The development of retinal ganglion cell dendritic stratification in ferrets.

A signature feature of mature ferret retinal ganglion cells (RGCs) is the stratification of their dendrites within either ON or OFF sublayers of the retinal inner plexiform layer (IPL). Dendritic stratification is achieved through the gradual restriction of RGC dendrites which initially ramify throughout the IPL. We examined the time course of stratification by retrogradely labeling ferret retinas with DiI at various postnatal ages. Stratification of beta and alpha RGC dendrites into either the ON or OFF sublayers of the IPL begins around postnatal day 5, when class-specific morphologies begin to emerge, and is largely completed by eye opening, at the end of the first postnatal month. Our results imply that dendritic stratification of ferret ON and OFF RGCs, as in other mammals, occurs independently of visually driven activity.

Development and regulation of dendritic stratification in retinal ganglion cells by glutamate-mediated afferent activity.

In the mature retina, the dendrites of retinal ganglion cells (RGCs) are segregated into either ON or OFF sublaminae of the inner plexiform layer (IPL), but early in development the dendritic processes of these cells are multistratified, ramifying throughout the IPL. We examined the time course of dendritic stratification in developing beta cells, the largest class of ganglion cells in the cat retina, by retrograde labeling of fixed tissue with Dil. Dendritic stratification begins in the central and peripheral retina by embryonic day 50, about 2 weeks before birth and is not fully completed until 5 months postnatally. A clear central-to-peripheral gradient in the incidence of stratified beta cells first becomes evident shortly after birth. This stratification process was effectively halted by short-term intraocular injections (4-11 d) of the glutamate analog 2-amino-4-phosphonobutyrate (APB), which hyperpolarizes rod bipolar cells and ON cone bipolar cells, thereby preventing the release of glutamate by these interneurons. APB treatment did not alter the somal sizes or the tangential extent of the dendrites of developing beta cells, nor did it cause abnormal loss of these neurons. The organization of the inner nuclear layer, containing the APB-sensitive bipolar cells, was also not compromised by such injections. When APB treatment was discontinued there was a rapid resumption of dendritic stratification resulting in a normal incidence of stratified RGCs. Thus, short-term APB treatment causes a delay rather than a permanent arrest of the stratification process.(ABSTRACT TRUNCATED AT 250 WORDS)

Stratification of ON and OFF ganglion cell dendrites depends on glutamate-mediated afferent activity in the developing retina.

A fundamental attribute of the vertebrate visual system is the segregation of ON and OFF pathways signalling increments and decrements of light. In the mature retina, dendrites of ON- and OFF-centre retinal ganglion cells (RGCs) stratify in different sublaminae of the inner plexiform layer (IPL), and are differentially innervated by two types of bipolar cells which depolarize and hyperpolarize on exposure to light. This stratification of ON and OFF RGCs is achieved by the gradual restriction of their dendrites which ramify throughout the IPL early in development. The factors underlying this regressive event are unknown. Dendritic stratification occurs around the time that bipolar cells form synapses in the IPL, which raises the possibility that synaptic activity is involved in this process. Here we test this hypothesis by treating the developing cat retina with the glutamate analogue 2-amino-4-phosphonobutyric acid (APB), which hyperpolarizes ON cone bipolar and rod bipolar cells, thereby preventing their release of glutamate. We report that intraocular injection of APB during the period when dendritic stratification normally occurs prevents the formation of structurally segregated ON and OFF retinal pathways. These results provide evidence that glutamate-mediated afferent activity regulates the remodelling of RGC dendrites during development.

Spatial organization of the retinal projection to the avian lentiform nucleus of the mesencephalon.

Utilizing the horseradish peroxidase retrograde tracing technique and the 2-deoxy-D-glucose metabolic mapping technique, we have demonstrated in chickens the distribution of retinal ganglion cells that project to the lentiform nucleus of the mesencephalon (LM) and the retinotopic organization of the projection in the LM. Retinal ganglion cells labeled after a nearly complete injection into the LM were found in the four quadrants, distributed in a wide horizontal belt lying along both sides of the retinal equator and stretching from the temporal to the nasal retina. The HRP-labeled cells, which appeared round or oval, ranged from 25 to 840 micron 2 in size with most in the smaller size range. Results of partial HRP injections into the LM and metabolic mapping patterns in the LM produced by stimulation of half the retina with horizontal visual motion suggest that there is an orderly mapping of the retina onto the LM. The inferior temporal quadrant projects to the rostrodorsal LM; the inferior nasal quadrant projects to the caudodorsal LM. The superior temporal quadrant projects to the middle and ventral LM, extending from the rostral to the caudal pole, whereas the superior nasal quadrant projects to a small zone in the caudal LM. The mapping of the retinal quadrants in the LM is remarkably similar to that reported in the optic tectum of birds. We suggest that a common embryological anlage with the optic tectum and the arrangement of retinal axons in the optic tract are important factors in establishing the retinotopic organization of the LM.

Phencyclidine during pregnancy in the rat: effects on locomotor activity in the offspring.

Either 5 or 10 mg/kg of phencyclidine hydrochloride (PCP) was administered by gastric intubation to gravid rats during the last two weeks of gestation. Intubation controls received the vehicle and all offspring were fostered to untreated controls at birth. PCP produced a decrement in maternal weight gain and a small but nonsignificant reduction in birth weight that was no longer evident at weaning. There were no maternal deaths nor were resorptions or stillbirths increased by PCP exposure. Offspring were tested for differences in locomotor activity from birth to weaning at 30 days of age and during adulthood. No behavioral differences were found among the preweanling or adult offspring. Results are compared with other prenatal studies of PCP toxicity and teratogenicity.

Fate of tritium derived from prenatally administered tritiated methadone in dams and neonatal rats.

Tritiated methadone (3HME) was administered to gravid rats on the last week of gestation, fostered neonates periodically sacrificed, and brain and liver tritium determined by combustion. Concentrations of tritium were highest in brain on the day of birth and declined rapidly so that after 5 days, 20% remained, and after 25 days, 2% remained; similar values were found in liver. In maternal brain, concentrations on the day of birth were essentially the same as offspring brain. The brain concentrations of methadone are discussed in relation to neurobehavioral effects.

Postnatal persistence of methadone following prenatal exposure in the rat.

Tritiated methadone (3HME) was administered daily by gastric intubation to gravid rats during the last week of gestation. Fostered neonates were sacrificed every 5 days from birth to 30 days of age and brains and livers removed. Tissue 3HME was extracted, isolated on a high pressure liquid chromatograph, and counted. Highest concentrations of 3HME were present on the day of birth; after 5 days, approximately 22% remained. However, small but significant concentrations of 3HME were detected in tissues through 30 days of age. These results are of interest in relation to persistent opiate withdrawal symptoms in rat and human neonates.