D-amphetamine disaggregates brain polysomes via a dopaminergic mechanism

Neonatal Escherichia coli infection alters glial, cytokine, and neuronal gene expression in response to acute amphetamine in adolescent rats

Neonatal bacterial infection in rats alters the responses to a variety of subsequent challenges later in life. Here we explored the effects of neonatal bacterial infection on a subsequent drug challenge during adolescence, using administration of the psychostimulant amphetamine. Male rat pups were injected on postnatal day 4 (P4) with live Escherichia coli (E. coli) or PBS vehicle, and then received amphetamine (15mg/kg) or saline on P40. Quantitative RT-PCR was performed on micropunches taken from medial prefrontal cortex, nucleus accumbens, and the CA1 subfield of the hippocampus. mRNA for glial and neuronal activation markers as well as pro-inflammatory and anti-inflammatory cytokines were assessed. Amphetamine produced brain region specific increases in many of these genes in PBS controls, while these effects were blunted or absent in neonatal E. coli treated rats. In contrast to the potentiating effect of neonatal E. coli on glial and cytokine responses to an immune challenge previously observed, neonatal E. coli infection attenuates glial and cytokine responses to an amphetamine challenge.

Neuropharmacology of TBI-induced plasticity

PRIMARY OBJECTIVE

The purpose of this report is to review both fundamental studies in laboratory animals and preliminary clinical data suggesting that certain drugs may affect behavioural recovery after brain injury.

MAIN OUTCOMES AND RESULTS

Laboratory studies show that systemically-administered drugs that affect specific central neurotransmitters including norepinephrine and GABA influence affect recovery in a predictable manner. Although some drugs such as d-amphetamine have the potential to enhance recovery, others such as neuroleptics and other central dopamine receptor antagonists, benzodiazepines and the anti-convulsants phenytoin and phenobarbital may be detrimental. In one study, 72% of patients with traumatic brain injury received one or a combination of the drugs that may impair recovery based on both animal experiments and studies in recovering stroke patients.

CONCLUSIONS

Until the true impact of these classes of drugs are better understood, care should be exercised in the use of medications that may interfere with the recovery process in patients with traumatic brain injury. Additional research needs to be completed before the clinical efficacy of drugs that may enhance recovery can be established.

Effects of amphetamine on protein synthesis and energy metabolism in mouse brain: role of drug-induced hyperthermia

Changes in brain protein synthesis activity, and in brain levels of glucose, glycogen, and several high-energy phosphate metabolites, were evaluated under conditions of amphetamine-induced hyperthermia in mice. Protein synthesis showed a striking dependence on rectal temperature (TR), falling abruptly at TR above 40 degrees C. A similar result was obtained following direct heating of the animals. Protein synthesis activity in liver showed the same temperature dependence observed for brain. Increased synthesis of a protein with characteristics of the major mammalian stress protein, hsp 70, was demonstrated in both brain and liver following amphetamine administration. Brain protein synthesis showed significant recovery within 2 h after amphetamine administration whereas that of liver remained below 30% of control activity, suggesting significant temporal and quantitative differences in the response of individual tissues to elevated temperatures. Brain glycogen levels after amphetamine administration were significantly lower under conditions of ambient temperature which resulted in more severe drug-induced hyperthermia but did not correlate as strikingly as protein synthesis with the temperatures of individual animals. Brain glycogen also fell in animals whose temperatures were increased by brief exposure at high ambient temperature. Brain glucose levels did not consistently change with hyperthermia. Slight decreases in high-energy phosphates with increasing TR were likely the result of fixation artifact. These results demonstrate the fundamental role of hyperthermia in the reduction of protein synthesis in brain and other tissues by amphetamine, and suggest that temperature also constitutes a significant source of variability in the effects of this drug on brain energy metabolism, in particular glycogenolysis.

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 initiation of 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 resulted in a lesion at the initiation stage of brain protein synthesis. Three inhibitors of initiation, edeine, poly(I), and aurintricarboxylic acid were used to demonstrate a reduction in initiation-dependent amino acid incorporation in the brain cell-free system. One hour after LSD injection, there was also a measurable decrease in the formation of 40S and 80S initiation complexes in vitro, using either [35S]methionine or [35S]Met-tRNAf. Analysis of the methionine pool size after LSD administration indicated there was no change in methionine levels. Analysis of the formation of initiation complexes in the brain cell-free protein synthesis system prepared 6 h after LSD administration indicated that there was a return to control levels at this time. The effects of LSD on steps in the initiation process are thus reversible.

In vivo inhibition of incorporation of [U-14C]glucose into proteins in experimental focal epilepsy

The in vivo incorporation of [14C] from [U-14C]-glucose into rat brain proteins from different cortical areas was examined in three different experimental focal epilepsies: cobalt, freeze-lesions, and tityustoxin. When [U-14C]-glucose was injected intraperitoneally into awake and unrestrained animals with marked signs of epileptic hyperactivity, the inhibition of incorporation of [14C]-amino acids into trichloracetic acid (TCA)-insoluble proteins was highest in the focal (sensorimotor) area when compared with distant regions (approx. 60%), but less when compared with the contralateral (sensorimotor) region (approx. 23%). Greatly decreased incorporation caused by both cobalt and freeze-lesion-induced epilepsies was also observed in the contralateral area when a comparison was made with distant regions (approx. 50%), but there were no significant differences in protein-specific radioactivity between the different distant areas.

Characterization of an initiating cell-free protein synthesis system derived from rabbit brain

Protein synthesis in the brain is known to be affected by a wide range of treatments. The detailed analysis of the mechanisms that are involved would be facilitated by the development of cell-free translation systems derived from brain tissue. To date, brain cell-free systems have not been fully characterized to demonstrate a capacity for initiation of translation. The following criteria were utilized to demonstrate that a cell-free protein synthesis system derived from rabbit brain was capable of initiation in vitro: (a) sensitivity of cell-free translation to the initiation inhibitor aurintricarboxylic acid (ATA); (b) binding of [35S]Met-tRNAf to 40S and 80S initiation complexes; (c) incorporation of labeled initiation methionine into high-molecular-weight proteins; and (d) the association of labeled exogenous mRNA with polysomes. The optimum conditions for amino acid incorporation in this system were 4 mM-Mg2+, 140 mM-K+, and pH 7.55. Incorporation was dependent on the addition of ATP, GTP, and an energy-generating system. Cell-free protein synthesis reflected the normal process, since a similar spectrum of proteins was synthesized in vitro and in vivo. This initiating cell-free translation system should have wide application in the analysis of the mechanisms whereby various treatments affect protein synthesis in the brain.

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.

Disaggregation of brain polysomes after LSD in vivo. Involvement of LSD-induced hyperthermia

LSD-induced hyperthermia is implicated in the brain-specific disaggregation of polysomes which is induced following intravenous administration of the drug to rabbits. Both LSD-induced hyperthermia and brain polysome disaggregation were found to increase in parallel under conditions which accentuated the effect of the drug on brain protein synthesis. Pretreatment with neurotransmitter receptor blockers or placing the animal at an ambient temperature of 4 degrees C after LSD administration prevented both hyperthermia and brain polysome disaggregation. The administration of apomorphine, which causes hyperthermia in rabbits also caused disaggregation of brain polysomes. Direct elevation of the body temperature to levels similar to that found after LSD was achieved by placing animals at an ambient temperature of 37 degrees C. Under these conditions a brain-specific disaggregation of polysomes resulted which was not due to RNAase activation. After either LSD or direct heating, the brain polysome shift was associated with a relocalization of polyadenylated mRNA from polysomes to monosomes as determined by [3H]polyuridylate hybridization. Since polysome disaggregation was found only in brain, it appears that the brain may be more sensitive to elevations in body temperature compared to other organs.

Electrotonic processing of information by brain cells

In contrast to well-studied through-protection neurons that propagate information from one region to another in the central nervous system, short-axon or axonless neurons form local circuits, transmitting signals through synapses and electrical junctions between their dendrites. Interaction in this dendritic network proceeds without spike action potentials. Interaction is mediated by graded electrotonic changes of potential and is transmitted through high sensitivity (submillivolt threshold) synapses rather than by lower sensitivity (20 to 100-mv threshold) synapses typical of projection neurons. A crucial feature of local circuits is their high degree of interaction both through specialized junctional structures and through the extracellular fields generated by local and more distant brain regions. The anatomical evidence for the nature and distribution of neuronal local circuits in the nervous system is surveyed. Bioelectric mechanisms are discussed in relation to the special properties of local circuits, including dendrodendritic synapses, synaptic sensitivity, electrotonic coupling, and field effects. Intraneuronal and interneuronal transport of various types of substances suggests that the biochemical and the bioelectrical parameters are functionally interwoven. Through such interactions neuronal local circuits, with their distinctive properties, may play an essential role in higher brain function.