Amygdalar NMDA receptor activation has been implicated in the acquisition of fear memories in rats. However, little is known about the role of endogenous modulators of the NMDA receptor, such as polyamines, in pavlovian fear-conditioning learning. Therefore, in the present study we investigated whether the immediate pretraining or post-training bilateral infusion of arcaine, an antagonist of the NMDA receptor polyamine-binding site, or spermidine, an agonist of the NMDA receptor polyamine-binding site, into the amygdala affected classical fear conditioning in rats. Bilateral microinjections of arcaine (0.0002-0.2 nmol) decreased, whereas spermidine (0.002-20 nmol) increased, contextual and auditory fear conditioning. Arcaine coadministration, at a dose that had no effect per se, reversed the facilitatory effect of spermidine. These results provide evidence that endogenous and exogenous polyamines modulate the acquisition or early consolidation (or both) of the fear-conditioning task in the amygdala.

The antinociceptive effect of six novel synthetic pyrazolines (3-ethoxymethyl-5-ethoxycarbonyl-1H-pyrazole (Pz 1) and its corresponding 1-substituted methyl (Pz 2) and phenyl (Pz 3) analogues, and 3-(1-ethoxyethyl)-5-ethoxycarbonyl-1H-pyrazole (Pz 4) and its corresponding 1-substituted methyl (Pz 5) and phenyl (Pz 6) analogues) was evaluated by the tail immersion test in adult male albino mice. The animals (N = 11-12 in each group) received vehicle (5% Tween 80, 10 ml/kg, sc) or 1.5 mmol/kg of each of the pyrazolines (Pz 1-Pz 6), sc. Fifteen, thirty and sixty minutes after drug administration, the mice were subjected to the tail immersion test. Thirty minutes after drug administration Pz 2 and Pz 3 increased tail withdrawal latency (vehicle = 3.4 ± 0.2; Pz 2 = 5.2 ± 0.4; Pz 3 = 5.9 ± 0.4 s; mean ± SEM), whereas the other pyrazolines did not present antinociceptive activity. Doseeffect curves (0.15 to 1.5 mmol/kg) were constructed for the bioactive pyrazolines. Pz 2 (1.5 mmol/kg, sc) impaired motor coordination in the rotarod and increased immobility in the open-field test. Pz 3 did not alter rotarod performance and spontaneous locomotion, but increased immobility in the open field at the dose of 1.5 mmol/kg. The involvement of opioid mechanisms in the pyrazoline-induced antinociception was investigated by pretreating the animals with naloxone (2.75 µmol/kg, sc). Naloxone prevented Pz 3-but not Pz 2-induced antinociception. Moreover, naloxone pretreatment did not alter Pz 3-induced immobility. We conclude that Pz 3-induced antinociception involves opioid mechanisms but this is not the case for Pz 2.

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Lead intoxication is a serious occupational disease that constitutes a major public health problem. Lead, a heavy metal, has been used by humans for many technological purposes, which is the main reason for its widespread distribution. The toxic mechanisms of lead on the molecular machinery of living organisms include metal transport, energy metabolism, diverse enzymatic processes, genetic regulation, and membrane ionic channels and signaling molecules. Since lead is able to cross the blood-brain barrier it may cause neurotoxicity. Creatine kinase and pyruvate kinase are two thiol-containing enzymes that exert a key role for cellular energy homeostasis in brain. Our main objective was to investigate the in vitro effect of lead on pyruvate kinase and creatine kinase activities of extracts and subcellular fractions from the brain cortex of rats in the presence or not of thiol-protecting substances such as glutathione and cysteamine. The results showed that lead inhibited the two enzyme activities and the thiol-protecting substances prevented their inhibition. These results suggest that lead inhibits creatine kinase and pyruvate kinase activity by interaction with their thiol groups. Therefore, lead may disrupt energy homeostasis and this effect may contribute to the neurological dysfunction found in lead exposed individuals.

The present study investigates the antinociceptive effect of the pyrazolyl-thiazole derivative 2-(5-trichloromethyl-5-hydroxy-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl)-4-(4-bromophenyl)-5-methylthiazole (B50) in mice. Male albino Swiss mice (30-40 g) were used in the acetic acid-induced abdominal writhes and tail-immersion tests. B50 caused dose-dependent antinociception (8, 23 and 80 µmol/kg, sc) in the acetic acid writhing assay (number of writhes: vehicle: 27.69 ± 6.15; B50 (8 µmol/kg): 16.92 ± 3.84; B50 (23 µmol/kg): 13.85 ± 3.84; B50 (80 µmol/kg): 9.54 ± 3.08; data are reported as means ± SEM for 9 animals per group). On the other hand, B50 did not cause antinociception in the tail immersion assay. Naloxone (2.75 µmol/kg, sc) prevented B50-induced antinociception (number of writhes: vehicle-saline: 31.11 ± 3.15; vehicle-naloxone: 27.41 ± 3.70; B50 (80 µmol/kg)-saline: 8.70 ± 3.33; B50 (80 µmol/kg)-naloxone: 31.84 ± 4.26; morphine-saline: 2.04 ± 3.52; morphine-naloxone: 21.11 ± 4.26; 8-9 animals per group). The removal of the methyl group of the thiazole ring of B50 or substitution of the bromo substituent with the methyl at position 4 of the phenyl group, which is attached to the thiazole ring of B50, resulted in loss of activity, suggesting that these substituents are important for antinociceptive activity. B50 had no effect on spontaneous locomotion or rotarod performance, indicating that the antinociceptive effect of B50 is not related to nonspecific motor effects. The antinociceptive profile of B50 seems to be closer to nonsteroidal anti-inflammatory drugs than to classic opioid agents, since it had no analgesic effect in a thermally motivated test. Key wordsThe pyrazole ring is a heterocycle compound containing two contiguous nitrogen atoms and three carbon atoms. Until 1995, in a few cases, only 5-trifluoromethyl-5-hydroxy-1H-pyrazolines and pyrazolidines could be synthesized, and pyrazolines other than 5-trifluoromethylated ones had been detected only by special nuclear magnetic resonance techniques (1). In 1999, Bonacorso et al. (2) described for the first time the synthesis and structural elucidation by nuclear magnetic resonance, Austin Model 1 calculations and X-ray diffraction of a novel series of twelve 3-aryl(alkyl)-5-hydroxy-1-