Nerve growth factor reduces apoptosis of axotomized retinal ganglion cells in the neonatal rat

It has recently been reported that the degeneration of retinal ganglion cells induced by transection of the optic nerve in the neonatal rat is due to an active process of apoptosis, as opposed to passive necrosis. Here we tested whether the administration of the trophic factor nerve growth factor could prevent the apoptotic death of the axotomized cells. We administered nerve growth factor by two intraocular injections, one immediately after the lesion and the second 12 h later. The retinas were taken at 24 h post-lesion and stained as whole mounts with Cresyl Violet. Pyknotic as well as surviving cells were counted in the retinal ganglion cell layer. In this layer at least 95% of the total cell population is composed by ganglion cells, as revealed by retrogradely labelling these cells with horseradish peroxidase injected in the superior colliculi. We found that intraocular administration of nerve growth factor diminishes the degeneration induced by optic nerve transection in the neonatal rat. After nerve growth factor injection, in fact, the number of pyknotic cells is reduced by 39% compared with controls (lesioned, injected with saline); in addition, nerve growth factor also increases the survival of retinal ganglion cells by 30% at 24 h post-lesion.

Nerve growth factor (NGF) uptake and transport following injection in the developing rat visual cortex

Recent investigations have shown that cortical nerve growth factor (NGF) infusions during the critical period inhibit ocular-dominance plasticity in the binocular portion of the rat visual cortex. The mechanisms underlying the effects of NGF on visual cortical plasticity are still unclear. To investigate whether during normal development intracortical and/or extracortical cells possess uptake/transport mechanisms for the neurotrophin, we injected 125I-NGF into the occipital cortex of rats at different postnatal ages. Within the cortex, only a few labelled cells were observed. These cells were confined to the vicinity of the injection site and their number depended on the animal's age at the time of injection. Labelled cells were absent at postnatal day (PD) 10 but could be detected between PD 14 and PD 18. They then decreased in number over the following period and were not detected in adult animals. Outside the cortex, neurons of the lateral geniculate nucleus (LGN) were not observed to take up and retrogradely transport NGF at any age after birth. In contrast, retrogradely labelled neurons were found in the basal forebrain. Labelled cells were first observed here at PD 14 and then increased in number until reaching the adult pattern. Our results show that intrinsic and extrinsic neurons are labelled following intracortical injections of iodinated NGF. In both neuronal populations, the uptake and transport of NGF is present over a period corresponding to the critical period for visual cortical plasticity. These findings suggest that NGF may play a role, both intra and extracortically, in plasticity phenomena.

Antibodies to nerve growth factor (NGF) prolong the sensitive period for monocular deprivation in the rat

Neural plasticity in the visual cortex, as tested by changes in its functional organization induced by monocular deprivation (MD), is present only during a restricted period of postnatal development (critical period). To investigate whether this process of synapse strengthening depends upon NGF, we antagonized endogenous NGF during the critical period by implanting anti-NGF producing cells. Anti-NGF treated and control rats were monocularly deprived after the end of the critical period. In anti-NGF treated but not in control rats MD was still effective. We conclude that antagonism of endogenous NGF prolongs the critical period, possibly by delaying the process of synapse consolidation in the visual cortex.

Apoptotic cell death induced by optic nerve lesion in the neonatal rat

Cell death can be ascribed to one of two distinct modes of degeneration: apoptosis (programmed or active cell death) or necrosis (passive degeneration). While apoptosis is generally assumed to occur in physiological conditions such as normal development or tissue turnover, necrotic cell degeneration is induced in pathological situations. Here we report that also in a pathological situation, such as after axotomy in the CNS, apoptotic type of cell death comes into play: following intracranial transection of the optic nerve in the neonatal rat in vivo, retinal ganglion cells undergo an active, apoptotic cell death. In fact, the administration of protein synthesis inhibitors (actinomycin D and cycloheximide) prevents the appearance of pyknotic nuclei as well as of fragmented DNA of ganglion cells at 24 hr postlesion. Correspondingly, the number of surviving cells after actinomycin D and cycloheximide treatment is comparable to normal, unlesioned retinas. In addition, cycloheximide decreases the number of pyknotic ganglion cells during spontaneous cell death.

Developmental expression of PC3 gene is correlated with neuronal cell birthday

We examined the developmental expression of PC3, a nerve growth factor (NGF) early induced gene in PC12 cells, in the rat central nervous system (CNS) and we found that it represents a molecular marker of ongoing postmitotic neurons production. PC3 is initially expressed in the ventral quarter of the neural tube, at the level of the presumptive cervical spinal cord just where and when (10-11 days post coitum (dpc)) the motor neurons are arising. Subsequently, the appearance of PC3 expression follows a ventro-dorsal and a rostro-caudal gradient in the spinal cord and a caudo-rostral gradient across the brain vesicles that coincide, both spatially and temporally, with the gradients of neurogenesis described in the literature. As in PC12 cells, PC3 mRNA expression appears to be transient in vivo. In all regions of the CNS, it is restricted to the ventricular zone of the neuroepithelium, while neuronal precursors cease to express PC3 as they migrate to the mantle zone. Moreover, PC3 mRNA disappears from the various regions of the CNS as neurogenesis ceases.

Schwann cells transplanted in the lateral ventricles prevent the functional and anatomical effects of monocular deprivation in the rat

We investigated whether the transplant of Schwann cells prevents the physiological and morphological effects of monocular deprivation in the rat. On the day of eye opening in rats (postnatal day 14), we transplanted Schwann cells in the lateral ventricles and sutured the eyelids of one eye. After 20-30 days, at the end of the critical period for the visual system development, we analyzed the functional properties of visual cortical neurons. Spontaneous discharge, orientation selectivity, and receptive field size of visual cortical neurons in transplanted animals were in the normal range. Transplantation of Schwann cells prevented the detrimental effects of monocular deprivation on ocular dominance and binocularity of cortical neurons. Visual acuity of the deprived eye estimated by visually evoked potentials was also normal. Schwann cells derived from adult animals were as effective as those derived from neonates. The effects of Schwann cells on monocular deprivation were dependent upon the number of cells present in the transplant so that 10(6) Schwann cells were sufficient to prevent the effect of monocular deprivation, whereas 10(5) and 3.3 x 10(5) Schwann cells were ineffective, and 6.3 x 10(5) cells gave variable results. Shrinkage of the deprived lateral geniculate neurons was prevented by a transplant of 10(6) cells. In rats transplanted with hybridoma cells producing an antibody that functionally blocks nerve growth factor (NGF), we found that the effect of cotransplanted Schwann cells on monocular deprivation was partly counteracted. We conclude that transplantation of Schwann cells prevents both functional and anatomical effects of monocular deprivation, presumably acting through the production of NGF. We propose that transplants of Schwann cells could be a promising technique for clinical applications.

Functional postnatal development of the rat primary visual cortex and the role of visual experience: dark rearing and monocular deprivation

Postnatal development of rat visual cortical functions was studied by recording extracellularly from the primary visual cortex of 22 animals ranging in age from postnatal day 17 (P17) to P45. We found that in the youngest animals (P17-P19) all visual cortical functions tested were immature. Selectivity for orientation and movement direction of visual stimuli was almost absent, most cells received binocular input and their mean receptive field size was 5-6 times the adult size. Visual acuity was half its adult value. These functional properties developed gradually during the following weeks and by P45 they were all adult-like. This functional development is affected by manipulations of the visual input such as dark rearing (DR) and monocular deprivation (MD). DR prevented the normal postnatal maturation of visual cortical functions: in P60 rats, dark reared from birth, their visual cortical functions resembled those of P19-P21 rats. MD from P15 to P45 resulted in a dramatic shift of the ocular dominance distribution (ODD) in favour of the open eye and in a loss of visual acuity for the deprived eye. To determine the sensitive period of rat visual cortex to MD (critical period) we evaluated the shift in ODD of visual cortical neurones in rats that were subjected to the progressive delay of the onset of fixed MD period (10 days). Our results show that the critical period begins around the end of the third postnatal week, peaks between the fourth and fifth week and starts to decline from the end of the fifth week.

Monoclonal antibodies to nerve growth factor affect the postnatal development of the visual system

Exogenous supply of nerve growth factor (NGF) prevents the effects of monocular deprivation. This suggests that visual afferents may be competing for an endogenous neurotrophic factor, related to NGF, whose production by postsynaptic cells depends on the activity of afferent fibers. To test the hypothesis that endogenous NGF may play a role in the functional and anatomical development of the rat geniculo cortical system, the physiological action of NGF in the rat visual system was antagonized by using two independent monoclonal antibodies which neutralize NGF (alpha D11 and 4C8). To provide a continuous supply of antibodies during the period of visual cortical plasticity, alpha D11 or 4C8 antibody-producing hybridoma cells were implanted in the lateral ventricle of rats at postnatal day 15. This resulted in dramatic alterations of two of the most important parameters characterizing the functional development of the visual system, namely, visual acuity and binocularity of cortical neurons and in shrinkage of cells in the lateral geniculate nucleus. This demonstrates that the action of endogenous NGF is necessary for the normal functional and anatomical development of the geniculocortical system.

Effects of nerve growth factor on neuronal plasticity of the kitten visual cortex

1. The effect of intraventricular administration of nerve growth factor (NGF) by means of a cannula-minipump system was studied in kittens monocularly deprived during the critical period. The ocular dominance of area 17 neurones of NGF-treated and control kittens was determined by conventional extracellular recordings. The soma size of cells in A and A1 laminae of the lateral geniculate nucleus (LGN) was also evaluated in Cresyl Violet preparations. 2. Binocularly responsive neurons were found to be significantly more numerous in NGF-treated than in control kittens. The shrinkage of cells from the deprived LGN laminae normally observed in control kittens was prevented by NGF administration. 3. Following an initial period of monocular deprivation (MD) kittens subsequently treated with NGF showed a substantial recovery of functional binocular connections. 4. These findings indicate that the administration of NGF during the period of deprivation reduces the amblyopic effects of MD, while its administration to kittens with both eyes open following the initial deprivation promotes recovery of the deprived eye. 5. Neurotrophic factors may contribute to the regulation of experience-dependent modifications of synaptic connectivity in the visual cortex.

Monocular deprivation effects in the rat visual cortex and lateral geniculate nucleus are prevented by nerve growth factor (NGF). I. Visual cortex

The effects of monocular deprivation done during the critical period are usually ascribed to competition between the two sets of monocular thalamic afferents taking place at cortical level. We have suggested that loss in competition for the deprived eye is explained by the lack of a neurotrophic factor, produced in the cortex and dependent on electrical activity. To test this hypothesis we have exogenously supplied nerve growth factor (NGF) to rats monocularly deprived (MD) during the critical period, and studied whether monocular deprivation still affected the functional and anatomical organization of the visual cortex. NGF is produced in the rat visual cortex during the critical period, and its expression, at least in the hippocampus, seems to be regulated by electrical activity. Ocular dominance distribution of area 17 neurons, visual acuity, and Parvalbumin immunoreactivity (Parva-LI) were determined in four sets of animals: normal rats, control untreated monocularly deprived rats, deprived rats treated with cytochrome c (to control for non-specific aspects of NGF treatment), and deprived rats treated with NGF. Parva-LI is an excellent marker for the effects of monocular deprivation on the functional organization of the rat visual cortex. We found that exogenous supply of NGF completely prevented the shift in ocular dominance distribution of visual cortical neurons, the loss of visual acuity for the deprived eye, and the strong reduction in Parva-LI induced by monocular deprivation in control rats.

Monocular deprivation effects in the rat visual cortex and lateral geniculate nucleus are prevented by nerve growth factor (NGF). II. Lateral geniculate nucleus

In the preceding paper (Berardi et al. Proc. R. Soc. Lond. B 251, 17 (1993)), it has been shown that nerve growth factor (NGF) prevents the functional and anatomical alterations induced by monocular deprivation (MD) at the level of the visual cortex. Here we report that an exogenous supply of NGF prevents the shrinkage of neurons in the deprived laminae of lateral geniculate nucleus (LGN). The soma size distribution for the deprived ipsilateral laminae of MD rats is shifted towards smaller sizes (mean percentage of shrinkage with respect to the ipsilateral undeprived lamina = 21%, s.d. = 2%). As in other mammals, MD affects LGN relay neurons and spares LGN neurons projecting to the monocular portion of primary visual cortex. In NGF-treated animals we found that the soma size distributions for the deprived and undeprived ipsilateral laminae extensively overlap. The results of the two papers show that an exogenous supply of NGF prevents MD effects at both levels, visual cortex and LGN, and suggest a role for NGF in the plasticity of the geniculo-cortical pathway.

Protein-DNA interactions in the 5'-flanking region of the bovine pancreatic ribonuclease gene

In the 5'-flanking region of the bovine pancreatic ribonuclease gene a sequence has been identified which specifically binds one or more factors present in nuclear protein extracts prepared from bovine pancreas. The binding site, as delineated by footprinting analysis, is located in a region extending from positions -113 to -146 relative to the transcription initiation site of the ribonuclease gene. This region contains consensus sequences for known control transcriptional elements. The observed pattern of protein-DNA interactions is likely to be pancreas-specific as it could not be detected with nuclear extracts prepared from HeLa or bovine aorta endothelium cells.

Nerve growth factor (NGF) prevents the shift in ocular dominance distribution of visual cortical neurons in monocularly deprived rats

The hypothesis that NGF could play a role in the plasticity of the developing mammalian visual cortex was tested in monocularly deprived (MD) rats. In particular, we have asked whether an exogenous supply of NGF could prevent the changes in ocular dominance distribution induced by monocular deprivation. Hooded rats were monocularly deprived for 1 month, starting at postnatal day 14 (P14), immediately before eye opening, by means of eyelid suture. In eight rats, only monocular deprivation was performed; in eight rats, monocular deprivation was combined with intraventricular injections of beta-NGF, and in three rats, with intraventricular injections of cytochrome C. Injections (2 microliters) were given every other day for a period of 1 month. Single neuron activity was recorded in the primary visual cortex of MD rats, MD rats treated with NGF, and MD rats treated with cytochrome C at the end of the deprivation period, and in normal rats of the same age. We found that monocular deprivation caused a striking change in the ocular dominance distribution of untreated MD rats, reducing binocular cells by a factor of two and increasing by a factor of eight the number of cells dominated by the nondeprived eye. In MD NGF-treated rats, the ocular dominance distribution was indistinguishable from the normal. Cytochrome C treatment was completely ineffective in preventing the ocular dominance shift induced by monocular deprivation. To test whether NGF affected cortical physiology or interfered with transmission of visual information, we evaluated in NGF-treated rats the spontaneous discharge and the orientation selectivity. We found these functional properties to be in the normal range. We conclude that NGF is effective in preventing the effects of monocular deprivation in the rat visual cortex and suggest that NGF is a crucial factor in the competitive processes leading to the stabilization of functional geniculocortical connections during the critical period.

Parvalbumin immunoreactivity: a reliable marker for the effects of monocular deprivation in the rat visual cortex

In mammals, monocular deprivation performed during the early stages of postnatal development (critical period) dramatically affects the functional organization of the visual cortex. Since the early work of Hubel and Wiesel, the effects of monocular deprivation are accounted for by the fibers driven by the two eyes competing for the control of cortical territories. In cat and monkey striking structural changes accompany the functional effects of monocular deprivation. Also, in the rat, monocular deprivation causes functional alteration at the level of visual cortex; no structural correlates of these effects, however, have so far been described. Parvalbumin is a calcium binding protein that in the neocortex colocalizes with a subpopulation of GABAergic neurons. Here we report that in the rat monocular deprivation results in a dramatic reduction of parvalbumin-like immunoreactivity in the visual cortex contralateral to the deprived eye. This effect is due to competitive phenomena and not to visual deprivation itself, it is restricted to the binocular portion of the visual cortex and neither binocular deprivation, nor dark rearing can induce it. We conclude that parvalbumin-like immunoreactivity is a useful immunohistochemical marker for the effects of monocular deprivation in the rat visual cortex.

Exogenous supply of nerve growth factor prevents the effects of strabismus in the rat

It has recently been reported that exogenous supply of nerve growth factor prevents the effects of monocular deprivation both in rats and in cats. Here we have extended these experiments to the case of strabismus. Repeated intraventricular injections of nerve growth factor were performed in rats made surgically strabismic early in the critical period. At the end of the critical period the ocular dominance distribution of visual cortical neurons was assessed in strabismic untreated, strabismic nerve growth factor-treated and strabismic Cytochrome C-treated (control) rats by means of extracellular recordings. We found that in rats surgical strabismus causes a consistent loss of binocular neurons. By contrast the treatment with nerve growth factor maintains the normal ocular dominance distribution of neurons in the primary visual cortex. We conclude that nerve growth factor exogenously supplied prevents the effects induced by surgical strabismus in rats and suggest that nerve growth factor has a role in visual cortical plasticity.

Nerve growth factor prevents the amblyopic effects of monocular deprivation

Monocular deprivation early in life causes dramatic changes in the functional organization of mammalian visual cortex and severe reduction in visual acuity and contrast sensitivity of the deprived eye. We tested whether or not these changes could be from competition between the afferents from the two eyes for a target-derived neurotrophic factor. Rats monocularly deprived during early postnatal development were treated with repetitive intraventricular injections or topical administration of nerve growth factor. The effects of monocular deprivation were then assessed electrophysiologically. In untreated animals visual acuity and contrast sensitivity of the deprived eye were strongly reduced, whereas in nerve growth factor-treated animals these parameters were normal.

Different effects of intracranial and intraorbital section of the optic nerve on the functional responses of rat retinal ganglion cells

A lesion to the optic nerve of adult mammals leads to the retrograde degeneration and finally to the death of injured retinal ganglion cells. In this study, we have evaluated the effects induced by different sites of axotomy on the functional changes occurring in the retinal ganglion cells after optic nerve section. We have investigated the functional properties of retinal ganglion cells of adult rats by recording the retinal responses to patterned stimuli (pattern electroretinogram) after unilateral section of the optic nerve at two different levels: intraorbital and intracranial. The results show that the site of lesion of the optic nerve affects the time of disappearance of the pattern electroretinogram. The pattern electroretinogram takes longer to be degraded after an intracranial section than an intraorbital section.

Expression of NGF receptor and NGF receptor mRNA in the developing and adult rat retina

Nerve growth factor (NGF) has been recently found to rescue axotomized retinal ganglion cells (RGCs) of the adult rat from degeneration. Because the trophic effect of NGF involves a receptor-coupling event, the characterization and cellular localization of the NGF receptor (NGFR) in the retina are essential to understanding the possible specific action of NGF in this district of the central nervous system. We report here that the NGFR mRNA is expressed in fetal, neonatal, and adult rat retina. Using monoclonal antibody 192-IgG to immunoprecipitate and immunohistochemically identify NGFR, we also found that the NGFR from the retina has a molecular weight identical to that of the NGFR from PC12 cells. The NGFR is localized on RGCs and Müller cells. Finally, following ligation of the optic nerve, NGFR-immunopositive material was found to accumulate both distal and proximal to the site of ligation, suggesting that RGC axons anterogradely and retrogradely transport the NGFR. These data raise the possibility that NGF may play a specific role in rat RGCs.

Transplant of embryonal nervous tissue preserves the responses of rat retinal ganglion cells after section of the optic nerve

We have investigated the effectiveness of embryonal tectal tissue transplants in preserving the physiological activity of lesioned ganglion cells by recording the visual responses from the adult rat retina after section of the optic nerve, with or without transplants of embryonal nervous tissue on the stump. We have found that transplant of embryonal nervous tissue at the level of the optic nerve section has dramatic effects in preserving visual retinal responses to patterned stimuli for times as long as five months after surgery. By this time retinal responses to patterned stimuli have almost completely disappeared in control animals with optic nerve section alone.

Correlation in the discharges of neighboring rat retinal ganglion cells during prenatal life

The spontaneous discharges of neighboring retinal ganglion cells were recorded simultaneously in anesthetized prenatal rats between embryonic days 18 and 21. We report here that in the majority of cases the firings of neighboring retinal ganglion cells are strongly correlated during prenatal life. Correlation in the discharges of neighboring cells during development has long been suggested as a way to consolidate synaptic connections with a target cell onto which they converge, a model first proposed by Hebb. Correlation in the activities of neighboring neurons in the retina could be the basis of developmental processes such as refinement of retinotopic maps in the brain and segregation of the inputs from the two eyes.

Pattern ERG in rats following section of the optic nerve

The aim of this study is to investigate in the rat the properties of the pattern electroretinogram (ERG) and to assess whether it depends upon the functional integrity of ganglion cells. Flash and pattern ERG were recorded from urethane anaesthetized hooded rats. The pattern ERG was evoked by phase alternating gratings of various spatial frequencies and contrasts. In the first part of the study we determined how the amplitude of the main harmonic of the pattern ERG (2nd harmonic) varies as a function of stimulus parameters such as spatial and temporal frequency, contrast and mean luminance. In the second part of the study we investigated the effects of the retrograde degeneration of ganglion cells following optic nerve section on the amplitude of pattern ERG. We found that the section of the optic nerve leads to the progressive disappearance of the P-ERG which is almost complete 4 months after surgery. By this time only few axotomized ganglion cells are left. The flash ERG remained unaffected. Thus, the pattern electroretinogram seems to be a simple and sensitive tool to investigate the functional integrity of retinal ganglion cells in rats.

Schwann cells promote the survival of rat retinal ganglion cells after optic nerve section

Schwann cells (SCs) are known to play an important role for the regeneration of mammalian peripheral nerves. Their effect is likely due to the production of neuronotrophic and/or supportive factors. Here we study the effect of intraocular transplant of SCs on the survival of rat retinal ganglion cells (RGCs) after the intracranial section of the optic nerve. SCs were injected intraocularly in adult hooded rats. Surviving RGCs were retrogradely labeled with horseradish peroxidase applied to the proximal stump of the optic nerve. Results show that intraocular transplants of SCs promote the survival of a large number of RGCs for periods as long as 9 and 14 weeks after optic nerve section. In experimental retinae, surviving RGCs were 2- to 8-fold more numerous than in controls. This finding suggests that SCs are the source of factors that promote the survival of RGCs. Nerve growth factor is produced by SCs, and the intraocular injection of nerve growth factor has been previously shown to promote RGC survival. The rescuing effect of SCs on RGCs is greater than that obtained by intraocular injection of nerve growth factor. This greater effect may be due to the action of other neurotrophic factors produced by SCs or by transplanted SCs producing NGF in a sustained fashion.

The visual acuity of the lynx

Visual evoked potentials were recorded from the occipital scalp of two anaesthetized Lynx (Lynx europea) in response to alternating gratings of various spatial frequencies and contrasts. The visual acuity of the Lynx was found to be around 5-6 c/deg, i.e. very close to the visual acuity of the cat and by far inferior to human acuity.

Monocular deprivation in split-chiasm kittens does not impair the development of visuo-motor behaviour

Development of visual acuity is known to be impaired by early monocular deprivation. This may be due to lack of visual experience or to abnormal binocular competition. We report here the results of behavioural experiments on monocularly deprived kittens in which the optic chiasm had been split. In these kittens it has been found that visual acuity of the deprived eye is as good as the visual acuity of the non-deprived eye, namely 2-2.5 c/deg.

Response properties in the dorsal lateral geniculate nucleus of the adult cat after interruption of prenatal binocular interactions

1. Single-cell recordings were made in the magnocellular layer of the dorsal lateral genicule nucleus (dLGN) of five adult cats in which prenatal binocular interactions were interrupted by monocular enucleation at known gestational ages. Three cats (early enucleates) had one eye removed on either embryonic day 44.48, or 49, before retinogeniculate inputs are segregated into uniocular layers. Two other (late enucleates) underwent this procedure on embryonic days 55 and 58, when segregation is well advanced. Responses were compared with those obtained from recordings in the A and A1 layers of the dLGN of seven normal adult cats. 2. Cells were classified as ON or OFF by the use of spots of light and as X or Y based on a test of linearity of spatial summation with the use of counterphased sinusoidal gratings. Receptive-field size and spatial resolution were also obtained. 3. The dLGN of prenatally enucleated cats contains a dorsal magnocellular layer and a ventral parvocellular layer. In early enucleates, only an occasional hint of a cell-sparse interlaminar zone was apparent, located between the magnocellular and parvocellular layers. In late enucleates, a prominent cell-sparse band was observed contralateral to the remaining eye, in a region that would most likely correspond to layer A1 in the normal dLGN. No such cell-sparse band was seen ipsilateral to the remaining eye in late enucleates. 4. Eighty-six X cells and 22 Y cells were studied in the enucleates. Both cell types were found at all depths of the magnocellular layer. All but a few neurons had concentric ON-center or OFF-center receptive fields that were normal in size. The topography of receptive fields also appeared normal. In addition, spatial resolution of X and Y cells was similar in experimental and control animals. 5. In early enucleates there was a higher percentage of X cells and a lower percentage of Y cells than normal. The change in X-to-Y ratio was shown to be because of both a gain in cells with X properties and a loss of cells with Y properties. The distribution of dLGN somal sizes in the early enucleates was comparable with controls, so the change in X-to-Y ratio most likely did not result from an electrode sampling bias. It was suggested that the X-to-Y ratio difference could stem from the abnormalities in retinogeniculate terminal arbors that have been shown to follow early eye removal.(ABSTRACT TRUNCATED AT 400 WORDS)