Potentiation of synaptic responses in slices from the chick forebrain.

Coronal slices, containing part of the medial hyperstriatum ventrale (MHV), were cut from the left forebrains of domestic chicks and maintained in vitro. Records were made of the field responses evoked in the MHV by local electrical stimuli provided at 0.1 Hz. Two 1 min periods of stimulation at 5 Hz, separated by 10 min, were used in attempts to induce a persistent increase in the size of the postsynaptic response to test stimulation at 0.1 Hz. This procedure produced a potentiation which usually lasted longer than 2 h. The probability of inducing this persistent potentiation of the response (PPR) is not distributed evenly over the whole anteroposterior length of the MHV but is higher in slices that also contain the septo-mesencephalic tract ventrally. These are the slices that contain the intermediate part of the medial hyperstriatum ventrale (IMHV); an area that is essential for early behavioural learning. At this level PPR is not confined to the IMHV. It can also be produced in the lateral neostriatum in response to similar local stimulation at 5 Hz. No PPR was observed in either the caudal ectostriatum, or the paleostriatum.     

Response characteristics of neurons in chick forebrain slices

Coronal sections were taken from the forebrains of domestic chicks, aged 1-20 days, and maintained in vitro. Extracellular recordings of neural activity were made from the intermediate part of the medial hyperstriatum ventrale (IMHV). Spontaneous activity was rarely recorded, but neuronal responses could be evoked by stimulation of various sites. Each recording point was surrounded by an arc of sites which, when stimulated, typically elicited a short-latency field potential. These 'local responses' could be recorded in slices from chicks of any age. Stimulation of more distant sites failed to evoke field potentials from the IMHV. Instead, trains of large, unit action potentials appeared on an undisturbed baseline. Such 'unit' responses could only be evoked by stimuli delivered at specific frequencies. They required facilitation, were of variable latency, and often finally decayed. The number of sites capable of evoking a 'unit' response from the IMHV fell dramatically in slices taken from chicks older than 4 days.     

2 Hz与100 Hz刺激在诱导大鼠视皮层长持续长时程增强中的不同作用

在哺乳动物的视皮层,多种不同参数的刺激可诱导出长时程增强(long-term potentiation,LTP)现象。但关于刺激参数与持续时间长于3h的长持续LTP(long lasting LTP,L-LTP)之间关系的研究较少。本研究用3周龄的大鼠视皮层脑片标本,在Ⅳ层刺激而在Ⅱ／Ⅲ层记录场电位,待场电位稳定后施加强直刺激诱导LTP,探讨2Hz与100Hz的强直刺激在诱发持续时间长于3h的L-LTP中的作用。结果表明,多于300个脉冲不同频率的刺激可稳定地诱导出L-LTP;2Hz与100Hz的刺激诱发的L-LTP有明显不同的表达形式,100Hz刺激可诱导出较大的L-LTP;频率相同而脉冲数不同的强直刺激诱发的L-LTP有相同的表达形式。以上结果提示,不同频率的强直刺激诱发的L-LTP机制可能不同;相同频率的刺激(脉冲数不同)诱发的L-LTP可能有相同的机制。     

The effects of regular handling on fear responses in the domestic chick

Reduction of fear in the domestic chick by regular handling was assessed and an attempt was made to determine whether such an effect was due specifically to reduced fear of human beings or to a general reduction in fearfulness. Regular handling decreased the tonic immobility response, a fear-potentiated phenomenon, and increased approach to a human being, but had no effect on approach towards an inanimate object. These findings were common to three strains (two layer, one broiler), and suggest that handling does not depress general fearfulness, but specifically reduces fear of human beings, presumably through habituation.     

Early visual experience, learning, and neurochemical plasticity in the rat and the chick.

Rats reared in the dark to 50 days show morphological and biochemical changes in the visual pathway. Light exposure results in elevated incorporation into protein in visual cortex, lateral geniculate and retina. Much of the visual cortex elevation is in a rapidly labelling, rapidly transported neuronal particulate protein. There are concomitant changes in lysosomal and transmitter enzyme activity. In chicks exposed to an imprinting stimulus (a flashing light) there are elevations in RNA polymerase and RNA and protein incorporation in the anterior forebrain roof (a.f.r.) compared with controls. There are changes in adenyl cyclase, cAMP and AChE. Behavioural controls show that although there are general biochemical sequelae of light exposure, the elevation in RNA synthesis in the a.f.r. is not a result of motor, stress or sensory activity, but is correlated with a measure of the learning of the stimulus characteristics. A model for neurochemical correlates of developmental plasticity, learning, and state-dependent transients is discussed.     

Social recognition and approach in the chick: lateralization and effect of visual experience

Chicks, Gallus gallus domesticus, tested monocularly on day 3 after hatching recognize familiar versus unfamiliar conspecifics and choose to approach one or other when they use the left eye, whereas they approach familiar and unfamiliar chicks at random when they use the right eye. In experiment 1 we investigated the effects of light exposure of embryos prior to hatching on this particular form of lateralization. Irrespective of whether they hatched from eggs incubated in the dark or from eggs exposed to light during the final days of incubation, chicks using the left eye had higher choice scores (meaning they chose to approach either a familiar or an unfamiliar chick) than chicks using the right eye or both eyes. Therefore, light experience prior to hatching did not influence the lateralization of individual recognition or choice behaviour, although it did affect latency to move out of, and time spent in, the centre of the runway. Experiment 2 showed that visual/social experience posthatching influences choice behaviour: chicks housed in a group in the light for 12 h on day 1 posthatching made a clear choice between familiar and unfamiliar chicks when tested on day 3, but chicks kept in a group in the dark on day 1 did not make a choice, instead alternating between the two stimuli. In experiment 3 we found that posthatching visual/social experience increased the choice scores of chicks using the right eye and thereby removed any lateralization of choice behaviour. The results suggest that visual experience of a social group is required before chicks using their right eye (and left hemisphere) will pay attention to the cues that distinguish one chick from another. Chicks using their left eye (and right hemisphere) recognize the difference between individuals without requiring visual experience with other chicks. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

The effects of the visual environment on responses to colour by domestic chicks

It is well known that development of vision is affected by experience, but there are few studies of environmental effects on colour vision. Natural scenes contain predominantly a restricted range of reflectance spectra, so such effects might be important, perhaps biasing visual mechanisms towards common colours. We investigated how the visual environment affects colour preferences of domestic chicks ( Gallus gallus), by training week-old birds to select small food containers distinguished from an achromatic alternative either by an orange or by a greenish-blue colour. Chicks that had been raised in control conditions, with long-wavelength-dominated reflectance spectra, responded more readily to orange than to blue. This was not due to avoidance of blue, as increasing saturation enhanced the chicks' preference for the same hue. The advantage of orange was, however, reduced or abolished for chicks raised in an environment dominated by blue objects. This indicates that responses to coloured food are affected by experience of non-food objects. If colours of ordinary objects in the environment do influence responses to specialised visual signals this might help explain why biological signals directed at birds are often coloured yellow, orange or red; long-wavelength-dominated spectra being more prevalent than short-wavelength-dominated spectra.     

The dextro and levorotatory isomers of N-phenylisopropyladenosine: stereospecific effects on cyclic AMP-formation and evoked synaptic responses in brain slices.

The stereoisomers of N⁶-phenylisopropyladenosine elicit accumulations of cyclic AMP in brain slices via interaction with adenosine-receptors. The response in guinea pig cerebral cortical slices and in rat hippocampal slices is blocked by theophylline and potentiated by biogenic amines. A chelator, EGTA, potentiates the response to phenylisopropyladenosine in guinea pig cerebral cortical slices. The $\text{1}$-isomer (EC₅₀ 25 μM) is four- to five-fold more potent than the $\text{d}$-isomer in eliciting accumulations of cyclic AMP in brain slices. In a rat coronal hippocampal slice $\text{in vitro}$, $\text{1}$-phenylisopropyladenosine (IC₅₀ ～ 0.7 μM) reduces the amplitude of evoked synaptic responses generated $\text{via}$ a monosynaptic pathway to the CA1 pyramidal neurons. The $\text{d}$-isomer is nearly one hundred-fold less potent. Thus, the adenosine-receptors involved in the electrophysical response appear much more stereoselective for the $\text{1}$-isomer of phenylisopropyladenosine than the adenosine-receptors involved in cyclic AMP-generation in brain slices.     

State-dependent parental care in the Antarctic petrel: responses to manipulated chick age during early chick rearing

Life histories are state-dependent, and an individual's reproductive decisions are determined by its available resources and the needs of its offspring. Here we test how a chick's needs for food and protection influence parental decisions in the Antarctic petrel, Thalassoica antarctica , where the parents, due to their long breeding lifespan, are expected to give priority to their own needs before those of the young. We exchanged one-day-old chicks with four-day-old chicks and studied how the parents subsequently provided care to the chick. The duration of the guarding period was adjusted, and parents left older chicks earlier and younger chicks later compared to controls. Three mechanisms were responsible for the adjustments. 1) Parents with an older chick co-ordinated fewer guarding spells whereas parents with a younger chick co-ordinated more guarding spells. 2) At the last guarding spell, i.e. where a parent left the chick alone before the partner returned, less time was spent with older chicks, and more time with younger chicks. 3) Foraging trip duration was shortened by parents given older chicks and prolonged by parents given younger chicks, probably in response to the chick's food demand. Hence, the parents responded quickly to the altered needs of the chick. Parents with high body mass guarded longer and were better able to co-ordinate the guarding spells compared to lighter parents. In conclusion, Antarctic petrels adjust reproductive decisions to their own, their mate's, and their chick's state, and they seem to respond to the chick's needs for both food and protection.     

血小板激活因子对大鼠海马脑片CA1区LTP的作用

目的:为了探讨血小板激活因子(platelet-activating factor,PAF)对大鼠海马脑片CA1区的长时程增强效应(long-term potentiation,LTP)的影响.方法:应用离体脑片电生理记录技术,记录大鼠海马CA1区的兴奋性突触后电位EPSP,研究了PAF对大鼠海马脑片CA1区的突触传递和可塑性的影响.结果:小剂量(1μmol/L)PAF可诱发大鼠海马CA1区LTP的产生;大剂量(10～50μmol/L)PAF不能诱发大鼠海马CA1区LTP的产生,且不能阻止高频电刺激(HFS,100 Hz,1 000 ms×2,每隔20 s给予)Schffer侧支引起的大鼠海马脑片CA1区LTP的形成和维持.大剂量PAF对海马CA1区基础EPSP没有影响.PAF受体拮抗剂银杏苦内酯(ginkgolide B,GB)可拮抗小剂量PAF诱发大鼠海马CA1区LTP的产生.结论:大剂量PAF具有神经毒性,可能是通过抑制海马CA1区的LTP的形成而参与艾滋病痴呆(HIV-1 associated dementia,HAD)的形成机制.     

The effects of methylxanthines on catecholamine-stimulated and normal chick embryos.

Dose of theophylline and caffeine which do not produce aortic arch anomalies in embryonic chicks have been shown to potentiate catecholamine-induced aortic arch malformations in that experimental animal. Theophylline (2.1 X 10(-5) mole per milliliter isotonic saline solution) potentiated the effective dose of norepinephrine more than 100 times. The greatest potentiation observed with epinephrine (2.5 X) was induced by 2.6 X 10(-5) mole caffeine. This study also demonstrated that both methylxanthines specifically induce aneurysms of the ascending aorta and complete absence (or nearly complete constriction) of the right ductus arteriosus. The incidences of these types of cardiovascular malformations proved to be dose dependent with theophylline a more potent teratogen than caffeine. The mobilization of calcium and/or cyclic nucleotide phosphodiesterase inhibition by the methylxanthines are suggested as significant actions in the potentiation of catecholamine-induced aortic arch anomalies.     

The effect of age and norepinephrine on renin release by rat kidney slices in vitro.

Basal renin release by rat kidney slices decreases with age in rats of SHR and Sprague-Dawley strains. In contrast, Kyoto-Wistar rats (from which SHR are derived) demonstrate no decrease in renin release with age. The decline in basal renin release observed in SHR occurs at a time when the animal develops hypertension. However, the ability of renin release to respond to stimuli, such as norepinephrine, is enhanced at the time of declining basal renin release and developing hypertension.     

Mechanism of developing "deprivation" potentiation of population responses of neurons in the CA1 field in hippocampal slices]

In rat hippocampal slices, synaptic transmission from Schaffer collaterals to CA1 neurons was studied by assessment of the effects of cessation of low-frequency testing stimulation to the population spike amplitude. A positive correlation between the duration of the stimulation interruption period (from 10 to 120 min) and the increment of the population spike amplitude (from 30 to 100% above baseline level). The "deprivational" potentiation (DP) offers a property of summation and is able to persist for long (testing was continued up to one hour). Prior induction of the long-term posttetanic potentiation (LPTP) that for 1-3 hours prevents the development of the late rather than the short-term LPTP phase, in our experiments also suppressed the DP induction after 60-min stimulation interruption interval. The same results were obtained in the presence of polymixin B (20 mcM), which is an inhibitor of protein kinase C (PKC) and PKC-dependent phase of the LPTP. This finding provides support for the earlier assumption about the similarity of the mechanisms responsible for the development of the DP and PKC-dependent LPTP phase related with protein phosphorylation.     

The teratogenic effects of 6-mercaptopurine on chick embryos in ovo.

Fertilized eggs of single-combed White Leghorn hens were each injected through a shell window directly beneath the embryo at 70 or 96 h of incubation with 2 mg of the sodium salt of 6-MP dissolved in 0.1 M phosphate buffer, and at 11 days of incubation the embryos were examined for gross morphological abnormalities. Various gross malformations and growth retardation were found, the most frequently and severely affected structures being limbs, beak, and eyes. Treatment at 70 h caused more severe abnormalities than at 96 h, but the spectrum of defects was not very different.     

The effects of retinoic acid on heart formation in the early chick embryo.

The vitamin A derivative retinoic acid has previously been shown to have teratogenic effects on heart development in mammalian embryos. The craniomedial migration of the precardiac mesoderm during the early stages of heart formation is thought to depend on a gradient of extracellular fibronectin associated with the underlying endoderm. Here, the effects of retinoic acid on migration of the precardiac mesoderm have been investigated in the early chick embryo. When applied to the whole embryo in culture, the retinoid inhibits the craniomedial migration of the precardiac mesoderm resulting in a heart tube that is stunted cranially, while normal or enlarged caudally. Similarly, a local application of retinoic acid to the heart-forming area disrupts the formation of the cardiogenic crescent and the subsequent development of a single mid-line heart tube. This effect is analogous to removing a segment of endoderm and mesoderm across the heart-forming area and results in various degrees of cardia bifida. At higher concentrations of retinoic acid and earlier developmental stages, two completely separate hearts are produced, while at lower concentrations and later stages there are partial bifurcations. The controls, in which the identical operation is carried out except that dimethyl sulphoxide (DMSO) is used instead of the retinoid, are almost all normal. We propose that one of the teratogenic effects of retinoic acid on the heart is to disrupt the interaction between precardiac cells and the extracellular matrix thus inhibiting their directed migration on the endodermal substratum.     

Influence of early neonatal experience on nociceptive responses and analgesic effects in rats

Early maternal separation has profound effects on nociception in rats. Cross-fostering is a standard husbandry procedure used by some commercial breeders. This study aimed to determine if cross-fostering altered nociception and the analgesic efficacy of buprenorphine and morphine. At seven and nine weeks of age, an elevated plus maze was used to assess anxiety and Hargreaves apparatus was used to measure thermal nociception at two intensities in cross-fostered and naturally-reared rats. At 10 weeks of age these rats were assigned to one of three treatment groups: saline, buprenorphine or morphine. The Hargreaves apparatus was used to evaluate the effect of analgesics on nociception. Differences were observed in nociception between the cross-fostered and naturally-reared rats at both intensities. At the lower intensity no significant differences were seen between the cross-fostered and naturally-reared rats post-administration of an analgesic. At the higher intensity significant differences were apparent. Morphine was less effective in inducing analgesia to thermal stimuli in cross-fostered rats compared with naturally-reared rats, whereas the opposite was found with buprenorphine which had a more pronounced analgesic effect in the cross-fostered rats. No significant differences in performance on an elevated plus maze were demonstrated between the cross-fostered and naturally-reared rats.     

Prolonged posttetanic potentiation in slices of mouse hippocampus with the kindling phenomenon

The characteristics of long-term potentiation (LTP) in Schaffer collaterals--CA1 system were compared in hippocampal slices from mice of control group and mice with pentylenetetrazol (PTZ) kindling, induced by daily i.p.-injection of 30 mg/kg of PTZ. The increase in LTP mean magnitude was found in the preparation from kindled mice. The enhancement of the paired-pulse potentiation was also shown in these slices. It is suggested that both the increase in LTP and paired-pulse potentiation are due to the depression of an inhibition in intrahippocampal synaptic systems.