Electrical activity of the visual cortex under conditions of altered monoamine levels in the brain of animals

In experiments on 8 rabbits and 12 rats changes in electrograms of the visual cortex of alert animals were studied under photic stimulation in conditions of pharmacological action on monoamine (MA) brain systems. After injection of MA precursors (5-oxitriptophane and d, 1-dioxiphenylalanine) following phenomena were observed: a) decrease of the amplitude of the averaged evoked potentials to rhythmic photic stimuli (1-20 imp. sec.-1); b) an enhancement of fast (15-25 Hz) oscillations in the cortical spontaneous electrical activity and weakening and modification of the effects of the blockader of synthesis of MA-alpha-methyl-dioxiphenylalanine. Under light stimulation potentiation of MA precursors effects was observed in the frequency spectra of electrocorticograms. In the same conditions the specificity of action of cathecholamines precursor was revealed in the form of an increase of power of rhythms of 5-7 Hz and it; decrease in 2-3 Hz. Possible mechanisms of the revealed phenomena are discussed.     

Effect of visual deprivation on evoked potentials in the visual cortex and superior colliculus in rabbits

Evoked potentials arising in the visual cortex and superior colliculus to stimulation of the collateral eye by single, paired, and repetitive flashes were recorded in rabbits reared in darkness or in normal illumination. The absence of significant change in the latent period and amplitudes of the first two components of the collicular responses and of the recovery cycle and response to repetitive stimulation in the light-deprived animals suggest that photic stimulation does not affect the normal functional development of the rabbit retinotectal system. However, functional deafferentation in the early postnatal period gives rise to serious disturbances of visual cortical function, as reflected in a marked decrease in amplitude of the primary response, lengthening of the recovery cycle, and narrowing of the range of rhythm-binding frequencies of flashes. These disturbances were reversible. The period of maximal sensitivity of the rabbit retinocortical system to visual deprivation begins at the end of the first month of postnatal life. The possible mechanisms lying at the basis of these functional disturbances in light-deprived animals are discussed.     

The topography of functional interhemispheric asymmetry in the visual cortex]

Functional interhemispheric asymmetry was investigated by evoked potentials method in experiments on ten cats under ethaminal anaesthesia at 200 points of the visual cortex during the action of binocular and monocular photic flashes of submaximal intensity. Topographic maps have been plotted of the functional interhemispheric asymmetry. In most of the animals a hemisphere dominant and non-dominant at the given moment can be singled out. Section of the callosal body leads to reduction of the functional interhemispheric asymmetry due to a decrease of the focus of maximum activity in the dominant hemisphere and its increase in the non-dominant one. A mozaic pattern of functional interhemispheric asymmetry has been demonstrated, as expressed in the existence of zones of inverse dominance along with prevailing zones of direct dominance. Section of the callosal body produced a decrease in the area of direct dominance and an increase in that of inverse dominance. Absolute interhemispheric asymmetry was most pronounced in the central part of the visual cortex (field 18 and its medial boundary) and the relative one, on the periphery of the visual area (fields 17 and 19).     

Dynamics of acetylcholinesterase activity in the brain during elaboration and stabilization of defensive conditioned reflexes

Electro-defensive condtioned reflexes (CR) to light were elaborated in rats in Y-maze in one experimental session and their training was continued during subsequent 20 sessions. Immediately after CR elaboration or the 20th session of its training, AChE activity in the motor and visual cortex and the hippocampus decreased, increasing again in 24 hours. Animals used as active control which received non-paired photic and electric stimuli, exhibited opposite changes of AChE activity.     

Recovery of the visual evoked response in the cat following administration of diisopropylfluorophosphate, an irreversible cholinesterase inhibitor

Visual evoked responses (VER) to counterphased gratings were recorded from area 17 of cat visual cortex prior to and following administration of diisopropylfluorophosphate (DFP). The VER and acetylcholinesterase (AChE) activity of blood, retina, and visual cortex were reduced significantly following DFP administration. Approximately two hours after exposure to 4 mg/kg DFP, the VER began to recover and in some cats returned to base line levels. In contrast, blood, retina, and cortex AChE activity showed little, if any, tendency for recovery throughout the experiment. Since atropine sulfate provided at least partial recovery of the VER following DFP without affecting AChE inhibition, an accumulation of acetylcholine (ACh) probably is involved in the initial visual loss. However, recovery of the VER over time while AChE remained severely inhibited implicates mechanisms other than, or in addition to, accumulation of ACh at receptor sites.     

Ambient temperature effects on brain and spinal cord acetylcholinesterase activity of two poikilotherms

The changes in AChE activity and protein content following cold or heat exposure and heat death were determined in the brain and spinal cord of both Rana ridibunda and Chalcides ocellatus. Cold exposure (10 degrees C) caused a decrease in the enzyme activity and protein content of both animals. Exposure to heat (36-40 degrees C) increased markedly the AChE activity and the amount of protein in the two experimental animals. Heat death was found to be associated with a prominent decrease in enzyme activity and the protein level of the brain and spinal cord of the two poikilotherms.     

Effects of phenylhydrazine or recombinant human erythropoietin on deformability and activity of dehydrogenase glucose-6-phosphate and acetylcholinesterase in Wistar rats blood enriched in reticulocytes

Deformability and activity of the enzymes: acetylcholinesterase (AChE) and dehydrogenase glucose-6-phosphate (G-6-PD), were assayed for RBC enriched in immature reticulocytes. Reticulocytosis was evoked by administration of two different drugs: recombinant human erythropoietin (rHuEPO) and phenylhydrazine (PHZ) to two groups of Wistar rats. After treatment with the former compound, a group of animals exhibited 17.33% reticulocytes in blood whereas a group of rats treated with the latter drug reached 57.66% of these cells in blood. A marked decrease in RBC deformability was found in both groups of animals. AChE did not significantly change activity neither in PHZ-treated nor in rHuEPO-treated rats, whereas G-6-PD activity was significantly decreased in the PHZ-treated group.     

Nuclear and cytoplasmic RNA in visual cortex neurons of adult rats following visual deprivation and photic stimulation

It has been shown by two-wavelength cytospectrophotometry of gallocyanin-chrome alum-stained sections that visual deprivation in adult rats kept in a complete darkness for 30 days resulted in an accumulation of cytoplasmic RNA by layer V neurons of the visual cerebral cortex and by the cells of the perineuronal neuroglia of this layer. The nuclear RNA content remained unchanged. Stimulation of intact rats with a flickering or constant light induced an increase in the cytoplasmic RNA in these neurons rather than in the nuclear RNA as well as in RNA in their glial satellite cells. Similar light stimulation of the deprived animals gave rise to a complete return of the neuronal RNA to normal with only a slight decrease in the deprivation-induced RNA accumulation by the neuroglial cells. Neither visual deprivation nor light stimulation affected the RNA content in the neurons and neuroglia of layer V of the motor cerebral cortex. Compartmentation of RNA metabolism within the neuronal-neuroglial unit is discussed.     

The influence of functional alteration on monoamine oxidase and catechol-O-methyl transferase in the visual pathway of rats

—Rats were reared in complete darkness or under chronic stimulation with flashing light from birth to the age of 7 weeks. Light deprivation caused a significant increase in monoamine oxidase activity (measured with [¹⁴C]serotonin) of about 30 per cent in the structures of the visual pathway. Chronic stimulation with flashing light had no influence on the activity of monoamine oxidase in either visual or non-visual structures. The activity of catechol-O-methyl transferase in the brain areas of light-deprived rats was reduced, in light-stimulated rats it was slightly increased. In mother rats kept together with their litters in either complete darkness or flashing light for 5 weeks no change in monoamine oxidase activity was observed. The activity of catechol-O-methyl transferase in mother rats kept in darkness was significantly decreased in all brain regions studied; in light-stimulated animals the enzyme activity was not affected.     

Effects of illumination and enucleation on substance-P-immunoreactive structures in subcortical visual centers of golden hamster and Wistar rat

The undecapeptide substance P is found in different entities of the visual system that control eye movement and synchronize endogenous rhythms with the light cycle (i.e., superior colliculus, suprachiasmatic nucleus, intergeniculate leaflet). Immunocytochemical methods were used to compare the reactivity to substance P in the brain of five groups of golden hamsters and two groups of Wistar rats: (1) untreated hamsters kept under 14L:10D and sacrificed at noon; (2) identically maintained animals sacrificed at midnight; (3) enucleated animals kept under control conditions; (4) hamsters kept under constant darkness; (5) hamsters kept under the same conditions as the controls, but intraventricularly injected with colchicine. The results obtained in golden hamsters of groups (1) and (3) were compared with findings in Wistar rats treated accordingly [groups (6) and (7)]. Substance P-immunoreactive perikarya were found in the suprachiasmatic nucleus and superior colliculus of hamsters and Wistar rats. Substance P-immunoreactive nerve fibers were abundant in the hypothalamic area ventral to the paraventricular nucleus, in the intergeniculate leaflet, in some thalamic nuclei, and in the superior colliculus. Immunoreactivity to substance P in the suprachiasmatic nucleus and intergeniculate leaflet did not vary among the experimental groups. However, a conspicuous decrease in reactivity to substance P was observed in the superficial layers of the superior colliculus of enucleated hamsters and rats, compared with all other groups. These results indicate that substance P immunoreactivity in the superior colliculus, but not that in the suprachiasmatic nucleus or intergeniculate leaflet, depends on the integrity of the retinal projection.     

Expression of acetylcholinesterase during visual system development in Drosophila

As in other insects acetylcholine (ACh) and acetylcholinesterase (AChE) function in synaptic transmission in the central nervous system of Drosophila. Studies on flies mutant for AChE indicate that in addition to its synaptic function of inactivating acetylcholine, this neural enzyme is required for normal development of the nervous system (J.C. Hall, S.N. Alahiotis, D.A. Strumpf, and K. White, 1980, Genetics 96, 939-965; R.J. Greenspan, J.A. Finn, and J.C. Hall, 1980, J. Comp. Neurol. 189, 741-774). In order to understand what role AChE may play in neural development, it is necessary to know, in detail, where and when the enzyme appears. The use of monoclonal antibodies to localize AChE in the developing visual system of wild type Drosophila has yielded the novel observation that AChE appears in photoreceptor (retinula) cells 4-6 hr after they differentiate and 3 to 4 days before they are functional. Three days later the staining in the cell body of these cells is reduced. Because retinula cells have no functional connections at the time when AChE is first detected, AChE can not be performing its standard synaptic function. Subsequent to the reduction of AChE in the retinula cells, midway through the pupal stage, the enzyme accumulates rapidly in the neuropils of the optic lobes of the brain. Thus, there is a biphasic accumulation of AChE in the developing visual system with the enzyme initially being expressed in the retinula cells and accumulating later in the optic lobes.     

Trace reactions following combination of a sensory stimulus with polarization of the visual region of the cortex]

Spontaneous activity and responses to photic flashes and tones of 133 neurones were recorded in the visual cortex during polarization of the same area (1.5 to 10 muA, 5 to 30 min) and after it (one to 52 min). Responses of cells to two unimodal stimuli of different parameters were analysed, of which one was presented repeatedly during the polarization ("positive"), and the other one to three times ("negative"). Depending on the previous "learning", 47.4% of the units responded after the polarization to "positive" photic stimulus and 37,8%--to acoustic stimulus. The trace effects of the stimuli pairings are reproduced in polarization after-effect by the action of the sensory signal alone. The recorded differences in the nature and duration of the reproduction of trace processes formed to an adequate and inadequate stimuli, are due to the dissimilar action of polarizing currents on neurones of the cortex cross-section and to different effectivity of the visual and non-visual influences related to it.     

Spectral tuning and the visual ecology of mantis shrimps

The compound eyes of mantis shrimps (stomatopod crustaceans) include an unparalleled diversity of visual pigments and spectral receptor classes in retinas of each species. We compared the visual pigment and spectral receptor classes of 12 species of gonodactyloid stomatopods from a variety of photic environments, from intertidal to deep water (> 50 m), to learn how spectral tuning in the different photoreceptor types is modified within different photic environments. Results show that receptors of the peripheral photoreceptors, those outside the midband which are responsible for standard visual tasks such as spatial vision and motion detection, reveal the well-known pattern of decreasing lambdamax with increasing depth. Receptors of midband rows 5 and 6, which are specialized for polarization vision, are similar in all species, having visual lambdamax-values near 500nm, independent of depth. Finally, the spectral receptors of midband rows 1 to 4 are tuned for maximum coverage of the spectrum of irradiance available in the habitat of each species. The quality of the visual worlds experienced by each species we studied must vary considerably, but all appear to exploit the full capabilities offered by their complex visual systems.     

Effect of diisopropylfluorophosphate on muscarinic and gamma-aminobutyric acid receptors in visual cortex of cats.

Administration of diisopropylfluorophosphate (DFP), an organophosphorus (OP) compound, irreversibly inhibits acetylcholinesterase (AChE) and results in cholinergic hyperactivity. This study investigated muscarinic and gamma-aminobutyric acid (GABA) receptor changes in visual cortex of cats following an acute exposure to DFP. A single acute administration of DFP (4 mg/kg) decreased the number of muscarinic receptors at 2, 10, and 20 hours after treatment. GABA receptors were elevated at 2 and 10 hours but returned to within control levels at 20 hours. No significant alteration in muscarinic or GABA receptor affinity was noted. In all cases cortical AChE activity was inhibited 60-90%. These findings show a down regulation of muscarinic receptors after DFP associated with low AChE activity. GABA receptors also are altered, and may be part of a compensatory mechanism to counteract excess cholinergic stimulation.     

Effect of experimental glaucoma on the non-image forming visual system

Glaucoma is a leading cause of blindness worldwide, characterized by retinal ganglion cell degeneration and damage to the optic nerve. We investigated the non-image forming visual system in an experimental model of glaucoma in rats induced by weekly injections of chondroitin sulphate (CS) in the eye anterior chamber. Animals were unilaterally or bilaterally injected with CS or vehicle for 6 or 10 weeks. In the retinas from eyes injected with CS, a similar decrease in melanopsin and Thy-1 levels was observed. CS injections induced a similar decrease in the number of melanopsin-containing cells and superior collicular retinal ganglion cells. Experimental glaucoma induced a significant decrease in the afferent pupil light reflex. White light significantly decreased nocturnal pineal melatonin content in control and glaucomatous animals, whereas blue light decreased this parameter in vehicle- but not in CS-injected animals. A significant decrease in light-induced c-Fos expression in the suprachiasmatic nuclei was observed in glaucomatous animals. General rhythmicity and gross entrainment appear to be conserved, but glaucomatous animals exhibited a delayed phase angle with respect to lights off and a significant increase in the percentage of diurnal activity. These results indicate the glaucoma induced significant alterations in the non-image forming visual system.     

Voluntary exercise stabilizes photic entrainment of djungarian hamsters (Phodopus sungorus) with a delayed activity onset

ABSTRACT

The Djungarian hamsters of our breeding colony show unstable daily activity patterns when kept under standard laboratory conditions. Moreover, part of them develops a delayed activity onset (DAO) or an arrhythmic phenotype. In former studies, we have shown that the system of photic entrainment works at its limits. If the period length (tau) increases, which is the case in DAO hamsters, the light-induced phase advances are too small to compensate the daily delay of the activity rhythm caused by tau being longer than 24 h. Accordingly, under natural conditions, there must be further (environmental) factors to enable a stable entrainment. One of these may be the higher level of motor activity. Animals must cover long distances to search for food, sexual partners and others. In the laboratory, hamsters are kept singly in small cages. This does restrict animals’ options for motor activity. Also, there is less need for moving around as the hamsters are fed ad libitum.

In the present study, a series of experiments was performed to investigate the putative effect of the activity level. To begin with, wild type (WT) and DAO animals were given access to running wheels. 50% of DAO hamsters developed a WT activity pattern. As the main reason for the DAO phenomenon is their long tau together with a too weak photic phase response, the effect of wheel running on these parameters was investigated in further experiments. With higher activity level, tau decreased in WT hamsters but increased in DAO animals even though the increase for the activity onset was only close to significance. Moreover, the photic phase responses were weaker though significant only for the activity offset of DAO hamsters.

Based on the assumptions that running wheel activity will affect the phase response and/or the free running period, the results of the present paper do not provide an explanation for why part of DAO hamsters developed a WT phenotype when they had access to running wheels. Obviously, mechanisms downstream from the suprachiasmatic nuclei must be taken into account when investigating the stabilizing, improving circadian entrainment effect of motor activity.     

Is it possible to train Achatina fulica using visual stimulation?]

The conditioned behavior to visual stimuli was obtained in Achatina fulica mollusk on the basis of its negative phototaxis. Directional moving of snails toward black cards was accompanied by the negative unconditioned stimulation (electric current). Learning was expressed in a statistically significant decrease in locomotor activity of animals and decrease in the rate of preference of sections with black cards. Learning developed within two daily training sessions with 30 trials in each of them. Learning traces were observed as defensive behavior at least during a month after reinforcement elimination.     

Effect of retinal ischemia on the non-image forming visual system

Retinal ischemic injury is an important cause of visual impairment. The loss of retinal ganglion cells (RGCs) is a key sign of retinal ischemic damage. A subset of RGCs expressing the photopigment melanopsin (mRGCs) regulates non-image-forming visual functions such as the pupillary light reflex (PLR), and circadian rhythms. We studied the effect of retinal ischemia on mRGCs and the non-image-forming visual system function. For this purpose, transient ischemia was induced by raising intraocular pressure to 120?mm Hg for 40?min followed by retinal reperfusion by restoring normal pressure. At 4 weeks post-treatment, animals were subjected to electroretinography and histological analysis. Ischemia induced a significant retinal dysfunction and histological alterations. At this time point, a significant decrease in the number of Brn3a(+) RGCs and in the anterograde transport from the retina to the superior colliculus and lateral geniculate nucleus was observed, whereas no differences in the number of mRGCs, melanopsin levels, and retinal projections to the suprachiasmatic nuclei and the olivary pretectal nucleus were detected. At low light intensity, a decrease in pupil constriction was observed in intact eyes contralateral to ischemic eyes, whereas at high light intensity, retinal ischemia did not affect the consensual PLR. Animals with ischemia in both eyes showed a conserved locomotor activity rhythm and a photoentrainment rate which did not differ from control animals. These results suggest that the non-image forming visual system was protected against retinal ischemic damage.     

Decreased muscarinic binding sites in small intestine from mice treated with neostigmine

It has been reported by several authors that animals given repeated sublethal doses of an organophosphate, acetylcholinesterase (AChE) inhibitor, develop tolerance to its toxicity. This phenomenon seems to be due, at least partially, to a decrease of central and peripheral cholinergic receptors. In the present study, we report that a decrease of muscarinic receptors, as measured by [³H]-quinuclidinyl benzilate (³H-QNB) binding, occurs in the small intestine of mice treated with the carbamate, AChE inhibitor, neostigmine. Male mice were given neostigmine in the drinking water at daily increasing concentrations (from 20 to 1000 ppm). Methylatropine (20mg/kg, i.p.) was administered twice a day for the same period to two groups of control and neostigmine-treated animals. AChE activity was inhibited 60–70% in small intestine and diaphragm and [³H]-QNB binding was significantly reduced in the small intestine of neostigmine-treated mice; both the number of receptors and the affinity were lower than control. This decrease was not present in the tissue of mice given methylatropine together with neostigmine. Administration of methylatropine alone caused a significant increase of [³H]-QNB binding in the small intestine.     

Experience-driven axon retraction without binocular imbalance in developing visual cortex

Refinement of the neural circuit during brain maturation is regulated by experience-driven neural activity. In the mammalian visual cortex, monocular visual deprivation (MD) in the early postnatal life causes a significant loss of cortical responses to a deprived eye and the retraction of input axons serving the deprived eye. A competitive interaction between inputs serving both eyes has been supposed to underlie the effects of MD because the loss of cortical response is much weaker when both eyes are deprived of vision. Also, the input axons do not retract after binocular deprivation. Here, we report that uncorrelated activity between presynaptic and postsynaptic neurons can solely lead to the retraction of geniculocortical axons in the absence of activity imbalance between two inputs. We analyzed the morphology of geniculocortical axons in a pharmacologically inhibited visual cortex of animals with normal vision and of binocularly deprived animals. In the normal vision animals, the axonal arbors in the inhibited cortex showed robust retraction. On the other hand, the arbors in binocularly deprived animals remained mostly intact. These results suggest that a homosynaptic associative mechanism, rather than a heterosynaptic competition between inputs, may play an important role in experience-driven axon retraction.