Pavlovian conditioning of eating induced by spreading depression in cortex, striatum and hippocampus of rats.

A single wave of unilateral spreading depression in the cortex, hippocampus or caudate nucleus of rats elicits eating after 2-6 min. The present experiments provide evidence that such spreading depression-induced eating can be classically conditioned to a complex conditioned stimulus. A wave of spreading depression was triggered by injection of 0.5-2.0 mul of 25 percent KCl solution. In a first experiment successful conditioning was demonstrated in 20 rats, involving 7 cortical, 5 caudate and 8 hippocampal spreading depression sites. Four animals failed to show any conditioned eating. A control group of 8 animals, in which cortical spreading depression did not induce eating, showed no increase in eating in the presence of the CS after conditioning trials. A second experiment, which included pseudoconditioning and NaCl control groups, confirmed the results obtained in Experiment 1. Classical conditioning was successful in 11 animals, involving 6 cortical and 5 caudate spreading depression sites. Neither the pseudoconditioning (14 animals, involving 8 cortical and 6 caudate spreading depression sites) not the NaCl control group (8 animals, all with cortical sites), showed eating in the presence of the CS. In both experiments the conditioned eating underwent gradual extinction.     

The influence of repeated spreading depression-induced calcium transients on neuronal viability in moderately hypoglycemic rats

The calcium transients which are associated with spreading depression (SD) do not lead to neuronal necrosis, even if the SDs are repeated over hours. We have previously shown that a restriction of energy production by moderate hypoglycemia prolongs the calcium transients during SD. In the present experiments, we explored whether such prolonged transients lead to neuronal necrosis. To that end, SDs were elicited for 2 h by topical application of KC1 in anesthetized rats at plasma glucose concentrations of 6, 3, and 2 mM. The animals were then allowed to recover, and they were studied histopathologically after 7 days. In two other groups, hypoglycemic coma of 5 min duration (defined in terms of the d.c. potential shift) was induced either without or with a preceding train of SDs. These animals were also evaluated with respect to histopathological alterations. SDs elicited for 2 h did not give rise to neuronal damage when elicited at plasma glucose concentration of 6 mM, and, of the animals maintained at 3 and 2 mM, only a few animals showed (mild) damage. In general, therefore, repeated SDs with calcium transients of normal or increased duration fail to induce neuronal damage. The results suggest that, if calcium transients are responsible for a gradual extension of the infarct into the penumbra zone of a focal ischemie lesion some additional pathophysiological factors must be present, such as overt energy failure, acidosis, or microvascular damage. A hypoglycemia-induced calcium transient of 5 min duration gave no or only moderate neuronal damage. However, if a series of SDs were elicited in the precoma period, the damage was exaggerated. The results demonstrate that, normally, brain tissues can tolerate a hypoglycemic calcium transient of up to 5 min duration without incurring neuronal necrosis. They also demonstrate that calcium transients preceding a subsequent insult involving calcium influx into cells exaggerate the damage incurred. It is tentatively concluded that the priming transients alter membrane properties in such a way that cellular calcium homeostasis is perturbed.     

Pupillary paralysis evoked by thalamic spreading depression in rats

Summary Spreading depression elicited in the thalamus of albino rats anesthetized with Dial by microinjection of 0.2–1.0 l 25% KCl is accompanied by a maximal pupillary dilatation of the paralytic type. The mydriasis starts immediately after KCl application, culminates about 90 sec later and then slowly subsides with a half time of about 5 min. Although with lateralized KCl application thalamic spreading depression reaches the ipsilateral lateral geniculate body approximately 1 min earlier than the contralateral one, the pupillary reactions are strictly synchronous in both eyes. Participation of the sympathetic fibres was ruled out by the observation that thalamic spreading depression evokes the same mydriasis in the encéphale isolé rats. Cortical spreading depression, on the contrary, elicits only slight and shortlasting mydriasis. Comparison of the spatial march of spreading depression through the thalamus with the time course of the pupillary reaction indicates that the maximum mydriasis is probably caused by direct invasion of the Edinger-Westphal nucleus by the spreading depression process.     

Neocortical and hippocampal EEG in rats during lateral hypothalamic lesion-induced hyperkinesia: relations to behavior and effects of atropine.

Rats received ferric ion depositing lateral hypothalamic lesions. Initially the lesions produced an area of cavitation surrounded by necrotic tissue. Subsequently, over 48 hr, this was surrounded by chromatolysis. Within 1 hr following lesioning and lasting for up to 8 hr the animals showed intense hyperkinesia, which consisted of stereotyped forward locomotion. The hyperkinesia was not blocked by atropine treatment. The atropine-resistant neocortical desynchronization and hippocampal RSA, which accompanies walking in normal rats, was absent in the hyperkinetic rats. The results suggest that hyperkinesia is produced by stimulation from lesion deposited Fe⁺⁺⁺ and may be related to the development of chromatolysis. The absence of normal forebrain EEG activity suggests that the stereotyped nature of the hyperkinesia may result from the absence of normal forebrain control over the motor systems for walking.     

Effects of short-term and long-term treatment with medium- and long-chain triglycerides ketogenic diet on cortical spreading depression in young rats

The ketogenic diet (KD) is a high fat and low carbohydrate and protein diet. It is used in the clinical treatment of epilepsy, in order to decrease cerebral excitability. KD is usually composed by long-chain triglycerides (LCT) while medium-chain triglycerides (MCT) diet is beginning to be used in some clinical treatment of disorders of pyruvate carboxylase enzyme and long-chain fatty acid oxidation. Our study aimed to analyze the effects of medium- and long-chain KD on cerebral electrical activity, analyzing the propagation of the phenomenon of cortical spreading depression (CSD). Three groups of weaned rats (21 days old) received, for 7 weeks, either a control (AIN-93G diet), or a MCT-KD (rich in triheptanoin oil), or a LCT-KD (rich in soybean oil). They were compared to another three groups (21 days old) receiving the same diets for just 10 days. CSD propagation was evaluated just after ending the dietary treatments. Results showed that short-term KD treatment resulted in a significant reduction of the CSD velocity of propagation (control group: 4.02 ± 1.04 mm/min; MCT-KD: 0.81 ± 1.46 mm/min and LCT-KD: 2.26 ± 0.41 mm/min) compared to the control group. However, long-term treatment with both KDs had no effect on the CSD velocity (control group: 3.10 ± 0.41 mm/min, MCT-KD: 2.91 ± 1.62 mm/min, LCT-KD: 3.02 ± 2.26 mm/min) suggesting that both short-term KDs have a positive effect in decreasing brain cerebral excitability in young animals. These data show for the first time that triheptanoin has an effect on central nervous system.     

Effects of cortical spreading depression on behaviors elicited by hypothalamic stimulation in rats

Eating or drinking was elicited via electrical stimulation of the lateral hypothalamus of rats. To determine the effects of single waves of cortical spreading depression on elicited behavior, 1,1 animals were tested with 10 sec trains of stimulation at 20 sec intervals and administered 1–5 μl of 6% KCl through cannulae onto the frontal or occipital cortices of the contralateral or ipsilateral hemispheres. Under single waves of bilateral spreading depression the elicited consummatory behavior was blocked, but other signs of arousal were intact. Single waves of unilateral depression increased the onset-latencies and decreased the duration of elicited behavior, depending on the magnitude of the electrical stimulation. Anterior cortical injection blocked elicited behavior earlier than occipital injection. No differences were apparent between ipsilateral and contralateral injection of KCl. In some animals single waves of unilateral depression were accompanied by a reversible shifting from one elicited consummatory response to another, usually from eating to drinking. The results were interpreted to reflect cortico-hypothalamic interactions in the control of motivated behavior.     

苯丙胺对大鼠行为、学习能力及海马CA3区突触素表达的影响

目的观察苯丙胺对大鼠行为、空间辨别性学习能力和海马CA3区突触素表达的影响。方法将45只健康雄性SD大鼠随机分为:正常对照组、生理盐水组和苯丙胺组。①苯丙胺组每天肌注0.5mg/kg苯丙胺1次;②生理盐水组即注射等体积生理盐水;③正常对照组不予任何处理。每组大鼠分14d、28d和42d三个时间段进行一般行为学、学习记忆能力及海马CA3区突触素表达的检测。结果①苯丙胺组大鼠在注射苯丙胺10d后出现直立、点头、狂躁等行为改变。正常对照组、生理盐水组均无此现象出现;②苯丙胺组大鼠空间辨别性学习记忆能力的影响,在第1、2个时间段与对照组的比未见组间差异,在第3时间段的平均运行时间和正确率比对照组的延长和降低(P<0.05)。③苯丙胺组大鼠海马CA3区突触素表达在第一阶段比对照组的减少,并随着用药时间的延长减少的更明显(P<0.05)。结论苯丙胺对空间辨别性学习记忆时大鼠行为及海马CA3区突触素表达有影响。     

Effects of glycine receptor antagonism on spreading depression in the rat

Spreading depression (SD) in the rat brain is inhibited by (NMDA) receptor antagonists. Because the NMDA receptor glycine recognition site must be occupied for activation of the NMDA ionophore, we hypothesized that antagonism of the glycine receptor would also affect SD. In halothane anesthetized rats, SD was initiated by electrocortical stimulation. Both the initiation threshold and propagation rate of SD were recorded. Rats were then administered the glycine receptor antagonist ACEA-1021 (or vehicle only) or ketamine and the stimulus was repeated. Rats were then killed and terminal depolarization was observed for. Ketamine completely inhibited initiation of SD. In contrast, all rats treated with ACEA-1021 exhibited SD. While ACEA-1021 caused no difference in the stimulation threshold for SD, propagation rate was decreased in a dose-dependent fashion. Terminal depolarization occurred in all rats. Antagonism of glycine at the NMDA receptor recognition site did not inhibit initiation of SD but played a modulatory role in the mechanism of its propagation.     

Sexual behavior elicited in cage-mates of olfactory tubercle stimulated rats

Fourteen male albino rats kept in pairs were implanted with bipolar electrodes in the olfactory tubercle. Electrical stimulation elicited a behavioral change in the cage-mates of the stimulated rats. This change consisted of increased exploratory activity in six animals. In three of these six rats, sexual behavior with mounting and pelvic thrusting was observed. The changes are described and discussed with special attention to sexual behavior.     

Audiogenic seizures associated with a cortical spreading depression wave suppress spike-wave discharges in rats

To study the role of the cortex and sub-cortical structures in the generation of epileptic spike-wave discharges in more detail, cortical and striatal activity was eliminated by the induction of spreading depression in a non-invasive way. EEG and DC potentials were recorded from the cortex and striatum of WAG/Rij rats. Several of these rats show two forms of generalised epilepsy: spontaneously occurring non-convulsive absence seizures, together with convulsive audiogenic seizures. The latter can be evoked by a brief sound stimulation, provoking a fit of wild running, which is regarded as the first phase of an audiogenic seizure. In a majority of fits the cortical DC potential does not show main changes, while the spontaneously occurring spike-wave discharges are briefly suppressed for some minutes. In a minority of fits, however, audiogenic seizures are associated with a spreading depression wave, clearly expressed in the cortical DC potential. This wave is bilaterally initiated in the cortex and propagates to the caudate nucleus of the striatum. In these cases spontaneously occurring spike-wave discharges are fully suppressed for about 1 h. It is suggested that cortical spreading depression, triggered by a short audiogenic seizure, induces a long-lasting suppression of spike-wave discharges. These results are in line with the concept that spike-wave discharges are originally initiated in the cortex, as proposed by the 'cortical focus' theory. The precise role of the striatum remains less clear, although this structure seems not to play a pivotal role in spike-wave generation.     

Habituation to intense acoustic stimulation during cortical spreading depression in rats

Few investigations have focused on the effects of cortical spreading depression (CSD) on habituation. In the 2 experiments to be reported here long-term habituation to intense acoustic stimulation was investigated. Arrest of ongoing drinking behavior was used as an index of habituation. In the first experiment habituation training during bilateral CSD was compared to habituation training under nondepressed conditions; testing for long-term habituation took place under nondepressed conditions in both groups. In contrast to the control group the bilateral CSD group did not show long-term habituation. In the second experiment habituation training during CSD in one hemisphere did not result in long term habituation when testing took place during CSD in the contralateral hemisphere. Possible explanations of these results are discussed.     

Direct evidence of inter-hemispheric modulation by callosal fibers: a cortical spreading depression study in well-nourished and early-malnourished adult rats

Inter-hemispheric modulation has been extensively studied, as it is critical for human behavior and could be involved in the development of neuropsychiatric disorders, such as major depression, epilepsy and stroke. Malnutrition early in life can alter brain processes such as inter-hemispheric modulation and these alterations can persist into adulthood. Here, we used cortical spreading depression (CSD) as a neurophysiological parameter to investigate inter-hemispheric modulation in 19 well-nourished and 18 early-malnourished male adult rats. CSD was evoked on the right frontal region and monitored at two parietal points on the same hemisphere. After a 2 h baseline recording, fibers projecting from the left to the right hemisphere via the corpus callosum were cut with a longitudinal lesion in the contralateral cortex and recording continued for two more hours. The results show that (1) baseline CSD propagation velocities were higher in the malnourished rats, as compared to the respective well-nourished controls; (2) post-lesion velocities increased in both nutritional groups, as compared with the baseline values; (3) this CSD increase persisted 3–7 days after lesion, suggesting a lasting effect and (4) in the malnourished group the post-lesion CSD enhancement was of smaller amplitude. Furthermore, a midline lesion (callosotomy) in eight well-nourished rats similarly facilitated CSD, suggesting the involvement of callosal fibers on this effect. No differences were found in sham-operated rats (21 well-nourished and 21 malnourished), as well as in a superficial (1 mm deep) contralateral lesion group (8 well-nourished). Results support the hypothesis of a lasting inhibitory contralateral influence on CSD propagation, which is attenuated, but not abolished, by early malnutrition.     

Effects of nutritive and nonnutritive stomach loads on plasma glucose level and lateral hypothalamic eating threshold in the rat

Excitability of the rat's lateral hypothalamic feeding system was determined by measuring the threshold for electrically induced eating. The effects of different stomach loads on the magnitude and time course of this threshold and of blood glucose concentration were investigated. In a first experiment, 10 ml loads of either 50% (w/v) dextrose (21 kcal), 20% dextrose (8.5 kcal), bulk (50% kaolin in water), or tap water were compared against mock intubations with the empty syringe. Thresholds rose within minutes after loading with glucose, to a maximum at about 30 min, and then normalized slowly in a precise dose-response relationship. The nonnutritive kaolin load produced a comparable threshold increase to 20% glucose, but reached its maximum as soon as 10 min after intubation. The tap water load did not differ significantly from the mock control. In a second experiment, isocaloric 10 ml loads (20 kcal) of either dextrose, casein-hydrolysate or an emulsion of soyabean-oil were compared against mock intubations. The protein load was less effective than glucose, and the fat load less effective than protein, in increasing thresholds. While the glucose load produced a marked hyperglycemia, both the protein and fat load did not. Also, protein and fat loads did not maintain satiety longer than the simple bulk load.     

Involvement of GABA and ACh in retinal spreading depression: Effects of “low calcium — high magnesium” solutions

Summary Experiments have been performed on isolated chick retinas to demonstrate the participation of gabaergic and cholinergic systems in spreading depression (SD). Gamma-aminobutyric acid (GABA) and acetylcholine (ACh) were measured in the effluent solution of superfused retinas. The influence of changes in the concentration of calcium/ magnesium on the release of these neurotransmitters was studied. GABA and ACh are released in the superfusate of retinas during SD. Such release was observed during experimental periods longer than 2 h during which SD was elicited regularly at 15–20 min intervals. Decreasing calcium concentration from 1.0 to 0.5 mM and simultaneously increasing magnesium from 1.0 to 2.0–4.0 mM led to a decrease in GABA and ACh release during SD. Variations in light-scattering and increases in potassium concentration, usually occurring during SD, also decreased when supervising with low calcium/ high magnesium solutions. Lowering calcium concentration to 0.5 mM and increasing magnesium to 2.0 mM eventually turned the tissue refractory to SD. Sometimes a magnesium concentration of 2.0 mM was not effective in blocking SD. However, this blockage could be attained by increasing the concentration of magnesium to 4.0 mM. The effects of low calcium — high magnesium solutions on GABA and ACh release during SD suggests that the release of the substances is at least partially due to synaptic activity. It is not yet possible to establish whether GABA and ACh release is essential for the occurrence of SD. Nevertheless such release suggest that these neurotransmitters could influence the characteristics of SD manifestations in the retina.     

The minimum volume of depolarized neural tissue required for triggering cortical spreading depression in rat

Summary Cortical spreading depression (CSD) was evoked in anaesthetized rats by intracortical microinjection of 3.4·10^–8 mol KCl (the single injection threshold T₁). With two simultaneous injections at 1 mm tip separation 59% T₁ had to be applied to each point to elicit CSD. For interfocal distances 2, 3 and 4 mm the double injection thresholds T_1,2 were 65%, 74% and 97% of T₁ respectively. The spatial summation effect was still significant at 3 mm and undetectable at 4 mm tip separation. Recording electrodes placed 1–3 mm from the point of injection detected local slow potential changes which attained with subthreshold KCl injections 16% of the maximum CSD negativity at the 1.5 mm distance. The threshold amount of KCl required to trigger CSD at different intervals (30–480 sec) after initial injection of 0.8 T₁, exponentially increased with time from 28.2% t₁ at 30 sec to 88.9% at 480 sec with the slope 16.8% T₁ for a twofold increase of the interinjection interval. Quantitative analysis of results based on equations describing diffusion from an instantaneous point source indicates that the critical volume of depolarization is reached 61 sec after injection. According to the value of the diffusion coefficient of potassium the critical K+ concentration lies between 45 and 12 mequ/l and is reached at a distance of 600–950 from the injection.Visiting scientist from Department of Physiology, Gifu University, School of Medicine, Gifu City, Japan.     

Self-induced splitting of spiral-shaped spreading depression waves in chicken retina

 Spreading depression (SD) of electroencephalographic activity is a dynamic wave phenomenon in the central nervous system (CNS). The retina, especially the isolated chicken retina, is an excellent constituent of the CNS in which to observe the dynamic behavior of the SD wave fronts, because it changes its optical properties during a SD attack. The waves become visible as milky fronts on a black background. It is still controversial what the basic mechanistic steps of SD are, but certainly SD belongs to the self-organization phenomena occurring in neuronal tissue. In this work, spiral-shaped wave fronts are analyzed using digital video imaging techniques. We report how the inner end of the wave front, the spiral tip, breaks away repeatedly. This separation process is associated with a Z-shaped trajectory (extension ∼1.2 mm) that is described by the tip over one spiral revolution (period 2.45±0.1 min). The Z-shaped trajectory does not remain fixed, but performs a complex motion across the retina with each period. This is the first time, to our knowledge, that established imaging methods have been applied to the study of the two-dimensional features of SD wave propagation and to obtaining quantitative data of their dynamics. Since these methods do not interfere with the tissue, it is possible to observe the intrinsic properties of the phenomenon without any external influence. Received: 1 August 1996 / Accepted: 5 November 1996     

Bilateral kindled amygdala foci and inhibitory avoidance behavior in rats: A functional lesion effect

The repeated administration of brief low level electrical stimulation can be used to produce latent kindled epileptic foci in discrete regions of brain. Three groups of rats with kindled amygdala foci were trained and tested on a one-trial inhibitory avoidance task. The training-retention test interval was 24 hr. Animals with bilateral foci were impaired on this task. Animals experiencing either 6 convulsions or 12 convulsions from a unilateral focus were not impaired. This result is interpreted as support for the hypothesis that a kindled focus can act as a functional lesion.     

Re-emergence of hypothalamically elicited eating following change in food

Rats with lateral hypothalamic electrodes were administered electrical stimulation until the elicited eating of one type of food had emerged to asymptotic levels. Experimental animals later were presented with a different diet, and elicited eating underwent another emergence process. This re-emergence occurred despite the fact that animals had had deprivation experience with the second food immediately prior to stimulation experience with it. These data present interpretative difficulties for the hypothesis that elicited behavior reflects the activation of neural systems underlying deprivation-induced consummatory activity and that the anomalous characteristics of elicited responding can be attributed to an emotionality state which theoretically is also evoked by the stimulation.     

Redirected oral behavior in rats induced by tail-pinch and electrical stimulation of the tail

Two seemingly non-specific stimuli, tail-pinch and electrical stimulation of the tail (EST), produce different responses to food in rats: tail-pinch induces eating whereas EST elicits licking of food pellets. However, even if administered several months earlier, prior tail-pinch changes the response to pellets during EST from licking to eating. If their tail is within reach, naive rats lick it rather than food pellets. However, they rarely pursue the tail after their initial attempts to reach it are prevented; instead, they eat or lick food. In fact, if they have prior tail-pinch experience, they first eat during EST even with the tail in sight and reach. Thus the response to tail stimulation is directed specifically at the tail and is redirected towards food when the tail is not available. Different oral responses during tail-pinch and EST suggest that the two stimuli induce different sensations; however, the redirected response is modifiable by learning.     

Influence of diet palatability on maintenance feeding behavior in rats with dorsolateral tegmental damage

Lesions in the dorsolateral tegmentum that depleted hypothalamic norepinephrine induced (a) substantial hyperphagia and weight gains in rats maintained on either high-fat or wet-mash diets, (b) moderate overeating and body weight gains in rats maintained successively on 0.4, 0.3, 0.2, and 0.1% quinine high-fat diets, and (c) body weight maintenance at same-diet control levels in rats maintained successively on 0.2, 0.4, and 0.6% quinine wet-mash diets. Similarities and differences of the present findings with reference to previous observations obtained from rats with ventromedial hypothalamic lesions are discussed.