Biomedical subjects

R G Foster

Publications and source records attributed to R G Foster.

At least 73 records · Page 4Linked to original sources

PubMed1992

Photic regulation of Fos-like immunoreactivity in the suprachiasmatic nucleus of the mouse.

In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus functions as the primary pacemaker of the circadian system. Light has been shown to induce Fos-like immunoreactivity (Fos-LI) in the SCN of rats and hamsters. The purpose of the present study was to evaluate extensively the effect of light on Fos-LI in the mouse SCN. Brief pulses of light administered to animals otherwise in constant darkness were found to induce Fos-LI. This photic induction was unaffected by the rd mutation, which causes the profound loss of photoreceptors but fails to affect circadian responses to light. Light regulation of Fos-LI was dependent upon the phase of the circadian cycle in which the light pulse was administered. Phases at which light causes phase shifts of the circadian system were permissive for Fos-LI induction (CT 16 and 24), while phases in which light does not cause phase shifts were not permissive (CT 6 and 9). The time course of the induction at CT 16 was also described. In a light/dark cycle, Fos-LI was found to be rhythmically expressed with Fos-LI elevated soon after the lights came on but remaining low throughout the rest of the cycle. However, this rhythm is a direct consequence of the light because in constant darkness Fos-LI was always low. These results have implications regarding the possible functional roles of Fos in the circadian system and add to our understanding of light regulation of circadian physiology in the mouse.

Animals↗

PubMed1992

5' avian leukosis virus sequences and osteopetrotic potential.

Recombinants of Rous-associated virus-0 and Br21 have been used to localize 5' viral sequences that affect the osteopetrotic potential of avian leukosis viruses. Rous-associated virus-0 is a benign subgroup E virus of endogenous origin that does not cause osteopetrosis. Br21 is a constructed subgroup E virus with high osteopetrotic potential. 5' sequences that affected osteopetrotic potential resided in an 834-bp region near the 5' LTR. Sequence analysis of this region revealed differences between Br21 and RAV-0 in the mRNA leader and codons for MA.

Animals↗

PubMed1992

Vitamin A2-based visual pigments in fully terrestrial vertebrates.

As part of a broad study of the ocular and extraocular photoreceptors of reptiles, we have used high performance liquid chromatography (HPLC) to identify the retinoids present in whole eye extracts of the arboreal lizard Anolis carolinensis and the non-arboreal ruin lizard Podarcis sicula. Unexpectedly, only vitamin A2-derived chromophore was detected in Anolis, while a mixture of vitamin A1- and vitamin A2-derived chromophores was detected in Podarcis. These are the first examples of fully terrestrial vertebrates using vitamin A2-derived chromophore for visual pigment generation. Furthermore, microspectrophotometric (MSP) data for Anolis show a class of photoreceptor having a visual pigment with maximum absorbance at about 625 nm, some 40 nm further into the red than has been found in any terrestrial vertebrate examined to date.

Animals↗

PubMed1992

Changes in extrahepatic bile duct caliber in liver transplant recipients without evidence of biliary obstruction.

To better understand changes in the size of the extrahepatic bile duct after liver transplantation, we retrospectively studied the luminal diameter of the extrahepatic bile duct on serial cholangiograms in 40 liver transplant recipients with choledochocholedochostomy biliary anastomoses and without biliary complications. Forty operative and 105 postoperative cholangiograms were reviewed. The average interval between operative and last postoperative cholangiogram was 5 weeks (range, 1-17 weeks). The mean diameter of the donor common hepatic duct increased from 5.5 +/- 2.1 mm to 6.3 +/- 2.4 mm (p = .015). The mean diameter of the native common bile duct increased from 5.1 +/- 1.4 mm to 6.8 +/- 2.4 mm (p less than .001). The diameter of the donor common hepatic duct increased by 3 mm or more in six patients (15%); the diameter of the native common bile duct increased by 3 mm or more in nine (23%). Increased diameter of the native common bile duct was associated with T-tube migration into the duct in four cases. The size of the extrahepatic bile duct on cholangiograms is stable or increases slightly in most liver transplant recipients. Mild increases unassociated with a specific cause of obstruction or hepatic dysfunction do not portend biliary obstruction and are clinically benign.

Bile Ducts↗

PubMed1992

Expression of developmentally defined retinal phenotypes in the histogenesis of retinoblastoma.

Retinoblastoma, the most common intraocular tumor of childhood, is a malignant neoplasm that arises during retinal development. The embryonal cell target for neoplastic transformation is not yet clearly defined. To better understand the histogenetic potential of this tumor, the expression of photoreceptor and glial cell-associated proteins were examined in 22 primary retinoblastomas. Interphotoreceptor retinol-binding protein (IRBP), cone and rod opsins were selected as the photoreceptor specific proteins due to their different temporal patterns of expression during normal retinal development. Neoplastic Müller cell differentiation, and non-neoplastic reactive astrocytes were identified using cellular retinaldehyde binding-protein (CRAlBP), and glial fibrillary acidic protein (GFAP), respectively. Photoreceptor proteins were present in 16 cases and showed different cellular patterns of expression. IRBP and cone opsin were usually abundant. Although rod opsin was clearly identified in eight tumors, its expression was more restricted than either IRBP or cone opsin. This differential pattern of expression, opposite to the normal pattern of photoreceptor gene expression in the adult retina, corresponded to a marked decrease in mRNA for rod opsin. Cone opsin and IRBP colocalized in fleurettes demonstrating that neoplastic human cone cells are capable of IRBP synthesis. Müller cell differentiation was present in 12 of the 16 cases in which photoreceptor proteins were detected. In contrast, GFAP was only present in reactive, stromal astrocytes associated with blood vessels. Our data suggest that the retinoblastoma has the histogenetic potential of the immature neural retinal epithelium which can give rise to both photoreceptor and Müller cell lineages. The differential expression of cone and rod phenotypes in retinoblastoma is consistent with the "default" mechanism of cone cell differentiation.

Blotting, Northern↗

PubMed1991

NMDA receptor antagonists block the effects of light on circadian behavior in the mouse.

We report here the results of experiments designed to evaluate whether NMDA receptors mediate the phase shifting effects of light on the circadian rhythm of wheel-running activity in mice. Intraperitoneal administration of either the non-competitive NMDA receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,b]cyclohepten-5,10-imine maleate (MK-801), or the competitive NMDA receptor antagonist, 3(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) blocked light-induced phase advances and delays. Neither drug, by itself, caused any consistent effect on the phase of the rhythm. Furthermore, there was no significant difference between the effects of MK-801 on light-induced phase shifts in a retinally degenerate and retinally normal strain of C57 mouse. These data, coupled with previous findings, indicate that excitatory amino acid receptors play an important role in the transmission of light information from the retina to the circadian system.

Animals↗

PubMed1991

Circadian photoreception in the retinally degenerate mouse (rd/rd).

We have examined the effects of light on circadian locomotor rhythms in retinally degenerate mice (C57BL/6J mice homozygous for the rd allele: rd/rd). The sensitivity of circadian photoreception in these mice was determined by varying the irradiance of a 15 min light pulse (515 nm) given at circadian time 16 and measuring the magnitude of the phase shift of the locomotor rhythm. Experiments were performed on animals 80 days of age. Despite the loss of visual photoreceptors in the rd/rd retina, animals showed circadian responses to light that were indistinguishable from mice with normal retinas (rd/+ and +/+). While no photoreceptor outersegments were identified in the retina of rd/rd animals (80-100 days of age), we did identify a small number of perikarya that were immunoreactive for cone opsins, and even fewer cells that contained rod opsin. Using HPLC, we demonstrated the presence and photoisomerization of the rhodopsin chromophore 11-cis retinaldehyde. The rd/rd retinas contained about 2% of 11-cis retinaldehyde found in +/+ retinas. We have yet to determine whether the opsin immunoreactive perikarya or some other unidentified cell type mediate circadian light detection in the rd/rd retina.

Animals↗

PubMed1991

Obstructive dilatation of extrahepatic recipient and donor bile ducts complicating orthotopic liver transplantation: imaging and laboratory findings.

Biliary obstruction in liver transplants is most commonly due to stricture at the biliary anastomosis. The native common bile duct typically is normal. We retrospectively studied 28 patients with choledochocholedochostomy anastomoses who had marked native and donor extrahepatic bile duct dilatation associated with clinical evidence of biliary obstruction. Operative cholangiograms were compared with postoperative cholangiograms obtained a mean of 50 weeks (range, 2-246 weeks) later. Mean caliber of the native common bile duct increased from 7.5 +/- 2.0 mm on operative cholangiograms to 14.8 +/- 3.9 mm on postoperative cholangiograms (p less than .001). Mean caliber of the donor common hepatic duct increased from 5.9 +/- 1.3 mm on operative cholangiograms to 12.8 +/- 3.8 mm on postoperative cholangiograms (p less than .001). Dilatation of the cystic duct remnant was seen in 15 patients. All patients had surgical revision to choledochojejunostomy with improved results of liver function studies in most cases. Diffuse dilatation of native and donor extrahepatic bile ducts may develop in liver transplant recipients. Typical features include native and donor extrahepatic ducts greater than 12 mm in diameter and a dilated cystic duct remnant on postoperative cholangiography in a patient with otherwise unexplained hepatic dysfunction.

Adult↗

PubMed1990

Transplanted suprachiasmatic nucleus determines circadian period.

The pacemaker role of the suprachiasmatic nucleus in a mammalian circadian system was tested by neural transplantation by using a mutant strain of hamster that shows a short circadian period. Small neural grafts from the suprachiasmatic region restored circadian rhythms to arrhythmic animals whose own nucleus had been ablated. The restored rhythms always exhibited the period of the donor genotype regardless of the direction of the transplant or genotype of the host. The basic period of the overt circadian rhythm therefore is determined by cells of the suprachiasmatic region.

Animals↗

PubMed1989

A comparison of some photoreceptor characteristics in the pineal and retina. II. The Djungarian hamster (Phodopus sungorus).

A rod-specific antiserum was used to immunolabel elements within the retina and pineal of the adult Djungarian hamster and Welsh Mountain sheep. In the retina immunostaining was localized to the outer segments and perikarya of photoreceptor cells, while in the pineal limited numbers of labelled pinealocytes were scattered throughout the gland. An enzyme-linked immunosorbent assay (ELISA) was then used to obtain a quantitative measure of rod opsin in total eye and pineal extracts from the Djungarian hamster. Total rod opsin (+/- SEM) in the eye was measured by absorbance spectroscopy (1.88 +/- 0.10 nmoles opsin/eye) and by using the ELISA (1.75 +/- 0.02 nmoles opsin/eye). The opsin content from a total of 56 pineals gave a mean value of 0.34 +/- 0.01 pmoles opsin/pineal. Since a functional photopigment should be coupled in a 1:1 ratio to a chromophore, we investigated whether we could identify 11-cis and/or all-trans retinaldehydes in the pineal extracts by quantitative extraction and HPLC analysis as the oximes. No evidence of 11-cis or all-trans retinaloxime could be found, the chromatograms were indistinguishable from those produced by extracts of cortical brain tissue. We conclude that the opsin present within the adult hamster pineal is not coupled to the common vertebrate retinaldehyde chromophore, and as a result, is unlikely to be part of a functional photopigment.

Adaptation, Physiological↗

PubMed1988

Immunocytochemical studies on the LHRH system of the Japanese quail: influence by photoperiod and aspects of sexual differentiation.

Immunocytochemistry was used to determine if photoperiod and/or sex have any effect on the pattern of the luteinizing hormone-releasing hormone (LHRH) system in the brain of the Japanese quail. Immunopositive perikarya were found within three major areas of the brain: the rostral paraolfactory lobe, the preoptic, and the septal region. A quantitative analysis of LHRH cell numbers was performed on male and female quail after two photoperiodic treatments: sexually mature birds exposed to 24 weeks of 20 h light: 4 h darkness (20L:4D), and birds with a regressed reproductive system (induced by transfer from a photoregime of 20L:4D to 25 short days of 8L:16D). Two-way analysis of variance showed that short-day males display significantly (p less than 0.05) more immunopositive perikarya (607 +/- 134) than long-day males (291 +/- 114), short-day females (293 +/- 103) or long-day females (330 +/- 92). The density of LHRH-immunoreactive nerve fibres and the intensity of the immunostaining in the median eminence were always greater in long-day sexually mature quail (male and female) than in animals exposed to 25 days of 8L:16D. These results demonstrate that the LHRH system of the quail is influenced by photoperiod and mirrors sexual differentiation.

Animals↗

PubMed1988

The LH-RH system of the male European starling: photoperiod induces changes to a possible multifunctional peptide system.

In many birds reproduction is triggered by long daylengths but, paradoxically, continued exposure to long days leads to photorefractoriness and a complete shut down of the reproductive system. As these effects are thought to be mediated through the secretion of LH-RH, immunocytochemical techniques were used to investigate changes in the LH-RH system when European starlings were exposed to different photoperiods. Starlings exposed to 11L:13D and with mature testes show strong immunostaining both of LH-RH perikarya and fibers. Photosensitive short-day (8L:16D) starlings with undeveloped testes show an almost identical distribution of strongly immunoreactive perikarya but with less dense fibre staining. However, long-day (18L:6D) photorefractory starlings with fully regressed testes, show a profound reduction in LH-RH immunostaining. Perikarya have the same distribution but show a much reduced intensity of staining and fibers had almost entirely disappeared from all regions of the brain. Preliminary observations on the ultrastructure of immunocytochemically identified LH-RH neurones are also reported.

Animals↗

PubMed1987

Antibodies against retinal photoreceptor-specific proteins reveal axonal projections from the photosensory pineal organ in teleosts.

With the aid of specific antisera to the retinal proteins S-antigen and alpha-transducin and to the rhodopsin apoprotein opsin, we have labeled various cell populations in the pineal organ, parapineal organ, habenular nucleus, and subcommissural organ in two teleost species: the rainbow trout and the European minnow. Although these proteins are associated with photoreceptor functions, not only photoreceptor cells but also the majority of parenchymal cells in the pineal organ were immunoreactive. Immunoreactive cells with dendrite- and axonlike processes were observed also in the parapineal organ and the habenular nucleus. Furthermore, S-antigen-immunoreactive, long, axonal processes were observed in the pineal organ and could be traced from the pineal organ to the habenular nucleus and to the pretectal area. In the light of recent HRP electron microscopical and immunocytochemical studies we propose (1) that not only the classical pineal photoreceptor cells of poikilothermic vertebrates but also other types of CSF-contacting neurons may be the phylogenetic ancestors of mammalian pinealocytes, and (2) a close interrelationship between the pineal organ and the limbic system, effectuated by the direct projections from pineal photoreceptors/CSF-contacting neurons/pinealocytes to the habenular nucleus, and by displaced "pinealocytelike" elements scattered in the habenular nucleus.

Animals↗

PubMed1987

Evidence for a daily rhythmicity in the acute release of luteinizing hormone in response to electrical stimulation in the Japanese quail.

This study was undertaken to examine the effect of electrical stimulation of the hypothalamus at different times of day on luteinizing hormone (LH) secretion in male castrated quail on short days (8L:16D). The posterior hypothalamus was stimulated with square-wave pulses of 80 microA for 2 min through chronically-implanted platinum microelectrodes. Stimulation was carried out on each quail at 4 (treatment A), 10 (B), or 14 h (C) after dawn. Plasma LH levels were increased markedly within 2 min of ending the stimulation but reached basal levels again over the next 20 min or so. The absolute increase was significantly greater in treatment B (10 h after lights on) than at the other times tested. This is consistent with a rhythm in hypothalamic responsivity. The results are discussed in the context of the rhythm of photoinducibility which occurs early in the night and which is used by quail as a photoperiodic clock to regulate seasonal reproduction.

Animals↗

PubMed1987

Immunocytochemical markers revealing retinal and pineal but not hypothalamic photoreceptor systems in the Japanese quail.

The retinal proteins opsin, alpha-transducin, S-antigen and interstitial retinol-binding protein (IRBP) are essential for the processes of vision. By use of immunocytochemistry we have employed antibodies directed against these "photoreceptor proteins" in an attempt to identify the photoreceptor systems (retina, pineal and deep brain) of the Japanese quail. Opsin immunostaining was identified within many outer (basal portion) and inner segments of retinal photoreceptor cells and limited numbers of photoreceptor perikarya. Opsin immunostaining was also demonstrated in limited numbers of pinealocytes with all parts of these cells being immunoreactive. These results differ from previous observations. In contrast to the results obtained with the antibody against opsin, S-antigen and alpha-transducin immunostaining was seen throughout the entire outer segments and many photoreceptor perikarya of the retina, in the pineal organ immunostaining was seen in numerous pinealocytes in all follicles. These results conform to previous findings in birds. In addition, IRBP has been demonstrated for the first time in the avian retina and pineal organ. These findings underline the structural and functional similarities between the retina and pineal organ and provide additional support for a photoreceptive role of the avian pineal. No specific staining was detected in any other region of the brain in the Japanese quail; the hypothalamic photoreceptors of birds remain unidentified.

Animals↗

PubMed1987

Interstitial retinol-binding protein and cellular retinal-binding protein in the mammalian pineal.

Antibodies against bovine interstitial retinol-binding protein (IRBP) and cellular retinal-binding protein (CRA1BP) were used in immunochemical and immunocytochemical studies of the pineal glands of cattle, hamsters and rats (RCS and RCS-rdy+). On immunoblots, IRBP (Mr 144,000) was identified in cattle, hamster and rat pineal extracts. The abundance of IRBP in bovine pineals was 33 +/- 6 ng.mg-1 (mean +/- SD, n = 12) soluble protein. RCS (Royal College of Surgeons) rat pineals gave a strong IRBP reaction on immunoblots, even when virtually no IRBP could be found in the eye due to photoreceptor degeneration. In the hamster retina IRBP immunostaining was distributed throughout the entire interphotoreceptor matrix and the outer segment layer. The pineal also showed strong IRBP-like immunostaining scattered uniformly throughout the gland. Other hamster brain regions showed no specific immunostaining; however, an immunoreactive protein with the same Mr as IRBP was detected on Western blots of bovine cerebral cortex, spinal cord and brainstem soluble proteins. Immunoreactive proteins at lower Mr were also detected in these tissues. CRA1BP immunoreactivity (Mr about 32,000) was observed in immunoblots of bovine, hamster and rat pineal proteins. These findings suggest that some mammalian pinealocytes are related to the retinal cells that contain CRA1BP (i.e. pigment epithelium, Muller cells) while others are related to the photoreceptors, which synthesize IRBP.

Animals↗

PubMed1987

Immunohistochemical demonstration of marked changes in the LHRH system of photosensitive and photorefractory European starlings (Sturnus vulgaris).

Immunocytochemistry was used to determine the effects of photoperiod on the LHRH neurosecretory system in the brain of male European starlings. In this species, as in other birds, reproduction is triggered by long daylengths but continued exposure leads to photorefractoriness and to a complete shut-down of the reproductive system. These effects are thought to be mediated through changes in the secretion of LHRH. In starlings exposed to a photoperiod of 11 h light:13 h darkness (11L:13D) and with fully developed testes there was strong immunostaining of both LHRH perikarya (n = 522 +/- 43 S.E.M.) and fibres. Photosensitive short-day (8L:16D) starlings with undeveloped testes had an almost identical distribution of strongly immunoreactive perikarya (n = 523 +/- 62) but there were fewer fibres. In the median eminence, fibre number was reduced significantly (P less than 0.01) by some 30%. In long-day (18L:6D) photorefractory starlings with fully regressed testes there was an even more obvious change in the LHRH system. Perikarya were only weakly immunoreactive and there was a significant (P less than 0.01) reduction in mean diameter from 10 to 6.5 micron. In addition, there was a significant (P less than 0.05) reduction in cell number (312 +/- 62), although this may well result from the fact that some weakly stained cells fell below the limits of resolution and could not be counted. LHRH fibres disappeared almost entirely from the median eminence, and were not visible elsewhere in the brain. The higher neural pathways regulating photorefractoriness induced by long days are unknown but clearly both production of LHRH in the perikarya and release/storage of LHRH in the terminals is being profoundly modified.

Animals↗

PubMed1985

Photoperiodism in birds.

Birds show a circadian rhythm in melatonin secretion and, as expected, the pattern of output changes with photoperiod. Somewhat surprisingly then, in view of the mechanisms in mammals, birds do not seem to use this seasonal message in the photoperiodic control of reproduction. Some further experiments are needed, however, because in birds the pineal gland is not the only source of melatonin. Another difference from mammals is that birds detect the photoperiodic light not with the retina but by brain photoreceptors, which probably lie in the hypothalamus. An action spectrum for these receptors has now been obtained for the quail and this shows a peak absorption at 492 nm, suggesting that the photoreceptor is rhodopsin-based. The sensitivity of the brain receptors to 500 nm light was calculated at 2 X 10(4) photons mm-2s-1. For light to induce the photoperiodic response it must be interpreted by the bird's clock as a long day. This happens if the light falls 12-20 h after dawn and coincides with a rhythm of photosensitivity. The subsequent neuroendocrine response to the light signal is both precise and relatively long-term. A single 4 h light pulse initiates a wave of gonadotropin secretion lasting for 10 days. The light stimulus can be replaced by a brief (2 min) daily electrical stimulus given to the hypothalamus 10-12 h after dawn. Over the next few years it should be possible to disentangle further the neural processes involved.

Animals↗