Combined GABA-immunocytochemistry and TMB-HRP histochemistry of pretectal nuclei projecting to the inferior olive in rats, cats and monkeys

Cells in the pretectal nucleus of the optic tract (NOT) of rats, cats and monkeys were retrogradely labeled with horseradish peroxidase (HRP) stereotaxically injected into the inferior olive (IO). A procedure for stabilizing the tetramethylbenzidine (TMB)-HRP reaction product was used to visualize combined TMB-HRP and immunohistochemically localized gamma-aminobutyric acid (GABA) in the same sections. Positive GABAergic reaction product was found to be restricted to smaller-size intrinsic neurons. Larger NOT cells projecting to the IO were consistently free of GABA reaction product and, in addition, appeared to be contacted by relatively few GABAergic terminals.

Horizontal optokinetic reflex in light reared and dark reared Israelian gerbils (Meriones tristrami)

Israelian gerbils (Meriones tristrami) reared in the dark from birth to 7-13 weeks of age show a clear optokinetic reflex in both horizontal directions under monocular viewing conditions. This is very different from gerbils reared in the light, which like many other mammals with lateral eyes show a clear monocular optokinetic reflex only in response to stimuli moving from temporal to nasal in the visual field. It is concluded that exposure to day light during the first postnatal weeks prevents the development of the naso-temporal component of the optokinetic reflex in the Israelian gerbil.

[Effect of carbamazepine on the velocity of saccades]

In 5 female patients suffering from focal epilepsies, the maximal velocity of saccades was determined before and during carbamazepinE therapy. A decrease in the velocity of saccades was followed by an increase at the same serum level.

Variability in the effects of monocular deprivation on the optokinetic reflex of the non-deprived eye in the cat

Six cats monocularly deprived by eye lid closure within the first week after birth showed the same deficits in the optokinetic reflex (OKR) when tested through the deprived eye as adults irrespective of whether the deprivation period was 6, 24 or 36 months. Closed loop gain (eye velocity/stimulus velocity) during temporo-nasal stimulus movement was below 0.8 and approached zero at stimulus velocities above 20 degrees/s. Naso-temporal stimulus movement was ineffective in eliciting OKR gain higher than 0.1 at velocities above 10 degrees/s. Different optokinetic deficits were found when the non-deprived eye was tested. In 3 cats OKR gain of the non-deprived eye was reduced with temporally directed stimulus movement when compared to normal whereas the gain of nasal OKR was uneffected. In these cats only monocular cells could be found in the nucleus of the optic tract (NOT), a pretectal cell aggregation involved in the optokinetic reflex pathway. In the other 3 cats the OKR of the non-deprived eye was not different from normal and could be elicited almost equally well in both directions. In these cats binocular cells were found in the NOT ipsilateral to the non-deprived eye. Again duration (6, 24 or 36 months) of monocular deprivation had no influence on this dichotomy. In a cat with asymmetric OKR of the non-deprived eye, the removal of the visual cortex ipsilateral to the non-deprived eye produced a small but significant gain decrease for temporal OKR of the non-deprived eye but no change when the deprived eye was tested. Visual cortex lesion ipsilateral to the deprived eye in the same cat had also no effect on the deprived eye's performance but reduced nasal OKR gain for the non-deprived eye at high velocities. The effects induced by long term monocular deprivation were not reversed after intensively forcing the use of the deprived eye by closing the non-deprived eye. Also enucleation of the deprived eye had no effect on the gain of the non-deprived eye. These optokinetic deficits are discussed in relation to functional changes in the NOT.

Velocity selectivity in the cat visual system. I. Responses of LGN cells to moving bar stimuli: a comparison with cortical areas 17 and 18

Velocity selectivity of 92 LGN cells was measured quantitatively using long, narrow light or dark bars of high contrast in N2O-anesthetized and paralyzed cats. The optimal velocities of the main responses to a moving light bar, representing center responses (i.e., due to entering the ON center or leaving the OFF center) were significantly lower for X-cells than for Y-cells. The velocity upper cutoffs were significantly higher for Y-cells than for X-cells, whereas responses to slow movement were significantly stronger in X-cells than in Y-cells. The velocity range over which secondary responses were found was significantly lower for X-cells than for Y-cells. The velocity characteristics of LGN cells were compared with those measured under precisely the same experimental conditions in areas 17 and 18. Overall, the LGN cells were sensitive to much faster velocities than cortical cells. The differences between these cortical areas were found to be much larger than the differences in velocity selectivity observed in the LGN between X- and Y-cells or within the X and Y classes. In particular, the ubiquitous presence of cells responding only to very low velocities (less than 10 degrees/s) in area 17 subserving central vision cannot directly reflect LGN velocity selectivity, since such extreme preference for low velocities was not found in the LGN sample. Changes in eccentricity had much less effect on the velocity characteristics in the LGN than in the cortex. The latency of responses to a moving light bar as estimated using a spatial lag-velocity method was on average 46 and 37 ms for X-ON and Y-ON cells as opposed to 75 and 68 ms for X-OFF and Y-OFF cells, respectively. These latencies were slightly shorter than the ON and OFF latencies (time to peak) measured with stationary presentations of the same light bar (averages 61 and 53 ms for X-ON and Y-ON, 113 and 93 ms for X-OFF and Y-OFF). For a moving dark bar the average latency was 35 and 29 ms for X-OFF and Y-OFF cells, respectively, whereas it was 47 and 54 ms for X-ON and Y-ON cells. There were no significant differences in response strength between ON and OFF cells nor between X- and Y-cells. Many Y-OFF cells had nonlinear spatial lag-velocity relationships. This indicates a shift in response origin from distal to more proximal parts of the receptive field when going from low to high velocities.(ABSTRACT TRUNCATED AT 400 WORDS)

A correlation between receptive field properties and morphological structures in the pretectum of the cat

Retinal terminals in the pretectum were labelled by anterograde axonal transport of horseradish peroxidase (HRP) after injecting the enzyme into one eye. Pretectal neurons were retrogradely labelled by HRP-injections into the dorsal cap of the inferior olive. Electrophysiological recordings were performed in the same animal. This procedure showed that direction-selective neurons in the nucleus of the optic tract (NOT) projecting to the dorsal cap of the inferior olive lie dorsal and lateral to the retinal terminal clusters. Direction-unselective neurons sensitive to high stimulus velocities (jerk-neurons) were localized within the areas of retinal terminal clusters. Both jerk-neurons and retinal terminal clusters never overlapped with retrogradely labelled neurons. Latency measurements to stimulation of the optic chiasm (OX) confirmed a monosynaptic W-cell projection to the direction-selective NOT cells and indicated a predominantly monosynaptic Y-cell projection to the jerk-neurons.

The development of eye alignment in normal and naturally microstrabismic kittens

The development of interocular alignment was pupillographically measured from eye opening throughout the first half year of life in normal kittens and in kittens deriving from a naturally strabismic cat colony. Whereas the cyclorotatory component of age dependent changes did not differ between the two groups, the horizontal divergence of the optical axes was increased in the future esotropes during the whole observation period. Surprisingly the divergence angle of the optical axes was correlated with the convergence angle of the visual axes as determined during cortical receptive field analysis at 7-9 months of age. The authors suggest a theory that might explain the microstrabismic misalignment of the visual axes with an intraretinal defect.

Retinal input to the nucleus of the optic tract of the cat assessed by antidromic activation of ganglion cells

We have studied the physiological properties of ganglion cells in the retina of the cat. The experiments were designed to identify those ganglion cells which project to direction-selective cells in the nucleus of the optic tract (NOT), by demonstrating their antidromic activation at low threshold from an electrode in the NOT. These ganglion cells presumably provide the retinal drive to the optokinetic reflex. Altogether, 11 such ganglion cells were identified in a population of 578 cells studied. All 11 were W-cells, with slow-conducting axons. Five of the 11 had on-centre direction-selective receptive fields; the other 6 had a variety of receptive field patterns. Thus, on centre-selective cells form a much higher proportion of the retinal input to direction-selective cells in the NOT than of the overall ganglion cell population. However, their receptive field properties were too varied fully to account for the selectivity of NOT cells for horizontal stimulus movement. In summary the retinal input to the NOT appears to be formed principally or entirely by W-class ganglion cells, including many which are direction selective. It still seems necessary, however, to postulate, some non-retinal mechanism to account for all the receptive field properties of direction-selective NOT cells.

Shortage of binocular cells in area 17 of visual cortex in cats with congenital strabismus

Twenty-nine pigmented offspring of an innately esotropic female cat exhibited varying deficits in the number of binocular cells recorded in area 17 of the visual cortex as compared to 12 normal cats. Misalignment of the two eyes in these cats was found in the awake as well as in the paralysed state. Pupillography combined with measurements of visual disparity yielded abnormal esotropia of up to 8.4 degrees under paralysis, which corresponds to an abnormal convergence of the freely moving eyes of up to 14 degrees (average 7.4 degrees). In the majority of animals cortical binocularity was found reduced by the two eyes controlling independent sets of separate units (U-shaped ocular dominance distribution) whereas in 7 cats the reduction was due to a partial loss of one eye's influence. The proportion of monocular units correlated with the degree of crossover of the visual axes (r = 0.73). Anatomical investigation of the retinofugal projections revealed normal appearance in three previously recorded cats in which more than 50% of cortical units had been monocularly driven. The small angles of esotropia and the "normal" appearance of eye position judged by the pupillary positions in the orbit of these cats, might suggest that we found an animal model for microstrabismus.

Performance in the cat's visual system: a behavioural and neurophysiological analysis

Behavioural research, neurophysiological experiments and computer simulations are used in an attempt to analyze pattern recognition in the cat's visual system. The methods were chosen in such a way that the measurable performance data resulting from behavioural and neurophysiological experiments can be combined simply. It is shown that, with minor modifications, the methods can be adapted to every estimation and detection problem like pattern discrimination, movement detection and to the assessment of lesion effects, so that they are widely applicable. The system analysis permits the correct prediction of behavioural experiments and an approximate assignment of functions to the areas 17, 18 and 19 for the task set.

Double labelling of retinofugal projections in the cat: a study using anterograde transport of 3H-proline and horseradish peroxidase

A new method is described for combining 3H-proline and horseradish peroxidase (HRP) as anterograde neuronal tracers. By this method the presence of both substances can be demonstrated in the same histological section. We developed this method to investigate the retinofugal projections from the two eyes in the cat. One eye was injected with 3H-proline the other with HRP. Cryostat sections of the brain were mounted on emulsion coated slides in the dark. Sections were first exposed to the emulsion for 2-3 weeks at -40 degrees C and developed for autoradiography. Only then they were reacted for HRP-activity with tetramethylbenzidine (TMB). Keeping to this sequence autoradiographic procedures could not abolish the HRP-reaction product and silver grains and TMB can be visualized on the same slide. The wellknown projection pattern in the lateral geniculate nuclei was confirmed as a control for the new method. In the superior colliculus and in the pretectum a clear overlap of retinal terminals from the two eyes could be demonstrated for the first time.

Single cell activity in area 18 of the cat's visual cortex during optokinetic nystagmus

Single cell activity was recorded in area 18 during optokinetic nystagmus (OKN) in awake cats. The search coil technique was used to record the horizontal and vertical eye movements. Cells showing direction specific responses to a moving large area random dot pattern (70%) were tested with different velocities in the preferred and in the null-direction. Their response characteristics can be classified according to the two phases of the OKN. 41% responded specifically to the retinal slip velocity, having their response optimum at different values between 2 and 100 degrees/s. Additionally, in 60% of all tested cells the resetting saccades of the OKN were correlated with brief activity bursts of 39 ms latency on the average. These results are discussed in terms of two concepts: the classic concept of a corollary discharge from the oculomotor system and the concept of a gating function of the reticular system on thalamic and cortical transmission.

Effects of early monocular deprivation on visual input to cat nucleus of the optic tract

Single cells were recorded extracellularly in the nucleus of the optic tract (NOT) in monocularly deprived cats. Monocular deprivation had no effect on the direction specificity of these neurons, i.e. all cells in the left nucleus preferred movements from right to left and all units in the right nucleus preferred movements from left to right in the visual field. Neurons driven from the deprived eye failed to respond to stimuli moving at velocities above 10 degrees/s whereas neurons driven from the non-deprived eye responded to velocities up to and above 100 degrees/s as do neurons in normal cats. In 8 out of the 10 cats tested all cells in the two nuclei could be influenced only from the contralateral eye irrespective whether this was the deprived or the non-deprived eye. In the other two cats the influence from the non-deprived eye on cells in the ipsilateral NOT was found to be normal. This influence is mediated probably via cortico-fugal projections. In the 8 abnormal cats a clear deprivation effect could be assigned for the first time to the non-deprived eye consisting in a loss of its connections to the ipsilateral NOT. Electrical stimulation of the visual cortex revealed, however, the existence of a connection between the visual cortex and the NOT. A possible explanation for the specific deficit with visual stimulation in the cortico-pretectal synapse ipsilateral to the non-deprived eye is discussed in relation to developmental mechanisms. The conduction velocity of retinal input to the NOT and the output of the NOT to the inferior olive remained uninfluenced by visual deprivation.

Recovery of vision with the deprived eye after the loss of the non-deprived eye in cats

Closing one eye from birth to adulthood in kittens leads to well documented deficits in the visual system and has therefore frequently been used as an animal model for occlusion amblyopia. This study deals with the question whether vision through the deprived eye can be improved by appropriate postdeprivation manipulations and training. The performance of longterm monocularly deprived cats in a pattern discrimination task (bars of light had to be extracted from static two-dimensional visual noise) was measured quantitatively. The threshold in this test was three times higher than normal for the deprived eye when the non-deprived eye was closed by lid-suture, but only twice as high when the non-deprived eye was enucleated. This difference was statistically significant at the p less than 0.01 level in a t-test. The possible explanation for these behavioural findings is discussed on the basis of neurophysiological data from single cells in the visual cortex of the same animals obtained using a testing procedure similar to the behavioural tests. The better performance with the deprived eye after the non-deprived eye was lost may be related to an increase in the number of cortical cells driven from the deprived eye or to a reduction of "internal noise" after degeneration of the dominant pathway.

Layer-specific labelling of cat visual cortex after stimulation with visual noise: a [3H]2-deoxy-d-glucose study

Tritiated 2-deoxy-D-glucose (2-DG) was used to demonstrate layer specific uptake of 2-DG at the cellular level in the visual cortex of the cat after stimulation with different kinds of visual stimuli. Two-dimensional static Gaussian visual noise drifting across the visual field led to an increased accumulation of 2-DG in layers III and V as compared to the amount of radioactivity in layer IV. In unstimulated control tissue of visual cortex a homogeneous pattern of labelling was found. Horizontal bars moving vertically across the visual field increased the uptake in layer IV more than in all other layers. Analysis of the 2-DG uptake at the cellular level revealed that visual noise activated two bands of cells, one above and one below layer IV, whereas bar stimuli activated cells mainly in layer IV. Accumulation of 2-DG was always higher in the perikarya than in the surrounding neuropil. These results confirm the physiologically recorded properties of cells in different cortical layers.

Retinal projection to the nucleus of the optic tract in the cat as revealed by retrograde transport of horseradish peroxidase

Retrograde transport of horseradish peroxidase injected iontophoretically into the nucleus of the optic tract of cats revealed that the direction-selective cells in this pretectal nucleus receive direct retinal projections from small retinal ganglion cells, the so-called gamma-cells. These cells from a horizontal band on the contralateral retina. Few labeled cells are found in the ipsilateral temporal retina. The input from the contralateral retina is 10 times more numerous than from the ipsilateral one. In both retinae the highest concentration of labeled cells is near the area centralis.

A quantitative analysis of the direction-specific response of Neurons in the cat's nucleus of the optic tract

All cells in the nucleus of the optic tract (NOT) of the cat, that could be activated antidromically from the inferior olive, were shown to be direction-specific, as influenced by horizontal movements of an extensive visual stimulus. Cells in the left NOT were activated by leftward and inhibited by rightward movement, while those in the right NOT were activated by rightward and inhibited by leftward movement. Vertical movements did not modulate the spontaneous activity of the cells. The mean spontaneous discharge rate in 50 NOT cells was 30 spikes/s. This direction-specific response was maintained over a broad velocity range (Less Than 0.1 degrees - Greater Than 100 degrees/s). Velocities over 200 degrees/s could inhibit NOT cells regardless of stimulus direction. All cells in the NOT were driven by the contralateral eye, about half of them by the ipsilateral eye also. In addition, activation through the contralateral eye was stronger in most binocular units. Binocular cells preferred the same direction in the visual space through both eyes. An area approximately corresponding to the visual streak in the cat's retina projected most densely onto NOT cells. This included an extensive ipsilateral projection. No clear retinotopic order was seen. The most sensitive zone in the very large receptive fields (most diameters being Greater Than 20 degrees) was along the horizontal zero meridian of the visual field. The retinal input to NOT cells was mediated by W-fibers. The striking similarities between the input characteristics of NOT-cells and optokinetic nystagmus are discussed. The direction selectivity and ocular dominance of the NOT system as a whole can provide a possible explanation for the directional asymmetry in the cat's optokinetic nystagmus when only one eye is stimulated.

Strabismus disrupts binocular convergence in cat nucleus of the optic tract

Rendering kittens strabismic by surgical section of the medial rectus muscles results in disruption of binocular convergence in the nucleus of the optic tract. Visual input through the ipsilateral eye of strabismic cats does not influence cells in this nucleus although nearly one half of the cells encountered in normal cats receive inputs from both eyes. The results provide a basis for the deficits in optokinetic nystagmus found in strabismic cats and suggest a new mechanism underlying competition between inputs from the two eyes during postnatal development.

Olivary afferents from the pretectal nuclei in the cat

The organization of the projection from the pretectal region to the inferior olive in the cat was studied by means of retrograde protein tracing and experimental degeneration. Small injections of horseradish peroxidase (HRP) were made into various parts of the inferior olive from a ventral approach. The number of nerve cells in the pretectal nuclei retrogradely labelled with HRP was counted and put in relation to the site of injection. Labelled cells were only found in the posterior pretectal nucleus (NPP), the nucleus of the optic tract (NOT) and the anterior pretectal nucleus (NPA). Most labelled cells were found in NPP and NOT in cases in which the rostral or caudal levels of the principal olive were labelled by the injection. NAP labelling occurred in one case with a very rostral injection of the inferior olive. Unilateral electrolytical destruction of the pretectal region produced terminal degeneration in the ipsilateral inferior olive. The heaviest ipsilateral degeneration was found in the upper half of the principal and dorsal accessory olives, and caudally in the ventrolateral outgrowth, the dorsal cap and nucleus beta with the adjacent part of the medial accessory olive. Some functional implications of the findings are discussed.

A comparison of visual responses in two pretectal nuclei and in the superior colliculus of the cat

Single unit recordings from 220 units were obtained from the nuclei praetectalis anterior (NPA) and posterior (NPP) of 30 immobilized, anesthetized cats. Quantitative analysis of pretectal (PT) visual activity was mainly based on recordings from the NPP. For comparison, 160 collicular (CS) neurons were studied. A strong sensitivity for moving objects was evident in both samples. The following main types of PT activity were categorized: (A) slow movement, direction-selective units (21%); (B) slow movement, nondirection-selective units (19%); (C) units nonselective for stimulus velocity and direction (24%); (D) jerk movement selective, nondirection-selective units (36%). Latency measurements following single shocks to optic chiasm (OX) and tract (OT) showed mainly slow conducting fiber input to the PT and CS which can be divided into two different groups by conduction properties and synaptic delay: direct W-input and delayed W-input. Fast Y-fiber input of both types, direct and indirect, was recorded at both sites, PT and CS.

Monocular deprivation and the signal transmission by X- and Y-neurons of the cat lateral geniculate nucleus

1. In adult cats deprived monocularly from the second week of life, single neurons were recorded from the optic tract (OT), the lateral geniculate body (pars dorsalis, LGN) and the optic radiation (OR). The neurons were classified according to their visual response properties (Y/X) or their latencies to OT electrical stimulation (class I/II). 2. A close positive correlation (greater than 95%) was found between the visual classification and the latency classification (Y = I, X = II). 3. The relative frequency of class I/Y-neurons was reduced in the group of pattern-deprived LGN neurons, but normal in the pattern-deprived OR neurons. 4. The ratio of the r1 and r2 wave amplitude of the OR-evoked potentials elicited by electrical stimulation of the normal or the deprived eye optic nerve was not affected by pattern deprivation. 5. The activity pattern of neurons recorded from the LGN or the OR did not differ in normal and pattern-deprived neurons belonging to the same class (on-center/off-center; Y/X). The same was true for the neuronal responses to electrical stimulation of the OT at different stimulus frequencies (1-200 stimuli/s). 6. The average maintained activity of pattern-deprived OT or OR neurons recorded while the eyelids of the deprived eye were still closed was either equal to or even somewhat higher than the average activity of the corresponding normal neurons. This was true when the patterned stimuli were presented stationary or were moved at random within the visual field simulating the effect of eye and head movements. The pattern deprivation effects found morphologically and physiologically in the visual cortex are, therefore, not induced by a diminished average activity of the input neurons from the deprived eye.

Psychophysical and neurophysiological investigations of the effects of early visual deprivation in the cat

Cats can locate objects with their monocularly deprived eye best in the monocular segment of their visual field. In contrast they show a marked deficit towards the midline and an almost total failure in the binocular segment contralateral to the deprived eye. This correlates well with the relative frequency of units in the superior colliculus activated by that eye. The performance of the cat in a pattern discrimination task is three times better with the normal eye than with the deprived eye if the patterns have to be detected on a background of visual noise. This correlates well with the loss of units in the visual cortex activated by the deprived eye. There is no loss of visual acuity in the units in lamina A of the lateral geniculate body, but in lamina A1 visual acuity is reduced to half the normal value due to monocular deprivation.

Functional aspects of plasticity in the visual system of adult cats after early monocular deprivation

Responses to visual stimuli and to electrical stimulation of the optic chiasma were analysed in neurons of the lateral geniculate nucleus, visual cortex and superior colliculus in monocularly deprived cats with different post-deprivation periods. If the cats had both eyes open in their post-deprivation period (1 year) no recovery from the effects of early deprivation was found in the responses of neurones in all 3 visual structures. In cats with a post-deprivation reverse closure we found an increase in the proportion of Y-cells recorded in the early deprived layer of LGN when compared to the Y-cell proportion found in the same layers immediately after the deprived eye was opened. In neurons of the visual cortex and superior colliculus the functional abnormalities remained unaltered. The late closure of the non-deprived eye for up to 3 years did not effect neurons normally activated through that eye. Removal of the non-deprived eye unmasked connections of the deprived eye’s pathway onto neurons in the visual cortex and the superior colliculus. The neurons showed no specificity for the direction of movement or the orientation of visual stimuli. This recovery from deprivation was greater after enucleating the cats at the age of 6 months than at 18 months after birth. In the lateral geniculate nucleus of these cats the proportion of Y-cells in the recorded sample driven by the deprived eye had recovered to the value of normal cats. The difficulties in relating these physiological findings to results from morphological or behavioural studies are discussed.

Effects of early binocular deprivation on visual input to cat superior colliculus

1. Recent work has demonstrated at least three distinct inputs to the superior colliculus in normal cats: a) the W-direct retinotectal pathway; b) the Y-direct retinotectal pathway; and c) the Y-indirect pathway which involves Y-cells in retina and lateral geniculate nucleus plus complex cells in cortex, the last being the corticotectal cells. 2. We investigated these inputs in five cats raised with binocular eyelid closure by studying the electrophysiological properties of 164 collicular neurons. After such binocular deprivation, the Y-indirect pathway was missing and the Y-direct pathway appeared reduced, although the W-direct input seemed unaffected. 3. Despite the loss of the Y-indirect input, collicular activation to electrical stimulation of cortex seemed normal in these cats. This suggested that the Y-indirect loop was affected between the optic tract and cortex, and this, in turn, correlated to the previously described reduction in recordable Y-cells from the lateral geniculate nucleus of binocularly deprived cats. 4. We found receptive-field correlates to this loss of Y-direct and Y-indirect input in the binocularly deprived cats. Compared to collicular neurons in normal cats, those in deprived cats exhibited abnormally strong dominance by the contralateral eye, loss of directional selectivity, and loss of responsiveness to fast visual stimuli. 5. These and other data lead to the suggestion that in normal and monocularly deprived cats, the corticotectal input dominates collicular receptive-field properties, whereas in binocularly deprived cats, the remaining retinotectal input dominates these properties.