node groups. In the three-field group, Level I axillary nodes were in 16/16 tangential fields either alone or with level II nodes (8 patients). In 8 patients, Level III and the supraclavicular nodes were included in the anterior field and in the other 8, Levels II, III, and the supraclavicular nodes were in the anterior field. There was considerable variation in the nodal groups present in the posterior axillary boost field. No nodal groups were observed in 6 patients. CONCLUSION: There is considerable variation both in the depth of supraclavicular and axillary lymph nodes and the fields in which these nodal groups appear. To be certain that nodal groups which one plans to treat are actually treated, as well as to minimize nodal treatment when such treatment is not planned, it is recommended that before the placement of radiation fields, the nodal groups be outlined on a CT scan much as one would outline a tumor volume in other disease sites.

Adult↗
PubMed2001

Oestradiol microimplants in the ventromedial preoptic area inhibit secretion of luteinizing hormone via dopamine neurones in anoestrous ewes.

Oestradiol exerts a season-specific negative feedback effect on the GnRH/LH neurosecretory system of the Suffolk ewe. This neuroendocrine suppression is mediated in part by dopamine A15 neurones, but these neurones do not possess the oestrogen receptor. Based on indirect evidence, we hypothesized that oestrogen receptor-containing neurones in the ventromedial preoptic area (vmPOA) may be the initial step in a neuronal system whereby oestradiol suppresses GnRH secretion during the non-breeding season. To test this, three experiments were conducted using ovariectomized ewes receiving either empty or oestradiol-containing bilateral microimplants directed at the vmPOA or s.c. subcutaneous oestradiol-containing implants. In the first experiment, LH pulse frequency was measured on days 0, 1, 7 and 14 of treatment during seasonal anoestrus. In vmPOA oestradiol and s.c. oestradiol groups only, LH pulse frequency was suppressed on days 7 and 14, with maximal suppression evident by day 7. In the second experiment, this protocol was repeated during the breeding season, with LH pulses examined on days 0 and 7; LH pulse frequency did not change in any group. The third experiment tested if the effect of vmPOA oestradiol during anoestrus could be overcome by an injection of the dopamine-D2 receptor antagonist (-)-sulpiride. The vmPOA microimplants and s.c. oestradiol implants again suppressed LH pulse frequency and this was reversed by sulpiride in vmPOA oestradiol ewes. We conclude that oestradiol acts on cells in the vmPOA to stimulate a system involving dopamine neurones that inhibits GnRH/LH pulsatility in the anoestrous ewe.

Anestrus↗
PubMed2001

Case report: myopic shift in a stable corneal graft following high altitude exposure.

Refractive changes in patients after radial keratotomy who are exposed to high altitudes have been reported previously. Hypoxic environments may cause corneal curvature changes in surgically altered corneas that result in refractive error shifts. We report a patient who experienced a partially reversible myopic shift in a previously stable corneal transplant after prolonged exposure to high altitude.

Aged↗
PubMed2000

Estradiol increases multiunit electrical activity in the A15 area of ewes exposed to inhibitory photoperiods.

Seasonal anestrus in ewes results from an increase in response to the negative feedback action of estradiol (E(2)). This increase in the inhibitory effects of E(2) is controlled by photoperiod and appears to be mediated, in part, by dopaminergic neurons in the retrochiasmatic area of the hypothalamus (A15 group). This study was designed to test the hypothesis that E(2) increases multiunit electrical activity (MUA) in the A15 during inhibitory long days. MUA was monitored in the retrochiasmatic area of 14 ovariectomized ewes from 4 h before to 24 h after insertion of an E(2)-containing implant subcutaneously. In six of these ewes, MUA activity was also monitored before and after insertion of blank implants. Three of the 14 ewes were excluded from analysis because E(2) failed to inhibit LH. When MUA was recorded within the A15, E(2) produced a gradual increase in MUA that was sustained for 24 h. Blank implants failed to increase MUA in the A15 area, and E(2) did not alter MUA if recording electrodes were outside the A15. These data demonstrate that E(2) increases MUA in the A15 region of ewes and are consistent with the hypothesis that these neurons mediate E(2) negative feedback during long photoperiods.

Animals↗
PubMed2000

The ability of estradiol to induce Fos expression in a subset of estrogen receptor-alpha-containing neurons in the preoptic area of the ewe depends on reproductive status.

In the ewe, seasonal anestrus results from a change in the hypothalamic responsiveness to estradiol (E2) negative feedback. Considerable evidence has implicated a specific group of dopaminergic neurons (the A15 group) in this seasonally dependent E2 effect, but these neurons do not appear to contain estrogen receptor-alpha (ERalpha). This apparent discrepancy raises the possibility that at least one other neural system is also involved in mediating E2 inhibition. The purpose of this study was to determine whether ERalpha-containing neurons are activated by the negative feedback action of E2 in anestrus. In Exp 1, we examined the effects of E2 on expression of the immediate early gene products, Fos and Fos-related antigens, in ERalpha-positive cells in anestrous ewes. ERalpha and Fos/Fos-related antigens were colocalized using a dual immunofluorescence procedure in sections throughout the hypothalamus from ovariectomized and E2-treated ovariectomized anestrous ewes. A low dose E2 treatment that inhibited LH pulse frequency and induced Fos in A15 dopaminergic neurons in a previous study significantly increased the percentage of ERalpha-containing neurons expressing Fos (17.8% vs. 1.7%) in the medial preoptic area, but not in other hypothalamic areas. In Exp 2, we determined whether there was a seasonal difference in the effect of E2 on Fos/ERalpha colocalization in this region. E2 treatment produced a 3-fold increase in the percentage of ERalpha-positive cells expressing Fos (15.1% vs. 3.4%) in anestrus, but failed to increase ERalpha/Fos colocalization (1.8% vs. 3.5%) during the breeding season. These data raise the possibility that a subset of ERalpha-containing neurons in the medial preoptic area plays a role in the seasonal change in response to E2 negative feedback in the ewe.

Anestrus↗
PubMed1999

A new method for simultaneous demonstration of anterograde and retrograde connections in the brain: co-injections of biotinylated dextran amine and the beta subunit of cholera toxin.

In studying reciprocally connected brain networks, it is advantageous to use techniques that allow simultaneous visualization of both efferent and afferent connections from a single injection site. We report on a new technique to achieve this using pressure injections of a mixture of biotinylated dextran amine (BDA) and the beta subunit of cholera toxin (Ctb). Adult male hamsters (n = 12) received 20-30-nl injections of either a 1:1 mixture of BDA (Sigma, 10%) and Ctb (List Biological, 0.5%), or each tracer by itself, into the medial amygdala. Adult female sheep (n = 4) received 200-300 nl of the combined tracer into the A15 region of the hypothalamus. After 1 (hamster) or 2 weeks' (sheep) survival, animals were perfused with 4% paraformaldehyde. Sections were double-labeled, first for BDA histochemistry using nickel-enhanced DAB, then for Ctb using a PAP technique and unenhanced DAB. In all animals, combined injections resulted in clear and consistent patterns of both anterograde and retrograde labeling. Ctb immunoreactivity was distinct and easily distinguished from BDA labeling. There was no evidence for loss of sensitivity of either tracer due to the combined delivery; no differences were seen between combined or single tracer injections in numbers of retrogradely-labeled cells or in the distribution of anterogradely-labeled fibers. In summary, the combined delivery of BDA and Ctb is an easy and reliable technique for simultaneous afferent and efferent tract tracing in both small and large animals; it could potentially be combined with immunocytochemistry to determine the neurochemical content of labeled cells or fibers.

Animals↗
PubMed1999

A subset of gonadotropin-releasing hormone neurons in the ovine medial basal hypothalamus is activated during increased pulsatile luteinizing hormone secretion.

GnRH neurons active in the preovulatory LH surge have been identified in several species using the early intermediate gene product, Fos, but the GnRH neurons active during episodic LH secretion remain unknown. In this study, we have used Fos and Fos-related antigens (FRA) to determine whether a subset of GnRH neurons is active when pulsatile LH secretion is acutely stimulated in sheep. In experiment 1, episodic LH secretion was stimulated in five of six ewes by injection of an opioid antagonist to luteal phase ewes. These five ewes had a 6-fold increase in the percentage of GnRH neurons in the medial basal hypothalamus (MBH) expressing Fos/FRA, compared with control ewes that had no LH pulses before death. Fos/FRA expression was not increased in GnRH neurons found in any other area. In experiment 2, episodic LH secretion was induced in rams by introduction of estrous ewes. This treatment increased Fos/FRA expression in MBH GnRH neurons approximately 10-fold compared with control rams. Again, this increase in Fos/FRA expression in GnRH neurons was limited to the MBH. This selective activation of MBH GnRH neurons could reflect the preferential inhibition of these perikarya by endogenous opioid peptides. It also raises the possibility that a subset of GnRH neurons in the MBH may be responsible for episodic GnRH secretion in sheep.

Animals↗
PubMed1998

The negative feedback actions of progesterone on gonadotropin-releasing hormone secretion are transduced by the classical progesterone receptor.

Progesterone (P) powerfully inhibits gonadotropin-releasing hormone (GnRH) secretion in ewes, as in other species, but the neural mechanisms underlying this effect remain poorly understood. Using an estrogen (E)-free ovine model, we investigated the immediate GnRH and luteinizing hormone (LH) response to acute manipulations of circulating P concentrations and whether this response was mediated by the nuclear P receptor. Simultaneous hypophyseal portal and jugular blood samples were collected over 36 hr: 0-12 hr, in the presence of exogenous P (P treatment begun 8 days earlier); 12-24 hr, P implant removed; 24-36 hr, P implant reinserted. P removal caused a significant rapid increase in the GnRH pulse frequency, which was detectable within two pulses (175 min). P insertion suppressed the GnRH pulse frequency even faster: the effect detectable within one pulse (49 min). LH pulsatility was modulated identically. The next two experiments demonstrated that these effects of P are mediated by the nuclear P receptor since intracerebroventricularly infused P suppressed LH release but 3alpha-hydroxy-5alpha-pregnan-20-one, which operates through the type A gamma-aminobutyric acid receptor, was without effect and pretreatment with the P-receptor antagonist RU486 blocked the ability of P to inhibit LH. Our final study showed that P exerts its acute suppression of GnRH through an E-dependent system because the effects of P on LH secretion, lost after long-term E deprivation, are restored after 2 weeks of E treatment. Thus we demonstrate that P acutely inhibits GnRH through an E-dependent nuclear P-receptor system.

Animals↗
PubMed1997

The GnRH system of seasonal breeders: anatomy and plasticity.

Seasonal breeders, such as sheep and hamsters, by virtue of their annual cycles of reproduction, represent valuable models for the study of plasticity in the adult mammalian neuroendocrine brain. A major factor responsible for the occurrence of seasonal reproductive transitions is a striking change in the responsiveness of gonadotropin-releasing hormone (GnRH) neurons to the inhibitory effects of gonadal steroids. However, the neural circuitry mediating these seasonal changes is still relatively unexplored. In this article, we review recent findings that have begun to define that circuitry and its plasticity in a well-studied seasonal breeder, the ewe. Tract tracing studies and immunocytochemical analyses using Fos and FRAs as markers of activation point to a subset of neuroendocrine GnRH neurons in the MBH as potential mediators of pulsatile GnRH secretion. Because the vast majority of GnRH neurons lack estrogen receptors, seasonal changes in responsiveness to estradiol are most probably conveyed by afferents. Two possible mediators of this influence are dopaminergic cells in the A14/A15 cell groups of the hypothalamus, and estrogen receptor-containing cells in the arcuate nucleus that project to the median eminence. The importance of GnRH afferents in the regulation of season breeding is underscored by observations of seasonal changes in the density of synaptic inputs onto GnRH neurons. Thyroid hormones may participate in this remodeling, because they are important in seasonal reproduction, influence the morphology of other brain systems, and thyroid hormone receptors are expressed within GnRH neurons. Finally, in the hamster, neonatal hypothyroidism affects the number of caudally placed GnRH neurons in the adult brain, suggesting that thyroid hormones may influence development of the GnRH system as well as its reproductive functions in the adult brain.

Animals↗
PubMed1996

Alpha adrenergic neurons inhibit luteinizing hormone pulse amplitude in breeding season ewes.

It is now clear that estradiol acts in the brain to inhibit LH pulse amplitude in breeding season ewes, but the neural mechanisms underlying this action of estradiol have yet to be determined. In this study, we performed four experiments to examine the role of alpha-adrenergic neurons in the control of LH pulse amplitude in the ewe. In the first experiment, implantation of the alpha-adrenergic antagonist phenoxybenzamine into the preoptic area (POA) during the follicular phase of the ovine estrous cycle significantly increased LH pulse amplitude. A similar stimulatory effect of POA implants of this antagonist was observed in estradiol-treated ovariectomized (OVX+E) ewes, but phenoxybenzamine implants had no effect in the absence of estradiol. In contrast, systemic administration of phenoxybenzamine decreased LH pulse amplitude in both OVX and OVX+E ewes. Finally, POA implants of the alpha 1-adrenergic antagonist, prazosin, increased LH pulse amplitude in OVX+E ewes, whereas the alpha 2-adrenergic antagonist, yohimbine, had no effect in these animals. These results suggest that a noradrenergic (or adrenergic) system acts in the POA via alpha 1-adrenergic receptors to inhibit LH pulse amplitude in the ewe. They also raise the possibility that this system may be involved in the negative feedback action of estradiol during the breeding season.

Adrenergic alpha-Antagonists↗
PubMed1996

Dopaminergic A14/A15 neurons are activated during estradiol negative feedback in anestrous, but not breeding season, ewes.

A major factor responsible for seasonal anestrus in sheep is a striking increase in the ability of estradiol (E) to inhibit pulsatile GnRH and LH secretion. Previous studies suggest that dopaminergic neurons in the A14 and A15 groups of the ovine hypothalamus play a key role in conveying the inhibitory effects of E in anestrous ewes. The present study tested the hypothesis that A14/A15 neurons in anestrous ewes are activated in response to E, and that this activation is specifically related to seasonal changes in E negative feedback. Expression of the immediate early gene products, Fos and the Fos-related antigens (FRAs), was used as a marker of neuronal activation. Ovariectomized anestrous ewes received either blank implants (no E) or 0.5-cm long E implants sc and were killed 6 h later (E+6h) or 7 days later (E+7d and no E groups). During the breeding season, two additional groups of ovariectomized ewes were perfused 7 days after insertion of either blank or E implants. During anestrus, E completely suppressed LH pulses in the E+7d group, but had no effect in the E+6h group. In the E+7d anestrous group, there was also a significant increase in the mean percentage of tyrosine hydroxylase (TH)-positive cells that expressed nuclear Fos/FRAs in A14 and A15 areas compared to that in either the no E or E+6h group. By contrast, during the breeding season, E had no effect on LH pulse frequency, and there were relatively few TH-positive cells in A14 and A15 that coexpressed Fos/FRAs in either the no E or E+7d group. No significant steroidal or seasonal differences in Fos/FRA expression were seen in other hypothalamic dopaminergic cell groups (A12 and A13) or in the preoptic area-anterior hypothalamus or suprachiasmatic nucleus. Furthermore, E did not alter the total number of TH-positive neurons in A14/A15 or other cell groups. There were seasonal differences in the number of TH-positive neurons, with a significantly greater number of cells in the A13 and A15 of breeding season animals compared to anestrous ewes. Thus, E increased Fos/FRA expression in A14/A15 neurons only during anestrus at a time when it also inhibited LH pulse frequency. These findings are consistent with the view that activation of dopaminergic cells in A14 and A15 is a critical link in the chain of events leading to seasonal shifts in sensitivity to E negative feedback in the ewe.

Anestrus↗