Antidepressant-relevant behavioral and synaptic molecular effects of long-term fasudil treatment in chronically stressed male rats.

Several lines of evidence suggest that antidepressant drugs may act by modulating neuroplasticity pathways in key brain areas like the hippocampus. We have reported that chronic treatment with fasudil, a Rho-associated protein kinase inhibitor, prevents both chronic stress-induced depressive-like behavior and morphological changes in CA1 area. Here, we examined the ability of fasudil to (i) prevent stress-altered behaviors, (ii) influence the levels/phosphorylation of glutamatergic receptors and (iii) modulate signaling pathways relevant to antidepressant actions. 89 adult male Sprague-Dawley rats received intraperitoneal fasudil injections (10 mg/kg/day) or saline vehicle for 18 days. Some of these animals were daily restraint-stressed from day 5-18 (2.5 h/day). 24 hr after treatments, rats were either evaluated for behavioral tests (active avoidance, anxiety-like behavior and object location) or euthanized for western blot analyses of hippocampal whole extract and synaptoneurosome-enriched fractions. We report that fasudil prevents stress-induced impairments in active avoidance, anxiety-like behavior and novel location preference, with no effect in unstressed rats. Chronic stress reduced phosphorylations of ERK-2 and CREB, and decreased levels of GluA1 and GluN2A in whole hippocampus, without any effect of fasudil. However, fasudil decreased synaptic GluA1 Ser831 phosphorylation in stressed animals. Additionally, fasudil prevented stress-decreased phosphorylation of GSK-3ß at Ser9, in parallel with an activation of the mTORC1/4E-BP1 axis, both in hippocampal synaptoneurosomes, suggesting the activation of the AKT pathway. Our study provides evidence that chronic fasudil treatment prevents chronic stress-altered behaviors, which correlated with molecular modifications of antidepressant-relevant signaling pathways in hippocampal synaptoneurosomes.

Aromatic Bromination Abolishes the Psychomotor Features and Pro-social Responses of MDMA ("Ecstasy") in Rats and Preserves Affinity for the Serotonin Transporter (SERT).

The entactogen MDMA (3,4-methylenedioxy-methamphetamine, "Ecstasy") exerts its psychotropic effects acting primarily as a substrate of the serotonin transporter (SERT) to induce a non-exocytotic release of serotonin. Nevertheless, the roles of specific positions of the aromatic ring of MDMA associated with the modulation of typical entactogenic effects, using analogs derived from the MDMA template, are still not fully understood. Among many possibilities, aromatic halogenation of the phenylalkylamine moiety may favor distribution to the brain due to increased lipophilicity, and sometimes renders psychotropic substances of high affinity for their molecular targets and high potency in humans. In the present work, a new MDMA analog brominated at C(2) of the aromatic ring (2-Br-4,5-MDMA) has been synthesized and pharmacologically characterized in vitro and in vivo. First, binding competition experiments against the SERT-blocker citalopram were carried out in human platelets and compared with MDMA. Besides, its effects on platelet aggregation were performed in platelet enriched human plasma using collagen as aggregation inductor. Second, as platelets are considered an appropriate peripheral model for estimating central serotonin availability, the functional effects of 2-Br-4,5-MDMA and MDMA on ATP release during human platelet aggregation were evaluated. The results obtained showed that 2-Br-4,5-MDMA exhibits higher affinity for SERT than MDMA and fully abolishes both platelet aggregation and ATP release, resembling the pharmacological profile of citalopram. Subsequent in vivo evaluation in rats at three dose levels showed that 2-Br-4,5-MDMA lacks all key MDMA-like behavioral responses in rats, including hyperlocomotion, enhanced active avoidance conditioning responses and increased social interaction. Taken together, the results obtained are consistent with the notion that 2-Br-4,5-MDMA should not be expected to be an MDMA-like substrate of SERT, indicating that aromatic bromination at C(2) modulates the pharmacodynamic properties of the substrate MDMA, yielding a citalopram-like compound.

Hippocampal Memory Recovery After Acute Stress: A Behavioral, Morphological and Molecular Study.

Several studies have shown that a single exposure to stress may improve or impair learning and memory processes, depending on the timing in which the stress event occurs with relation to the acquisition phase. However, to date there is no information about the molecular changes that occur at the synapse during the stress-induced memory modification and after a recovery period. In particular, there are no studies that have evaluated-at the same time-the temporality of stress and stress recovery period in hippocampal short-term memory and the effects on dendritic spine morphology, along with variations in N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits. The aim of our study was to take a multidimensional approach to investigate concomitant behavioral, morphological and molecular changes induced by a single restraint stress exposure (2.5 h) and a recovery period of 6 and 24 h in rats. We found that acute stress elicited a reduced preference to explore an object placed in a novel position (a hippocampal-dependent task). These changes were accompanied by increased activity of LIM kinase I (LIMK; an actin-remodeling protein) and increased levels of NR2A subunits of NMDA receptors. After 6 h of recovery from stress, rats showed similar preference to explore an object placed in a novel or familiar position, but density of immature spines increased in secondary CA1 apical dendrites, along with a transient rise in GluA2 AMPA receptor subunits. After 24 h of recovery from stress, the animals showed a preference to explore an object placed in a novel position, which was accompanied by a normalization of NMDA and AMPA receptor subunits to control values. Our data suggest that acute stress produces reversible molecular and behavioral changes 24 h after stress, allowing a full reestablishment of hippocampal-related memory. Further studies need to be conducted to deepen our understanding of these changes and their reciprocal interactions.Adaptive stress responses are a promising avenue to develop interventions aiming at restoring hippocampal function impaired by repetitive stress exposure.

On the Role of DT-Diaphorase Inhibition in Aminochrome-Induced Neurotoxicity In Vivo.

Dopamine oxidation in the pathway leading to neuromelanin formation generates the ortho-quinone aminochrome, which is potentially neurotoxic but normally rapidly converted by DT-diaphorase to nontoxic leukoaminochrome. However, when administered exogenously into rat striatum, aminochrome is able to produce damage to dopaminergic neurons. Because of a recent report that substantia nigra pars compacta (SNpc) tyrosine hydroxylase (T-OH) levels were unaltered by aminochrome when there was cell shrinkage of dopaminergic neurons along with a reduction in striatal dopamine release, the following study was conducted to more accurately determine the role of DT-diaphorase in aminochrome neurotoxicity. In this study, a low dose of aminochrome (0.8 nmol) with or without the DT-diaphorase inhibitor dicoumarol (0.2 nmol) was injected into the left striatum of rats. Intrastriatal 6-hydroxydopamine (6-OHDA, 32 nmol) was used as a positive neurotoxin control in other rats. Two weeks later, there was significant loss in numbers of T-OH immunoreactive fibers in SNpc, also a loss in cell density in SNpc, and prominent apomorphine (0.5 mg/kg sc)-induced contralateral rotations in rats that had been treated with aminochrome, with aminochrome/dicoumarol, or with 6-OHDA. Findings demonstrate that neurotoxic aminochrome is able to exert neurotoxicity only when DT-diaphorase is suppressed-implying that DT-diaphorase is vital in normally suppressing toxicity of in vivo aminochrome, generated in the pathway towards neuromelanin formation.

Percepción del ambiente educacional en dos escuelas de medicina con currículo tradicional: Estudio longitudinal / Longitudinal perception of the educational environment in two medical schools with traditional curricula in Chile and Spain

Background: To establish an educational environment that ensures the quality of the teaching-learning process is a challenge for any educational institution. The questionnaire DREEM (Dundee Ready Educational Environment Measure) is used to identify strengths and weaknesses of an educational environment and to compare different medical schools. Aim: To evaluate the changes in the perception of educational environment by students of the Schools of Medicine of the University of Zaragoza, UZar (Spain) and the University of Chile, UCh (Chile) at two points in their curricula. Material and Methods: DREEM questionnaire was answered by 90 students from the UZar and 87 students of the UCh, when they were in the first year (2009) and in the fourth year of their career (2012). Results: At both universities the overall mean scores of DREAM were significantly higher in students in their first year than those obtained in the fourth year (137.5/118.3 for UZar and 128.6/118.8 for UCh). Items with worse perception in the fourth year were observed in subscales Learning Perception and Atmosphere Perception. Items with good evaluation (≥ 3.0) were the subscales Perception of teachers, academic self-perception, perception of Environment and Social Self-perception. Conclusions: The perception of Chilean and Spanish students about their educational environments indicates that the stage of their medical training is more important than the geographical context or educational institution.

Aminochrome induces dopaminergic neuronal dysfunction: a new animal model for Parkinson's disease.

L-Dopa continues to be the gold drug in Parkinson's disease (PD) treatment from 1967. The failure to translate successful results from preclinical to clinical studies can be explained by the use of preclinical models which do not reflect what happens in the disease since these induce a rapid and extensive degeneration; for example, MPTP induces a severe Parkinsonism in only 3 days in humans contrasting with the slow degeneration and progression of PD. This study presents a new anatomy and develops preclinical model based on aminochrome which induces a slow and progressive dysfunction of dopaminergic neurons. The unilateral injection of aminochrome into rat striatum resulted in (1) contralateral rotation when the animals are stimulated with apomorphine; (2) absence of significant loss of tyrosine hydroxylase-positive neuronal elements both in substantia nigra and striatum; (3) cell shrinkage; (4) significant reduction of dopamine release; (5) significant increase in GABA release; (6) significant decrease in the number of monoaminergic presynaptic vesicles; (7) significant increase of dopamine concentration inside of monoaminergic vesicles; (8) significant increase of damaged mitochondria; (9) significant decrease of ATP level in the striatum (10) significant decrease in basal and maximal mitochondrial respiration. These results suggest that aminochrome induces dysfunction of dopaminergic neurons where the contralateral behavior can be explained by aminochrome-induced ATP decrease required both for anterograde transport of synaptic vesicles and dopamine release. Aminochrome could be implemented as a new model neurotoxin to study Parkinson's disease.

[Longitudinal perception of the educational environment in two medical schools with traditional curricula in Chile and Spain]. / Percepción del ambiente educacional en dos escuelas de medicina con currículo tradicional: Estudio longitudinal.

BACKGROUND: To establish an educational environment that ensures the quality of the teaching-learning process is a challenge for any educational institution. The questionnaire DREEM (Dundee Ready Educational Environment Measure) is used to identify strengths and weaknesses of an educational environment and to compare different medical schools. AIM: To evaluate the changes in the perception of educational environment by students of the Schools of Medicine of the University of Zaragoza, UZar (Spain) and the University of Chile, UCh (Chile) at two points in their curricula. MATERIAL AND METHODS: DREEM questionnaire was answered by 90 students from the UZar and 87 students of the UCh, when they were in the first year (2009) and in the fourth year of their career (2012). RESULTS: At both universities the overall mean scores of DREAM were significantly higher in students in their first year than those obtained in the fourth year (137.5/118.3 for UZar and 128.6/118.8 for UCh). Items with worse perception in the fourth year were observed in subscales Learning Perception and Atmosphere Perception. Items with good evaluation (≥ 3.0) were the subscales Perception of teachers, academic self-perception, perception of Environment and Social Self-perception. CONCLUSIONS: The perception of Chilean and Spanish students about their educational environments indicates that the stage of their medical training is more important than the geographical context or educational institution.

Association of N-cadherin levels and downstream effectors of Rho GTPases with dendritic spine loss induced by chronic stress in rat hippocampal neurons.

Chronic stress promotes cognitive impairment and dendritic spine loss in hippocampal neurons. In this animal model of depression, spine loss probably involves a weakening of the interaction between pre- and postsynaptic cell adhesion molecules, such as N-cadherin, followed by disruption of the cytoskeleton. N-cadherin, in concert with catenin, stabilizes the cytoskeleton through Rho-family GTPases. Via their effector LIM kinase (LIMK), RhoA and ras-related C3 botulinum toxin substrate 1 (RAC) GTPases phosphorylate and inhibit cofilin, an actin-depolymerizing molecule, favoring spine growth. Additionally, RhoA, through Rho kinase (ROCK), inactivates myosin phosphatase through phosphorylation of the myosin-binding subunit (MYPT1), producing actomyosin contraction and probable spine loss. Some micro-RNAs negatively control the translation of specific mRNAs involved in Rho GTPase signaling. For example, miR-138 indirectly activates RhoA, and miR-134 reduces LIMK1 levels, resulting in spine shrinkage; in contrast, miR-132 activates RAC1, promoting spine formation. We evaluated whether N-cadherin/ß-catenin and Rho signaling is sensitive to chronic restraint stress. Stressed rats exhibit anhedonia, impaired associative learning, and immobility in the forced swim test and reduction in N-cadherin levels but not ß-catenin in the hippocampus. We observed a reduction in spine number in the apical dendrites of CA1 pyramidal neurons, with no effect on the levels of miR-132 or miR-134. Although the stress did not modify the RAC-LIMK-cofilin signaling pathway, we observed increased phospho-MYPT1 levels, probably mediated by RhoA-ROCK activation. Furthermore, chronic stress raises the levels of miR-138 in accordance with the observed activation of the RhoA-ROCK pathway. Our findings suggest that a dysregulation of RhoA-ROCK activity by chronic stress could potentially underlie spine loss in hippocampal neurons.

Prenatal stress down-regulates Reelin expression by methylation of its promoter and induces adult behavioral impairments in rats.

Prenatal stress causes predisposition to cognitive and emotional disturbances and is a risk factor towards the development of neuropsychiatric conditions like depression, bipolar disorders and schizophrenia. The extracellular protein Reelin, expressed by Cajal-Retzius cells during cortical development, plays critical roles on cortical lamination and synaptic maturation, and its deregulation has been associated with maladaptive conditions. In the present study, we address the effect of prenatal restraint stress (PNS) upon Reelin expression and signaling in pregnant rats during the last 10 days of pregnancy. Animals from one group, including control and PNS exposed fetuses, were sacrificed and analyzed using immunohistochemical, biochemical, cell biology and molecular biology approaches. We scored changes in the expression of Reelin, its signaling pathway and in the methylation of its promoter. A second group included control and PNS exposed animals maintained until young adulthood for behavioral studies. Using the optical dissector, we show decreased numbers of Reelin-positive neurons in cortical layer I of PNS exposed animals. In addition, neurons from PNS exposed animals display decreased Reelin expression that is paralleled by changes in components of the Reelin-signaling cascade, both in vivo and in vitro. Furthermore, PNS induced changes in the DNA methylation levels of the Reelin promoter in culture and in histological samples. PNS adult rats display excessive spontaneous locomotor activity, high anxiety levels and problems of learning and memory consolidation. No significant visuo-spatial memory impairment was detected on the Morris water maze. These results highlight the effects of prenatal stress on the Cajal-Retzius neuronal population, and the persistence of behavioral consequences using this treatment in adults, thereby supporting a relevant role of PNS in the genesis of neuropsychiatric diseases. We also propose an in vitro model that can yield new insights on the molecular mechanisms behind the effects of prenatal stress.

Repetitive fluoxetine treatment affects long-term memories but not learning.

Fluoxetine is currently being administered for long-term maintenance and for prophylactic reasons following the remission of depressive symptoms and several other psychiatric and neurological conditions. We have previously found that in naïve adult male rats, repetitive administration of fluoxetine induced maturation of telencephalic dendritic spines. This finding was associated with the presence of a higher proportion of GluA2- and GluN2A-containing glutamate receptors. To gain further insight into the possible consequences of such synaptic re-organization on learning and memory processes, we evaluated hippocampal- and non-hippocampal-dependent memories following administration of 0.7 mg/kg fluoxetine for four weeks. Standard behavioral tasks were used: the Morris Water Maze (MWM) and Object Location Memory (OLM) tasks to assess spatial memory and the Novel Object Recognition (NOR) task to assess recognition memory. We found that treated rats showed normal learning and short-term memory (1 h post-learning). However, either recent (24 h) or remote (17 days) memories were impaired depending upon the task. Interestingly, spatial memory impairment spontaneously reverted after 6 weeks of fluoxetine withdrawal.

Behavioral profiles in rats distinguish among "ecstasy," methamphetamine and 2,5-dimethoxy-4-iodoamphetamine: Mixed effects for "ecstasy" analogues.

3,4-methylenedioxymethamphetamine (MDMA; "ecstasy") is a psychoactive drug structurally related to other phenylisopropylamines acting as stimulants or hallucinogens in humans. Although MDMA has a pharmacological identity of its own, the distinction of its acute effects from those of stimulants or even hallucinogens is controversial. In this work, dose-response curves (0.25, 0.5, 1, 3, 5, and 10 mg/kg) representing the acute in vivo effects of MDMA were compared with those of a structurally related stimulant (methamphetamine, MA) and a hallucinogenic analogue (2,5-dimethoxy-4-iodoamphetamine, DOI) in a set of behavioral protocols in rats, including spontaneous psychomotor activity, anxiolytic/anxiogenic-like effects and active avoidance conditioning responses. The behavioral profiles obtained allowed us to differentiate among racemic MDMA, MA, and DOI at different dose ranges. In addition, the evaluation of four MDMA analogues (1, 5, and 10 mg/kg) comprising two well-known MDMA analogues (MDA [3,4-methylenedioxyamphetamine] and MDE (N-ethyl-MDA, believed to substitute for MDMA) and two other structural analogues (MDOH [N-hydroxy-MDA] and MMDA-2 [2-methoxy-4,5-methylenedioxyamphetamine]) showed that none of these exactly resembles MDMA in their pharmacological profiles, highlighting the unique character of this prototypical entactogen. In fact, their effects exhibited similarities with the behavioral profiles of either MA or DOI, as well as novel profiles in specific behavioral paradigms.

Desipramine prevents stress-induced changes in depressive-like behavior and hippocampal markers of neuroprotection.

Extracellular signal-regulated kinases (ERKs) are widely implicated in multiple physiological processes. Although ERK1/2 has been proposed as a common mediator of antidepressant action in naive rodents, it remains to be determined whether the ERK1/2 pathway plays a role in depressive disorder. Here, we investigated whether chronic restraint stress (14 days) and antidepressant treatment [desipramine (DMI), 10 mg/kg intraperitoneally] induce changes in animal behavior and hippocampal levels of phospho-ERK1/2 and its substrate phospho-cAMP response element-binding protein (CREB). The results indicated that stress-induced depressive-like behaviors were correlated with an increase in P-ERK1/2 and P-CREB in the hippocampus evaluated by immunoblot analysis. As an indication of CREB activity, we evaluated changes in mRNA levels of its target genes. Brain-derived neurotrophic factor (BDNF) mRNA was reduced by stress, an effect prevented by DMI only in the CA3 area of hippocampus. Bcl-2 mRNA was reduced in all hippocampal regions by stress, an effect independent of DMI treatment. However, immunoblot from hippocampal extracts revealed that stress increased BCL-2 levels, an effect prevented by chronic DMI. These results suggest that ERKs and BDNF may be altered in depressive disorder, modifications that are sensitive to DMI action. In contrast, the stress-induced increase in BCL-2 may correspond to a neuroprotective response.

Chronic stress induces dendritic atrophy in the rat medial geniculate nucleus: effects on auditory conditioning.

Chronic stress induces dendritic atrophy in the inferior colliculus (IC, auditory mesencephalon) and impairs auditory avoidance conditioning. The aim of this study was to determine in Golgi preparations and in cued fear conditioning whether stress affects other auditory components, like the thalamic medial geniculate nucleus (MG) or the posterior thalamic nucleus (PO), in Sprague-Dawley rats. Chronic restraint stress produced a significant dendritic atrophy in the MG (stress: 407+/-55 microm; control: 808+/-120 microm; p<0.01) but did not affect auditory fear conditioning. The last result was in apparent contrast with the fact that stress impairs both the acquisition of auditory avoidance conditioned responses and the dendritic structure in two major nuclei of the auditory system. In order to analyze this disagreement, we investigated whether the stress-related freezing to tone occurring in the fear conditioning protocol corresponded to a conditioned or an unconditioned fear response, using changes in tone instead of light throughout conditioning trials. Chronic stress significantly enhanced visual fear conditioning in stressed animals compared to controls (stress: 58.9+/-8.42%, control: 23.31+/-8.01%; p<0.05), but this fear enhancement was related to unconditioned fear. Conversely, chronic stress did not affect the morphology of the PO (subserving both auditory and somatosensory information) or the corresponding auditory and somatosensory unconditioned responses (acoustic startle response and escape behavior). Our results suggest that the auditory conditioned stimulus can be processed in part independently of the IC and MG in the stressed animals, and sent to the amygdala via the PO inducing unconditioned fear. Comparable alterations could be produced in major depression.

Copper neurotoxicity in rat substantia nigra and striatum is dependent on DT-diaphorase inhibition.

The dependence of copper neurotoxicity on DT-diaphorase inhibition was suggested from results obtained from a cell line derived from substantia nigra. Therefore, the aim of this study was to evaluate whether CuSO4 neurotoxicity in vivo, which was evaluated by determining the contralateral rotation and loss of tyrosine hydroxylase immunostaining, was dependent on DT-diaphorase inhibition by dicoumarol. Animals unilaterally and intranigrally injected with 0.25 nmol of CuSO4 and 2 nmol of dicoumarol presented a significant and characteristic contralateral rotational behavior ( P < 0.01) when they were systemically stimulated with apomorphine (0.5 mg/kg s.c.), similar to that observed in rats injected unilaterally with 6-hydroxydopamine as a positive control. The behavioral effects correlated with the lost of tyrosine hydroxylase-positive staining, since animals unilaterally and intranigrally injected with 0.25 nmol of CuSO4 together with 2 nmol of dicoumarol exhibited extensive loss of tyrosine hydroxylase-positive fiber density in the striatum ( P < 0.01) and cell loss in the substantia nigra ( P < 0.01). Our results support the idea that CuSO4 neurotoxicity is dependent upon DT-diaphorase inhibition.

Chronic stress induces upregulation of brain-derived neurotrophic factor (BDNF) mRNA and integrin alpha5 expression in the rat pineal gland.

Chronic stress affects brain areas involved in learning and emotional responses. These alterations have been related with the development of cognitive deficits in major depression. Moreover, stress induces deleterious actions on the epithalamic pineal organ, a gland involved in a wide range of physiological functions. The aim of this study was to investigate whether the stress effects on the pineal gland are related with changes in the expression of neurotrophic factors and cell adhesion molecules. Using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, we analyzed the effect of chronic immobilization stress on the BDNF mRNA and integrin alpha5 expression in the rat pineal gland. We found that BDNF is produced in situ in the pineal gland. Chronic immobilization stress induced upregulation of BDNF mRNA and integrin alpha5 expression in the rat pineal gland but did not produce changes in beta-actin mRNA or in GAPDH expression. Stressed animals also evidenced an increase in anxiety-like behavior and acute gastric lesions. These results suggest that BDNF and integrin alpha5 may have a counteracting effect to the deleterious actions of immobilization stress on functionally stimulated pinealocytes. Furthermore, this study proposes that the pineal gland may be a target of glucocorticoid damage during stress.

Antidepressant and anxiolytic effects of hydroalcoholic extract from Salvia elegans.

Salvia elegans Vahl (Lamiaceae), popularly known as "mirto", is a shrub that has been widely used in Mexican traditional medicine for the treatment of different central nervous system (CNS) diseases, principally, anxiety. Nevertheless, the available scientific information about this species is scarce and there are no reports related to its possible effect on the CNS. In this work, the antidepressant and anxiolytic like effects of hydroalcoholic (60%) extract of Salvia elegans (leaves and flowers) were evaluated in mice. The extract, administered orally, was able to increase the percentage of time spent and the percentage of arm entries in the open arms of the elevated plus-maze, as well as to increase the time spent by mice in the illuminated side of the light-dark test, and to decrease the immobility time of mice subjected to the forced swimming test. The same extract was not able to modify the spontaneous locomotor activity measured in the open field test. These results provide support for the potential antidepressant and anxiolytic activity of Salvia elegans.

Chronic stress decreases the expression of sympathetic markers in the pineal gland and increases plasma melatonin concentration in rats.

Chronic stress affects brain areas involved in learning and emotional responses. Although most studies have concentrated on the effect of stress on limbic-related brain structures, in this study we investigated whether chronic stress might induce impairments in diencephalic structures associated with limbic components of the stress response. Specifically, we analyzed the effect of chronic immobilization stress on the expression of sympathetic markers in the rat epithalamic pineal gland by immunohistochemistry and western blot, whereas the plasma melatonin concentration was determined by radioimmunoassay. We found that chronic stress decreased the expression of three sympathetic markers in the pineal gland, tyrosine hydroxylase, the p75 neurotrophin receptor and alpha-tubulin, while the same treatment did not affect the expression of the non-specific sympathetic markers Erk1 and Erk2, and glyceraldehyde-3-phosphate dehydrogenase. Furthermore, these results were correlated with a significant increase in plasma melatonin concentration in stressed rats when compared with control animals. Our findings indicate that stress may impair pineal sympathetic inputs, leading to an abnormal melatonin release that may contribute to environmental maladaptation. In addition, we propose that the pineal gland is a target of glucocorticoid damage during stress.

Analgesic and behavioral effects of amphetamine enantiomers, p-methoxyamphetamine and n-alkyl-p-methoxyamphetamine derivatives.

The analgesic effects of (+)- and (-)-amphetamine (AMPH), (+/-)-p-methoxyamphetamine (MA), (+/-)-N-methyl-p-methoxyamphetamine (MMA) and (+/-)-N-ethyl-p-methoxyamphetamine (EMA) were compared using two different algesimetric tests in rats. In the formalin test, (+)-AMPH elicited significant antinociception at doses of 0.2, 2 and 8 mg/kg (i.p.); (-)-AMPH was active at 2 and 8 mg/kg, but not at 0.2 mg/kg; MA elicited very potent and long-lasting antinociception; MMA was less active than MA; EMA showed significant effects only at doses of 2 and 8 mg/kg. In the C-fiber evoked nociceptive reflex assay, i.v. (+)- and (-)-AMPH were ineffective, but the methoxy derivatives showed a similar pattern of action combining inhibitory and excitatory actions. To clarify apparent discrepancies between both algesimetric tests, some behavioral motor performance tests were carried out. These tests confirm the motor stimulatory properties of (+)-AMPH, not shared by the methoxylated amphetamine derivatives. The three methoxy derivatives elicited some stereotypies related to dopaminergic activation such as grooming behavior. (+)-AMPH was also the only drug to increase the acquisition of CARs while MA and EMA were without effect. Avoidance conditioning was seriously impaired in rats injected with MMA. This conditioned behavior can be related to the significant decrease of spontaneous motor activity observed with this drug. In conclusion, the introduction of a para-methoxy group strongly increases the analgesic effects of amphetamine without its stimulatory behavioral effects. The introduction of N-alkyl substituents decreases the analgesic potency of MA.

Behavioral effects of manganese injected in the rat substantia nigra are potentiated by dicumarol, a DT-diaphorase inhibitor.

The purpose of this study was to evaluate the contribution of DT-diaphorase inhibition to in vivo neurodegenerative effects of dopamine (DA) oxidation to the corresponding o-quinones. The neurotoxicity to nigrostriatal DA neurons was induced by injection of manganese pyrophosphate (Mn(3+)) complex as a prooxidizing agent alone or together with the DT-diaphorase inhibitor dicumarol into the right rat substantia nigra. The behavioral effects were compared with those induced after selective lesions of dopaminergic neurons with 6-hydroxydopamine (6-OHDA). Intranigral injection of Mn(3+) and Mn(3+) plus dicumarol produced significant impairment in motor behavior compared with control animals. However, the effect seen in the Mn(3+) plus dicumarol injected group was significantly more severe than that observed in the Mn(3+) alone injected group. In motor activity and rearing behavior, the simultaneous injection of Mn(3+) plus dicumarol produced a 6-OHDA-like impairment. Similar effects were observed in the acquisition of a conditioned avoidance response (CAR). Dicumarol significantly impaired avoidance conditioning although without affecting the motor behavior. The behavioral effects were correlated to the extent of striatal tyrosine hydroxylase (TH)-positive fiber loss. Rats receiving unilateral intranigral Mn(3+) and Mn(3+) plus dicumarol injections exhibited a significant reduction in nigrostriatal TH-positive fiber density in medial forebrain bundle compared with the contralateral noninjected side. In conclusion, this study provides evidence that the neurotoxicity of Mn(3+) in vivo is potentiated by DT-diaphorase inhibition, suggesting that this enzyme could play a neuroprotective role in the nigrostriatal DA systems.