Neurotransmitter amino acid variations in striatum of rats exposed to 50 Hz electric fields.

Concentration of neurotransmitter amino acids (Tau, Gly, Asp, Glu, Gln, Ala, GABA) were measured in rat striatum following varying exposure (320 to 1408 h) to high intensity (50 Hz) electric fields. Tissue extracts in methanol, after drying, were derivatized with dansyl chloride and the amino acids quantitated by high-pressure liquid chromatography with ultraviolet detection. Short exposures (320 h) to 100 kV/m field induced a decrease in almost all tested amino acids. Longer exposure times (640 h) to 25 and 100 kV/m were only associated with a decrease in Tau. A further increase of the exposure time (1240 and 1408 h) both at 25 and 180 kV/m were mainly associated with a reduction of the amino acid levels. It is concluded that electric fields in the range 20-180 kV/m generate bimodal variations in neurotransmitter amino acids with troughs at very short and longer exposure times, independent from the field strength.

Muscimol antagonism of morphine analgesia in rats.

1 Muscimol, a gamma-aminobutyric acid (GABA) receptor agonist, when injected intraventricularly antagonizes the antinociceptive effect of morphine given either subcutaneously or intraventricularly. The antagonistic effect of muscimol on morphine analgesia appears to be linearly related. 2 This finding provides support for the view that a GABA-ergic system is involved in morphine analgesia.

Purine involvement in morphine antinociception.

The effects of a series of adenosine derivatives on morphine antinoceptive effect were investigated in rats by the 'tail-flick' method. 2-Chloroadenosine (CADO) and L-N6-phenylisopropyladenosine (L-PIA), given intraperitoneally, caused decreased morphine antinociception. Intracerebroventricular injections of CADO, L-PIA and 5'-N-ethylcarboxamide adenosine (NECA), but not of 2'-deoxyadenosine, antagonized morphine antinociception. The effects of both central and peripheral injections of CADO and L-PIA on morphine antinociception were partially reversed by caffeine. Intracerebroventricular injection of dibutyryl-cyclic 3', 5' adenosine monophosphate (db cyclic AMP) had no effect on morphine antinociception. These data indicate that adenosine plays a role in morphine-induced antinociception. The results are discussed in terms of postulated effects of adenosine derivatives on adenylate cyclase.

Modification of the antinociceptive effect of morphine by centrally administered diazepam and midazolam.

1 Intracerebroventricular administration of diazepam or midazolam decreased the antinociceptive effect of morphine in rats as measured by the "tail flick" method. 2 Midazolam, injected into the periaqueductal grey matter (PAG) antagonized the analgesic effect of morphine. The action of midazolam was partially reversed by bicuculline. 3 These findings support the view that the effect of benzodiazephines on morphine antinociception may be mediated through gamma-aminobutyric acid receptors.

Effects of interleukin-1 beta and interleukin-2 on amino acids levels in mouse cortex and hippocampus.

We measured the levels of glutamine, aspartic acid, glutamic acid and GABA in cortex and hippocampus of mice acutely treated with i.p. human recombinant interleukin-2 (IL-2) or human recombinant interleukin-1 beta (IL-1 beta). Administration of IL-2 (5.0 micrograms kg-1) induced a slight but statistically significant increase in glutamine concentrations in both brain areas, while similar administration of IL-1 beta (20 micrograms kg-1) significantly reduced the hippocampal levels of glutamine, glutamic acid and GABA. Our data suggest that brain amino acid pathways are involved in the central modifications induced by IL-1 beta.

Neurochemical changes of long-term adrenalectomy in rat brain: effects on neurotransmitter amino acids.

The levels of five amino acids together with glutamine synthetase activity, were measured in brain regions of rats with bilateral adrenalectomy, performed in newly weaning rats on postnatal day 22 and sacrificed 3 months later. Adrenalectomy caused a general decrease of glutamine concentration in three hippocampal regions (CA1-CA2, CA3, CA4-dentate gyrus), in hypothalamus, striatum and cerebellum. This reduction, which was particularly significant in hippocampus and cerebellum, was paralleled by a decrease of glutamine synthetase activity. Treatment with corticosterone reversed the effect of adrenalectomy. Little or no change was observed in the tissue levels of taurine, aspartic, glutamic or gamma-amino butyric acids.

Effects of some GABA-mimetic drugs on the antinociceptive activity of morphine and beta-endorphin in rats.

Intracerebroventricular administration of muscimol, a potent GABA-receptor agonist, counteracted the antinociceptive effect of morphine or beta-endorphin in rats as measured by the "tail flick" method. Muscimol's activity was reversed by bicuculline. Isoguvacine, another GABA agonist, as well as nipecotic acid and guvacine, two inhibitors of neuronal and glial uptake of GABA, also antagonized morphine's antinociceptive effect. A role of the central GABA-ergic system in mediating opiate antinociception is proposed.

Effects of diazepam on nociception in rats.

Acute i.p. injection of diazepam (1 mg/kg) resulted in a moderate increase in the tail-flick latency in rats. Tolerance to this diazepam effect developed after 10 days of diazepam treatment (1 mg kg-1 day-1). The benzodiazepine antagonist Ro 15-3505 only partially reversed the effect of diazepam on nociception. Naloxone (5 mg/kg i.p.) failed to affect the effect of diazepam on nociception, while the kappa antagonist MR 2266 fully antagonized the diazepam-induced increase of the tail-flick latency. Diazepam injected intracerebroventricularly (1, 5, 20 micrograms/rat) did not alter basal nociceptive threshold, however, diazepam injected intrathecally (20 micrograms/rat) prolonged the tail-flick latency. Furthermore, intracerebroventricular injection of muscimol partially antagonized the i.p. diazepam-induced increase of the tail-flick latency. These results suggest that benzodiazepine receptor sites are partially involved in the effect of diazepam on nociception and indicate that an indirect kappa-opioid-receptor-mediated mechanism may be involved. The anatomical site of diazepam action on tail-flick latency seems to be at the spinal level. Descending axons to the spinal cord from brain areas reached by intracerebroventricular injection of muscimol seem to modulate the effect of diazepam effect on nociception.

Reversal of the effect of centrally-administered diazepam on morphine antinociception by specific (Ro 15-1788 and Ro 15-3505) and non-specific (bicuculline and caffeine) benzodiazepine antagonists.

Diazepam, injected into the lateral ventricles reduced the antinociceptive effect of morphine in rats, as measured by the tail-flick method. Specific antagonists of diazepam (Ro 15-1788 and Ro 15-3505) had no effect themselves but prevented inhibition by diazepam of morphine antinociception. Furthermore, the action of diazepam was partially reversed by intracerebroventricular injection of bicuculline or caffeine. These findings support the view that the depressant effect of diazepam on morphine antinociception is specific and GABAergic in nature and that some actions of diazepam are also mediated via the purinergic system.

Zopiclone potentiates the antinociceptive effect of morphine in rats.

The antinociceptive effect of morphine, as determined by the tail-flick test, was dose-dependently increased by the intraperitoneal injection of zopiclone. The benzodiazepine antagonists Ro 15-1788 (flumazepil) and Ro 15-3505, when intraperitoneally injected, significantly antagonized the effect of intraperitoneal injection of zopiclone on morphine antinociception. Intrathecal injection of zopiclone potentiated morphine antinociception, while the intracerebroventricular injection of zopiclone failed to enhance morphine antinociception and the intracerebroventricular injection of flumazepil to antagonize the intraperitoneal-zopiclone-induced increase in morphine antinociception. These results suggest that benzodiazepine sites are specifically involved in the potentiating effect of zopiclone on morphine antinociception. The anatomical locations of the receptors involved seem to be at the spinal level.

Modification of GABA turnover in the striatum and hippocampus of the rat after zopiclone.

The effects of zopiclone, a non-benzodiazepine compound that interacts with benzodiazepine receptors, on GABA turnover rate and GABA content in the rat striatum and hippocampus have been studied. Intraperitoneal administration of zopiclone reduced the GABA turnover rates in both the striatum and hippocampus, as estimated from the rate of GABA accumulation after inhibition of GABA transaminase by aminooxyacetic acid (AOAA). The effect of zopiclone on AOAA-induced accumulation of GABA in the hippocampus and striatum was blocked by the intraperitoneal injection of the benzodiazepine receptor antagonist Ro 15-3505. Furthermore, zopiclone slightly but significantly decreased GABA content in the hippocampus, the decrease being blocked by coadministration of the benzodiazepine receptor antagonist Ro 15-1788. Our results confirm that the GABAergic system plays a role in the mechanism of action of zopiclone.

Periaqueductal gray matter involvement in the muscimol-induced decrease of morphine antinociception.

Microinjections of muscimol, a GABA receptor agonist, into the periaqueductal gray matter (PAG) counter-acted the antinociceptive effect of morphine in rats, as measured by the "tail-flick" method. Muscimol's effect was partially reversed by bicuculline.

Analysis of pirprofen in cerebrospinal fluid, plasma, and synovial fluid by high-performance liquid chromatography with electrochemical detection.

We describe a high-performance liquid chromatographic method, using electrochemical detection, for the determination of pirprofen in cerebrospinal fluid (CSF), plasma, and synovial fluid (SF). A C-18 column with a mobile phase containing acetonitrile acetate:phosphate buffer (pH 3.0) was employed. Samples were added with phosphoric acid, then extracted into dichloromethane, evaporated, and injected into the chromatograph. A detection potential of +0.85 V was applied on the basis of current-potential curves. Good linearity was found for each fluid in the expected range of therapeutic concentrations. The detection limit was 0.1 ng/mL for CSF, and 1 ng/mL for plasma and SF, with a recovery greater than 96% and intraday coefficient of variation less than 5% in all cases. The main advantages of this method include high specificity and sensitivity which allow the analysis of CSF and the use of small volumes of plasma and SF. The application of the method for the analysis of plasma and SF samples and the kinetic profile in CSF are shown.

Peripherally administered benzodiazepines increase morphine-induced analgesia in the rat. Effect of RO 15-3505 and FG 7142.

The influence of alprazolam, chlordiazepoxide and midazolam on the antinociceptive effect of subcutaneous morphine was investigated in rats, using the tail-flick test. After intraperitoneal administration, all drugs significantly enhanced the morphine-induced analgesia. Both the benzodiazepine receptor antagonist RO 15-3505 and the benzodiazepine receptor inverse agonist FG 7142 antagonized the potentiating effect of alprazolam, chlordiazepoxide and midazolam. Our results suggest that the interaction between benzodiazepines and opioids in modulating nociceptive responses involves primarily benzodiazepine receptors and that different pathways are involved in the anxiolytic and pro-analgesic actions of benzodiazepines.

Effects of 2-chloroadenosine on hippocampal GABA content and turnover.

The effects of 2-Chloroadenosine (CADO), a stable analog of adenosine, on GABA turnover rate and GABA content in the rat hippocampus in vivo have been studied. The intracerebroventricular injection of CADO reduced the GABA turnover rate in the hippocampus, as estimated from the rate of GABA accumulation after inhibition of GABA transaminase (GABA-T) by aminooxyacetic acid (AOAA). The effect of CADO on AOAA-induced accumulation of GABA in the hippocampus was blocked by the intraperitoneal injection of the adenosine receptor antagonist caffeine. Furthermore, CADO at the dose of 5 micrograms per ventricle produced a significant decrease in GABA content in the hippocampus. Our results support the hypothesis that adenosine exerts inhibitory effects on GABAergic circuits in the hippocampus.

Pharmacokinetics of buflomedil after various dosage forms.

The pharmacokinetic disposition of buflomedil was compared in humans after oral administration of solution, tablets and film tablets. Six healthy male volunteers received a single oral dose of the three different dosage formulations. Blood and urine samples were taken before dosing and at selected times over 24 h and 72 h, resp., after dosing. The concentration of the drug in samples was measured by gas-chromatography with nitrogen detector. The absorption of buflomedil was faster after solution administration, while other plasma parameters did not show any major differences. Also the amount of drug excreted in urines was higher with solution dosing.