In vivo inhibition of rat brain protein synthesis by L-dopa

Inhibition of rat brain and liver protein synthesis by amphetamine

Dose-dependent, amphetamine-induced reductions in protein synthesis were determined in vivo by measuring [3H]lysine incorporation into trichloroacetic acid precipitated protein in homogenates prepared from different regions of the brain or liver. Low-to-moderate doses of amphetamine (1-5 mg/kg) decreased striatal protein synthesis whereas higher doses (10 mg/kg) reduced it in the cerebral cortices, cerebellum, and remaining portions of the cerebrum, as well as in the striatum and liver. Reductions in regional brain protein synthesis occur following amphetamine treatment in relatively low doses known to change various aspects of physiology and behavior.

Preparation of a cell-free extract from rat brain which can initiate protein synthesis in vitro

A cell-free protein synthesis system, derived from brains of 3 mo-old male Fischer-344 rats, has been characterized. The optimum conditions for amino acid incorporation in the system were 5 mM magnesium ion and 200 mM potassium ion. Incorporation depended on the addition of ATP, GTP, and an energy-generating system, and was sensitive to addition of the drugs aurintricarboxylic acid and sodium fluoride, inhibitors of initiation of protein synthesis. Both 40S and 80S initiation complexes were labeled in vitro, using [35S]methionine. Such labeling was sensitive to the protein synthesis inhibitors, aurintricarboxylic acid and sodium fluoride. The system, which can initiate protein synthesis, should be of use for examining mechanisms which underlie alterations in rat brain protein synthesis induced by various treatments.

Effect of intravenous administration of d-lysergic acid diethylamide on subsequent protein synthesis in a cell-free system derived from brain

An initiating cell-free protein synthesis system derived from brain was utilized to demonstrate that the intravenous injection of d-lysergic acid diethylamide (LSD) to rabbits induced a transient inhibition of translation following a brief stimulatory period. Subfractionation of the brain cell-free system into postribosomal supernatant (PRS) and microsome fractions demonstrated that LSD in vivo induced alterations in both of these fractions. In addition to the overall inhibition of translation in the cell-free system, differential effects were noted, i.e., greater than average relative decreases in in vitro labeling of certain brain proteins and relative increases in others. The brain proteins of molecular weights 75K and 95K, which were increased in relative labeling under conditions of LSD-induced hyperthermia, are similar in molecular weight to two of the major "heat shock" proteins reported in tissue culture systems. Injection of LSD to rabbits at 4 degrees C prevented LSD-induced hyperthermia but behavioral effects of the drug were still apparent. The overall decrease in cell-free translation was still observed but the differential labeling effects were not. LSD appeared to influence cell-free translation in the brain at two dissociable levels: (a) an overall decrease in translation that was observed even in the absence of LSD-induced hyperthermia and (b) differential labeling effects on particular proteins that were dependent on LSD-induced hyperthermia.

The sympathetic superior cervical ganglia as peripheral neuroendocrine centers

The superior cervical ganglia (SCG) provide sympathetic innervation to the pineal gland, cephalic blood vessels, the choroid plexus, the eye, carotid body and the salivary and thyroid glands. Removal of the ganglia brings about several neuroendocrine changes in mammals, including the disruption of water balance in pituitary stalk-sectioned rats, and the alteration of normal photoperiodic control of reproduction in hamsters, ferrets, voles, rams and goats. These effects are commonly attributed to pineal denervation. However pinealectomy does not always mimic ganglionectomy in its neuroendocrine sequelae. This paper discusses several examples illustrating the lack of homology of ganglia and pineal removal, including the prolactin release brought about by gonadal steroids in spayed rats, the changes in drinking behaviour caused by ganglionectomy and the control of goitrogenic response to methylmercaptoimidazole in rats. All these examples indicate that SCG removal, at least as far as for neuroendocrinologists and pineal experimenters are concerned, should not be considered simply as "pineal denervation". A functionally relevant link between SCG and the hypothalamus may occur in rats inasmuch as ganglionectomy depresses norepinephrine uptake and increases the number and responses of alpha-adrenoceptors in medial basal hypothalamus. Lastly the SCG are active points of concurrency for hormone signals, as revealed by the metabolic changes induced by steroid and anterior pituitary hormones in these structures even in the absence of intact preganglionic connections, as well as by the existence of putative receptors for some of the hormones, namely, estradiol, testosterone and corticosteroids. The SCG appear to constitute a peripheral neuroendocrine center.

[The effect of chloramphenicol on sleep in cat -- comparison with thiamphenicol, erythromycine, and oxytetracycline (author's transl)]

The effects of various antibiotics, which inhibit protein synthesis, has been studied on the sleep-waking cycle of cats. Chloramphenicol (CAP) selectively inhibits paradoxical sleep (SP). Thiamphenicol (TAP) and oxytetracycline however are ineffective; erythromycine induces only a small decrease of SP. When CAP is injected after TAP, the SP inhibition is longer than after CAP alone. Combining erythromycine and CAP produces the same effect as one or other of the antibiotic alone, depending only on the interval between administration of the two drugs. Slow wave sleep is decreased only with high doses of CAP and is unaffected by TAP, oxytetracycline or erythromycine. These results suggest that CAP may inhibit a peptide or protein synthesis involved in the mechanisms of SP.

Incorporation of 4,5-3H leucine into the neurons of locus ceruleus and other nerve cells in stressed rats: effect of diazepam

Incorporation of 4,5-3H leucine into neurons of locus ceruleus, neurons of the terminal principal nucleus of the trigeminal nerve and spinal moto-neurons in stressed rats (S group), animals, stressed after a single injection of diazepam (DS group), and controls (C group) was studied by quantitative autoradiography. Both in the S and DS groups the planimetrically measured neuronal areas were bigger than in the C group of spinal motoneurons and trigeminal neurons. Stress, however, had no effect on the size of neurons in locus ceruleus. No significant differences of grain density among C and S group were found in the three investigated neuronal groups; diazepam pretreatment (DS group), however, increased markedly the grain density in all types of neurons investigated.

Mechanism of D-amphetamine inhibition of protein synthesis

At 1 h after intraperitoneal administration of D-amphetamine sulphate (15 mg/kg), rat brain polyribosomes show disaggregation accompanied by reduced capacity for in vitro peptide chain elongation. The direct action of amphetamine on cell-fine protein-synthesizing systems was therefore explored. When brain or liver polyribosomes from untreated rats were incubated with pH 5 enzyme, peptide chain elongation was not inhibited by the addition 4 mM amphetamine to the medium. On the other hand, an initiation-dependent system consisting of rat liver of brain mRNA and wheat germ S-30 fraction showed inhibition of [3H]leucine incorporation by 50% when 4 mM amphetamine were added. The metabolites of amphetamine, p-hydroxyamphetamine and p-hydroxynorephedrine, had no inhibitory action in either system, but the potent neurotoxin p-chloroamphetamine was a more powerful inhibitor of initiation than amphetamine. By using [3H]amphetamine, it was shown that amphetamine binds to the 80-S ribosomes of the wheat germ system. This binding depended on the presence in the system of natural liver or brain mRNA or several synthetic mRNAs, but was not promoted by polyuridylic acid as the messenger. Significantly, polyuridylic acid-dependent polyphenylalanine synthesis by the wheat germ system was not inhibited by amphetamine or p-chloroamphetamine. Therefore, it was concluded that amphetamine inhibits protein synthesis by interfering with initiation through a step related to formation of the mRNA ribosome complex.

D-amphetamine disaggregates brain polysomes via a dopaminergic mechanism

Brain polysomes are disaggregated in rats given moderate to large doses of d-amphetamine sulfate; this response is rapid in onset, lasts for at least 4-6 hr, and varies with the age of the animal. Pretreatment with a dopamine receptor blocking agent, haloperidol or pimozide, blocks the amphetamine-induced disaggregation.