[The protective effect of tea polyphenols on chronic alcoholic liver injury in rats].

OBJECTIVE: To investigate the protective effects and potential mechanisms of tea polyphenols intervention on excess alcohol intake induced liver injury in rats. This study established the animal model of chronic liver injury rats induced by alcohol. Our results will provide experimental evidence for the effects of tea polyphenol on chronic alcoholic liver injury. METHODS: Alcohol-induced liver injury rat models were established, and the tea polyphenols intervention was performed in the meantime. After 8 weeks, rats were anesthetized, and visceral fat and liver samples were separated, weighted and stored. Visceral fat content was evaluated in fat/body weight ratio. Liver lipid accumulation was assessed by liver index and the result of Oil Red O staining. Hepatic superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, total antioxidant capacity assay (T-AOC) and glutathione peroxidase (GSH-Px) activity were detected. And fatty acid translocase (FAT/CD36) protein level in liver was detected. RESULTS: Compared with the control group rats, the fat/body weight ratio, SOD/MDA, T-AOC and GSH-Px activity of chronic liver injury rats were decreased significantly (P<0.05,P<0.01). Meanwhile the liver index, FAT/CD36 protein level and lipid deposition in liver of chronic liver injury rats were increased (P<0.01). Compared with chronic liver injury rats, the tea polyphenols intervention increased fat/body weight ratio (P<0.05), and significantly increased SOD/MDA, T-AOC and GSH-Px activity (P<0.01). Meanwhile the tea polyphenols intervention reduced liver index (P<0.01), FAT/CD36 protein level (P<0.01) and lipid deposition in liver. CONCLUSIONS: Tea polyphenols intervention can improve lipid deposition and oxidative stress in chronic alcoholic liver, which is concurrent with decreased FAT/CD36 protein expression on the hepatocyte membrane.

Effects of senescence on the expression of BDNF and TrkB receptor in the lateral geniculate nucleus of cats.

To explore the neural mechanisms mediating aging-related visual function declines, we compared the expressions of brain-derived neurotrophic factor (BDNF) and its high affinity receptor-tyrosine kinase B (TrkB) between young and old adult cats. Nissl staining was used to display neurons in each layer of the lateral geniculate nucleus (LGN). The BDNF- and TrkB receptor-immunoreactive neurons were labeled immunohistochemically, observed under optical microscope and photographed. Their neuronal density and immunoreactive intensity were measured. Results showed that the mean density of the Nissl stained neurons in each LGN layer were comparable between old and young adult cats, and their BDNF and TrkB proteins were widely expressed in all LGN layers. However, compared with young adult cats, both the density and optical absorbance intensity of BDNF- and TrkB-immunoreactive cells in each LGN layer in old cats were significantly decreased. These findings indicate that the decreased expressions of BDNF and TrkB proteins in the LGN may be an important factor inducing the compromised inhibition in the central visual nucleus and the functional visual decline in senescent individuals.

[A wireless telemetry study on the electrical activity in nucleus accumbens of heroin-induced place preference rats].

OBJECTIVE: To analyze the electrical activity property changes in nucleus accumbens (NAc) of heroin-induced conditioned place preference (CPP) rats during different stages of heroin dependence and to explore NAc's roles in the formation of drug dependence. METHODS: Recording electrodes were bilaterally embedded into the NAcs of rats with the aid of stereotaxic apparatus, followed by establishment of heroin-dependent rat model. The NAc electrical activity during 3 different stages of heroin dependence, including heroin pre-exposure, immediate post-exposure and heroin withdrawal, were respectively recorded using EEG wireless telemetry techniques. The frequency distribution (ranging from 0.5 to 30 Hz) and the amplitude of NAc electrical activity were analyzed and measured. RESULTS: Heroin-dependent rat models were successfully established and their withdrawal symptoms were evident. All rats showed a conditioned place preference (CPP) for the white box after 5-10 days of heroin-exposure, and displayed a maximum withdrawal symptoms on 2d after heroin- withdrawal. During all statges of heroin-dependence, the NAc electrical activity contained the highest proportion of delta rhythm and the lowest proportion of alpha2 rhythm. The discharge frequence band was similar across different stages. There was a significantly increased ratio of low-frequency discharges (delta rhythm) and decreased ratio of high-frequency discharges (beta rhythm) in NAc of rats during the immediate post- heroin exposure stage when compared with that during pre-exposure and heroin withdrawal stages. During the withdrawal stage, the ratio of at rhythm was significantly lower than during pre- and post-heroin exposure stages (P < 0.01). Further, the mean discharge amplitude in NAcs during immediate post-exposure and withdrawal stages was significantly increased relative to pre-exposure stage. However, the mean discharge amplitude during heroin withdrawal stage was significantly lower than during immediate post-exposure stage. CONCLUSION: The electrical activity properties in rat NAcs showed a significant change during different stages of heroin-dependence, which suggested that neuronal activities in NAcs might contribute to the modulation of drug-dependence.

Effects of surround suppression on response adaptation of V1 neurons to visual stimuli.

The influence of intracortical inhibition on the response adaptation of visual cortical neurons remains in debate. To clarify this issue, in the present study the influence of surround suppression evoked through the local inhibitory interneurons on the adaptation effects of neurons in the primary visual cortex (V1) were observed. Moreover, the adaptations of V1 neurons to both the high-contrast visual stimuli presented in the classical receptive field (CRF) and to the costimulation presented in the CRF and the surrounding nonclassical receptive field (nCRF) were compared. The intensities of surround suppression were modulated with different sized grating stimuli. The results showed that the response adaptation of V1 neurons decreased significantly with the increase of surround suppression and this adaptation decrease was due to the reduction of the initial response of V1 neurons to visual stimuli. However, the plateau response during adaptation showed no significant changes. These findings indicate that the adaptation effects of V1 neurons may not be directly affected by surround suppression, but may be dynamically regulated by a negative feedback network and be finely adjusted by its initial spiking response to stimulus. This adaptive regulation is not only energy efficient for the central nervous system, but also beneficially acts to maintain the homeostasis of neuronal response to long-presenting visual signals.

Adaptation to visual stimulation modifies the burst firing property of V1 neurons.

The mean firing rate of visual cortical neurons is reduced after prolonged visual stimulation, but the underlying process by which this occurs as well as the biological significance of this phenomenon remains unknown. Computational neuroscience studies indicate that high-frequency bursts in stimulus-driven responses can be transmitted across synapses more reliably than isolated spikes, and thus may carry accurate stimulus-related information. Our research examined whether or not adaptation affects the burst firing property of visual cortical neurons by examining changes in the burst firing changes of V1 neurons during adaptation to the preferred visual stimulus. The results show that adaptation to prolonged visual stimulation significantly decreased burst frequency (bursts/s) and burst length (spikes/burst), but increased burst duration and the interspike interval within bursts. These results suggest that the adaptation of V1 neurons to visual stimulation may result in a decrease of feedforward response gain but an increase of functional activities from lateral and/or feedback connections, which could lead to a reduction in the effectiveness of adapted neurons in transmitting information to its driven neurons.

[Effects of ketamine and urethane on stimulation-induced c-fos expression in neurons of cat visual cortex].

The effects of ketamine and urethane on neuronal activities remain in debate. As a member of immediate early genes family, the expression of c-fos is stimulation dependent and could be treated as an index to evaluate the strength of neural activities. In this study, SABC immunohistochemical techniques were applied to compare the c-fos expression in neurons of the primary visual cortex (V1) of cats and therefore, to evaluate the effects of acute anesthesia with ketamine HCl and uethane on inhibiting neural activities. Our results showed that compared with control cats, there were no significant differences with the average densities of Nissl-stained V1 neurons in each cortical layers of either urethane or ketamine anesthetized cats. In urethane anesthetized cats, neither the average densities nor the immunoreactive intensities of c-fos positive V1 neurons showed significant difference with that of control ones. However, both the average densities and immunoreactive intensities of c-fos positive V1 neurons in ketamine anesthetized cats decreased significantly compared with that of control and urethane anesthetized cats. These results suggested that ketamine has strong inhibitory effects on the activities of visual cortical neurons, whereas urethane did not.

Acute lesions of primary visual cortical areas in adult cats inactivate responses of neurons in higher visual cortices.

Psychophysical studies suggest that lateral extrastriate visual cortical areas in cats may mediate the sparing of vision largely by network reorganization following lesions of early visual cortical areas. To date, however, there is little direct physiological evidence to support this hypothesis. Using in vivo single-unit recording techniques, we examined the response of neurons in areas 19, 21, and 20 to different types of visual stimulation in cats with or without acute bilateral lesions in areas 17 and 18. Our results showed that, relative to the controls, acute lesions inactivated the response of 99.3% of neurons to moving gratings and 93% of neurons to flickering square stimuli in areas 19, 21, and 20. These results indicated that acute lesions of primary visual areas in adult cats may impair most visual abilities. Sparing of vision in cats with neonatal lesions in early visual cortical areas may result largely from a postoperative reorganization of visual pathways from subcortical nucleus to extrastriate visual cortical areas.

Decreased contrast sensitivity of visual cortical cells to visual stimuli accompanies a reduction of intracortical inhibition in old cats.

Psychophysical experiments on human and animal subjects have proven that aged individuals show significantly reduced visual contrast sensitivity compared with young adults. To uncover the possible neural mechanisms, we used extracellular single-unit recording techniques to examine the response of V(1) (primary visual cortex) neurons as a function of visual stimulus contrast in both old and young adult cats (Felis catus). The mean contrast sensitivity of V(1) neurons to visual stimuli in old cats decreased significantly relative to young adult cats, consistent with findings reported in old primates. These results indicate that aging can affect contrast sensitivity of visual cortical cells in both primate and non-primate mammalian animals, and might contribute to the reduction of perceptual visual contrast sensitivity in aged individuals. Further, V(1) cells of old cats exhibited increased responsiveness, decreased signal-to-noise ratio, and enlarged receptive field (RF) size compared with that of young adult cats, which indicated that decreased contrast sensitivity of V(1) neurons accompanied a reduction of intracortical inhibition during senescence.

Effects of urethane on the response properties of visual cortical neurons in young adult and old cats.

Previous studies have shown that visual cortical neurons in old mammals exhibit higher spontaneous activity, higher responsiveness to visual stimuli, and lower selectivity for stimulus orientations and motion directions than did neurons in young adult counterparts. However, whether the responsive difference in cortical neurons between young and old animals resulted from different effects induced by anesthetics has remained unclear. To clarify this issue, we recorded the response properties of individual neurons in the primary visual cortex of old and young adult cats while systematically varying the anesthesia level of urethane, a widely used anesthetic in physiology experiments. Our results showed that cumulatively administrating 50 mg and 100 mg of urethane upon the minimal level of urethane required to anesthetize an old or young adult cat did not significantly alter the degree of neuronal response selectivity for stimulus orientations and motion directions nor significantly change the visually-driven response and spontaneous activity of neurons in old and young adult cats. Cumulatively administrating 150 mg of urethane decreased neuronal responsiveness similarly in both age groups. Therefore, urethane appears to exert similar effects on neuronal response properties of old and young adult animals.

Decline of selectivity of V1 neurons to visual stimulus spatial frequencies in old cats.

OBJECTIVE: To examine whether the selectivity of visual cortical neurons to stimulus spatial frequencies would be affected by aging in cats. METHODS: In vivo extracellular single-unit recording techniques were employed to record the tuning responses of V1 neurons to different stimulus spatial frequencies in old and young adult cats. RESULTS: Statistical analysis showed that the mean optimal spatial frequency of grating stimuli that evoked the maximal response of V1 neurons in old cats was significantly lower than that in young adult cats. Furthermore, the mean high cut-off spatial frequency of grating stimuli that evoked the half amplitude of the maximal response of V1 neurons in old cats was also significantly lower than that in young adult cats. CONCLUSION: These results are consistent with those reported in the V1 of old monkeys, suggesting that the age-related decline in the selectivity of visual cortical cells to spatial frequency could be generalized to all mammalian species and might contribute to visual acuity reduction in senescent individuals.

Competition and convergence between auditory and cross-modal visual inputs to primary auditory cortical areas.

Sensory neocortex is capable of considerable plasticity after sensory deprivation or damage to input pathways, especially early in development. Although plasticity can often be restorative, sometimes novel, ectopic inputs invade the affected cortical area. Invading inputs from other sensory modalities may compromise the original function or even take over, imposing a new function and preventing recovery. Using ferrets whose retinal axons were rerouted into auditory thalamus at birth, we were able to examine the effect of varying the degree of ectopic, cross-modal input on reorganization of developing auditory cortex. In particular, we assayed whether the invading visual inputs and the existing auditory inputs competed for or shared postsynaptic targets and whether the convergence of input modalities would induce multisensory processing. We demonstrate that although the cross-modal inputs create new visual neurons in auditory cortex, some auditory processing remains. The degree of damage to auditory input to the medial geniculate nucleus was directly related to the proportion of visual neurons in auditory cortex, suggesting that the visual and residual auditory inputs compete for cortical territory. Visual neurons were not segregated from auditory neurons but shared target space even on individual target cells, substantially increasing the proportion of multisensory neurons. Thus spatial convergence of visual and auditory input modalities may be sufficient to expand multisensory representations. Together these findings argue that early, patterned visual activity does not drive segregation of visual and auditory afferents and suggest that auditory function might be compromised by converging visual inputs. These results indicate possible ways in which multisensory cortical areas may form during development and evolution. They also suggest that rehabilitative strategies designed to promote recovery of function after sensory deprivation or damage need to take into account that sensory cortex may become substantially more multisensory after alteration of its input during development.

Contrast detection learning improves visual contrast sensitivity of cat.

Psychological studies on human subjects show that contrast detection learning promote learner's sensitivity to visual stimulus contrast. The underlying neural mechanisms remain unknown. In this study, three cats (Felis catus) were trained to perform monocularly a contrast detection task by two-alternative forced choice method. The perceptual ability of each cat improved remarkably with learning as indicated by a significantly increased contrast sensitivity to visual stimuli. The learning effect displayed an evident specificity to the eye employed for learning but could partially transfer to the na?ve eye, prompting the possibility that contrast detection learning might cause neural plasticity before and after the information from both eyes are merged in the visual pathway. Further, the contrast sensitivity improvement was evident basically around the spatial frequency (SF) used for learning, which suggested that contrast detection learning effect showed, to some extent, a SF specificity. This study indicates that cat exhibits a property of contrast detection learning similar to human subjects and can be used as an animal model for subsequent investigations on the neural correlates that mediate learning-induced contrast sensitivity improvement in humans.