Inhibition Of Cerebral Protein Synthesis Research Articles

THE HEAT SHOCK STRESS RESPONSE AFTER BRAIN LESIONS: INDUCTION OF 72 KDA HEAT SHOCK PROTEIN (CELL TYPES INVOLVED, AXONAL TRANSPORT, TRANSCRIPTIONAL REGULATION) AND PROTEIN SYNTHESIS INHIBITION

The cerebral stress response is examined following a variety of pathological conditions such as focal and global ischemia, administration of excitotoxins, and hyperthermia. Expression of 72 kDa heat shock protein (Hsp70) and hsp70 mRNA, the mechanism underlying induction of hsp70 mRNA involving activation of heat shock factor 1, and inhibition of cerebral protein synthesis are different aspects of the stress response considered here. The results are compared with those in the literature on induction, transcriptional regulation, expression, and cellular location of Hsp70, with a view to getting more insight into the function of the stress response in the injured brain. The present results illustrate that Hsp70 can be expressed in cells affected at various degrees following an insult that will either survive or die as the brain lesion develops, depending on the severity of cell injury. This indicates that, under certain circumstances, synthesized Hsp70 might be necessary but not sufficient to ensure cell survival. Other situations involve uncoupling between synthesis of hsp70 mRNA and protein, probably due to very strict protein synthesis blockade, and often result in cell loss. Cells eventually will die if protein synthesis rates do not go back to normal after a period of protein synthesis inhibition. The stress response is a dynamic event that is switched on in neural cells sensitive to a brain insult. The stress response is, however, tricky, as affected cells seem to need it, have to deal transiently with it, but eventually be able to get rid of it, in order to survive. Putative therapeutic treatments can act either selectively, potentiating the synthesis of Hsp70 protein and recovery of protein synthesis, or preventing the stress response by deadening the insult severity. © 1997 Elsevier Science Ltd. All rights reserved.

NBQX reduces threshold of protein synthesis inhibition in focal ischaemia in rats.

The effect of the AMPA antagonist NBQX on peri-infarct inhibition of cerebral protein synthesis (CPS) was studied in rats subjected to 3 h occlusion of the left middle cerebral artery (MCA). Cerebral blood flow and CPS were measured with double tracer autoradiography and local ATP content was monitored by bioluminescence imaging. In untreated MCA-occluded animals the perfusion threshold of ATP depletion in cerebral cortex was 17 +/- 5 ml 100 g-1 min-1 and that of CPS inhibition was 49 +/- 13 ml 100 g-1 min-1. NBQX treatment (2 x 30 mg kg-1 after vascular occlusion) reduced the perfusion threshold of CPS inhibition to 16 +/- 6 ml 100 g-1 min-1 (p < 0.05) whereas that of ATP depletion was not affected (11 +/- 6 ml 100 g-1 min-1). The NBQX-induced pharmacological improvement of peri-infarct CPS is similar to the previously described amelioration of peri-infarct CPS by MK-801 and may contribute to the reduction of infarct size by this treatment.

Temporal and pharmacological parameters of puromycin-induced amnesia

Mice were trained in step-down passive avoidance behavior. Bitemporal injections of puromycin (PM) were given either immediately or delayed until 24 hrs after training. PM produced a marked amnesia in both cases during retention testing 3 days later. The amnesia persisted during a second retention test 6 days after training. Of all the antibiotics, only PM is effective as an amnestic agent when injections are delayed 24 or more hours after training. Cycloheximide (CXM) was also injected bitemporally immediately after training. However, CXM produced a weaker amnestic effect even though it produced a much greater inhibition of cerebral protein synthesis, more rapidly, and of longer duration. In an effort to attenuate the amnesia produced by PM, in separate experiments, the mice were injected with combined injections of PM and CXM (bitemporally); mice were also given combined injections of PM (bitemporally) and amphetamine (subcutaneously). The amnesia produced by immediate injections of PM was not attenuated by either CXM or amphetamine. However, the amnesia produced by delayed injections of PM was attenuated by both CXM and amphetamine. These results suggest that delayed injections of PM (24 hours after training) block the e expression or retrieval of memory. This study also supports the contention that puromycin has two separate effects on memory with different temporal parameters depending on when the drug is injected relative to initial training.

Inhibition of cerebral protein synthesis does not prolong short-term memory.

Male Swiss albino CD-1 mice given a single subcutaneous injection of a cerebral protein synthesis inhibitor, anisomycin (ANI; 1 mg/animal), 20 min prior to a single trial of passive avoidance training demonstrated impaired retention at tests given 3 hr, 6 hr, 1 day, and 7 days after training. Retention was not significantly different from that of saline controls when tests were given .5 or 1.5 hr after training. Prolonging inhibition of brain protein synthesis by giving either one or two additional injections of ANI at 2 hr or at 2 and 4 hr after training did not prolong good retention performance. The temporal development of impaired retention in ANI-treated mice could not be accounted for by drug dosage, duration of protein synthesis inhibition, or nonspecific sickness at test. In contrast to the suggestion that protein synthesis inhibition prolongs short-term memory, the results of this experiment indicate that short-term memory is not prolonged by antibiotic drugs that inhibit cerebral protein synthesis. All evidence seems consistent with the hypothesis that short-term memory is independent of protein synthesis and that the establishment of long-term memory depends on protein synthesis during or shortly after training.

Inhibition of cerebral protein synthesis: Dissociation of nonspecific effects and amnesic effects

Injection of 210 mg/kg of anisomycin 5 hr prior to training produced more nonspecific behavioral side effects at the time of training than did a low dosage (30 mg/kg) given 20 min prior to training. Yet the low dosage 20 min pretraining produced greater protein synthesis inhibition at training and greater impairment of retention of passive avoidance training than did the high dosage 5 hr pretraining. These results demonstrate that the level of protein synthesis inhibition at or near the time of training is the critical factor for inducing amnesia, and not nonspecific side effects of a protein synthesis-inhibiting drug. Various alternative hypotheses would also predict greater amnesia after the high dosage of anisomycin given 5 hr prior to training than after the amnestic low dose given 20 min prior to training. Thus, these results provide further support for the hypothesis that brain protein synthesis is required for long-term memory formation.

Similar effects of a monoamine oxidase inhibitor and a sympathomimetic amine on memory formation

Amnesia resulting from inhibition of cerebral protein synthesis by cycloheximide can be prevented by subcutaneous injection of the monoamine oxidase inhibitor pargyline (25 mg/kg) or the sympathomimetic amine metaraminol (3.0 mg/kg) administered up to 30 min following learning of a single trial passive avoidance task in day-old chickens. The injection has to be made during the life time of labile memory for the prevention of cycloheximide-induced amnesia. On the other hand amnesia induced by the Na/K ATP'ase inhibitor ouabain can only be prevented if these two agents are administered up to 5 min after learning, i.e. during the life time of short-term memory. In addition, both agents produce a retrieval deficit 90 min after the injection, but only when memory is in long-term storage. These results are compared to those obtained with administration of norepinephrine, d-amphetamine and diphenylhydantoin.

Recovery as a function of the degree of amnesia due to protein synthesis inhibition

Retrograde amnesia following inhibition of cerebral protein synthesis has generally been explained as either a failure of consolidation or impairment of a retrieval mechanism. Major evidence for the retrieval hypothesis is provided by studies which utilize a reminder (usually footshock) to attenuate the effect of the protein inhibitor. To examine this question, mice were injected subcutaneously with anisomycin (1 mg/animal, 7 mg/animal, or 1 mg/animal every 2 hr × 7) and given one training trial in a passive avoidance box. All animals received a single retention test on each of four consecutive days, starting either 1,7, or 21 days after training. One-half of the mice in each group received a footshock reminder 1 hr after their initial test. The footshock reminder did not attenuate the inhibitor-induced amnesia, but multiple testing did produce partial recovery in animals demonstrating some memory of training (both Saline and Anisomycin animals). Animals injected with anisomycin whose testing began 1 day after training demonstrated partial recovery irrespective of drug dosage level. The extent of amnesia and recovery were dependent upon both drug dosage and training-test interval. Implications for the consolidation and retrieval hypotheses are discussed.

Protein synthesis inhibition and memory for pole jump active avoidance and extinction

This study utilizes a pole jump active avoidance task to investigate the effects of protein synthesis on memory formation. An extinction training procedure for this task is also described. Amnesia for extinction is produced by inhibition of protein synthesis and is also demonstrated by active responding, so it is clear that there is no general impairment sufficient to disrupt motor skill, motivation, or retrieval of stored memories. It was found that while inhibition of protein synthesis in brain for 2 hr did not produce amnesia, inhibition for 6 to 8 hr did. These results demonstrate that for both shock-motivated learning and non-shock motivated extinction learning, the duration of inhibition of protein synthesis is important in determining whether amnesia occurs. We conclude that inhibition of cerebral protein synthesis can best account for amnesia induced by anisomycin, cycloheximide, and acetoxycycloheximide.

The effect of stimulants, depressants, and protein synthesis. Inhibition on retention

This study tested the hypothesis that the level of arousal is an important determinant of memory trace formation. The amnesia was caused in mice by inhibition of cerebral protein synthesis with anisomycin. The level of arousal was modified by the use of excitant and depressant drugs. Post-training administration of a stimulant (d-amphetamine, strychnine, or picrotoxin) counteracts the amnesic effects of protein synthesis inhibition, so that amnesia does not occur unless the duration of inhibition is lengthened. Stimulants show a time dependency, since they are less effective when administered at longer intervals after training. Depressants enhance the amnesia resulting from protein synthesis inhibition. Biochemical experiments showed that depressants alone had only slight effects on the rate of protein synthesis. In combination with anisomycin, the depressant did not markedly prolong the duration or increase the degree of inhibition. Stimulants, either by themselves or in combination with the inhibitors, had little or no effect on protein synthesis. The results are all consistent with the hypothesis that the level of arousal following acquisition plays an important role in determining the length of time over which the biosynthetic phase of memory formation will last.

Effects of cycloheximide on experimental epilepsy induced by daily amygdaloid stimulation in rabbits.

Daily electrical stimulation of the amygdala caused a progressive change in electrographic afterdischarge and behavioral responses that ultimately resulted in generalized convulsions (kindling). Cycloheximide blocked the completion of kindling when administered 4 hours prior to daily electrical stimulations of the amygdala, but exerted no effect when administered shortly before the stimulation. The temporal relation between administration of cycloheximide and stimulation of the amygdala revealed that the blockade of kindling by cycloheximide was due to the suppression of focal afterdischarge rather than to the persistent inhibition of cerebral protein synthesis during the interstimulus periods.

Protein synthesis and amnesia: Studies with emetine and pactamycin

Two antibiotic inhibitors of protein synthesis, emetine and pactamycin, have been tested for their effects on cerebral and peripheral protein synthesis and amnesia. Peripherally administered emetine but not pactamycin inhibited cerebral protein synthesis, although this inhibition was lower than that observed with cycloheximide or anisomycin. Pactamycin had a lesser effect on adrenal protein synthesis than emetine. This was reflected in the ability of emetine but not pactamycin to block ACTH-induced corticosteroidogenesis. Anisomycin and cycloheximide caused amnesia in a passive avoidance task, whereas pactamycin and emetine did not. These results are inconsistent with the amnesia being due to inhibition of protein synthesis in a peripheral organ. They are also inconsistent with the amnesia being due to the suppression of an adrenocortical response as previously suggested. No obvious correlation between amnesia and the mechanism of protein synthesis was observed. The most parsimonious explanation is that inhibition of cerebral protein synthesis is necessary for amnesia.

Inhibition of cerebral protein synthesis: performance at different times after passive avoidance training

Inhibition of cerebral protein synthesis impairs long-term memory in a variety of species and tasks. Recently it was reported that subcutaneous injection of the protein synthesis inhibitor cycloheximide impaired short-term retention, measured 10 min after training in a passive avoidance task. To examine the possibility that inhibition of cerebral protein synthesis may sometimes disrupt short-term memory, mice were injected subcutaneously with cycloheximide (120 mg/kg) or anisomycin (150 mg/kg), or bitemporally with cycloheximide or anisomycin (100 μg/side) and given one training trial in a passive avoidance box. Subcutaneously injected cycloheximide reduced step-through latencies 10 min after training as reported previously, but anisomycin or bitemporally injected cycloheximide did not. All 4 drug groups exhibited impaired long-term memory. Since the results obtained at short intervals after training varied depending on the drug and route of injection, the impairment produced by subcutaneous cycloheximide at 10 min after training cannot be attributed to inhibition of cerebral protein synthesis. It is suggested that performance at short intervals after training reflects drug side effects on step-through behavior. By contrast, the impairment obtained at long intervals after training is consistent with the hypothesis that cerebral protein synthesis is required for formation of long-term memory.

Inhibition of cerebral protein synthesis impairs long-term habituation

Inhibition of cerebral protein synthesis impairs long-term habituation

Inhibitors of cerebral protein synthesis: Dissociation of aversive and amnesic effects

It has been reported that cycloheximide, a protein synthesis inhibitor, produces conditioned aversion. This finding raised the possibility that the amnesic effect of this drug could be due to its aversive effects rather than to inhibition of cerebral protein synthesis required for the formation of long-term memory. The present study indicates that (1) amnesic doses of cycloheximide and anisomycin, two protein synthesis inhibitors, produced conditioned gustatory aversion; (2) lithium chloride produced as much conditioned aversion as an amnesic dose of anisomycin and more aversion than cycloheximide, but did not affect memory. Therefore the aversive effect of protein synthesis inhibitors, as measured by the conditioned gustatory aversion test, is not sufficient to explain their amnesic effect.

Regional alterations of synaptic O-phosphorylethanolamine in differentially housed mice

Summary In three experiments, the relationship between brain O-phosphorylethanolamine (PE) and isolation-induced behavioral effects was considered. It was observed that following eight weeks of isolation, male CF-1S strain mice showed highly significant elevations in synaptosomal PE in structures of the limbic system and in the cerebellar cortex; such changes did not occur in the cerebral cortex. Elevation of brain PE in mice by exogenous means led to profound rapid changes in the neurological status of the animal, with a subsequent behavioral status resembling that brought about by isolation housing. A PE-mediated inhibition of cerebral protein synthesis was demonstrated in vitro for microsomal fractions, particularly for those derived from the cerebellar cortex. The present data have been considered with a view toward introducing PE as a potential link to inhibitory changes in the central nervous system.

Inhibition of cerebral protein synthesis by epileptic seizures without motor manifestations.

Repetitive seizures were induced electrically in 109 male CFN rats that were paralyzed and ventilated with oxygen. Compared with the results in paralyzed, oxygen-ventilated controls receiving sham shocks, incorporation of radioactive leucine into cerebral proteins was decreased up to twofold in the cerebral hemispheres, cerebellum, and brain stem of the experimental animals. The extent of inhibition increased with the duration of seizures. The size of the leucine and protein pools was unaffected by seizures, but the specific activity of the cerebral leucine pool was 61 to 64 percent greater in experimental animals. The findings provide a potential explanation of some of the complications that often follow sustained cerebral paroxysmal activity even in the absence of convulsions.

Memory impairment during prolonged training in mice given inhibitors of cerebral protein synthesis

When mice were given prolonged discrimination training to escape shock in an automated apparatus shortly after subcutaneous administration of the protein synthesis inhibitor cycloheximide (CXM), acquisition was normal during the initial (15–21) trials. Beyond this point, however, mice given CXM did not continue to improve as rapidly as mice given saline. Similar results were found when training occurred 4 h after intracerebral injection of CXM or puromycin. In contrast, isoCXM which depresses activity like CXM but does not inhibit cerebral protein synthesis had no effect on acquisition. Studies of the effects of different doses of CXM on activity, cerebral protein synthesis, the acquisition effect, and memory 24 h after brief training tended to associate the acquisition effect with inhibition of cerebral protein synthesis rather than to side effects of CXM. The results suggest that impairment in learning observed a few minutes after the beginning of prolonged training is due to inhibition of protein synthesis. Expression of normal memory may depend on cerebral protein synthesis within minutes after the beginning of training.

Age dependent effects of 5-hydroxytryptamine upon memory consolidation and cerebral protein synthesis

In four experiments consideration was given to the effect of intracranially administered 5-Hydroxytryptamine (5-HT) upon several age dependent cerebral processes. These included (1) the tissue uptake of exogenously administered intracranial 5-HT, which in 17-day old CF-IS strain mice did not lead to increases in forebrain 5-HT level; (2) when administered in close temporal proximity with a single trial passive avoidance training trial, intracranial 5-HT produced a significant degree of retrograde amnesia in 15, 20, and 30-day-old mice, with a temporal gradient for this amnesic effect measured out to eight min. No significant retrograde amnesic effect for such passive avoidance behavior was produced in 17-day old animals. The amnesic effect appeared to be specific to 5-HT, in that (3) other amines or 5-HT analogs administered intracranially in equimolar concentration, had no amnesic effect. The relationship between age and the effect of intracranially administered 5-HT was considered with regard to regional cerebral protein synthesis. The incorporation of radioactive leucine into proteins of several regions of the brain, including cerebral cortex, basal ganglia and diencephalon, midbrain, and cerebellum, was significantly inhibited within 20 min following 5-HT administration. No significant inhibition of cerebral protein synthesis was observed in 17-day old mice of the same strain given identical treatment. The data from the series of experiments generally supported the view that inhibition of protein synthesis may be effected by increases in the regional concentration of 5-HT, and under circumstances wherein such increases are precluded either because of endogenous metabolic circumstances or tissue uptake properties, protein synthesis inhibition may not occur. Such was the case for the 17-day old CF-1S strain mouse wherein protein synthesis inhibition was attenuated and the retrograde amnesic effect of intracranial 5-HT was antagonized.

Protein synthesis in the cat brain after prolonged cerebral ischemia

Complete cerebral ischemia for 30 min was produced in normothermic cats by clamping the innominate and the left subclavian arteries and simultaneous lowering of the systemic blood pressure. Recovery of neuronal function after ischemia was ascertained by recording the EEG and the pyramidal response to electrical stimulation of the sensorimotor cortex. The incorporation of [ 14Clabeled amino acids into brain proteins was determined at different time intervals after ischemia. Specific radioactivity of brain proteins approached control values within 4 h. At the same time, however, the specific radioactivity of total amino acids in the free pool of the brain was considerably increased. Sucrose density gradient analysis and electron microscopic studies revealed a distribution of polysomes and monosomes during ischemia similar to that in control animals, but a marked disaggregation of polysomes was observed in the postischemic recovery phase. The data are discussed with regard to the possible mechanism of inhibition of cerebral protein synthesis during and after ischemia.

Cycloheximide: its effects on activity are dissociable from its effects on memory.

Cycloheximide, when injected subcutaneously or intracerebrally, produces changes in the activity level of mice. Isocycloheximide, injected intracerebrally, produces identical effects on activity, but it does not produce inhibition of cerebral protein synthesis or amnesia. Amphetamine, in doses that can antagonize the amnesic action of cycloheximide, does not antagonize the effect of cycloheximide on activity. Effects of cycloheximide on activity do not appear to be responsible for its amnesic action.