Dark rearing and visual stimulation in the rat: effect on brain enzymes

Influence of visual deprivation on the visual and oculomotor system: acetylcholinesterase activity in oculomotor neurons

The effects of visual deprivation (dark-rearing) on neurons in both the visual and oculomotor systems of black mice were studied using morphologic and histochemical techniques. In the neurons of the dorsal nucleus of the lateral geniculate body, the cytoplasm of dark-reared mice was less developed and the cytoplasm/nucleus ratio was significantly smaller in the dark-reared mice than in the controls. In contrast, large motoneurons in the oculomotor nucleus did not show any ultrastructural changes and the cytoplasm/nucleus ratio was normal. However, in large motoneurons of dark-reared mice, acetylcholinesterase (AChE)-positive areas were scattered in the cytoplasm, and the ratio of the AChE-positive areas to the cytoplasm area was significantly smaller than that in the controls.

Developmental and neurochemical specificity of neuronal deficits produced by electrical impulse blockade in dissociated spinal cord cultures

Blockade of spontaneous electrical activity in dissociated fetal spinal cord cultures produced neuronal deficits as measured by biochemical and morphological techniques. Spinal cord cultures exhibited an age-dependent vulnerability to impulse blockade with tetrodotoxin (TTX) or xylocaine. Neuronal cell counts, [125I]tetanus toxin fixation and [125I]scorpion toxin binding indicated that TTX application produced neuronal deficits during the second or third week in culture. Application of TTX during the first or fourth week did not produce a difference in tetanus toxin fixation from controls. Radioautography of [125I]tetanus toxin revealed no obvious change in the label distribution after TTX treatment. Suppression of electrical activity during the first 6 days in culture had no effect on choline acetyltransferase (CAT) activity and no apparent effect on the appearance of the cultures. Application of TTX during the seventh day in culture decreased CAT activity to 68% of control. Chronic electrical blockade produced a progressively greater loss of CAT activity through 21 days in culture. GABAergic neurons, as indicated by high-affinity GABA uptake, glutamic acid decarboxylase activity and [3H]GABA radioautography, were not affected by electrical blockade. These data indicate that there is developmental and neurochemical specificity in the neuronal death produced by blocking spontaneous electrical activity in dissociated spinal cord cultures.

Effects of early monocular deprivation on choline acetyltransferase and glutamic acid decarboxylase in pigeon visual Wulst

Choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities were measured in various visual structures of the pigeon brain after long-term monocular deprivation followed by short-term binocular presence or absence of light stimulation. The short-term phase (45 min) was coupled with a 2-deoxyglucose experiment in order to select the adequate brain samples. After mononuclear deprivation during the first 6-11 months, ChAT activity was higher by 40-60% in the dorsolateral visual Wulst contralateral to the deprived eye, as compared to the other side. In the same structure, animals, either monocularly deprived or undeprived and exposed binocularly to environmental light for 45 min, had higher ChAT activities on both sides than those maintained in the dark. Mononuclear deprivation performed in adult animals did not affect the ChAT activity in visual Wulst. GAD activity was bilaterally decreased in the visual Wulst after early monocular deprivation. These results suggest that early monocular deprivation has an effect on biochemical systems involved in synaptic transmission at selected relays of the visual pathways.

Increased incorporation of [3H]lysine into synaptic membranes of the visual cortex following first exposure of dark-reared rats to light is confined to particular polypeptides

The incorporation of [3H]lysine into separated polypeptides of synaptic-membrane fractions prepared from the visual cortices of dark-reared rats and littermates exposed to light for 1 h was examined. Increased incorporation of [3H]lysine was found in synaptic membranes from light-exposed compared to dark-reared rats in polypeptides of four molecular weights: 100,000, 71,000, 44,000, and 38,000. The 44,000-molecular-weight peak has been suggested to be actin on the basis of its comigration with pure brain actin. These results indicate that increased incorporation of [3H]lysine into synaptic membranes of the visual cortex, following first exposure of dark-reared rats to light, is confined to particular polypeptides.

The role of pattern vision in the increase of visual cortex acetylcholinesterase after first exposure of dark reared rats to light

Acetylcholinesterase (AChE) activity in homogenates from motor and visual cortex of rats reared for 7 weeks in darkness was compared to levels in normally reared and dark reared littermates exposed to 3-h periods of controlled illumination. AChE levels in the visual cortex of animals fitted with light-diffusing scleral contact occluders, and therefore lacking normally organized visual information, were elevated 17% over dark-reared animals, but were not significantly different from levels in animals exposed to lighting conditions permitting detailed pattern discrimination. There were no differences between conditions in motor cortex AChE. We conclude that higher order perceptual processing is not necessary for the light-stimulated increase in visual cortex AChE in the rat.