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R Silver

Publications and source records attributed to R Silver.

At least 73 records · Page 4Linked to original sources
PubMed1994

A putative suprachiasmatic nucleus of birds responds to visual motion.

In mammals, the suprachiasmatic nucleus (SCN) is a pacemaker regulating daily rhythms. In birds, two retinorecipient nuclei have been called the avian SCN, one in the lateral hypothalamus and the other more medial and rostral. We asked whether the proto-oncogene c-fos is expressed in either nucleus after light exposure during subjective night, but not during subjective day, as is the case in the SCN of mammals. Chicks raised with one eye covered by a diffuser were exposed to vertically moving surroundings, after the diffuser had been switched to the other eye. Surprisingly, we saw strong Fos label only in the lateral nucleus contralateral to the eye newly exposed to visual motion, but not in the ipsilateral nucleus nor in either medial SCN. No label was seen in animals kept in darkness or if the diffuser was not switched. Fos labeling did not differ between subjective day and night. The sensitivity to "novel" motion is also seen in motion-processing nuclei of the accessory optic system and pretectum; this suggests either that the lateral SCN is not the SCN, but part of the motion pathway, or that the avian SCN may by motion-sensitive during both day and night.

Animals↗
PubMed1994

Detection and transduction of daylength in birds.

Daylength is an important environmental cue used by temperate zone avian species to time the onset of seasonal reproductive activity. Photic cues are detected by extra-retinal, extra-pineal central nervous system elements, and are rapidly transduced to an efferent signal. In this paper, we describe the brain locus of putative encephalic photoreceptors in birds, and explore the pathway of information transfer from photic input to the reproductive axis. To this end, we examine how photoreceptors might communicate with the hypothalamic-pituitary axis, and how brain peptides vary seasonally. Recent studies indicate that brain photoreceptors lie in the lateral septum and in the tuberal hypothalamus, and co-express proteins characteristic of retinal photoreceptors, as well as vasoactive-intestinal polypeptide (VIP). At the light microscopic level, photoreceptor cells appear to communicate with gonadotropin-releasing hormone (GnRH) neurons, and vice versa. Expression of VIP-like immunoreactivity is highest in photorefractory animals while GnRH-like immunoreactivity is highest in photosensitive birds. Expression of these CNS peptides is correlated with changes in plasma prolactin and luteinizing hormone (LH), suggesting a mechanism mediating seasonal cyclicity.

Animals↗
PubMed1993

Identification of BCR/ABL-negative primitive hematopoietic progenitor cells within chronic myeloid leukemia marrow.

Chronic myeloid leukemia (CML) is a malignant disorder of the hematopoietic stem cell. It has been shown that normal stem cells coexist with malignant stem cells in the bone marrow of patients with chronic-phase CML. To characterize the primitive hematopoietic progenitor cells within CML marrow, CD34+DR- and CD34+DR+ cells were isolated using centrifugal elutriation, monoclonal antibody labeling, and flow cytometric cell sorting. Polymerase chain reaction analysis of RNA samples from these CD34+ subpopulations was used to detect the presence of the BCR/ABL translocation characteristic of CML. The CD34+DR+ subpopulation contained BCR/ABL(+) cells in 11 of 12 marrow samples studied, whereas the CD34+DR- subpopulation contained BCR/ABL(+) cells in 6 of 9 CML marrow specimens. These cell populations were assayed for hematopoietic progenitor cells, and individual hematopoietic colonies were analyzed by PCR for their BCR/ABL status. Results from six patients showed that nearly half of the myeloid colonies cloned from CD34+DR- cells were BCR/ABL(+), although the CD34+DR- subpopulation contained significantly fewer BCR/ABL(+) progenitor cells than either low-density bone marrow (LDBM) or the CD34+DR+ fraction. These CD34+ cells were also used to establish stromal cell-free long-term bone marrow cultures to assess the BCR/ABL status of hematopoietic stem cells within these CML marrow populations. After 28 days in culture, three of five cultures initiated with CD34+DR- cells produced BCR/ABL(-) cells. By contrast, only one of eight cultures initiated with CD34+DR+ cells were BCR/ABL(-) after 28 days. These results indicate that the CD34+DR- subpopulation of CML marrow still contains leukemic progenitor cells, although to a lesser extent than either LDBM or CD34+DR+ cells.

Adult↗
PubMed1993

Age of donor influences ability of suprachiasmatic nucleus grafts to restore circadian rhythmicity.

Previous studies have shown a high (80-90%) rate of restoration of circadian rhythmicity in suprachiasmatic nucleus (SCN)-lesioned adult hamsters given anterior hypothalamic tissue containing the SCN taken from fetal day 13-15 donors. In the present experiments we explored the influence of age of donor on morphological and functional characteristics of the SCN graft, using tissue taken from animals at postnatal day 1, 3, 5, 7 and 10. Grafts taken from older donors tend to reach a smaller overall final size than those from younger donors, and are more likely to contain isolated, medium sized NP-positive neurons. The rate of restoration of locomotor rhythmicity following transplantation of postnatal day (PN) 1 grafts is as high as that of embryonic grafts. By PN 3, the rate of restoration falls to about 50%, and grafts of PN 7 and 10 do not restore function. As in the case of fetal grafts, there is a strong correlation between the ability of a graft to restore locomotor rhythmicity, and the presence of a cluster of vasoactive intestinal peptide (VIP) and neurophysin (NP) cells characteristic of the intact SCN within the graft. Since the period of neurogenesis for the hamster SCN occurs between day 10.5 and day 13 postfertilization, the results indicate that the SCN can be transplanted successfully well beyond the period of neurogenesis.

Aging↗
PubMed1993

Reproductive behavior, endocrine state, and the distribution of GnRH-like immunoreactive mast cells in dove brain.

Previous studies indicate that there is an increase in the number of detectable mast cells expressing gonadotropin-releasing hormone-like immunoreactivity (GnRH-ir) in the medial habenular region of the brain in ring doves after a period of 2 hr of courtship. In the present experiment the overall distribution of GnRH-ir mast cells in the brain is described, and the influence of behavioral and endocrine state on brain mast cell distribution and detectable mast cell number is explored. Four groups of male birds were studied: (1) paired with a female and displaying courtship behavior, (2) paired with a squab and displaying aggressive behavior, (3) visually isolated from other doves, and (4) long-term castrates housed communally. In all four groups, GnRH-ir mast cells were observed in the following areas: the medial habenula, circumventricular organs, organum vasculosum lamina terminalis and organum subseptale, the pia mater, and blood vessels. Cell counting revealed differences among groups in numbers of habenular mast cells. Courted doves had the most habenular mast cells, followed by doves paired with squabs, and then visually isolated doves, while castrates had the fewest. One-way ANOVA indicates significant differences among groups. All pairwise comparisons show that the courting animals had significantly more detectable mast cells in the habenular area than did visually isolated and castrated groups. These results suggest that the appearance and/or detectability of GnRH-ir mast cells in the habenula is related to the behavioral state and possibly to the endocrine state of the animal and suggest a novel mechanism for interactions among the nervous, endocrine, and immune systems.

Aggression↗
PubMed1993

Heavy water lengthens the period of free-running rhythms in lesioned hamsters bearing SCN grafts.

Heavy water (D2O) lengthens the period of free-running circadian rhythms in most organisms. We compared the effect of D2O on free-running locomotor activity rhythms in intact and SCN-lesioned (SCN-X) hamsters that had recovered circadian rhythmicity following implantation of SCN grafts. The animals were housed individually in cages equipped with running wheels, and locomotor activity was monitored using a computer-based data acquisition system. At the end of the behavioral tests, animals were anesthetized and perfused. Brain sections were immunostained for vasoactive intestinal peptide (VIP) and vasopressin (VP) to evaluate the extent of the lesion and the presence of a functional graft. The D2O similarly lengthened the period of free-running activity without affecting amount of activity in both intact and in SCN-X grafted animals. The results indicate that D2O acts directly on the SCN to lengthen the free-running period, and suggest that coupling between pacemakers within the grafted SCN is as efficient as in the intact SCN.

Animals↗
PubMed1993

Efferent signals of the suprachiasmatic nucleus.

It is well established that the mammalian suprachiasmatic nucleus (SCN) is a biological pacemaker that entrains the activity of organisms to their environment and controls circadian rhythmicity. However, neither the nature of these coupling signal or signals from the SCN, nor their target or targets in the brain, are well understood. Fiber efferents from the SCN reach nearby hypothalamic regions, suggesting a coupling role for neural efferent pathways. The SCN produces diffusible signals that reach nearby hypothalamic sites and the cerebrospinal fluid, suggesting a role for a diffusible efferent pathway. We consider the possibility of redundant coupling signals of the SCN, and review evidence suggesting that diffusible elements may be sufficient to sustain locomotor rhythmicity in adult animals and to restore locomotor rhythmicity in lesioned hamsters bearing SCN grafts. We also provide data for the occurrence of signals that synchronize oscillators, regardless of initial phase. The distinct role of neural and diffusible SCN coupling signals, and the role of SCN-driven rhythmic systems (pineal melatonin rhythms, body temperature), remain to be explored.

Animals↗
PubMed1993

Comparison of maternal serum lipids before and during parturition.

OBJECTIVE: To investigate peripartum progesterone metabolism by measuring its lipid precursors. METHODS: Serum was collected from eight pregnant women not in labor during the third trimester and again during active labor. Samples were analyzed using quantitative spectrophotometric absorbance techniques for apolipoprotein A-1, high-density lipoprotein cholesterol (HDL), and total cholesterol. RESULTS: Remote from labor, the mean gestational age antepartum was 35.6 weeks; during active labor it was 39.2 weeks. The amount of apolipoprotein A-1 present was 182.0 mg/dL before labor and 156.8 mg/dL during active labor; HDL cholesterol was 59.3 mg/dL before labor and 37.5 mg/dL during active labor, and total cholesterol was 226.6 mg/dL before labor and 144.1 mg/dL during active labor. All differences were significant at P < .05. CONCLUSION: Maternal serum lipids associated with progesterone metabolism appear to decrease in the peripartum period. Progesterone metabolism and parturition may be correlated with these lipid changes, thus identifying patients about to enter labor.

Apolipoprotein A-I↗
PubMed1992

Operant and Pavlovian contributions to the ontogeny of pecking in ring doves.

This series of experiments analyzes the role of learning in the development of pecking in ring dove squab. Experiment 1 showed that there is a high probability that parents will feed squab after a period of separation (Experiment 1). Such feedings may have been essential for producing the previous observation (Graf, Balsam, & Silver, 1985) that pecking develops normally if squab which have been separated from their parents are given a daily 20-min interaction with seed followed by an immediate return to their parents. Experiment 2 showed that exposure to seed followed by experimenter-provided feedings were sufficient for inducing adult pecking levels. Experiment 3 showed that general experience with conspecifics was not necessary for the development of pecking and that maturation alone could not account for the pecking observed in previous experiments. Experiment 4 showed that Pavlovian contingencies consisting of visual exposure to seed followed by feeding was sufficient to induce high levels of pecking. There did not appear to be an additional contribution of an operant contingency present when squab were allowed to both see and peck at seed prior to feedings in Experiment 5. However, squab must actually be given experience in handling and ingesting seeds before adult levels of pecking can be obtained. These results are discussed in terms of the developmental pathways whereby experience leads to adult behavior.

Animals↗
PubMed1992

Gonadal hormones determine sex differences in timing of incubation by doves.

Male and female ring doves express a sexually dimorphic pattern of incubation. The dimorphism is temporal rather than motoric. The male incubates for a block of time in the middle of the day and the female incubates the rest of the time. The present study explored the role of gonadal hormones in the control of the temporal dimorphism. Female-female pairs incubated their eggs, but it could not be predicted which of the partners would be sitting on the nest at any given time. Male-male pairs did not incubate and instead destroyed the nests that were provided and displayed aggressive behavior. Some intact males incubated when paired with gonadectomized males, although the castrates tended to ignore the nest. In contrast, when castrated birds were given heterotypical hormonal replacement therapy, they and their same-sex partners incubated the eggs that had been provided, with the gonadectomized birds sitting at a time appropriate to the hormonal state. The results indicate that gonadal hormones influence not only the expression of incubation behavior, but also its phase and duration.

Animals↗
PubMed1991

Neither triazolam nor activity phase advance circadian locomotor activity in SCN-lesioned hamsters bearing fetal SCN transplants.

Both triazolam (Tz) and exercise can phase advance free-running locomotor activity rhythms in intact hamsters. Furthermore, Tz increases activity at the time of injection, and this appears to be the mechanism whereby Tz produces phase shifts. This study tested the phase-shifting effect of Tz in SCN-lesioned (SCN-X) hamsters that had regained circadian rhythms of locomotor activity after transplantation of fetal SCN into the third ventricle. The results indicate that in both groups, increases in locomotor activity are seen at the time of Tz injection, and most intact animals, but no grafted animals show a phase advance in response to Tz administration. Given that hamsters bearing SCN grafts have limited neural connections between the host brain and transplanted SCN tissue, the results suggest that a site outside the SCN, with afferents to these nuclei, mediates the phase-shifting effect of Tz and of exercise.

Animals↗
PubMed1991

Tracing SCN graft efferents with Dil.

The suprachiasmatic nuclei (SCN) regulate circadian rhythmicity in many biological and behavioral responses. Hamsters are made permanently arrhythmic by bilateral destruction of the SCN. Circadian locomotor rhythmicity is restored by fetal tissue transplants placed in the 3rd ventricle (3V). If intact animals are implanted with fetal SCN grafts, they maintain locomotor activity rhythms when the host SCN are subsequently destroyed. The mechanism(s) whereby the SCN (either grafted or in situ) regulate locomotor rhythmicity is not known. Evidence from other graft models point to the possibility of efferents to appropriate targets in the host. In the present study, efferent connections of transplanted fetal SCN were examined using the carbocyanine dye, Dil. Intact or SCN-lesioned animals were sacrificed 7 or 40 days after receiving fetal SCN grafts into 3V. Dil crystals were placed on the grafts in fixed brains which were then incubated for 3-6 weeks before sectioning. Sections bearing Dil-labelled efferents from the graft were photographed and then stained for immunoreactive VIP and NP cells to locate donor SCN. Although labelled efferents were observed in a majority of the grafts, most were confined to the limits of the graft. The few labelled efferents that entered the host tissue when the graft seemed to merge with the host did not extend very far regardless of whether the graft contained immunohistochemical evidence for donor SCN or not. The observation of limited graft-host connectivity suggests either that a limited number of efferents is sufficient to support circadian locomotor rhythmicity, or that the mechanism mediating restoration of function entails a diffusible substance.

Animals↗
PubMed1991

Circadian locomotor rhythms, but not photoperiodic responses, survive surgical isolation of the SCN in hamsters.

Surgical isolation of the suprachiasmatic nuclei (SCN) within a hypothalamic island is reported to produce loss of circadian rhythmicity. The results have been interpreted to indicate that SCN efferents are necessary for the expression of circadian rhythms. It is not clear, however, whether the loss of circadian rhythms in behavioral responses following SCN isolation is attributable to transection of efferents, to loss of cells within the island, or to gliosis produced by the knife cut. To explore this issue, we examined locomotor activity and gonadal state of male golden hamsters housed in constant darkness (DD, with a dim red light for maintenance) for at least 10 weeks following isolation of the SCN from the rest of the brain by cuts by means of a Halasz wire microknife. Brain sections were immunocytochemically stained for the peptides vasoactive intestinal polypeptide (VIP), vasopressin (VP) or neurophysin II (NP II), and neuropeptide Y (NPY) to localize the SCN and to assess its viability, and for glial fibrillary acidic protein (GFAP) to delimit the border of the knife cut. Experimental animals with VIP and VP/NP II immunoreactivity in the SCN within the island retained free-running locomotor rhythms following transection of SCN efferents. Animals with cuts that failed to sever SCN efferents, and sham-operated animals (in which the Halasz knife was lowered but not rotated), also maintained circadian rhythmicity. Hamsters sustaining severe damage to the SCN showed disrupted locomotor activity. In those hamsters that retained circadian locomotor rhythmicity following SCN isolation, gonads failed to regress in DD, demonstrating the absence of an appropriate photoperiodic response. The results suggest a multiplicity of SCN coupling mechanisms in the control of circadian rhythms.

Animals↗
PubMed1991

Comparison of mononuclear cell proteins and plasma proteins before and during parturition by two dimensional electrophoresis.

Two dimensional electrophoresis is a technique whereby protein sources are organized by molecular weight and electrical charge on a polyacrylamide gel. To detect changes that may be associated with the onset of parturition, we compared electrophoresis patterns of mononuclear cell proteins and plasma proteins before and during active labor. Mononuclear cells and plasma were obtained from 5 pregnant volunteers. It appears that A-1 apolipoprotein, identified by Western Blot analysis, is increased in mononuclear cells during active labor. Conversely, a decrease in the concentration of A-1 apolipoprotein was seen in plasma during parturition. These "normal" protein patterns can now be compared with those observed in pathologic conditions including preterm labor and may allow early detection of disease by protein abnormalities before clinical signs and symptoms develop.

Blood Proteins↗
PubMed1990

Time course of peptidergic expression in fetal suprachiasmatic nucleus transplanted into adult hamster.

The time course of peptidergic expression in fetal suprachiasmatic nucleus (SCN) grafted into the third ventricle of adult hamsters was compared to SCN in situ in age-matched animals. Specifically, vasoactive intestinal polypeptide- (VIP), vasopressin- (VP) and neuropeptide Y- (NPY) like immunoreactivity in SCN was examined after transplantation into adult hosts on embryonic day 15 (E15) and in age-matched control SCN tissue. The results indicate that the grafted SCN expresses VIP by day 7-10, VP by day 10-16, and NPY by day 19-25 after transplantation. The SCN in situ expresses VIP by E14, VP by postnatal day 1 (P1), and NPY by P7. The transplantation procedure seems to produce a developmental regression or delay of a few days in detectable peptidergic expression in the SCN. The developmental delay seen in tissue implanted into the third ventricle is substantially less than that previously reported in SCN tissue implanted into the anterior chamber of the eye. The delay in peptidergic expression in transplanted SCN tissue may account, in part, for the delay in restoration of circadian locomotor rhythmicity following transplantation of SCN into lesioned adult hosts.

Animals↗
PubMed1990

Dispersed cell suspensions of fetal SCN restore circadian rhythmicity in SCN-lesioned adult hamsters.

Overt circadian rhythms are permanently disrupted following lesions of the suprachiasmatic nucleus (SCN) in hamsters. It has previously been demonstrated that whole tissue grafts which include the fetal SCN restore circadian locomotor rhythms to hamsters previously made arrhythmic by SCN lesions. In the present study, we ask whether the intrinsic peptidergic organization of the SCN is a prerequisite for functional recovery of circadian rhythms of locomotor activity. To this end, dispersed cell suspensions of [3H]thymidine-labelled fetal anterior hypothalamic tissue which contains the SCN, were injected stereotaxically into the brain of adult hamsters. Dispersed cell suspensions restored free-running locomotor rhythms, but not entrainment or gonadal regression. The period of the restored free-running rhythms following injections of SCN cell suspensions was shorter than 24 h, in contrast to intact hamsters and SCN-lesioned hamsters whose rhythms are restored by whole tissue grafts. In animals with restored rhythms, a majority of [3H]thymidine-labelled cells were located within nuclei of the midline thalamus and zona incerta. In a few individuals, donor cells were also deposited along the injection tract as far ventrally as the medial hypothalamus. Restoration of free-running locomotor rhythmicity was correlated with the presence of small numbers of isolated VIP cells along with small plexuses of VIP fibers. In animals which did not recover locomotor rhythmicity, grafts were identical in location and size to those in recovered hamsters, but did not contain peptidergic cells characteristic of the SCN. The results suggest that structural integrity of the fetal SCN is not necessary for restoration of rhythmicity after grafting.

Animals↗
PubMed1990

Distribution of vasoactive intestinal peptide-like and neurophysin-like immunoreactive neurons and acetylcholinesterase staining in the ring dove hypothalamus with emphasis on the question of an avian suprachiasmatic nucleus.

Two nuclei, termed here the medial hypothalamic nucleus and the lateral hypothalamic retinorecipient nucleus, are possible homologs of the mammalian suprachiasmatic nucleus. As the mammalian suprachiasmatic nucleus is characterized by a dense concentration of vasoactive intestinal peptide (VIP)- and neurophysin (NP)-immunoreactive neurons and an absence of acetylcholinesterase (AChE) staining, we decided to examine these factors in the ring dove hypothalamus. Neither the medial hypothalamic nucleus nor the lateral hypothalamic retinorecipient nucleus contained either VIP- or NP-like immunoreactive neurons. The lateral hypothalamic retinorecipient nucleus stained darkly for AChE. Although there was some overlap in the distribution of VIP- and NP-like immunoreactive neurons, a clustering of both types into a well defined nucleus was not observed. Therefore, an avian homolog to the mammalian suprachiasmatic nucleus must differ in its chemoarchitecture from that of mammalian species described to date.

Acetylcholinesterase↗