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S R Robinson

Publications and source records attributed to S R Robinson.

At least 109 records · Page 6Linked to original sources
PubMed1988

Cell death in the inner and outer nuclear layers of the developing cat retina.

The occurrence and distribution of pyknotic profiles (dying cells) in the inner (INL) and outer nuclear layers (ONL) were mapped from radial sections through 13 kitten retinae aged from the 30th postconceptional day (30PCD) to the 81PCD (17th postnatal day). Cell death in the INL occurs in two consecutive waves, each beginning at the area centralis and proceeding toward the retinal edge. The first wave involves cells located in the inner part of the INL, adjacent to the inner plexiform layer. It begins on the 50PCD and lasts until the 66PCD, with a peak of 72,000 profiles on the 58PCD. This wave of cell death seems to be associated with the formation of the inner plexiform layer and may be due to the elimination of amacrine cells which have failed to establish sustaining connections with their appropriate target cells. The second wave involves cells located in the outer part of the INL, adjacent to the outer plexiform layer. It begins on the 60PCD and lasts until after the 81PCD, with a peak of 65,000 on the 71PCD. This wave appears to be due to the elimination of ectopic photoreceptor cells displaced by the formation of the OPL and presumably prevented from establishing sustaining connections with their appropriate target cells. A phase of cell death in the ONL begins on about the 42PCD and lasts until after the 81PCD, with a peak of 10,300 pyknotic profiles on the 60PCD.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Fetal expression of the leg extension response to anogenital stimulation.

The leg extension response (LER) is normally exhibited by rat pups in response to maternal anogenital licking. Data in the present report document that (1) LER is elicited by anogenital stimulation of the 20-day-old rat fetus, and (2) fetal LER continues to be expressed following thoracic spinal transection. Prenatal development of the leg extension response anticipates its postnatal function.

Anal Canal↗
PubMed1988

Response of the rat fetus to acute umbilical cord occlusion: an ontogenetic adaptation?

Occlusion of the umbilical cord on days 19, 20 or 21 of gestation results in a stereotypic behavioral response by the rat fetus. The intensity of this response is diminished in older fetuses. Abrupt changes in fetal heart rate accompany the behavioral response to hypoxia. Changes in fetal activity and heart rate appear to be dissociated, however, because bradycardia immediately after umbilical cord occlusion is more pronounced in older fetuses. The possibility that these behavioral and cardiac responses to hypoxia are ontogenetic adaptations restricted to the prenatal period is discussed.

Animals↗
PubMed1988

Behavior of rat fetuses following chemical or tactile stimulation.

The behavior of fetal rats was examined on Day 19 of gestation with procedures that enabled chemical stimulation and direct observation of fetuses. Rat fetuses are sensitive to both tactile stroking and intraoral infusion of chemical solutions, but the pattern and amount of activity depend upon the modality of stimulation. Fetal responsiveness is affected by prior experience with chemical stimuli. Repeated exposure within a 10-min period results in a waning of response, and repeated exposure across a delay of 48 hr results in a different pattern of response than is seen to a novel stimulus. Reexposure to a stimulus experienced earlier in gestation also alters fetal responsiveness to other forms of tactile and chemical stimulation. These findings indicate that the rat fetus exhibits olfactory function in utero and suggest central processing of sensory information, including evidence of habituation, a fetal orienting reflex to novel stimuli, and the existence of prenatal behavioral states associated with different patterns of response.

Animals↗
PubMed1988

Development of the retinofugal pathway in birds and mammals: evidence for a common 'timetable'.

We have compared changes in axon numbers in the developing optic nerves of eight homeotherms (seven mammals and one bird) using data from the available literature and our own material. The proportion of axons lost during development is smaller in the chick (35%) than in mammals (54-74%). The relative magnitude of this loss does not correlate with the extent of the binocular visual field or the size of the retinofugal ipsilateral projection. The timing of developmental events in the retinofugal pathway was compared as a proportion of the period between conception and eye opening (percentage of the 'caecal period', CP). In eutherian mammals, retinal ganglion cells and their target neurons are generated between 30 and 49% of CP (a duration of 19% of CP). In homeotherms, a phase of rapid axon generation begins around 38% of CP and the peak number of axons is reached at about 56% of CP (a duration of 18% of CP). A phase of rapid axon loss begins thereafter, and in most species it ends at about 74% of CP (a duration of 18% of CP), the rate of rapid axons loss being about half the rate of rapid axon generation. The similarity in relative timing (homochrony), like the similarity in the relative magnitude of the axon loss, suggests that cell generation and loss in the retinofugal pathway are influenced by a mechanism common to all homeotherms. We propose that in homeotherms each cohort of retinal ganglion cells is numerically matched with a group of target cells that is at an appropriate stage of maturation ('temporal matching' hypothesis). About twice as many ganglion cells are produced in each cohort than are needed, and their survival is determined by natural selection.

Animals↗
PubMed1987

Differential retinal growth appears to be the primary factor producing the ganglion cell density gradient in the rat.

We have studied the distribution of retinal ganglion cells (RGCs) that had been retrogradely labelled from bilateral injections of horseradish peroxidase into the retino-recipient nuclei of albino rats aged from the 22nd postconceptional day (22PCD-day of birth) to adulthood. During the period in which most (85%) of the naturally occurring RGC loss takes place (22-26 PCD) the distribution of RGCs remains almost uniform. Between the 26 and 32PCD (11th postnatal day), the peak RGC density decreases by only 20% while the RGC density at the superior retinal periphery decreases by 80%. In the same period a centro-peripheral RGC density difference of 4:1 becomes apparent. We have interpreted these changes to be due to a phase of rapid differential retinal growth (with more growth occurring at the retinal periphery). Thereafter the reduction in RGC density (and presumably retinal growth) is more uniform resulting by adulthood in a centro-peripheral RGC density ratio of 5:1.

Aging↗
PubMed1987

Ontogeny of the area centralis in the cat.

Previous studies have shown that after embryonic day 50 (E50) the kitten retina undergoes a relatively rapid period of maturation that begins at the area centralis and spreads toward the retinal periphery. The mechanism controlling this pattern is unknown. One possibility is that the area centralis is the most developmentally advanced region of retina from the earliest stages of eyecup formation. The present study tests this hypothesis. Retinae from ten kittens aged between E21 and E54 were sectioned horizontally at 10 micron and stained with haematoxylin and eosin. During the earliest stages of development in other vertebrate species, the oldest part of the retina is at the posterior pole of the eyecup, just dorsal to the optic fissure. At E21 in the kitten retina, this site appeared to be developmentally advanced by several criteria. A developmentally advanced region (DAR) was recognized at each subsequent age. It gradually became displaced temporally toward the site of the area centralis in the adult. Developmental events beginning here include the formation of cell-free channels at the vitreal margin; the appearance of the first ganglion cells and their axons; the formation of continuous inner and outer plexiform layers; the differentiation of cells in the ganglion cell, inner, and outer nuclear layers; and the cessation of cytogenesis at the outer limiting membrane. By E54 the DAR could be recognized as the area centralis by the criteria used in the adult. Between E25 and E37 cell density in the ganglion cell layer is higher in the DAR than at other retinal eccentricities. During the E40s cell density becomes uniform across the retina because more cells migrate into the ganglion cell layer in peripheral retina than in the DAR. Several observations suggest that cells added to the ganglion cell layer from E37 onward are not ganglion cells. The proportion of retinal area occupied by the DAR decreases geometrically between E21 and E54, indicating that this region grows at a slower rate than the rest of the retina. It is suggested that this differential growth combined with differential cell addition may be the principal mechanism responsible for generating centroperipheral cell gradients in the retina.

Animals↗
PubMed1987

Influences of the early olfactory environment on the survival, behavior and pituitary-adrenal activity of caesarean delivered preterm rat pups.

In a first experiment, vaginally delivered Day 21 and Caesarean delivered Day 20 and Day 21 rat pups were isolated in the presence of various odorants or no odorant for 1 hr immediately following birth. For Day 20 pups, exposure to novel mint odor resulted in higher mortality during isolation than did exposure to the odor of amnion/placenta. In the preterm pups, whole body corticosterone levels were higher in all isolation treatments than they were immediately following birth. For Day 21 pups, isolation treatments had no effect on corticosterone concentrations, but overall, corticosterone levels were higher following Caesarean section than they were following vaginal delivery. A second experiment replicated the mint odor-induced increase in mortality and revealed a lower activity level in preterm pups exposed to mint odor than in those exposed to the odor of amnion/placenta. Mechanical movement of the pups during exposure eliminated the effects of mint odor on mortality and activity. There was a positive correlation between corticosterone concentrations and pup activity during isolation. These results demonstrate potent influences of seemingly minor changes in early sensory stimulation on the preterm pup. The paradigm might provide a useful animal model for studying the effects of variations in ambient stimulation on premature infants.

Amnion↗
PubMed1987

Changes in the numbers of retinal ganglion cells and optic nerve axons in the developing albino rabbit.

In albino rabbits aged from the 16th postconceptional day (16PCD) to adulthood, the number of axons in the optic nerves were estimated from sample areas totalling 1-12% of the cross-sectional area of the nerve. On the 16PCD there are about 20,000 axons in the optic stalk. The number of axons in the retrobulbar part of the optic nerve reaches a peak value of 766,000 on the 23PCD, and then decreases to about 350,000 by the 32PCD (the day of birth). The number of axons does not change between the 32PCD and 50PCD, but thereafter it slowly decreases, reaching the adult number (294,000) by the 84PCD. A similar trend is apparent in pigmented animals. Thus, on the 25PCD there are 736,000 axons in the retrobulbar part of the optic nerve and the number decreases to 428,000 by the 31PCD. In the adult pigmented rabbit there are 280,000 axons in the optic nerve. In animals younger than the 32PCD, growth cones are present, and the number of axons in the prechiasmal part of the optic nerve was 8-22% lower than in the retrobulbar part of the same nerve. These observations suggest that there is a continued outgrowth of axons from the eye towards the target nuclei. By the 32PCD, the numbers of axons in the retrobulbar and prechiasmal parts of the nerve were very similar, suggesting that by this age all axons had reached the chiasm. The numbers of retinal ganglion cells (RGCs) labelled by massive injections of horseradish peroxidase into the retino-recipient nuclei were estimated in albino rabbits aged from the 24PCD to adulthood. RGCs were counted in evenly spaced sample areas totalling 4-11% of the retinal area. On the 24PCD, the number of labelled RGCs (500,000) was lower than the number of axons in the optic nerve (probably because not all RGC axons had reached their target nuclei by this age). However, by the 27PCD the number of labelled RGCs (550,000) was very similar to the number of prechiasmal axons (568,000). At all ages thereafter, the numbers of both RGCs and axons were very similar, with adult RGC numbers (about 291,000) being reached by the 85PCD. We conclude that axon loss in the rabbit optic nerve after the 27PCD is almost certainly due to the elimination (presumably death) of the parent RGCs, and we suggest that RGC death is also the most likely cause of axon loss prior to the 27PCD.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1987

Stereotypic behavioral response of rat fetuses to acute hypoxia is altered by maternal alcohol consumption.

Transient compression of the umbilical cord has been implicated as a potential cause of unexplained brain damage and/or fetal death. We induced acute fetal hypoxia by compressing the umbilical cord of the fetal rat with a microvascular clamp. Direct observation of fetal behavior immediately after cord compression identified a three-phase behavioral response to acute hypoxia, consisting of an initial suppression in motor activity, a brief period of hyperactivity, and a secondary suppression of movement. All three phases occurred in less than 2 minutes from the onset of hypoxia. The stereotypic hypoxic response of rat fetuses may be adaptive as a means of removing mechanical sources of umbilical cord compression. Among fetuses exposed to alcohol in utero, the response to hypoxia was diminished in intensity and duration. Because of their altered hypoxic response, alcohol-exposed fetuses may therefore be at greater risk from transient cord compression in utero.

Acute Disease↗
PubMed1987

Prenatal expression of species-typical action patterns in the rat fetus (Rattus norvegicus).

We investigated sensory and behavioral responsiveness of the rat fetus. On Days 19, 20, or 21 of gestation, rat fetuses received intraoral infusions of a biologically important stimulus, milk, or a novel chemical stimulus, lemon. Using a technique to directly observe behavior in utero, we found that rat fetuses discriminate between intraoral infusions of milk and lemon, exhibiting different levels and patterns of overall activity after infusion. Milk was found to evoke a low magnitude, delayed increase in overall fetal activity from Day 19 through Day 21, whereas lemon evoked a high-magnitude, spiked pattern of activity that diminished from Day 19 to Day 21. Late in gestation these two stimuli elicited species-typical action patterns. Milk infusions elicited a stretch response much like the one shown by pups at the nipple; lemon infusions elicited face wiping typical of older pups and adults exposed to aversive gustatory stimuli.

Animals↗
PubMed1986

A reversible preparation for observing the behavior of fetal rats in utero: spinal anesthesia with lidocaine.

A technique is described whereby lidocaine with epinephrine is injected into the spinal cord of the pregnant rat to produce reversible spinal anesthesia. This technique is useful for preparing pregnant females to study the spontaneous behavior of their fetuses in utero. Comparison of this procedure with an alternative, but irreversible, spinal preparation (chemomyelotomy) indicates that reversible lidocaine anesthesia does not differentially influence the activity of rat fetuses on Day 19 of gestation. This procedure will enable repeated observation of the same fetus at various stages of gestation and provide a means for the longitudinal study of behavioral development across the transition from prenatal to postnatal life.

Anesthesia, Spinal↗
PubMed1986

Spontaneous fetal behavior after maternal exposure to ethanol.

Acute and chronic intubations of ethanol to pregnant rats produced changes in spontaneous fetal behavior four hours later. Fetuses from mothers in intermediate alcohol groups (4 and 6 g/kg) were substantially less active than controls (0 g/kg), but fetuses from low (2 g/kg) and high (8 g/kg) alcohol groups showed little indication of behavioral suppression. Circulating levels of alcohol in maternal blood, fetal homogenate and amniotic fluid at the time fetuses were observed confirmed that fetuses were exposed to alcohol in utero, but the measured concentrations of alcohol were not predictive of fetal activity. We suggest that some of the developmental consequences of Fetal Alcohol Syndrome may be the consequence of fetal inactivity induced by alcohol in utero.

Amniotic Fluid↗
PubMed1985

The morphology of relay neurons in the dorsal lateral geniculate nucleus of the marsupial brush-tailed possum (Trichosurus vulpecula).

The retinal terminal zones and the morphology of relay neurons within the dorsal lateral geniculate nucleus (LGNd) of the brush-tailed possum (Trichosurus vulpecula) have been investigated with horseradish peroxidase (HRP) tracing techniques. Anterograde transport of HRP from the retina confirmed previous descriptions of the laminar distribution of retinal afferents in this nucleus. In addition, it was found that lamina III consists of two adjacent bands (IIIa and IIIb) of contralateral retinal input, separated by a terminal-free zone 20-40 micron wide. This zone is not apparent with Nissl or fibre stains. Relay neurons in the LGNd were retrogradely filled following cortical injections of HRP, and two classes (A and B) were distinguished. Class A neurons are found in the alpha portion of the LGNd (laminae I, II, III, and IV) and class B neurons in the beta portion (laminae V, VI, and VII). Class A cells are more densely packed and have shorter and more numerous dendrites, less-extensive dendritic arbors, and thicker axons than class B cells. No significant differences were found between the two classes in perikaryal size or thickness of proximal dendrites. Neurons in each lamina of the nucleus have dendritic arbors which ramify extensively within adjacent laminae, except cells in lamina IIIb, which have relatively few dendrites that cross into the cell-free zone and lamina IV.

Animals↗
PubMed1985

Cell division in the developing cat retina occurs in two zones.

Cytogenesis in the kitten retina has been investigated with [3H]thymidine autoradiography and a stain for mitotic figures. The nuclei of cells in S-phase are located adjacent to the inner margin of the cytoblast layer, near the inner plexiform layer. The nuclei then migrate toward the outer limiting membrane (OLM) to divide. Evidence is presented that in a small population of mitotic cells, the nucleus does not migrate to the OLM, but divides in the inner part of the cytoblast layer or, after the outer plexiform layer has formed, in the inner nuclear layer. Cell division in this inner zone begins and ends later than at the OLM. Cells dividing there are fewer in number than those at the OLM, their mitotic spindles are oriented randomly rather than parallel to the retinal surface and their nuclei move little between S- and M-phases of the mitotic cycle. The zones of cytogenesis at the OLM and in the inner cytoblast layer resemble, respectively, the ventricular and subventricular zones of other areas of the developing central nervous system.

Animals↗
PubMed1985

The rat fetus in its environment: behavioral adjustments to novel, familiar, aversive, and conditioned stimuli presented in utero.

With the pregnant rat under ether anesthesia, rat fetuses were exposed on Day 17 of gestation to a taste/odor stimulus (mint) injected into the amniotic fluid and/or lithium chloride injected into the peritoneum. Behavior of injected fetuses was directly observed on Day 19 of gestation following chemomyelotomy and laparotomy of the female and immersion of the uterus into a warm saline bath. With these procedures, a series of four experiments was conducted to assess the behavioral effects of (a) the mint taste/odor alone, (b) the LiCl alone, (c) the pairing of mint and LiCl on the day of conditioning, and (d) the reexposure to mint after an earlier pairing of mint and LiCl. These experiments provide clear evidence that rat fetuses are capable of forming conditioned taste/odor aversions as early as Day 17 of gestation and, further, that rat fetuses are capable of expressing these learned aversions in utero.

Animals↗