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M J Friedlander

Publications and source records attributed to M J Friedlander.

At least 37 records · Page 2Linked to original sources
PubMed1990

Effect of passive eye position changes on retinogeniculate transmission in the cat.

1. Extracellular recordings were made from single neurons in layer A of the left dorsal lateral geniculate nucleus (LGNd) of anesthetized and paralyzed adult cats. Responses to retinotopically identical visual stimuli (presented through the right eye) were recorded at several positions of the left eye in its orbit. Visual stimuli consisted of drifting sinusoidal gratings of optimal temporal and spatial frequencies at twice threshold contrast. Visual stimulation of the left eye was blocked by a variety of methods, including intravitreal injection of tetrodotoxin (TTX). The change in position of the left eye was achieved by passive movements in a randomized and interleaved fashion. Of 237 neurons studied, responses were obtained from 143 neurons on 20-100 trials of identical visual stimulation at each of six eye positions. Neurons were classified as X- or Y- on the basis of a standard battery of physiological tests (primarily linearity of spatial summation and response latency to electrical stimulation of the optic chiasm). 2. The effect of eye position on the visual response of the 143 neurons was analyzed with respect to the number of action potentials elicited and the peak firing rate. Fifty-seven (40%) neurons had a significant effect [by one-factor repeated-measure analysis of variance (ANOVA), P less than 0.05] of eye position on the visual response by either criterion (number of action potentials or peak firing rate). Of these 57 neurons, 47 had a significant effect (P less than 0.05) with respect to the number of action potentials and 23 had a significant effect (P less than 0.05) by both criteria. Thus the permissive measure by either criterion and the conservative measure by both criteria resulted in 40% and 16%, respectively, of all neurons' visual responses being significantly affected by eye position. 3. For the 47 neurons with a significant effect of eye position (number of action potentials criterion), a trend analysis of eye position versus visual response showed a linear trend (P less than 0.05) for 9 neurons, a quadratic trend (P less than 0.05) for 32 neurons, and no significant trend for the 6 remaining neurons. The trends were approximated with linear and nonlinear gain fields (range of eye position change over which the visual response was modulated). The gain fields of individual neurons were compared by measuring the normalized gain (change in neuronal response per degree change of eye position). The mean normalized gain for the 47 neurons was 4.3. 4. The nonlinear gain fields were generally symmetric with respect to nasal versus temporal changes in eye position.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1990

Effect of passive eye movement on retinogeniculate transmission in the cat.

1. The nature and time window of interaction between passive phasic eye movement signals and visual stimuli were studied for dorsal lateral geniculate nucleus (LGNd) neurons in the cat. Extracellular recordings were made from single neurons in layer A of the left LGNd of anesthetized paralyzed cats in response to a normalized visual stimulus presented to the right eye at each of several times of movement of the left eye. The left eye was moved passively at a fixed amplitude and velocity while varying the movement onset time with respect to the visual stimulus onset in a randomized and interleaved fashion. Visual stimuli consisted of square-wave modulated circular spots of appropriate contrast, sign, and size to elicit an optimal excitatory response when placed in the neurons' receptive-field (RF) center. 2. Interactions were analyzed for 78 neurons (33 X-neurons, 43 Y-neurons, and 2 physiologically unclassified neurons) on 25-65 trials of identical visual stimuli for each of eight times of eye movement. 3. Sixty percent (47/78) of the neurons tested had a significant eye movement effect (ANOVA, P less than 0.05) on some aspect of their visual response. Of these 47 neurons, 42 (89%) had a significant (P less than 0.05) effect of an appropriately timed eye movement on the number of action potentials, 36 (77%) had a significant effect on the mean peak firing rate, and 31 (66%) were significantly affected as evaluated by both criteria. 4. The eye movement effect on the neurons' visual responses was primarily facilitatory. Facilitation was observed for 37 (79%) of the affected neurons. For 25 of these 37 neurons (68%), the facilitation was significant (P less than 0.05) as evaluated by both criteria (number of action potentials and mean peak firing rate). Ten (21%) of the affected neurons had their visual response significantly inhibited (P less than 0.05). 5. Sixty percent (46/78) of the neurons were tested for the effect of eye movement on both visually elicited activity (visual stimulus contrast = 2 times threshold) and spontaneous activity (contrast = 0). Eye movement significantly affected the visual response of 23 (50%) of these neurons. However, spontaneous activity was significantly affected for only nine (20%) of these neurons. The interaction of the eye movement and visual signals was nonlinear. 6. Nine of 12 neurons (75%) tested had a directionally selective effect of eye movement on the visual response, with most (8/9) preferring the temporal ward direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1990

Evaluation of long-term potentiation of small compound and unitary EPSPs at the hippocampal CA3-CA1 synapse.

Long-term potentiation (LTP) was evaluated for small monosynaptic CA3-mediated EPSPs in CA1 neurons in the guinea pig hippocampal slice. Small EPSPs included those elicited by stimulation of Schaffer axon collaterals of several CA3 neurons (160-480 microV amplitude, n = 40 EPSPs in 40 neurons) and those elicited by stimulation of an individual CA3 neuron (89-563 microV amplitude, n = 14 EPSPs in 11 neurons). Various protocols were employed to induce LTP and were deemed successful as evaluated by recording sustained enhancement of the mean peak amplitude of conventionally elicited large compound EPSPs and extracellular field potentials. However, in 47 of 54 cases, tetanization did not lead to a potentiation of the small or unitary EPSPs. In 9 cases, it was possible to directly evaluate the compound EPSP (elicited by stimulating a group of CA3 neuron's axons) and the unitary EPSP (elicited by stimulating a single CA3 neuron) in the same CA1 neuron. The tetanization protocol was successful in inducing LTP in 7 of 9 of these CA1 neurons as evaluated by the compound EPSP but resulted in LTP for only 1 of 9 of the unitary EPSPs for the same neurons. One explanation for these results is a threshold mechanism controlling the expression of LTP. Although LTP induction occurred in most cases, it is proposed that a critical level of depolarization (achieved by the test activation of a sufficient number of CA3 neurons) is necessary so that the enhancement at the modified synapse is expressed.

Action Potentials↗
PubMed1990

The time course and amplitude of EPSPs evoked at synapses between pairs of CA3/CA1 neurons in the hippocampal slice.

Unitary EPSPs were evoked in CA1 pyramidal neurons by activation of single CA3 pyramidal neurons. Seventy-one EPSPs were recorded. The peak amplitudes of these EPSPs ranged from 30 to 665 microV with a mean of 131 microV. Rise times and half-widths were measured, the means +/- SD being 3.9 +/- 1.8 and 19.5 +/- 8.0 msec, respectively. The time courses of these EPSPs were consistent with a brief synaptic current at a localized electrotonic region of the dendritic tree followed by passive spread of current to the soma. EPSPs varied in amplitude from trial to trial. Sufficient records were collected for 12 EPSPs to demonstrate that this variation was greater than could be accounted for by baseline noise. The amplitude variations of one EPSP were reliably resolved from the background noise, and this EPSP fluctuated between 4 discrete amplitudes (including failures) separated by a quantal increment of 278 microV.

Animals↗
PubMed1989

Physiological, morphological, and cytochemical characteristics of a layer 1 neuron in cat striate cortex.

We have recorded from a small neuron in layer 1 of the striate visual cortex in a 34-day-old kitten. It had a simple, orientation-selective receptive field that was nondirectional and showed length summation. The neuron was injected intracellularly with horseradish peroxidase. Computer-aided reconstruction revealed that it had a dense axonal plexus confined to layer 1, elongated in the anteroposterior dimension. By means of an antibody directed against a GABA-like antigen, and postembedding immunocytohemistry, the neuron was found to be strongly immunoreactive. The main input to soma and dendrites of the neuron was from synapses that were not GABA-L-immunoreactive, and probably originated from pyramidal cells. The axon of the cell formed synapses on dendritic shafts and spines, whose most likely sources were the apical tufts of pyramidal cell dendrites. These data suggest that such neurons may be involved in local circuits that contribute to the formation of pyramidal cell receptive fields.

Animals↗
PubMed1989

Gating of retinal transmission by afferent eye position and movement signals.

Vision in most vertebrates is an active process that requires the brain to combine retinal signals with information about eye movement. Eye movement information may feed forward from the motor control areas of the brain or feed back from the extrinsic eye muscles. Feedback signals elicited by passive eye movement selectively gate retinal outflow at the first relay, the dorsal lateral geniculate nucleus. The gating predominantly facilitates retinogeniculate transmission immediately after eye movement and inhibits transmission when a new steady-state eye position is achieved. These two gating effects are distributed in a complementary fashion across the dorsal lateral geniculate nucleus such that the spatiotemporal activity profile could contribute to object detection and localization.

Action Potentials↗
PubMed1989

Expression of an intrinsic growth strategy by mammalian retinal neurons.

Postnatal cat retinal ganglion cells (RGCs) were retrogradely labeled with fluorescent microspheres, dissociated from the retina using a peeling procedure, and monitored in cell culture with a time-lapse video microscopy system. The spatial patterns formed by the growing neurites were analyzed using conventional and fractal measures (Hausdorff dimension, H) of their extent and complexity. The results presented were obtained from the arborizations formed by the neurites of 48 labeled and isolated ganglion cells growing separate from each other and separate from a feeder layer of astrocytes. Cells were obtained from animals when the RGCs were postmitotic and after dendritic differentiation in vivo at age 0-1 week (4/48), 2-5 weeks (35/48), or 6-8 weeks (9/48). By 48 hr after plating, the number of surviving labeled RGCs was reduced to 22-28% of its initial value. After removal of all processes and isolation in vitro, these RGCs expressed neurite patterns strikingly similar to those seen in the intact retina, although the RGCs had been deprived of potential cues from the intact retina and target tissue. Self crossings of the growing neurites were rare (less than 0.5%, 20 cells, n = 2500 neurites). Calculation of the Hausdorff dimension, a metric for the space-filling capacity of the neurite patterns, revealed that after 3-day culture 77% (n = 56) of the RGCs achieved relatively uniform coverage of territory (1.6 less than H less than 1.9). This coverage was independent of the number of interbranchpoint segments and/or the total neurite length of a particular neurite pattern. A sample of dendritic arbors from RGCs in intact retina yielded similar values for the Hausdorff dimension (H = 1.73, SD = 0.12, n = 18, range 1.54-1.94). These results reveal that a mammalian central nervous system neuron, for at least 8 postnatal weeks, has the intrinsic capacity for reexpression of in vivo structure characteristic of that cell type in the absence of interaction with neighboring neurons, afferent input, and target tissue. These neurons exhibit stereotyped growth resulting in uniform coverage of a restricted territory by the strategic selection of the length, location, and orientation of interbranchpoint segments.

Aging↗
PubMed1989

Development of Y-axon innervation of cortical area 18 in the cat.

1. Geniculocortical Y-axons (n = 38) in the optic radiations of 4-5-week-old kittens (n = 20) and adult cats (n = 18) were studied both physiologically and morphologically. Axons were recorded from intracellularly and subsequently filled ionophoretically with horseradish peroxidase (HRP). The HRP filled the axons' terminal arborizations in visual cortex (particularly well for those innervating area 18). Fourteen axons appeared to be completely filled with HRP (n = 8 in kitten, n = 6 in adult) and served as the basis for the quantitative analysis of the terminal arborizations reported in this study. 2. The distribution and correspondence of the axonal boutons to presynaptic elements in cortical layer 4A was analysed at both the light and electron microscope level using computerized three-dimensional analysis and serial section reconstruction, respectively. Compared to adult axons, the boutons of the kitten axons were smaller (means = 0.75 vs. 1.75 microns length, P less than 0.001) and more densely spaced both along individual axon branches (means = 6.60 vs. 11.20 microns interbouton interval, P less than 0.001) and between neighbouring branches of the same axon (means = 4.7 vs. 6.4 microns nearest-neighbour distance, P less than 0.01). 3. Most kitten boutons made a single Gray's type 1 synapse on a cortical neurone, unlike adult boutons which usually contacted two or more postsynaptic targets. Both kitten and adult axons had dendritic spines as their major target. Occasionally, HRP reaction-product was observed in cortical neurones postsynaptic to the labelled geniculocortical axon, which gave some estimate of the number of synaptic contacts between a single geniculocortical axon and target cell (about five). 4. The kitten Y-axons innervated the visual cortex in a pattern similar to that of the adult, with the richest terminal branching and bouton density in layer 4A with some additional boutons distributed in layers 3, 4B and 6. The extent of the terminal arborizations primarily in layer 4A (as measured in surface views) of kitten Y-axons in area 18 was significantly less than that of adult Y-axons in area 18 (means = 0.9 mm2 vs. means = 1.2 mm2, P = 0.04). 5. We conclude that between 4 and 5 postnatal weeks and 1 year, geniculocortical Y-axons projecting to cortical area 18 undergo four major changes. These include a reduction in synaptic bouton density (both in three-dimensional space and along individual branches), a concomitant moderate expansion in the surface area of cortex innervated, an increase in bouton size and an increase in the number of synaptic contacts made by each bouton. A general proportional growth of the individual axons' terminal arborization together with fusion and/or separation of neighbouring boutons is sufficient to explain this development.

Aging↗
PubMed1989

Postnatal development of the spatial contrast sensitivity of X- and Y-cells in the kitten retinogeniculate pathway.

The sensitivity to spatial contrast patterns of single retinal ganglion cell axons and neurons in the A-layers of the dorsal lateral geniculate nucleus (LGNd) was measured in 4 1/2- and 6 1/2-week-old kittens and adult cats. Drifting sinusoidal grating stimuli were presented at 6-12 spatial frequencies to obtain spatial contrast sensitivity functions (SCSFs). The SCSFs were normalized for the postnatal growth of the kitten eye and were interpreted using a difference of Gaussians model of the receptive field (RF). The average optimal spatial frequency, spatial frequency bandwidth, and the proportion of cells that were selective for spatial frequency did not differ significantly between the kittens and adults for ganglion cells belonging to the cluster 1 (X-) or cluster 2 (Y-) functional types. The spatial resolution of kitten ganglion cells was also adultlike, except for that of Y-ganglion cells with peripheral RFs, which was significantly higher than in the adult. The spatial resolution of X-LGNd neurons with peripheral RFs was significantly poorer at 4 1/2 weeks than in the older animals. The proportion of X-LGNd neurons that were selective for spatial frequency increased between 4 1/2 and 6 1/2 weeks postnatally, but the spatial frequency bandwidth of selective cells did not change. The increased proportion of spatially selective LGNd neurons is probably due to the maturation of intrageniculate inhibitory circuits. Developmental changes in spatial resolution were interpreted as resulting from an increase (Y-retinal ganglion cells) or decrease (X-LGNd neurons) in RF center size. A model of retinogeniculate development is presented that attributes postnatal expansion of Y-retinal ganglion cell RF centers to increased functional convergence from more distal retinal neurons and reduction in LGNdX-cell RF center size to decreased convergence from X-retinal ganglion cells.

Animals↗
PubMed1988

Identification of X versus Y properties for interneurons in the A-laminae of the cat's lateral geniculate nucleus.

Roughly 25% of the neurons in the A-laminae of the cat's lateral geniculate nucleus are local interneurons, while the remaining 75% are relay cells that project to the visual cortex. The interneurons form the focus of our study. The relay cells are either X or Y cells and are thereby integral links in the parallel and independent retino-geniculo-cortical X and Y pathways. Little is known about the response properties of interneurons, largely because it is difficult to identify them clearly during electrophysiological recording. However, they can be identified by morphological criteria. We thus studied their response properties by recording intracellularly from geniculate neurons to characterize them and then injecting them with horseradish peroxidase (HRP); the HRP labeling subsequently allowed us to distinguish relay cells from interneurons. In this manner, we studied 171 relay cells (83 X and 88 Y) and 15 interneurons. The response properties tested for each of the interneurons were indistinguishable from those of the relay X cells. We conclude that these interneurons are directly innervated by retinogeniculate X axons and are firmly embedded in the X pathway. We found no evidence for interneurons in the Y pathway.

Action Potentials↗
PubMed1987

Evidence for interlaminar inhibitory circuits in the striate cortex of the cat.

An interlaminar, ascending, and GABAergic projection is demonstrated in the striate cortex of the cat. We have examined a basket cell, with soma and smooth dendrites in layers V and VI, that was injected intracellularly with HRP in the kitten. Three-dimensional reconstruction of its axon revealed a horizontal plexus in layer V and upper VI, extending about 1.8 mm anteroposteriorly and 0.8 mm mediolaterally; a dense termination in the vicinity of the soma in layers V and VI; and an ascending tuft terminating in layers II and III in register above the soma and about 250 microns in diameter. Many boutons of this cell contacted neuronal somata and apical dendrites of pyramidal cells and subsequent electron microscopy showed that these boutons formed type II synaptic contacts with these structures. A random sample of postsynaptic targets (n = 199) in layers III, V, and VI showed that somata (20.1%), dendritic shafts (38.2%), and dendritic spines (41.2%) were contacted. The fine structural characteristics of postsynaptic elements indicated that the majority originated from pyramidal cells. Direct identification of postsynaptic neurons was achieved by Golgi impregnation of four large pyramidal cells in layer V, which were contacted on their somata and apical dendrites by between three and 34 boutons of the HRP-filled basket cell. Layer IV neurons were not contacted. Golgi-impregnated neurons similar to the HRP-filled basket cell were also found in the deep layers. The axonal boutons of one of them were studied; it also formed type II synapses with somata and apical dendrites of pyramidal cells. Boutons of the HRP-filled neuron were shown to be GABA-immunoreactive by the immunogold method. This is direct evidence in favour of the GABAergic nature of deep layer basket cells with ascending projections. The existence of an ascending GABAergic pathway was also demonstrated by injecting [3H]GABA into layers II and III. The labelled amino acid was transported retrogradely by a subpopulation of GABA-immunoreactive cells in layers V and VI, in addition to cells around the injection site. The axonal pattern and mode of termination of deep basket cells make them a candidate for producing or enhancing directional selectivity, a characteristic of layer V cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Postnatal development of receptive field surround inhibition in kitten dorsal lateral geniculate nucleus.

We recorded the responses to visual stimulation of single neurons in the A-layers of the dorsal lateral geniculate nucleus (LGNd) of 4- to 5-wk-old kittens and adult cats. Visual stimuli were generated on a cathode-ray tube (CRT) display and consisted of circular spots and annuli whose contrast was twice the threshold for each neuron and was modulated about a background luminance of 28 cd/m2 at 0.5 Hz. Neural responses were collected as interspike intervals and displayed as instantaneous firing rates for individual trials. From the responses to a series of sizes of spot stimuli, area-response functions were constructed and used to derive a quantitative measure of the strength of the receptive field (RF) surround inhibition of each neuron, the spatial density minimum ([SDmin[). To separate neural from optical factors that affect measurements of surround inhibition, published values for the posterior nodal distances of the kitten and adult eye were used to scale stimuli in terms of the retinal area subtended. Of 153 kitten and 95 adult LGNd neurons studied, the responses to a complete series of spot stimuli of different sizes (areas) were obtained for 52 kitten neurons [44 with linear spatial summation (L) and 8 with nonlinear spatial summation (NL)] and 45 adult (24 X-and 21 Y-) neurons. In addition, intracellular recordings were made from 30 of the kitten neurons that were filled iontophoretically with horseradish peroxidase (HRP) and were evaluated structurally. In the adult, neurons were classified as X-or Y-cells on the basis of a battery of physiological properties, including linearity of spatial summation, latency to electrical stimulation of the optic chiasm, and ability to respond reliably to rapidly moving stimuli. Kitten neuronal responses allowed them to be clearly identified as exhibiting linear or nonlinear spatial summation, but application of additional criteria produced ambiguous results for classification into X-or Y-categories. Kitten L or NL neurons showed differences typical of adult X-and Y-cells on some [e.g., RF center size (P less than 0.01)] but not other [e.g., latency to stimulation of optic chiasm (P greater than 0.40)] properties. In addition, by direct comparison of morphological features with these physiological responses, some kitten cells with adult X-cell physiological properties on these tests were found to have typical adult Y-cell somadendritic structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗
PubMed1985

The structure of the terminal arborizations of physiologically identified retinal ganglion cell Y axons in the kitten.

Retinal ganglion cell (r.g.c.) axons (n = 17) in the optic tract of 4-5 week-old kittens and adult cats (n = 4, this study, n = 27 from other reports) were studied both physiologically and morphologically. Axons were initially classified during extracellular recording with a battery of physiological tests that included Fourier analysis of the response to a sinusoidally counterphased sine-wave grating. Y axons had a significant second harmonic response component (greater than twice the fundamental) present independent of the spatial phase position of the grating. These axons were then recorded from intracellularly and subsequently filled ionophoretically with horseradish peroxidase (HRP). The HRP filled the axons' terminal arborizations in the dorsal lateral geniculate nucleus (l.g.n.). The innervation pattern and and structure of the terminal arborizations of the kitten r.g.c. Y axons were compared to those of the adult. The kitten Y axons innervated the l.g.n. in a pattern similar to that of the adult (individual branches from a single axon always innervated lamina A or A1 and may also have innervated lamina C, the medial interlaminar nucleus (m.i.n.) and/or sent branches that coursed medial to the l.g.n.). Fourteen of seventeen of these Y axons in the kitten innervated either of the A-laminae heavily (greater than 200 terminal boutons per axon). The remaining three r.g.c. Y axons in the kitten had only small arborizations within lamina A (less than fifty terminal boutons per axon) but heavily innervated lamina C. The structure of the terminal boutons on the kitten r.g.c. Y axons was highly variable when compared to axons of adult cats. Some of the boutons were spherical or crenulated as in the adult. Many others had filopodia and growth cone-like terminals with fine extensions. This variable maturation of terminal boutons was seen both between axons and on individual axons. The number of boutons on the kitten r.g.c. Y axons in the A-laminae was significantly less than that of adult Y axons. The mean numbers of boutons per axon were 476 and 1553 in the kittens and adult cats, respectively (P less than 0.001, Mann-Whitney U test). The width of the terminal arborization of individual Y axons in the A-laminae of the kittens was considerably smaller than in adult cats (mean widths of the terminal arborizations are 192 and 293 micron in the kittens and adult cats, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1984

Fine structural morphology of identified X- and Y-cells in the cat's lateral geniculate nucleus.

Four physiologically identified neurons in the A laminae of the cat's dorsal lateral geniculate nucleus were filled with horseradish peroxidase and studied using the electron microscope. Two were X-cells and two were Y-cells. Each had electrophysiological properties appropriate for its X- Or Y-cell class, and each also had an axon that projected into the optic radiation, indicative of a geniculocortical relay cell. Representative samples from about 10% of each neuron's entire dendritic arbor (proximal and distal) were taken to obtain an estimate of the types and distributions of synapses contacting these arbors. One X-cell had a cytoplasmic laminar body, but there were no other significant cytological differences seen among the neurons. Common to each of the neurons were the following synaptic features: (i) retinal terminals (r.l.p.) were mostly or entirely restricted to proximal dendrites or dendritic appendages (less than 100 microns from the soma). These terminals constituted about 15-25% of the synapses on the proximal dendrites. (ii) Terminals with flattened or pleomorphic synaptic vesicles (f. terminals) were predominant on the proximal dendrites (30-55% of the total synapses for that region) and were mainly located near the retinal terminals. A smaller percentage (10-20%) were also distributed onto the distal dendrites. (iii) Small terminals with round synaptic vesicles (r.s.d.), many presumably having a cortical origin, predominated (60-80%) on distal dendrites (greater than 100 microns), but also formed a large proportion (40-70%) of the synapses on the intermediate (50-150 microns) dendrites. Total synaptic contacts for one X-cell and one Y-cell were estimated at about 4000 and 5000, respectively. The major fine structural differences observed between X- and Y-cells were almost entirely related to the retinal afferents. First, the retinal synapses for X-cells were mostly made on to dendritic appendages (spines, etc.), whereas Y-cells had most of their retinal synapses onto the shafts of primary and proximal secondary dendrites (that is, near branch points. Second, the retinal terminals that contacted X-cell dendrites nearly always formed triadic arrangements that included nearby f. terminals, but those on Y-cells rarely did so. Finally, the main type of f. terminals associated with X-cells were morphologically different from most of those associated with the Y-cells, and this also related directly to the triadic arrangements; that is, f. terminals in the triadic arrangements were morphologically distinguishable from f. terminals that did not participate in triadic arrangements.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Effects of monocular deprivation on the distribution of cell types in the LGNd: a sampling study with fine-tipped micropipettes.

Six cats were reared with monocular eyelid suture from 1 week of age. Two control animals were reared in the same colony. The sutured eye of the monocularly deprived (MD) cats was opened at 8-9 months of age. The effect of monocular deprivation on the distribution of functional classes of neurons in the dorsal lateral geniculate nucleus (LGNd) was evaluated by extracellularly recording the activity of single neurons in the A-laminae of the LGNd ipsilateral to the deprived eye. A similar sampling procedure was used in the LGNd of the two control animals. Recordings were made with extremely fine-tipped micropipettes (impedances = 50-80 M omega at 200 Hz when filled with 3M NaCl; tip diameters less than 0.3 micron when measured with scanning electron-microscopical methods). Micropipettes with these tip sizes were shown previously (Friedlander et al. 1981) to display no sampling bias on the basis of soma size in the LGNd of normal cats. Only data from complete penetrations through the non-deprived and deprived laminae were used in our analysis. Each animal's non-deprived lamina A also provided control data. In addition, we recorded from geniculocortical axons in the optic radiations above the LGNd (ipsilateral to the deprived eye in five cats and both ipsilateral and contralateral to the deprived eye in one cat). The percentages of X- and Y-cells encountered in the LGNd of our control animals is in agreement with previous estimates based on cell size (2:1 X- to Y-cells - Friedlander et al. 1981). In the present study, fewer normal X- and Y-cells were encountered in laminae innervated by the deprived eye than in laminae innervated by the non-deprived eye in every MD animal. When these values were normalized for the shrinkage of the deprived lamina, only the Y-cell population was significantly reduced. These differences are highly significant both when the data from all of the animals are pooled (chi 2 = 21.77; P less than 0.0001), and when the comparisons are made for individual animals (P less than 0.02, Mann-Whitney U-test). While some of the reduction in Y-cells may be due to an increase in the number of cells with abnormal receptive field properties, too few abnormal cells were encountered to totally account for the reduction in the number of Y-cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Structure of physiologically classified neurones in the kitten dorsal lateral geniculate nucleus.

The mammalian forebrain, including the dorsal lateral geniculate nucleus (LGNd) and the visual cortex, continues both structural and functional development postnatally and is therefore a useful model for the study of developmental processes in the central nervous system (CNS). We report here the first description and comparison of the structural development of individual, functionally identified neurones in the mammalian forebrain. This comparison is made for the three main cell groups of the central visual pathways (W-, X- and Y-cells), in the neonate and the adult. In the adult, these three classes of neurones have different characteristic electrophysiological properties(1-9) and relay information in parallel about different features of a visual scene8,9 from the retina through the LGNd to the visual cortex. In addition, each of the three functional cell types has a characteristic structure in the adult10,11. By injection of the enzyme marker substance, horseradish peroxidase, into electrophysiologically identified neurones, the present study demonstrates that each of these functional classes of neurones also has a characteristic morphology in the neonate (in the LGNd of kitten 3-4 postnatal weeks of age). However, striking differences in the rates of maturation are seen. The W-cells are already mature at this age. The X-cells are the least developed. Surprisingly, some Y-cells are mature. Due to the susceptibility of Y-cells to an abnormal visual environment during development12-18, they had previously been thought to be slower to mature.

Animals↗
PubMed1982

Effects of monocular deprivation on the structure-function relationship of individual neurons in the cat's lateral geniculate nucleus.

The retino-geniculo-cortical pathways of the cat composed of at least three parallel channels. The neurons in these channels (W-, X-, and Y-cells) have different physiological properties. In earlier studies, we used a direct structure-function for analysis for individual geniculate neurons in normal cats. This was accomplished by electrophysiological characterization of the neuron followed by intracellular iontophoresis of horseradish peroxidase into the same neuron. By this technique, we demonstrated that W-, X-, and Y-cells have distinctive morphological features in the lateral geniculate nucleus of the act. We have extended this analysis in cats reared with monocular eyelid suture to 24 geniculate neurons innervated by the sutured eye in lamina A or A1. Ten of the 24 neurons (42%) had abnormal structure-function relationships. All but 1 of the normal cells were X-cells. Abnormalities included: (1) Y-cells with normal physiology but abnormally small somata; (2) Y-cells with abnormal physiology and morphology, including poor responsiveness and unusually thin, tortuous, and beaded dendrites; (3) visually unresponsive cells with morphology similar to that of the physiologically abnormal Y-cells; and (4) cells with the physiology of normal X-cells but the morphology of normal Y-cells. Furthermore, soma size measurements indicate that the abnormally small somata found in deprived geniculate laminae result from a selective effect on Y-cells.

Animals↗