Effects of electroconvulsive shock and cycloheximide on the incorporation of amino acids into proteins of mouse brain subcellular fractions

Alteration of RNA synthesis in vitro in intact cerebral cortex nuclei induced by convulsions in seizure-susceptible El mice

We examined the effects of convulsive seizures on in vitro RNA synthesis by cerebral cortex nuclei in El mice. The rate of incorporation of [3H]uridine-5'-triphosphate by intact nuclei during seizures was decreased to 47.4% compared with the rate during the interictal period, but gradually recovered. During the 30-min period after onset of seizures, the rate of RNA synthesis was significantly lower in El mice than in identically stimulated ddY mice. Seizures in El mice had no effect on liver RNA synthesis, suggesting that the alteration of RNA polymerase activity is specific to the brain. Analysis of gel electrophoresis of polyadenylated RNA synthesized in the presence of ammonium sulphate revealed a marked decrease in high-molecular weight RNA species 15 min after seizures in El mice compared with the pattern in nonstimulated ddY mice. This shift from high- to low-molecular weight RNA species was not attributable to RNase activity, but it appeared to be related RNA polymerase.

Regional impairment of protein synthesis in the rat brain during bicuculline-induced seizures

Protein synthesis was investigated in rats subjected to 30 min of bicuculline-induced seizures using biochemical and autoradiographic techniques. Incorporation studies were performed on freely convulsive animals following systemic administration of either a tracer dose of L-[1-14C]tyrosine or a flooding dose (7.5 mmol/kg) of L-[1-14C]valine. Using a tracer dose, amino acid incorporation was only moderately reduced (forebrain) or slightly enhanced (cerebellum/brainstem and spinal cord) but the specific radioactivity of [14C]tyrosine in the acid-soluble pool was increased 3- to 5-fold in experimental animals. After a flooding dose of [14C]valine the specific activity of the precursor amino acid was similar in control and convulsed animals. Under these conditions incorporation rates in forebrain and cerebellum/brainstem were reduced to 54 and 75%, respectively. Reduction of amino acid incorporation was even more pronounced in extraneural tissues, e.g. liver (6%), intestine (14%) and kidney (15%). Inhibition of protein synthesis in forebrain and cerebellum/brainstem was paralleled by a similar extent of polyribosome disaggregation in these regions (53 adn 78% of controls). In anaesthetized, mechanically ventilated rats, 30 min of seizure activity reduced forebrain polyribosomes to a similar extent (57%). Extraneural (hepatic) protein synthesis was also affected in physiologically controlled rats, but cerebellar polysomes were completely preserved. Autoradiographic studies using 3H-labelled amino acids were carried out to identify nerve cell populations most heavily affected. In freely convulsive rats both tracer dose and pool overloading revealed a similar regional pattern with preferential inhibition of amino acid incorporation in forebrain cortex, thalamus and the pyramidal cell layer of the hippocampus. These sites were also affected in the physiologically controlled animal, but the focal distribution of hippocampal and thalamic neurones with reduced protein synthesis differed from that in freely convulsive rats.

Focal seizures disrupt protein synthesis in seizure pathways: an autoradiographic study using [1-14C]leucine

We have used a new autoradiographic technique developed by Smith et al.22,33 for visualizing rates of incorporation of [1-14C]leucine into protein in brain. Focal seizures caused by topical convulsants resulted in a marked decrease in autoradiographic density. This was primarily confined to the seizure focus, especially marked in pyramidal cell layers, and to subcortical seizure pathways. There were no distinct changes in cortico-cortical pathways beyond the seizure focus. Pure orthodromic pathways through basal ganglia showed an 18% inhibition of leucine incorporation in caudate nucleus and substantia nigra, pars compacta (P less than 0.05). By contrast, thalamic nuclei connected both ortho- and antidromically to the focus showed a 30-63% inhibition (P less than 0.01). The topographic pattern and intensity of the thalamic changes were related to the site, size and intensity of the seizure focus. As seizures became severe there was a more generalized depression of metabolism beyond seizure pathways, especially in the ipsilateral hemisphere. The results suggest that seizures block incorporation of leucine into protein either by an increase oxidation of the precursor, and/or an inhibition of protein synthesis per se. The effect is most severe in neurons undergoing epileptic burst discharge in the focus and in thalamic neuronal beds connected reciprocally with the focus.

Effect of epileptogenic agents on the incorporation of 3H-glycine into proteins in the cat's cerebral cortex

Filter paper strips soaked in 3H-glycine solution were applied to acoustic cortex of cats, anaesthetized with Nembutal and pretreated with epileptogenic agents (Metrazol, G-penicillin, and 3-amino-pyridine) and cycloheximide. The untreated contralateral hemisphere served as control. After 1 h incubation, both cortical samples were excised simultaneously and fixed in Bouin solution for autoradiography. Incorporation was blocked by cycloheximide. There was no glycine incorporation on the penicillin-treated side, while pyramidal cells were intensively labelled in layers II-V of the mirror focus. 3-Aminopyridine produced the same result. Metrazol as convulsant proved to be far weaker than the previous two. The intensity of incorporation was significantly more intensive in the mirror focus than in the primary one. Penicillin and 3-aminopyridine, while provoking cortical seizures, seem to inhibit glycine incorporation into a neuron-specific, function-dependent protein contained by the labelled cells in the autoradiogram.

Changes in [3H]lysine incorporation into protein in a seizure focus in rat isocortex

A focus of epileptiform discharge was induced in rat isocortex by subpial injection of 5 microliters of 100 mM FeCl3. Control animals were prepared with saline injections. Protein synthesis was estimated by uptake of [3H]lysine and its incorporation into protein at the site of iron injection, in the contralateral homotopic isocortex, and in the midline cerebellum. We found diminished uptake of [3H]lysine into all regions of rat brain in the interictal or nonseizing iron-injected animals, whereas the corrected rate of incorporation of [3H]lysine into protein was not significantly different from control rates. Actively seizing animals showed no inhibition of uptake of [3H]lysine, but [3H]lysine incorporation into protein relative to the uptake was significantly inhibited within the epileptic focus but not in the other areas examined. This decreased incorporation of amino acids into protein parallels that found in animals convulsing after electroshock or pentylenetetrazol injection.

Regional protein synthesis in the rat brain during bicuculline-induced epileptic seizures

The incorporation of L-[3,5-3H]tyrosine into cerebral proteins was investigated during the initial phase (30 min) of bicuculline-induced status epilepticus. Autoradiographs of different parts of the cerebral hemispheres, brain stem, and cerebellum were prepared. Marked local reduction of amino acid incorporation was evident in bilaterally symmetrical areas of the cerebral cortex, hippocampus, thalamic nuclei, and the region of the medial geniculate body. No apparent difference of local [3H]tyrosine incorporation was observed in the lower brain stem nuclei and in the cerebellum of control and convulsed animals. The territories showing a decrease of protein synthesis during epileptic seizures coincide largely with the regions of maximal local glucose metabolism and cerebral blood flow. The present investigation demonstrates that autoradiography of regional protein biosynthesis is a suitable method for the visualization of neuronal populations at risk in the very early stages of seizure activity.

Corticotropin-induced changes in protein labelling: lack of molecular specificity

Previous studies in this and other laboratories have indicated that corticotropin (ACTH) administered to intact or hypophysectomized rats or mice increased the labelling of cerebral proteins by radioactive amino acids, presumably indicative of increased protein synthesis. This study was designed to reveal whether this increased labelling was specific for particular proteins by studying labelling patterns in SDS polyacrylamide gels using a double isotope procedure. Two strains of mice, two different amino acid precursors, leucine and lysine, and both peripheral and central administration of ACTH and amino acids were used. In no case were treatment dependent changes in labelling observed in any region of the gel. This included regions containing S-100 or NSP, two brain specific proteins whose content had been reported to be increased by treatment of rats with an ACTH analog.

Effect of stimulation on the incorporation of 14C from glial and neuronal specific substrates into brain proteins in vivo and in vitro

The incorporation of amino acids into brain proteins following brachial plexus stimulation (BPS) was studied in anaesthetised Sprague-Dawley rats following injection of radioactive precursors of both neuronal and glial compartments. Following intraperitoneal injection of [14C]glucose, which is the major neuronal pool precursor, BPS resulted in a significant increase of 37% (P < 0.001) in the incorporation of carbon from [14C]glucose into TCA-insoluble proteins in the contralateral sensorimotor cortex as compared with the ipsilateral area of the same animal. This increase was abolished totally when tetrodotoxin (10 micrograms ml-1) was applied topically to the surface of the stimulated area. Following intraperitoneal injection of [14C]acetate, which is considered to by mainly a glial cell precursor, the same afferent electrical stimuli caused a significant decrease of 21% in the incorporation of amino acids into proteins in the stimulated versus unstimulated sensorimotor cortex. With [4-(3)H]phenylalanine or [1-(14)C]leucine as precursors a significant decrease (12%) or no change was recorded, respectively. A similar decrease in protein synthesis in the stimulated sensorimotor cortex was achieved using different routes of injection. No significant changes were observed in the ratio of the specific radioactivities of the total amino acids of the two hemispheres using either precursor. In vitro, synaptosomes showed a large increase in incorporation into proteins after treatment with electrical pulses, both with [14C]glucose and with [U-14C]acetate as precursors.

ACTH and the stress-induced changes of lysine incorporation into brain and liver proteins

When mice were subjected to footshock treatment and subsequently injected with [3H] lysine, the cerebral uptake of [3H] lysine, its incorporation into brain protein and the relative radioactivity (RR = protein radioactivity divided by amino acid radioactivity) were all increased. In the liver, footshocked mice showed decreased free lysine radioactivity, and increased protein radioactivity and relative radioactivity compared to quiet mice. The possibility that ACTH mediated these effects was investigated. The injection of saline had no effect in the brain but partially mimicked the footshock responses in the liver. Injections of ACTH 1--24 mimicked the effects of footshock in the brain, and further augmented the saline-induced effect on the RR in the liver. ACTH 4--10 increased the RR of brain protein, but produced no significant change in brain free lysine radioactivity or in any measure in the liver. Pretreatment of mice with the synthetic glucocorticoid, dexamethasone, did not enhance these effects and diminished the effect of ACTH 4--10 in the brain. ACTH treatment did not alter the profiles of brain polyribosomes. Lysine vasopressin, which is also released during stress, did not alter the incorporation of [3H] lysine into brain or liver protein, except at high doses when it decreased plasma radioactivity. These results suggest that secretion of ACTH at least partially mediates the stress-induced changes of [3H] lysine incorporation into brain and liver proteins, but that it is probably not the only factor involved.

Stimulation increases incorporation of [3H]lysine into rat brain and liver proteins

Exposure of rats to electric footshocks or merely to the footshock apparatus increased the incorporation of [3H]lysine into brain and liver protein. The effect was present in both fore-and hindbrain. The footshock treatment was the more effective stimulus, producing larger and more significant changes. These results resemble those previously observed in C57Bl/6J mice, and thus suggest that altered protein or amino acid metabolism is a general response to stress in rodents.

The role of the pituitary-adrenal system in the footshock-induced increase of [3H]lysine incorporation into mouse brain and liver proteins

The brains of mice subjected to electric footshocks took up more free [3H]lysine and incorporated more [3H]lysine into protein than did the brains of undisturbed mice, suggesting that footshocks caused increased cerebral protein synthesis. The possible mediation of these effects by hormones of the pituitary-adrenocortical system was investigated. Despite adrenalectomy, footshock treatment still elevated the poolcorrected [3H]lysine incorporation into cerebral protein. Pretreatment with dexamethasone, which greatly suppressed the pituitary-adrenal response to footshocks, prevented the increase in [3H]lysine incorporation. It is suggested that ACTH itself may mediate this stress-induced increase in net free [3H]lysine uptake. Although the lysine uptake response thus appeared to depend upon the presence of the adrenal glands, the response was not mimicked by injection of corticosterone. The response of liver [3H]lysine metabolism was studied in the same experiments. Footshock treatment decreased the net uptake and increased the incorporation into protein, in normal, adrenalectomized and dexamethasone-pretreated mice. Corticosterone did not mimic these effects. Thus, the metabolic response to footshock of liver, unlike that of brain, appeared to be independent of the pituitary-adrenal system.

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.