Substantial reduction of noradrenaline in kitten visual cortex by intraventricular injections of 6-hydroxydopamine does not always prevent ocular dominance shifts after monocular deprivation.

Ten kittens had cannulas inserted into their lateral ventricles for daily injections of 6-hydroxydopamine (6-OHDA). At 5-6 weeks of age one eye was sutured shut, and one week later recordings were made from the visual cortex to assay the ocular dominance of a sample of cells. In six kittens the injections of 6-OHDA were continued until the day before recording, while in four kittens the injections were stopped around the time of eye suture, on the assumption that continued injections of 6-OHDA over several days has effects that are not specific to the noradrenaline (NA) system and that the two procedures might show different results. In all animals the concentration of NA in the visual cortex near the site of recording was reduced by approximately 90%. In all animals the ocular dominance histograms recorded from the visual cortex were shifted so that the majority of cells (83 +/- 13%) were dominated by the open eye. There were no substantial differences between the two groups of experimental animals or between the experimental animals and two control animals that had cannulas implanted and ascorbate alone injected without 6-OHDA. We conclude that the concentration of NA in the visual cortex can be reduced substantially by injections of 6-OHDA into the lateral ventricle without preventing the shift in ocular dominance that usually occurs after suturing shut the eyelids of one eye.

Comparison of signal and adaptive sensitivity profiles of the surround mechanism of cat retinal ganglion cells.

Signal and adaptive sensitivity profiles of the surrounds of cat retinal ganglion cells were determined by varying the position of concentric annuli whose outside and inside diameters varied but whose total area remained constant. Signal sensitivity profiles were determined by adjusting the luminances of these annuli so as to produce a weak suprathreshold response of constant magnitude and time course. Adaptive sensitivity profiles were determined by varying the luminances of concentric equal-area, unmodulated annuli until the response to a temporally modulated annulus attained a criterion level. The results provided evidence that the retinal region over which the surround mechanism of an X cell pools adaptive information and pools signals are the same, and that the distribution of adaptive and signal sensitivities within these regions is similar. A small number of X cells showed local adaptation effects. The adaptive pooling area appeared to be smaller than the signal pooling area for Y cells.

Substantial reduction of cortical noradrenaline by lesions of adrenergic pathway does not prevent effects of monocular deprivation.

We tested the theory that depletion of noradrenaline reduces the plasticity of the visual cortex in kittens by using another method of depletion. Lesions were made in the lateral hypothalamus to interrupt fibers in the dorsal noradrenergic bundle going from the locus ceruleus to the telencephalon. The lesions were induced at approximately 3 1/2 weeks of age in kittens; approximately 2 weeks later one eye was sutured shut, and about 10 days after that cells were recorded in the visual cortex. The location of the lesions was verified histologically, and the effect of the lesions was verified by noradrenaline analyses (high pressure liquid chromatography-electrochemistry) of samples from the visual cortex. The noradrenaline content of the visual cortex was reduced by 70 to 90%. However, the majority of cells recorded in the visual cortex could not be driven through the eye that had been sutured closed. The ocular dominance histograms for cells in the visual cortex were indistinguishable from those of kittens that were monocularly deprived for a similar period in the "critical period" and that had normal amounts of noradrenaline in their visual cortex. Therefore, we conclude that reduction of the noradrenaline content of the visual cortex by 70 to 90% is insufficient, by itself, to prevent the physiological changes that occur in the visual cortex after monocular deprivation.

Effects of 6-hydroxydopamine on visual deprivation in the kitten striate cortex.

We tested the effects of 6-hydroxydopamine (6-OHDA) on two forms of visual deprivation--monocular and directional deprivation. In normal kittens monocular deprivation leads to a change in the ocular dominance histogram recorded from the visual cortex, and directional deprivation leads to a change in the percentage of directionally sensitive cells responding to the appropriate direction of movement. 6-OHDA was infused into the occipital cortex prior to the peak of the critical period for the effects of visual deprivation. In agreement with the results of Kasamatsu et al. (Kasamatsu, T., and J. D. Pettigrew (1979) J. Comp. Neurol. 185: 139-162; Kasamatsu, T., J. D. Pettigrew, and M. Ary (1979) J. Comp. Neurol. 185: 163-182), suture of one eye (monocular deprivation) after the 6-OHDA treatment did not lead to a shift in ocular dominance in the area of striate cortex infused. Moreover, rearing kittens in an environment continually moving past them in one direction (directional deprivation) did not lead to a change in the percentage of cells preferring movement in that direction. In both rearing procedures the 6-OHDA did not make the cells in the cortex nonspecific, compared to cells recorded from the cortex of animals reared similarly but without infusion of 6-OHDA. Monocular and directional deprivation are forms of visual deprivation with different critical periods, probably involving different synapses. Therefore, the effect of 6-OHDA on visual deprivation is a general one, involving more than one kind of visual deprivation. In both cases 6-OHDA abolishes the plasticity of the visual cortex.

Effect of target position and size on adaptive sensitivity of the surround mechanism of cat retinal ganglion cells.

The spatial distribution of the surround's adaptive sensitivity was assessed in the receptive fields of cat retinal ganglion cells. The results provide evidence that the surrounds adaptive sensitivity is higher in the center of the receptive field of Y-cells than X-cells.

Adaptive sensitivity of the surround mechanism of cat retinal ganglion cells.

The spatial distribution of the surround's adaptation mechanism was studied in X- and Y-cells in the cat's retina. Adaptive sensitivity was assessed with adapting annuli with equal-area, but variable position and with adapting annuli with variable size. The results provide evidence that adaptive sensitivity of the surround's adaptive mechanism is higher in the center of the receptive field of Y-cells than of X-cells.

Hexamethonium modification of cardiovascular adjustments during combined static-dynamic arm exercise in monkeys.

In weight lifting and rowing, essentially the same groups of muscles contract in isometric (static) and isotonic (dynamic) fashion. To approximate the combined static-dynamic arm movements involved in rowing or lifting weights, four rhesus monkeys were trained to pull a T-bar and thereby avoid tail shock. Each animal received 8 daily test sessions in which loads (0.4, 0.8, 1.2, 1.6 kg), total pulls (3, 6, 9, 12 at a constant pull frequency, 0.5 Hz) and alternate sessions of pulling after injection of hexamethonium chloride (7 mg/kg) or saline were factorially combined. Our data indicate that heart rate in this model is primarily influenced by the duration of the dynamic exercise component (number of pulls) in this specific exercise task whereas both dynamic and static components affect systolic and diastolic blood pressure. After ganglionic blockade, heart rate and diastolic pressure do not change appreciably during T-bar pulling while the rise in systolic pressure is attenuated and varies primarily as a function of the static exercise component. The clinical implications of these experiments are discussed.

Development of the dorsal lateral geniculate nucleus in normal and visually deprived Siamese cats.

Neuronal cell bodies in the lateral geniculate nucleus of normal and of monocularly-deprived Siamese cats have been measured. Seventeen normally reared Siamese cats, ranging in age between 20 and 120 days, were used to determine rates of normal geniculate cell growth. A second group of five adult Siamese cats reared from bith with the lids of one eye closed were used to study the effects of monocular visual deprivation upon geniculate cell size. For each of the normal and visually deprived Siamese cats, the cross-sectional areas of 600 lateral geniculate cells were measured from camera lucida drawings of Nissl preparations. During normal development the geniculate cells rapidly increase in size during the first postnatal month of life and reach their adult size sometime between days 28 and 56. While this course of geniculate cell growth is similar to that seen in normally pigmented cats, the pattern of change seen after monocular deprivation is quite different in Siamese cats from that found in normally pigmented cats. In Siamese cats the regions of the nucleus receiving a contralateral projection from the deprived eye appear to be shielded from the effects of binocular competition. Cells throughout lamina A and in the abnormal, contralaterally innervated segment of lamina A1 show only about a 10% reduction in cell size. There are no noticeable differences between the parts of lamina A in the binocular and monocular segments of the nucleus. Cells in the ipsilaterally innervated segment of lamina A1, in contrast, show deprivation-induced changes that average 27.1%. Two mechanisms are proposed to explain why some geniculate cells in Siamese cats appear to be shielded from binocular competition: one depends on possible interactions between geniculo-cortical cells lying in adjacent parts of the same geniculate lamina, and the other depends on an anatomical segregation of the cell type ("Y-cells") most heavily affected by the binocular competition. Each proposed mechanism is related to earlier observations on monocularly deprived, normally pigmented cats.

Effect of adapting target size on the gain of the surround response mechanism in X- and Y-cells in cat retina.

The adaptation field of the surround mechanism of X and Y retinal ganglion cells in the cat was assessed with variable size, unmodulated adapting spots. Both an on-inhibition measure and an off-discharge measure of surround gain was used. Results suggest that the surround mechanism in Y-cells is strongest in the receptive field middle but weak or nonexistent in the middle of X-cell receptive fields.

Spatial distribution of the adaptation field of the surround response mechanisms in type X cat retinal ganglion cells.

The surround response mechanism in on-center X-cells in cat retina was found to be bimodally distributed and weak or nonexistent in the receptive field middle. An on-inhibition measure was used to assess surround mechanism gain.