RESUMEN
We examined the posthatch chick retina for the frequency of occurrence of localization and colocalization of four amino acid transmitter candidates: glutamate (Glu), aspartate (Asp), gamma aminobutyric acid (GABA), and glycine (Gly) using postembedding methods. We support previous studies of Glu, Asp, GABA, and Gly localization in the direct and indirect functional pathways of the chick retina and extend these studies with new qualitative and quantitative observations. We found that photoreceptors show distinct cellular immunoreactivity for both Glu (Glu+) and Asp+, but not for Gly (Gly-) or GABA. Moreover, there is compartmentalization of Glu and Asp staining within the photoreceptors. All horizontal cells react strongly with Asp and Glu, about three-fourths are GABA+ and three-fourths of these are Gly+. Bipolar cells are uniformly Glu+, heterogeneously Asp+, occasionally Gly+, but GABA-. A majority of amacrine cells stain heterogeneously with all antibodies: 90% are Gly+, slightly more than half colocalize Glu, GABA, and Gly. Furthermore, amacrine cells in the outer two or three rows of cells are more likely to be stained by Gly than Glu, Asp, or GABA. Confirming previous studies, ganglion cells were mostly immunoreactive for Glu and Asp with fewer reactive for GABA and Gly. Strong and distinctly cellular immunoreactivity was found in both central and peripheral retina. Our findings show: 1) there is extensive colocalization of Glu, Asp, GABA, and Gly among most retinal neurons, including some cells that contain all four; 2) cells of the direct functional pathway tend to be labeled by Glu and Asp generally to the exclusion of GABA and Gly, while those of the indirect pathway tend to be labeled by GABA+ and/or Gly+ in addition to Glu+ and Asp+; 3) different cell body layers have distinct patterns of colocalization; and 4) there is no qualitative difference in staining patterns between peripheral and central retina.
Asunto(s)
Neurotransmisores/análisis , Neurotransmisores/inmunología , Células Fotorreceptoras de Vertebrados/química , Células Ganglionares de la Retina/química , Animales , Anticuerpos , Ácido Aspártico/análisis , Ácido Aspártico/inmunología , Pollos , Ácido Glutámico/análisis , Ácido Glutámico/inmunología , Glicina/análisis , Glicina/inmunología , Inmunohistoquímica , Vías Visuales/química , Vías Visuales/citología , Ácido gamma-Aminobutírico/análisis , Ácido gamma-Aminobutírico/inmunologíaRESUMEN
Previous work has shown that nucleosides produce apoptosis in sympathetic ganglion (SG) cells in vitro. The present study examined the effects of nucleosides on the development of the chick embryo in vivo with special attention to the SG and the optic tectum of the central nervous system. In the presence of an adenosine deaminase inhibitor, adenosine and 2'-deoxyadenosine (2'-dAdo) produced different toxicity patterns: both adenosine and 2'-dAdo were toxic to E3 embryos, but only 2'-dAdo was toxic at later stages (E6 1/2, E11). Dosage experiments on E6 1/2 embryos showed that adenosine was less toxic than 2'-dAdo and that 2'-dAdo in sublethal doses was teratogenic. We also examined the effects of 2'-dAdo on embryonic chicken SG and optic tectum in vivo to determine whether sublethal doses of 2'-dAdo produced cell death in these centers on E6 1/2 and 10. In the E6 1/2 SG, 2'-dAdo produced significant neuron loss (83%) and a decrease in SG volume (65%); however, at E10, there was only minor cell loss (7%) and no significant change in SG volume. In the optic tectum at E6 1/2, cell loss was confined mainly to the tectal ventricular zone, but there was little sign of cell loss in this organ at E10. Since cell production is vigorous in the SG and optic tectum at E6 1/2 but relatively low at E10, 2'-dAdo appears to work by stopping cell proliferation. The ineffectiveness of 2'-dAdo at E10 may result from the lethality of 2'-dAdo to the embryo at low concentrations (30 microM) in vivo, well below the apoptosis-inducing concentrations employed in vitro (100-300 microM). These data extend previous findings showing that purine and pyrimidine metabolism plays an important role in development.
Asunto(s)
Encéfalo/embriología , Desoxiadenosinas/toxicidad , Ganglios Simpáticos/embriología , Neuronas/efectos de los fármacos , Animales , Tipificación del Cuerpo , Encéfalo/efectos de los fármacos , Encéfalo/patología , Muerte Celular , Embrión de Pollo , Ganglios Simpáticos/efectos de los fármacos , Ganglios Simpáticos/patología , Mutágenos/toxicidad , Neuronas/citología , Neuronas/patología , Colículos Superiores/efectos de los fármacos , Colículos Superiores/embriología , Colículos Superiores/patologíaRESUMEN
The illicit use of cocaine has increased dramatically over the last 10-12 years. There has been a corresponding increase in cocaine abuse among obstetric patients and in the number of "cocaine babies." According to some estimates, these children make up more than half of the drug-associated births. This problem is therefore a major public health concern. Consequently, our laboratory investigated the effects of prenatal cocaine exposure on hearing, vision, growth, and exploratory/stress behavior. This chapter summarizes the literature on animals and humans on these topics and presents new observations from our laboratory. In terms of maternal toxicity, prenatal cocaine exposure causes hypertension, placental abruption, spontaneous abortion, poor pregnancy weight gain, and undernutrition secondary to appetite suppression. Some offspring effects include in utero growth retardation, cephalic hemorrhage, fetal edema, altered body composition, congenital malformations, and even pre- and postnatal death. The offspring can also exhibit a variety of behavioral, visual, hearing, and language disorders. Differential effects of animal strain and late gestational cocaine exposure are discussed. Comparisons are made between prenatal cocaine, the fetal alcohol syndrome, and the effects of prenatal undernutrition. Recommendations for clinical assessment and intervention are made.
Asunto(s)
Cocaína , Audición/efectos de los fármacos , Complicaciones del Embarazo/fisiopatología , Efectos Tardíos de la Exposición Prenatal , Estrés Psicológico , Trastornos Relacionados con Sustancias , Visión Ocular/efectos de los fármacos , Anomalías Inducidas por Medicamentos , Animales , Niño , Cocaína/toxicidad , Desarrollo Embrionario y Fetal/efectos de los fármacos , Conducta Exploratoria/efectos de los fármacos , Femenino , Crecimiento/efectos de los fármacos , Humanos , Recién Nacido , EmbarazoRESUMEN
PURPOSE: An estimated 29 million individuals use cocaine in the United States. Studies have shown a high affinity for dose dependent binding of cocaine in the testes. Recent work done in our laboratory has shown that chronic administration of cocaine to male rats has an adverse effect on fertility and spermatogenesis by producing extensive morphological changes in the testes, leading to reduction in sperm production. As a first step toward understanding this process, we characterized and identified the pharmacological properties of [3H]cocaine binding sites in the testes. MATERIALS AND METHODS: Crude membranes from the testes were prepared from 35 days old male Sprague-Dawley rats. [3H]cocaine binding was measured by using the method of Madras et al. (1989) with modifications. The data from saturation binding assays were analyzed by Inplot (GraphPad Software, San Diego, CA) to determine the Kd and Bmax. RESULTS: Specific binding of [3H]cocaine was linearly dependent on membrane protein concentrations ranging from 0.2 to 8 mg./ml. The pooled data from three independent experiments revealed a mean affinity of 36 +/- 2.0 nM and Bmax of 1.84 +/- 0.13 pmol/mg. The present study demonstrates that testicular tissue has receptor protein that binds [3H]cocaine saturably and specifically. Competition displacement experiments revealed a shallow displacement curve for (-)cocaine and Win 35,428 with r2 = 0.96, indicative of multiple binding components. Computer analysis confirmed that a two component binding model was preferred statistically over a one component model in all three experiments (p < 0.001). CONCLUSION: The results from these studies suggest that the testicular tissue contains a protein that binds [3H]cocaine in a saturable and specific manner. It has a different sensitivity from the [3H]cocaine binding protein in the brain and placenta. Further clarification of the relationship between cocaine and its recognition site is necessary to understand the mechanism of testicular damage after cocaine exposure.
Asunto(s)
Cocaína/farmacocinética , Testículo/metabolismo , Animales , Sitios de Unión , Masculino , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
OBJECTIVE: Our goal was determine the effect of endoscopic white light on the developing mammalian retina by quantitative histological analysis. STUDY DESIGN: Albino rats at postnatal days 10 (n = 16) and 16 (n = 20) were exposed to endoscopic white light for 1 h, while an equal number of littermate controls were not exposed, but otherwise treated identically. The thickness of the outer nuclear layer (ONL) and the total retinal thickness were measured light microscopically using a computer-assisted morphometry program. RESULTS: We found no statistically significant decrease in the thickness of the ONL or the total retinal thickness, nor were any significant decreases found in the ONL or the total retinal thickness for male or female groups. CONCLUSION: Endoscopic white light does not cause damage to the developing rodent neural retina detectable at the light microscopic level.
Asunto(s)
Endoscopía/efectos adversos , Luz/efectos adversos , Retina/crecimiento & desarrollo , Animales , Animales Recién Nacidos , Femenino , Embarazo , Ratas , Ratas Sprague-Dawley , Retina/anatomía & histología , Retina/patologíaRESUMEN
To determine when the calcium-binding protein parvalbumin appears during development, neurons in the chick Edinger Westphal nucleus were examined for parvalbumin immunoreactivity at a variety of embryonic stages. Parvalbumin immunoreactivity appeared on embryonic day 14 (E14, Hamburger and Hamilton stage 40) in predominantly lateral Edinger Westphal neurons. Cytochrome oxidase activity within the nucleus was examined throughout development, as an indicator of physiological activity, and expression of cytochrome oxidase was compared with that of parvalbumin. Cytochrome oxidase activity was found to be uniformly high in all parts of the Edinger Westphal nucleus throughout development. Either the Edinger Westphal nucleus in physiologically active quite early in its development or other energy demands mask the correlation of cytochrome oxidase with electrical activity. Cytochrome oxidase was expressed well before parvalbumin immunoreactivity appeared. Voltage-activated calcium currents were characterized in E12 Edinger Westphal neurons. In both amplitude and composition, E12 calcium currents resemble those of E16 neurons, excluding the possibility that calcium currents appear de novo during or just prior to the appearance of parvalbumin. Both cytochrome oxidase activity and calcium currents are observed in Edinger Westphal neurons well before the appearance of parvalbumin during development. These findings do not exclude the possibility that physiological activity affects the expression of parvalbumin since other factors such as changing patterns of synaptic activity or the appearance of calcium conducting NMDA receptors have yet to be examined. However, they raise the possibility that additional factors such as an intrinsic developmental program or a change in the neuron's basal intracellular calcium requirements may also be involved.
Asunto(s)
Neuronas/inmunología , Nervio Oculomotor/inmunología , Parvalbúminas/inmunología , Animales , Canales de Calcio/efectos de los fármacos , Embrión de Pollo , Cuerpo Ciliar/inmunología , Cuerpo Ciliar/metabolismo , Complejo IV de Transporte de Electrones/inmunología , Complejo IV de Transporte de Electrones/metabolismo , Inmunohistoquímica , Neuronas/enzimología , Níquel/farmacología , Nervio Oculomotor/embriología , Nervio Oculomotor/metabolismo , Parvalbúminas/biosíntesis , Técnicas de Placa-ClampRESUMEN
OBJECTIVE: We examined the potential teratogenic effect of endoscopic white light on the developing visual pathways. STUDY DESIGN: The right eye of chicken embryos (n = 22) was exposed to maximal endoscopic light intensity on day 10 of development. At day 17 of development the histologic characteristics of the light-exposed retinas were compared with those of the control embryos (n = 4). Normal functioning of the light-exposed eye was assessed by intravitreal injection of wheat germ agglutinin-horseradish peroxidase and observation of its axonal transport pattern to the diencephalic and mesencephalic visual centers. Axonal transport patterns were compared with those found in previous studies of normal embryos. Behavioral feeding patterns were compared between two groups of newly hatched chickens, one exposed to endoscopic light after hatching (n = 13) and the other, an unexposed control group (n = 12). RESULTS: No evidence of retinal damage, altered axonal transport or altered feeding patterns could be found between control and experimental animals. CONCLUSION: Endoscopic white light does not appear to be harmful to the developing retina and visual pathway.
Asunto(s)
Conducta Animal/efectos de la radiación , Endoscopía/efectos adversos , Luz/efectos adversos , Vías Visuales/efectos de la radiación , Animales , Transporte Axonal/efectos de la radiación , Embrión de Pollo , Conducta Alimentaria/efectos de la radiación , Histocitoquímica , Retina/embriología , Retina/patología , Retina/efectos de la radiación , Vías Visuales/embriología , Vías Visuales/metabolismoRESUMEN
We have studied the morphology of silver-impregnated neurons (rapid Golgi technique) in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), a center involved in the control of vertical and torsional saccadic eye movements. This morphological study of riMLF neurons in the rhesus monkey was undertaken to further our understanding of the functional circuitry of the oculomotor system. Our study employed Nissl, Golgi, and computer-assisted methods. The cytoarchitectonic boundaries of the riMLF and its relationships to neighboring structures were determined in both Nissl and Golgi preparations. Five (I-V) distinct morphological types of riMLF neurons were distinguished in the Golgi impregnations on the basis of soma size, dendritic size, numbers of primary dendrites, number of dendritic branch points, as well as form, number, and distribution of dendritic appendages. Type I neurons impregnated most frequently and had the most extensive and highly branched dendritic tree. Type II neurons displayed thick dendrites with complex dendritic appendages, but the dendritic tree was much more compact than that of type I cells. Type III and type V cells had fusiform somas and relatively unbranched dendritic trees but differed greatly in size as well as dendritic morphology. The type IV cell was the smallest neuron and had many characteristics of the local interneurons found in other thalamic, subthalamic, hypothalamic and midbrain centers. The type V was the largest neuron, least frequently impregnated, and found only at rostral riMLF levels. Digitized reconstructions of each type of neuron were rotated by the computer, which revealed that the dendritic trees of types I, III, and V occupy a disk-like compartment in the riMLF neuropil. In contrast, the tree of types II and IV occupy a roughly spherical compartment. We suggest that three of the cell types are well suited for specific purposes: type II cells for receiving topographically organized inputs that contain spatial information, type I cells for short-lead burst neuron output to the motor neurons or other premotor centers, and type IV cells for inhibitory inputs to type I cells.
Asunto(s)
Macaca mulatta/anatomía & histología , Movimientos Sacádicos/fisiología , Tegmento Mesencefálico/anatomía & histología , Animales , Procesamiento de Imagen Asistido por Computador , Rotación , Tinción con Nitrato de Plata , Coloración y EtiquetadoRESUMEN
The chicken lateral spiriform nucleus (Spl) receives its major input from the paleostriatum primitivum of the forebrain, projects almost exclusively upon the optic tectum, but receives no projections from the tectum. In the present study we show that not only do tectal ablations reduce the volume of the Spl, the cross-sectional area, and the number of Spl neurons, but eye removal also produces a statistically significant reduction in Spl volume, cross-sectional area, and neuron number. Because the retina does not project upon the Spl directly, and because both the retina and the Spl project upon the optic tectum, we propose that the retina produces its effects upon the Spl by an anterograde transneuronally induced retrograde transneuronal mechanism.
Asunto(s)
Ganglios Basales/patología , Enucleación del Ojo , Degeneración Nerviosa , Neuronas/fisiología , Animales , Recuento de Células , Núcleo Celular/ultraestructura , Pollos , Desnervación , Neuronas/patología , Neuronas/ultraestructura , Colículos Superiores/fisiologíaRESUMEN
Immunohistochemical studies of the chicken embryo optic tract using an antibody to gamma-aminobutyric acid (GABA) reveal that the tract is initially free of GABA immunoreactive axons. During the second week of incubation, GABA+ axons appear in the tract, chiasm, and optic nerve. The number of GABA+ axons in the optic nerve increases through E18, although few are recognizable after hatching. Detailed staining of GABA+ growth cones confirmed that virtually all the GABA+ axons in the optic nerve were growing toward the retina. Taken together, the findings suggest that the GABA+ axons in the chiasm and nerve are largely a transient extension of the GABA+ optic tract cells, the tectogeniculate projection, or both.
Asunto(s)
Nervio Óptico/metabolismo , Vías Visuales/metabolismo , Ácido gamma-Aminobutírico/metabolismo , Animales , Embrión de Pollo , Inmunohistoquímica , Neuronas/metabolismo , Nervio Óptico/citología , Nervio Óptico/embriología , Vías Visuales/citología , Vías Visuales/embriologíaRESUMEN
A population of cells has been found in the chick optic tract and chiasm exhibiting GABA-like immunoreactivity (GABA+; Granda and Crossland, J. Comp. Neurol. 287:455-469, '89). It is not known, however, whether the cells are neurons. We have studied the GABA+ cells by using morphological and immunocytochemical methods. We found that there are more than 500 cells in each tract. At the light microscopic level, the cells possess processes resembling dendrites and axons. At the electron microscopic level, the organelle content of the cells is similar to that of neurons. The cells are immunoreactive with antibodies to MAP2 and neuron specific enolase, two proteins characteristic of neurons. Taken together the findings indicate that the GABA+ cells of the chick optic tract are neurons, perhaps similar to the interstitial neurons found in the white matter of other vertebrates.
Asunto(s)
Pollos/anatomía & histología , Quiasma Óptico/citología , Nervio Óptico/citología , Ácido gamma-Aminobutírico/análisis , Animales , Anticuerpos Monoclonales/inmunología , Enucleación del Ojo , Microscopía Electrónica , Proteínas Asociadas a Microtúbulos/análisis , Proteínas Asociadas a Microtúbulos/inmunología , Neuronas/química , Neuronas/ultraestructura , Quiasma Óptico/química , Nervio Óptico/química , Orgánulos/ultraestructura , Vías Visuales/anatomía & histologíaRESUMEN
The chick brain is a useful model system for studying the ontogeny and phylogeny of neural circuitry, especially that of the visual system. In this study the distribution of cells and processes showing GABA-like immunoreactivity (GABA+) in the diencephalon and mesencephalon of the posthatch chick was determined immunohistochemically with a polyclonal antibody to GABA and compared with the results of similar studies in mammals. Most of the small GABA+ cells were found in the chick visual centers such as the nucleus lateralis anterior, suprachiasmatic nucleus, ventral lateral geniculate, optic tract, dorsolateralis anterior pars lateralis, lentiformis mesencephali, ectomammillary nucleus, area pretectalis, and the optic tectum. Large GABA+ cells were found in the following nuclei: reticularis superior, posteroventralis thalami, subpretectalis, isthmi pars magnocellularis, interstitio-pretectosubpretectalis, mesencephalicus lateralis pars dorsalis. These large cell-containing nuclei receive projections from visual or auditory centers. GABA+ axons were found throughout the diencephalon and mesencephalon but were especially prominent in the ansa lenticularis, fasciculus medialis longitudinalis, and optic tract. The distribution of GABA+ cells in the chick is more widespread than in rodents and exhibits an increased association with the visual centers suggesting a correlation with the specialized visual requirements of the bird.
Asunto(s)
Pollos/metabolismo , Diencéfalo/metabolismo , Mesencéfalo/metabolismo , Vías Visuales/metabolismo , Ácido gamma-Aminobutírico/metabolismo , Animales , Diencéfalo/citología , Inmunohistoquímica , Mesencéfalo/citología , Vías Visuales/citologíaRESUMEN
The retinogeniculate projection in the chick undergoes apparent augmentation following lesions in the optic tectum. Using autoradiographic tracing techniques we determined that the alteration of the retinal projection required a minimum of 4 days to be detected if tectal lesions were made at hatching and could be produced by lesions placed up to 1.5 years posthatch.
Asunto(s)
Pollos/fisiología , Cuerpos Geniculados/fisiología , Plasticidad Neuronal , Factores de Edad , Animales , Autorradiografía , Prolina/metabolismo , Colículos Superiores/fisiología , Vías Visuales/fisiologíaRESUMEN
The dorsal lateral geniculate nucleus, suprachiasmatic nucleus and superior colliculus of the hamster were examined autoradiographically after administration of [3H]thymidine for the presence of spatiotemporal gradients of neuron production and for the relationship between neuron cell body size and birthdate. The dorsal lateral geniculate nucleus had a dorsolateral-to-ventromedial (superficial-to-deep) gradient of neuron production, the suprachiasmatic nucleus had a caudoventral to rostrodorsal gradient, and the superior colliculus had a complex laminar gradient. In the lateral geniculate nucleus and in the superior colliculus, labeled neurons were typically larger than unlabeled neurons at early stages and unlabeled neurons were typically larger than labeled neurons at late stages; however, variation in neuron size does not account for the neurogenetic gradients in hamsters.
Asunto(s)
Replicación del ADN , Neuronas/citología , Vías Visuales/citología , Animales , Cricetinae , Cuerpos Geniculados/citología , Colículos Superiores/citología , Núcleo Supraquiasmático/citología , Vías Visuales/embriologíaRESUMEN
The anterograde and retrograde rates of axonal transport of the lectin wheat germ agglutinin (WGA) were investigated using native and derivatized lectins in embryonic (stage 39) and posthatch chickens. Anterograde transport rates in the retinotectal projection of posthatch animals ranged from 168 mm/day for native WGA to 345 mm/day for horseradish peroxidase conjugated WGA. Anterograde transport rates in embryos were at least 258 mm/day based on experiments employing tritium and horseradish peroxidase conjugates. Retrograde rates measured by appearance of label in the isthmo-optic nucleus in both embryonic and posthatch chickens were in the range of 150-180 mm/day. A fluorescein isothiocyanate conjugate of WGA was transported retrogradely but not anterogradely. When the extraocular eye muscles were labeled accidentally during injection, cells in the oculomotor or trochlear nuclei were more intensely labeled than neurons in the isthmo-optic nucleus. It was concluded that at least some conjugates of WGA, and possible the native lectin as well, travel in the fastest component of axonal transport. In view of the known intercellular movement of WGA from labeled presynaptic processes, it is recommended that survival times be kept short in experiments using WGA as a neuronal tracing agent (less than 24 h) to minimize the possibility of uptake and redistribution of the lectin by nearby cells.
Asunto(s)
Transporte Axonal , Lectinas/metabolismo , Mesencéfalo/metabolismo , Retina/metabolismo , Factores de Edad , Animales , Embrión de Pollo , Pollos/metabolismo , Fluoresceína-5-Isotiocianato , Fluoresceínas/metabolismo , Peroxidasa de Rábano Silvestre/metabolismo , Colículos Superiores/metabolismo , Tiocianatos/metabolismo , Vías Visuales/metabolismo , Aglutininas del Germen de TrigoRESUMEN
Young chickens and rats were injected intravitreally with [3H]proline and sacrificed at short intervals thereafter. Regression lines calculated for the plotted points (survival time, transport distance) revealed a transport rate of 329 mm/day in the chick and 350 mm/day in the rat. Both rates are close to those reported for peripheral axons (410 +/- 50 mm/day).
Asunto(s)
Axones/metabolismo , Vías Visuales/metabolismo , Animales , Autorradiografía , Transporte Biológico Activo , Pollos , Masculino , Nervio Óptico/metabolismo , Prolina , Ratas , Ratas Endogámicas , Especificidad de la Especie , Colículos Superiores/análisis , Factores de TiempoRESUMEN
The effects of anterograde transneuronal atrophy were studied in two visual nuclei of the chick--the ectomamillary nucleus (EMN), which shows marked degenerative changes following enucleation, and the ventral lateral geniculate nucleus (GLv), which shows less severe changes following enucleation. The chicks were enucleated on the day of hatching and killed between 2 and 81 days later. Reconstructions of the EMN and GLv revealed that enucleation retarded the growth of these two nuclei. The volume of the control EMN and GLv, ipsilateral to the removed eye, continued to increase after eye removal. The experimental EMN did not increase in volume during this time while the experimental GLv increased in volume but at a slower rate than the control GLv. The volume of the experimental GLv remained smaller than the control volume. In order to determine whether the volumetric changes were due to arrest of cellular growth or to atrophy of the neurons, a morphometric study was carried out in the two nuclei. Measurements of the cross-sectional area of EMN neurons revealed a 20% decrease in soma area in the experimental EMN in comparison with those in the control EMN. Since neurons in the control EMN did not increase in area after hatching, it was concluded that the changes were due to atrophy rather than arrest of neuron growth. Furthermore, there was a 35% neuron loss in the EMN. The GLv, which is composed of two laminae, consistently showed a greater decrease in soma cross-sectional area and neuron loss in its neuropil lamina (comparable to the transneuronal effects in the EMN) than in its lamina interna. Thus, in both nuclei, eye removal led to neuron loss and a decrease in soma cross-sectional area when compared with the contralateral (control) nucleus.
Asunto(s)
Cuerpos Geniculados/patología , Vías Visuales/patología , Animales , Atrofia , Recuento de Células , Pollos , Neuronas/patología , Colículos Superiores/patologíaRESUMEN
Neurons in the ectomamillary nucleus (EMN) undergo both atrophy and cell death following eye removal at hatching. It is not known whether all EMN neurons are affected uniformly by transneuronal atrophy or whether cell loss is an artifact due to misidentification of atrophied neurons as glia. In a preliminary morphological study, four types of neurons were found in the EMN by using the rapid Golgi method: A large multipolar neuron (type I); two medium-sized spindle-shaped neurons, one possessing many dendritic branches (type II) and the other possessing few dendritic branches (type III); and a small round neuron (type IV). Horseradish peroxidase (HRP) was then injected into two of the EMN projection fields in enucleated chicks in order to label retrogradely as many EMN neurons as possible. Types, I, II, and III neurons were identified both in the control and experimental EMN. The three types of backfilled neurons showed different degrees of transneuronal atrophy ranging from 12 to 47%. The type IV neuron, which could not be backfilled, was inferred to atrophy by 33%. Substantial differences in transneuronal atrophy, therefore, exist among the different types of neurons within the same nucleus. Since no glialike neurons could be retrogradely labeled it was concluded that there is a true neuron loss in the EMN following eye removal rather than mistaken identification of neurons as glia.
Asunto(s)
Diencéfalo/patología , Vías Visuales/patología , Animales , Atrofia , Supervivencia Celular , Pollos , Diencéfalo/citología , Neuronas/citología , Neuronas/patología , Vías Visuales/citologíaRESUMEN
This study had 3 objectives: to determine if there are gradients of neuron production in the chick diencephalon and mesencephalon, to determine if large neurons are produced before small neurons, and to determine the period of neurogenesis in the ventral lateral geniculate nucleus (GLv) and ectomammillary nucleus (EMN). Tritiated thymidine autoradiography and a cumulative labeling analysis were used in determining neuron birthdates. In our studies the diencephalon, mesencephalon, and EMN did not exhibit clearcut gradients of neuron proliferation. The GLv possessed an inside to outside laminar gradient and a more subtle caudal to rostral gradient of neurogenesis. There was a consistent negative correlation between neuron size and embryonic age among nuclear groups of the diencephalon, in general, and within the GLv and EMN in particular. The neurons of the GLv and EMN were produced from the third to the seventh day of incubation. It was concluded that there is an irregular sequence of production of nuclear groups in the diencephalon and mesencephalon rather than a series of recognizable neurogenetic gradients. Neuron size, however, is an important factor in predicting the order of neuron production.
Asunto(s)
Cuerpos Geniculados/crecimiento & desarrollo , Neuronas/fisiología , Envejecimiento , Animales , Encéfalo/embriología , Embrión de Pollo , Pollos , Diencéfalo/crecimiento & desarrollo , Mesencéfalo/crecimiento & desarrollo , Nervio Óptico/crecimiento & desarrolloRESUMEN
Neurogenesis in the lateral geniculate body, superior colliculus and suprachiasmatic nucleus takes place on fetal day 9.5 through 13. The visual cortex is produced on fetal day 10 through postnatal day 1. Thus in spite of the short gestation period of the hamster, 15.75 days, neurons in the central visual nuclei (expect for the outer cortical layers) are produced before birth.