Biomedical subjects

R T Robertson

Publications and source records attributed to R T Robertson.

At least 55 records · Page 3Linked to original sources

PubMed1991

Transneuronal degeneration of thalamic neurons following deafferentation: quantitative studies using [3H]thymidine autoradiography.

Transneuronal degeneration of thalamic neurons following partial deafferentation was studied using [3H]thymidine autoradiography. Timed-pregnant female Sprague-Dawley rats received systemic injections of [3H]thymidine on embryonic day (E) 13, 14 and/or 15. On the day of birth, pups were anesthetized by hypothermia and subjected to unilateral enucleation, unilateral removal of the inferior colliculus or sham lesion. Animals were sacrificed on postnatal day 10 or 30 and the brains processed for autoradiography. Material from sham-lesioned animals demonstrates that neurons destined for the dorsal lateral geniculate nucleus (LGd) undergo final mitoses on E13, 14 and 15. Neurons in the ventral medial geniculate nucleus (MGv) undergo final mitoses on E13 and 14. Thirty days following neonatal unilateral eye removal, the contralateral LGd displays a loss of approximately 30-35% of [3H]thymidine labeled neurons. Neonatal unilateral removal of the inferior colliculus results in a loss of approximately 30-40% of labeled neurons in MGv. For both LGd and MGv, shorter survival times reveal less severe cell loss. Late generated (E15) LGd neurons show less severe loss following enucleation than do earlier generated neurons. These results document the degree of cell loss in sensory thalamic nuclei following deafferentation and demonstrate that [3H]thymidine autoradiography provides a useful quantitative method for assessing anterograde transneuronal cell loss in targeted populations of neurons in the developing central nervous system.

Afferent Pathways↗

PubMed1991

Molecular forms of acetylcholinesterase in cerebral cortex and dorsal thalamus of developing rats.

Histochemical studies show that primary sensory regions of rat cerebral cortex and dorsal thalamus display transient patterns of intense acetylcholinesterase (AChE) activity during early postnatal development. Sucrose gradient fractionation techniques were used to determine the molecular forms of AChE in developing rat brain at the time of onset (postnatal day 5), during peak expression (days 10-11), and after decline (day 18) of the transient AChE expression. Tissue from auditory and visual regions of cortex and from dorsal thalamus at each age examined contained 10S and 4S forms of AChE, similar to the pattern observed in mature brain. The 10S form was almost totally membrane bound; the 4S form was largely soluble. Hemithalamic lesions reduce both forms of AChE in cortex. These data indicate that transiently expressed AChE does not represent a unique or unusual form of the enzyme.

Acetylcholinesterase↗

PubMed1991

Early ingrowth of thalamocortical afferents to the neocortex of the prenatal rat.

The initial ingrowth of thalamocortical afferents into the presumptive somatosensory cortex was examined in the fetal rat. Thalamic fibers were labeled in fixed brains with the carbocyanine dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). On embryonic day 16, thalamocortical afferents arrive in the neocortex and course tangentially within the intermediate zone immediately underneath the cortical plate. By embryonic day 17, thalamocortical fibers have begun their radial growth into cortex and their arbors span the cell-sparse zone between layer VIb and the bottom of the cortical plate. By the day of birth (embryonic day 21), thalamocortical fibers from a dense plexus within layers VI and V below the dense cortical plate. Our observations indicate that in the rat thalamic afferents arrive in the cortex at a very early age and arborize within the forming cortical layers without an apparent "waiting" period.

Afferent Pathways↗

PubMed1991

Primary auditory cortex in the rat: transient expression of acetylcholinesterase activity in developing geniculocortical projections.

A characteristic pattern of acetylcholinesterase (AChE) activity is expressed transiently in primary auditory cortex (cortical area 41) of developing laboratory rats during early postnatal life. This AChE activity occurs as a dense plexus in cortical layer IV and the deep part of layer III. This transient band of AChE activity is first detected by histochemical techniques on postnatal day (P) 3, reaches peak intensity at approximately P8-10, and declines to form the adult pattern by P23. The ventral nucleus of the medial geniculate body of the thalamus also displays prominent, and transient, staining for AChE. This intense staining for AChE, found within neuronal somata and neuropil, is detected at the time of birth, reaches peak intensity around P8, and declines to adult levels by P16. The areal and laminar patterns of the transient band of AChE activity in temporal cortex correspond to the patterns of anterograde transneuronal labeling of geniculocortical terminals following injection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the inferior colliculus. Placement of lesions that include the medial geniculate nucleus or the geniculocortical axons results in a marked decrease in AChE staining in thalamorecipient layers of auditory cortex. Placement of lesions that include the medial globus pallidus reduce AChE staining of some axons in temporal cortex of developing rats, but the dense band of AChE in layers III and IV remains. Placement of lesions in the inferior colliculus in newborn animals results in marked decrease in AChE staining in cells of the ipsilateral ventral medial geniculate nucleus and in ipsilateral auditory cortex of developing pups. These data indicate that transiently expressed AChE activity is characteristic of geniculocortical neurons, including their somata in the medial geniculate body and their terminal axons in primary auditory cortex. This AChE activity is expressed early in postnatal development, probably during the time when thalamocortical axons are proliferating in cortical layer IV and forming synaptic contacts with cortical neurons.

Acetylcholinesterase↗

PubMed1991

Development of cholinesterase histochemical staining in cerebellar cortex: transient expression of "nonspecific" cholinesterase in Purkinje cells of the nodulus and uvula.

Patterns of "nonspecific" cholinesterase (ChE) and acetylcholinesterase (AChE) activity were studied in developing rat cerebellar cortex by enzyme histochemistry and light and electron microscopy. Three types of ChE histochemical reaction product were observed in cerebellar cortex: (i) ChE is found in capillary endothelium throughout the cerebellum. Capillary ChE staining is present by the time of birth and continues into adulthood. (ii) ChE is found in radial glial fibers and their parent cell bodies, the Golgi epithelial cells. Radial glial fiber staining is mot intense during the first 3 weeks of postnatal life. (iii) ChE is found in Purkinje cells of the nodulus and ventral uvula. No ChE staining of Purkinje cells was seen in other parts of the cerebellum. ChE staining of Purkinje cells appears to be transient, first appearing at Postnatal Day 2 (P2), reaching peak intensity at P7-9, and decreasing to adult levels by P16. AChE activity displays a pattern markedly different from ChE, with staining in deep cerebellar nuclei, in putative mossy fiber terminals, and in Golgi neurons of cerebellar cortex. No evidence was found for transient AChE staining in Purkinje cells in any part of the cerebellum. The function of transiently expressed ChE activity in developing Purkinje neurons is unknown, but may be related to reorganization of cerebellar cortical circuitry associated with growth of mossy fiber afferents.

Acetylcholinesterase↗

PubMed1991

Reversible decreases of fertility in male Sprague-Dawley rats treated orally with finasteride, a 5 alpha-reductase inhibitor.

Finasteride, a 5 alpha-reductase inhibitor, was investigated for its effects on fertility in male rats as part of its preclinical safety assessment. Studies were initiated when the male Sprague-Dawley rats were either young (4 to 6 weeks old) or mature (15 weeks old). Treatment duration ranged from 6 to 32 weeks. Each male was cohabited with two untreated females at various periods during and after treatment. Litter parameters were evaluated on either day 14 or 20 of gestation. Males were necropsied at the end of treatment or 7 to 11 weeks following the end of treatment. The major findings of these studies were that 1) young rats given 20 to 80 mg/kg/day of finasteride first showed mild to moderate decreases in fertility after 12 weeks of treatment, whereas mature males (given only 80 mg/kg/day) did not show a similar decrease until 24 weeks of treatment, 2) fewer copulatory plugs and atrophy of prostates and seminal vesicles were associated with finasteride treatment, 3) the decreased fertility was only partial (ie, fertility index did not decrease below 48% of control in any study) and was not due to decreases in mating, 4) formation of copulatory plugs, organ weights, and fertility returned to normal levels after at least 6 weeks of drug withdrawal, and 5) the testes showed no histologic or weight changes that would explain the effect on fertility. These results show that the decreased fertility in male rats was associated with finasteride-induced inhibition of accessory gland secretions, an expected pharmacologic effect.

5-alpha Reductase Inhibitors↗

PubMed1991

Effects of seminal vesicle and coagulating gland ablation on fertility in rats.

In rats the secretions of the seminal vesicles and coagulating glands clot after ejaculation in the female tract to form a copulatory plug. The plug plays a critical role in transcervical sperm transport. Factors that influence the secretions of accessory sex glands have the potential to alter fertility without adverse effects on the gametes themselves. In the present study, the effect of surgical removal of the rat seminal vesicles and coagulating glands (SVx) on mating and fertility was investigated. SVx males were completely infertile by natural mating. Observed mating of SVx males with LHRH synchronized females confirmed that mating performance was normal and that they were capable of ejaculating sperm but could not produce copulatory plugs. In the absence of the copulatory plug, no sperm was transported into the uterus. Epididymal sperm obtained from the same males were capable of fertilization after intrauterine insemination and gave comparable numbers of embryos and unfertilized oocytes as sham operated controls. These findings underscore the importance of examining the role of both males and females during insemination and that observed matings, uterine sperm counts, and intrauterine insemination are useful adjuncts to routine fertility assessment when effects on the accessory sex glands are suspected.

Animals↗

PubMed1991

Decreased fertility in male rats administered the 5 alpha-reductase inhibitor, finasteride, is due to deficits in copulatory plug formation.

Oral administration of 80 mg/kg/day of finasteride, a potent specific inhibitor of 5 alpha-reductase, to sexually mature male Sprague-Dawley rats for 24 to 38 weeks caused an approximate 30% to 40% decrease in fertility. There were no effects on mating indices or implants per pregnant female. From the mating trials, a selected group of treated males with poor reproductive performance was compared to a selected group of control males with good reproductive performance. Observed matings showed no qualitative effects on mating behavior or ejaculation. However, finasteride-treated males did not form or formed small and improperly positioned copulatory plugs, which are required in rats to transport sperm into the uterus. Intrauterine insemination of epididymal sperm from males that were nonfertile by natural mating resulted in similar numbers of embryos and unfertilized oocytes recovered from controls and finasteride-treated males, confirming that there was no effect of finasteride on the ability of sperm to fertilize. Decreased fertility of finasteride-treated males was due to failure to form copulatory plugs and is related to decreased weight of seminal vesicles and prostate, an expected pharmacologic effect. Testes weight was unaffected. Decreased fertility in male rats after finasteride administration is considered a species specific effect. The mechanism of the decrease in rats is not likely to be relevant to species that do not form copulatory plugs.

5-alpha Reductase Inhibitors↗

PubMed1990

Distribution of 'non-specific' cholinesterase histochemical staining in the dorsal thalamus: a comparative study in rodents.

Histochemical studies in rat dorsal thalamus demonstrate that 'non-specific' cholinesterase (ChE) enzyme activity is characteristic of neurons of the anterior dorsal (AD) and reuniens (Re) nuclei and in a cell group found as part of the central lateral (CL) and lateral dorsal (LD) nuclei. Extra-somatal ChE staining also is seen in the anterior ventral (AV) nucleus. Parallel histochemical studies in other rodents reveal slight ChE activity in neurons of the mouse AD and LD, but not in other thalamic nuclei. The dorsal thalami of hamsters, gerbils and guinea pigs show no detectable cellular staining of ChE, although low levels of extra-somatal ChE appear in AV and the internal medullary lamina. These data indicate that 'non-specific' cholinesterase activity is not found commonly in neurons of the dorsal thalamus and prominent ChE staining may be unique to the laboratory rat.

Animals↗

PubMed1990

Relationships between patterns of acetylcholinesterase activity and geniculocortical terminal fields in developing and mature rat visual cortex.

Intraocular injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) result in anterograde transneuronal labeling of geniculocortical axon terminals in cortical area 17. In area 17 of developing rat pups, transported WGA-HRP occurs primarily in layer I and in a band that includes layer IV and deep layer III; this pattern is virtually identical to the laminar pattern of endogenous acetylcholinesterase (AChE) activity. In adult animals, transported WGA-HRP again is localized in layer I and in deep layer III and layer IV, but the endogenous AChE activity is found most prominently in deep layer IV and layer V. These results indicate that geniculocortical terminal fields are co-extensive with transient patterns of AChE activity in the developing rat, but not with the mature pattern of AChE in the adult.

Acetylcholinesterase↗

PubMed1990

Neural systems contributing to acetylcholinesterase histochemical staining in primary visual cortex of the adult rat.

Histochemical studies demonstrate that cortical area 17 (primary visual cortex) of the adult rat displays a characteristic laminar pattern of acetylcholinesterase (AChE) activity. While AChE-positive axons are found throughout the cortical layers, most intense staining occurs in a band that corresponds to layer V and the deep portion of layer IV. The present studies were directed toward determining the neural systems containing this AChE activity. Unilateral electrolytic or excitatory amino acid induced lesions of the basal forebrain result in reductions of AChE staining in ipsilateral visual cortex, particularly in layers IV and V. Electrolytic or scalpel lesions, placed in white matter underlying dorsal and lateral neocortex to interrupt basal forebrain projections to visual cortex, also reduce AChE staining in visual cortex. Lesions in the cingulate bundle and supracallosal stria reduced AChE staining retrosplenial cortex but did not affect staining visual cortex. Placement of electrolytic lesions in the hypothalamus produced no detectable change in the pattern of AChE in visual cortex. Electrolytic lesions in the midbrain tegmentum, placed to interrupt ascending axons from brainstem monoamine neurons, produced no detectable change in the pattern of AChE in visual cortex. Placement of lesions in the dorsal thalamus that include all of the dorsal lateral geniculate nucleus did not alter AChE staining in visual cortex. The results indicate that AChE activity in adult visual cortex is found primarily within afferent axons from the basal forebrain system. These data demonstrate further that the AChE staining characteristic of adult visual cortex is associated with neural systems that are distinctly different from those associated with AChE staining in visual cortex of the infant rat.

Acetylcholinesterase↗

PubMed1990

Examination of a rodent limb bud micromass assay as a prescreen for developmental toxicity.

The mouse limb bud micromass assay is one of many short-term tests proposed as preliminary screens for potential developmental toxicity. Previous efforts to validate this assay have used too few "nonteratogens." The purpose of this study was to examine additional compounds, most of which, based on the literature, were perceived to have low potential for developmental toxicity in vivo. In addition, a method of data analysis was sought that would identify selective developmental toxins in the micromass assay, i.e., those that are effective at dosages not maternally toxic. The concentration of each of 23 compounds that produced a 50% inhibition (IC50) of radiolabeled thymidine (T) and sulfate (S) incorporation was determined and used to calculate a T/S ratio. The T/S ratio may be a useful measure of developmental hazard, since T incorporation measures toxicity toward a general cell function (DNA synthesis) and S incorporation measures mainly toxicity toward a developmentally specific cell activity (chondroitin sulfate synthesis). All compounds tested produced T/S ratios of less than 2.0. Since 22 of these 23 compounds are classified as "nonteratogens" or nonselective developmental toxins in vivo, a low T/S ratio in this in vitro assay system may be capable of discriminating potential for developmental hazard in vivo.

Animals↗

PubMed1990

External genitalia abnormalities in male rats exposed in utero to finasteride, a 5 alpha-reductase inhibitor.

A series of studies was conducted to determine the developmental toxicity of the 5 alpha-reductase inhibitor finasteride (MK-0906) in rats. This compound was administered orally once daily to pregnant rats during various extended treatment periods during gestation. F1 offspring were evaluated on Day 20 of gestation as well as postnatally through mating to produce an F2 generation. MK-0906 treatment induced dosage-related incidences of hypospadias (penischisis) in male offspring with a threshold dosage level near 0.1 mg/kg/day and a 100% effect level of 100 mg/kg/day (with dosing through Day 20 of gestation). MK-0906 also caused decreased anogenital distance in male offspring. The dosage response for this effect (ranging from a 4.2% decrease at 0.003 mg/kg/day to a 38% decrease at 100 mg/kg/day) was more shallow than that for hypospadias. The decreases in anogenital distance were at least partially reversible postnatally with essentially complete recovery at dosages up to 0.1 mg/kg/day. There was also a dosage-related, temporary induction of nipples in F1 males. All of these effects were apparent following treatment on Days 6 through 17 of gestation but were more pronounced when dosing extended to Day 20 of gestation. Slight maternal toxicity consisting of minor decreases in body weight gain occurred only at dosages of 3 mg/kg/day and higher, indicating the selective nature of the developmental toxicity. The 5 alpha-reductase enzyme located in the rat fetal genital tubercle was studied in vitro and compared to that in the adult ventral prostate. The values for Km, Vmax, and IC50 for inhibition by MK-0906 were similar in the two tissues, suggesting that the enzymatic proteins in the genital tubercle and ventral prostate may be similar.

5-alpha Reductase Inhibitors↗

PubMed1990

A chemically-defined medium for organotypic slice cultures.

Organotypic slice cultures provide an excellent system for the analysis of study of the molecular mechanisms of this development necessitates the use of a chemically defined culture medium. We report here the development of a medium, EOL1 defined medium, designed specifically for this purpose. Cultures of both cerebral cortex and basal forebrain demonstrate that this defined medium allows a high degree of cytoarchitectural maintenance while promoting neural metabolism and process outgrowth.

Animals↗

PubMed1990

Maternotoxicity and fetotoxicity of an angiotensin-converting enzyme inhibitor, enalapril, in rabbits.

When enalapril, an angiotensin-converting enzyme (ACE) inhibitor, was orally administered to inseminated rabbits at dosages of 0.1 to 30 mg/kg/day for 13 days in a range-finding study, nephrotoxicity, as measured by elevated serum urea nitrogen concentrations, occurred at 1 mg/kg/day and higher dosages and significant (p less than or equal to 0.05) increases in fetal wastage were observed at dosages as low as 3 mg/kg/day. Saline supplementation during treatment prevented this rise in urea nitrogen. Fetal wastage was significantly (p less than or equal to 0.05) increased in the absence of maternotoxicity when saline-supplemented females were treated with enalapril at 30 mg/kg/day. A developmental toxicity study of enalapril in saline-supplemented rabbits produced no evidence of teratogenicity at 3, 10, and 30 mg/kg/day. The period of sensitivity of fetuses to the toxic effects of enalapril was found to be limited to middle-to-late gestation (Gestational Days 14-27). A single oral dose of enalapril (30 mg/kg) on Day 26 of gestation resulted in 100% fetal deaths. On the basis of the work done by Broughton Pipkin et al. [1982, J. Physiol. (London) 323, 415-422] and Broughton Pipkin and Wallace (1986, Brit. J. Pharmacol. 87, 533-542), which demonstrated that the sheep fetus becomes markedly hypotensive when the dam is treated with captopril or enalapril during late pregnancy, we believe that the observed fetotoxicity of enalapril in rabbits is also due to fetal hypotension.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Patterns of transiently expressed acetylcholinesterase activity in cerebral cortex and dorsal thalamus of developing rats with cytotoxin-induced microencephaly.

Previous studies have demonstrated that acetylcholinesterase (AChE) activity is expressed transiently by thalamocortical neurons of primary sensory systems in developing rat pups. In the present study, prenatal treatment with methylazoxymethanol acetate (MAM) on embryonic day 15, 16, or 17 resulted in rat pups with cerebral cortices markedly reduced in thickness and areal extent. Histochemical studies demonstrated that AChE staining occurs in fiber-like plexuses in primary visual, auditory, and somatosensory regions of developing cerebral cortex of MAM-treated animals, just as in normal developing rats, but that the transient patterns of AChE are found more superficially than normal and they occur in an abnormal patchy distribution. Neuronal somata in thalamic lateral geniculate, medial geniculate and ventral basal nuclei of MAM-treated animals show transient AChE staining indistinguishable from that seen in normal animals. These data indicate: (1) AChE is expressed transiently by thalamocortical neurons in MAM-treated animals, (2) intensity of the transiently expressed AChE is not affected by MAM-induced loss of cortical neurons, and (3) the abnormal AChE patterns in cortex likely reflect the abnormal distributions of thalamocortical terminal fields that are characteristic of MAM-treated animals.

Acetylcholinesterase↗

PubMed1989

Transient patterns of acetylcholinesterase activity in developing thalamus: a comparative study in rodents.

This paper describes acetylcholinesterase (AChE) activity in the dorsal thalamus of several rodents, including rat, mouse, gerbil, hamster and guinea pig. Tissue from fetal, neonatal, and adult animals was studied using histochemical techniques. Developing animals of all species display prominent AChE staining in the ventral medial geniculate nucleus and the ventral posterior nucleus, while adult animals show very light staining in these thalamic regions. Similarly, the dorsal lateral geniculate nucleus of all species shows stronger staining in developing animals than in adults. These data indicate that transient expression of AChE activity in primary sensory thalamic nuclei is a characteristic common to a variety of rodents.

Acetylcholinesterase↗

PubMed1989

Neonatal enucleations reduce number, size, and acetylcholinesterase histochemical staining of neurons in the dorsal lateral geniculate nucleus of developing rats.

Previous studies have demonstrated that transient patterns of acetylcholinesterase (AChE) activity are characteristic of geniculo-recipient regions of rat cortical area 17 during the second and third postnatal weeks of life. Neonatal enucleation results in a marked reduction of this transiently expressed cortical AChE. Parallel studies have demonstrated that the dorsal lateral geniculate nucleus (dLGN) also expresses AChE transiently during development. The present study examines neuronal number and size as well as AChE histochemical staining in the dLGN of normal and neonatally enucleated rat pups to determine whether changes in dLGN neurons could account for the decreased visual cortical AChE staining that results from neonatal enucleation. Changes in 4 parameters in dLGN were noted after neonatal enucleation. First, a 26-37% shrinkage in the volume of dLGN occurred contralateral to enucleation. Second, enucleation resulted in a loss of 16-30% of AChE-stained neuronal somata. Third, remaining AChE-positive neuronal somata appeared shrunken by approximately 40%. Fourth, intensity of AChE histochemical staining of individual dLGN neurons was reduced by approximately 24% following neonatal enucleation. These data suggest that loss of transient AChE activity in cortical area 17 consequent to neonatal enucleation is secondary to enucleation-induced alterations in the dLGN; these alterations include loss of neurons, shrinkage of neurons, and an apparent decrease in the ability of neurons to synthesize AChE. These data support the hypothesis that geniculocortical projection neurons express AChE transiently during development of geniculocortical connectivity and indicate that normal afferent connections and/or activity are important for the transient expression of AChE by these neurons.

Acetylcholinesterase↗