Reversal of Object Recognition Memory Deficit in Perirhinal Cortex-Lesioned Rats and Primates and in Rodent Models of Aging and Alzheimer's Diseases

The integrity of the perirhinal cortex (PRh) is essential for object recognition memory (ORM) function, and damage to this brain area in animals and humans induces irreversible ORM deficits. Here, we show that activation of area V2, a brain area interconnected with brain circuits of ventral stream and medial temporal lobe that sustain ORM, by expression of regulator of G-protein signaling 14 of 414 amino acids (RGS14₄₁₄) restored ORM in memory-deficient PRh-lesioned rats and nonhuman primates. Furthermore, this treatment was sufficient for full recovery of ORM in rodent models of aging and Alzheimer's disease, conditions thought to affect multiple brain areas. Thus, RGS14₄₁₄-mediated activation of area V2 has therapeutic relevance in the recovery of recognition memory, a type of memory that is primarily affected in patients or individuals with symptoms of memory dysfunction. These findings suggest that area V2 modulates the processing of memory-related information through activation of interconnected brain circuits formed by the participation of distinct brain areas.

Chronic mild stress accelerates the onset and progression of the Alzheimer's disease phenotype in Tg2576 mice

The etiology of the more common (sporadic) forms of Alzheimer's disease (AD) remains unknown, although age is the most important risk factor. Nevertheless, interactions between environmental risk factors and genetic background may also influence the onset and progression of sporadic AD. Chronic stress, associated with altered memory and other neurological processes, is thought to influence the pathogenesis of AD. Hence, we evaluated the effect of unpredictable and consecutive chronic mild stressors on the onset of an AD-related pathology in the Tg2576 mouse line that overexpresses the human amyloid-β protein precursor with the Swedish mutation (hAβPP(Swe)). Two months after exposure to chronic mild stress, 4 month-old animals that normally display no pathological features of AD, not only expressed pathological markers but also experienced cognitive dysfunction in the Morris water maze test. These findings suggest that chronic mild stress accelerates the onset of cognitive impairment and produces an increase in hippocampal amyloid-β and phospho-tau levels on a background of AD susceptibility.

New serotonin 5-HT(1A) receptor agonists with neuroprotective effect against ischemic cell damage

We report the synthesis of new compounds 4-35 based on structural modifications of different moieties of previously described lead UCM-2550. The new nonpiperazine derivatives, representing second-generation agonists, were assessed for binding affinity, selectivity, and functional activity at the 5-HT(1A) receptor (5-HT(1A)R). Computational β(2)-based homology models of the ligand-receptor complexes were used to explain the observed structure-affinity relationships. Selected candidates were also evaluated for their potential in vitro and in vivo neuroprotective properties. Interestingly, compound 26 (2-{6-[(3,4-dihydro-2H-chromen-2-ylmethyl)amino]hexyl}tetrahydro-1H-pyrrolo[1,2-c]imidazole-1,3(2H)-dione) has been characterized as a high-affinity and potent 5-HT(1A)R agonist (K(i) = 5.9 nM, EC(50) = 21.8 nM) and exhibits neuroprotective effect in neurotoxicity assays in primary cell cultures from rat hippocampus and in the MCAO model of focal cerebral ischemia in rats.

Enhanced expression of the voltage-dependent anion channel 1 (VDAC1) in Alzheimer's disease transgenic mice: an insight into the pathogenic effects of amyloid-β

The mitochondrial voltage-dependent anion channel 1 (VDAC1) is involved in the release of apoptotic proteins with possible relevance in Alzheimer's disease (AD) neuropathology. Through proteomic analysis followed by Western blotting and immunohistochemical techniques, we have found that VDAC1 is overexpressed in the hippocampus from amyloidogenic AD transgenic mice models. VDAC1 was also overexpressed in postmortem brain tissue from AD patients at an advanced stage of the disease. Interestingly, amyloid-β (Aβ) soluble oligomers were able to induce upregulation of VDAC1 in a human neuroblastoma cell line, further supporting a correlation between Aβ levels and VDAC1 expression. In hippocampal extracts from transgenic mice, a significant increase was observed in the levels of VDAC1 phosphorylated at an epitope that is susceptible to phosphorylation by glycogen synthase kinase-3β, whose activity was also increased. The levels of hexokinase I (HXKI), which interacts with VDAC1 and affects its function, were decreased in mitochondrial samples from AD models. Since phospho-VDAC and reduced HXKI levels favors a VDAC1 conformational state more prone to the release proapoptotic factors, regulation of the function of this channel may be a promising therapeutic approach to combat AD.

[Perspectives on the amyloid cascade hypothesis of Alzheimer's disease]

The amyloid-beta peptide cascade hypothesis has provided a useful framework for the research on Alzheimer's disease for nearly 20 years. According to this hypothesis, an increase in amyloid-beta levels triggers all of the pathological features of the disease, including tau hyperphosphorylation, appearance of neurofibrillary tangles, synaptic dysfunction and neuronal cell death. Even though amyloid-beta peptide has an important role in the neurodegenerative process, different findings, such as the presence of abundant plaques in old cognitively normal individuals or the limited success of therapeutical approaches targeting only amyloid-beta, cast some doubt on a unique role for this peptide. At present, it is rather accepted that amyloid-beta peptide acts in parallel with other factors causing Alzheimer's disease that should be also considered at the time of designing useful therapeutic strategies.

Rosiglitazone rescues memory impairment in Alzheimer's transgenic mice: mechanisms involving a reduced amyloid and tau pathology

Clinical studies suggest that agonists at peroxisome proliferator-activated receptor gamma (PPARgamma) may exert beneficial effects in patients with mild-to-moderate Alzheimer's disease (AD), but the mechanism for the potential therapeutic interest of this class of drugs has not yet been elucidated. Here, in mice overexpressing mutant human amyloid precursor protein, we found that chronic treatment with rosiglitazone, a high-affinity agonist at PPARgamma, facilitated beta-amyloid peptide (Abeta) clearance. Rosiglitazone not only reduced Abeta burden in the brain but, importantly, almost completely removed the abundant amyloid plaques observed in the hippocampus and entorhinal cortex of 13-month-old transgenic mice. In the hippocampus, neuropil threads containing phosphorylated tau, probably corresponding to dystrophic neurites, were also decreased by the drug. Rosiglitazone switched on the activated microglial phenotype, promoting its phagocytic ability, reducing the expression of proinflammatory markers and inducing factors for alternative differentiation. The decreased amyloid pathology may account for the reduction of p-tau-containing neuropil threads and for the rescue of impaired recognition and spatial memory in the transgenic mice. This study provides further insights into the mechanisms for the beneficial effect of rosiglitazone in AD patients.

Phenylbutyrate ameliorates cognitive deficit and reduces tau pathology in an Alzheimer's disease mouse model

Chromatin modification through histone acetylation is a molecular pathway involved in the regulation of transcription underlying memory storage. Sodium 4-phenylbutyrate (4-PBA) is a well-known histone deacetylase inhibitor, which increases gene transcription of a number of genes, and also exerts neuroprotective effects. In this study, we report that administration of 4-PBA reversed spatial learning and memory deficits in an established mouse model of Alzheimer's disease (AD) without altering beta-amyloid burden. We also observed that the phosphorylated form of tau was decreased in the AD mouse brain after 4-PBA treatment, an effect probably due to an increase in the inactive form of the glycogen synthase kinase 3beta (GSK3beta). Interestingly, we found a dramatic decrease in brain histone acetylation in the transgenic mice that may reflect an indirect transcriptional repression underlying memory impairment. The administration of 4-PBA restored brain histone acetylation levels and, as a most likely consequence, activated the transcription of synaptic plasticity markers such as the GluR1 subunit of the AMPA receptor, PSD95, and microtubule-associated protein-2. The results suggest that 4-PBA, a drug already approved for clinical use, may provide a novel approach for the treatment of AD.

Rosiglitazone reverses memory decline and hippocampal glucocorticoid receptor down-regulation in an Alzheimer's disease mouse model

Clinical trials with rosiglitazone, a potent agonist at peroxisome proliferator-activated receptor gamma (PPARgamma) suggest an improvement of cognitive function in Alzheimer's disease (AD) patients. The mechanisms mediating this potential beneficial effect remain to be fully elucidated. In mice overexpressing mutant human amyloid precursor protein (hAPP), a model of AD, we found that memory impairment in the object recognition test was prevented and also reversed by chronic rosiglitazone treatment. Given the possible involvement of glucocorticoid receptors (GR) in the actions of PPARgamma-ligands, we studied the effect of chronic rosiglitazone treatment on GR levels in the hippocampus of hAPP mice. An early down-regulation of GR, not related to elevated plasma corticosterone levels, was found in different hippocampal subfields of the transgenic mice and this decrease was prevented by rosiglitazone. In parallel with behavioural studies, rosiglitazone also normalized GR levels in older animals. This effect may contribute to explain the attenuation of memory decline by PPARgamma activation in an AD mouse model.

Overexpression of wild-type human APP in mice causes cognitive deficits and pathological features unrelated to Abeta levels

Transgenic mice expressing mutant human amyloid precursor protein (APP) develop an age-dependent amyloid pathology and memory deficits, but no overt neuronal loss. Here, in mice overexpressing wild-type human APP (hAPP(wt)) we found an early memory impairment, particularly in the water maze and to a lesser extent in the object recognition task, but beta-amyloid peptide (Abeta(42)) was barely detectable in the hippocampus. In these mice, hAPP processing was basically non-amyloidogenic, with high levels of APP carboxy-terminal fragments, C83 and APP intracellular domain. A tau pathology with an early increase in the levels of phosphorylated tau in the hippocampus, a likely consequence of enhanced ERK1/2 activation, was also observed. Furthermore, these mice presented a loss of synapse-associated proteins: PSD95, AMPA and NMDA receptor subunits and phosphorylated CaMKII. Importantly, signs of neurodegeneration were found in the hippocampal CA1 subfield and in the entorhinal cortex that were associated to a marked loss of MAP2 immunoreactivity. Conversely, in mice expressing mutant hAPP, high levels of Abeta(42) were found in the hippocampus, but no signs of neurodegeneration were apparent. The results support the notion of Abeta-independent pathogenic pathways in Alzheimer's disease.

Neuroprotective effects of serotonin 5-HT 1A receptor activation against ischemic cell damage in gerbil hippocampus: Involvement of NMDA receptor NR1 subunit and BDNF

It is known that the activation of 5-hydroxytryptamine receptor type 1A (5HT(1A) receptor) may protect against brain damage induced by transient global ischemia. The biochemical mechanisms that underlie this neuroprotective effect remain however to be fully elucidated. Given that serotonergic drugs may regulate N-methyl-d-aspartate (NMDA) receptor function, which is implicated in events leading to ischemia-induced neuronal cell death, and also stimulate the expression of brain-derived neurotrophic factor (BDNF), which is down-regulated in cerebral ischemia, we sought to determine the effects of the selective 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), on the levels of NMDA receptor NR1 subunit and BDNF in gerbil hippocampus after transient global cerebral ischemia. Pretreatment with 8-OH-DPAT (1 mg/kg) prevented the neuronal loss in CA1 subfield 72 h after ischemia and also the dramatic decrease in BDNF immunoreactivity observed in this area at an earlier time. NMDA receptor NR1 levels in whole hippocampus were not affected 24 h after ischemia, but the levels of the subunit phosphorylated at the protein kinase A (PKA) site, pNR1(Ser897), were significantly increased, and this increase was prevented by the same 8-OH-DPAT dose, a probable consequence of the increased phosphatase 1 (PP1) enzyme activity found in ischemic gerbils pretreated with the 5-HT(1A) receptor agonist. The results indicate that both NR1 subunit phosphorylation and the neurotrophin BDNF account, at least in part, for the neuroprotective effect of 8-OH-DPAT on cell damage induced by global ischemia in the gerbil hippocampus and support the potential interest of 5-HT1A receptor activation in the search for neuroprotective strategies.

Neuronal proteins involved in synaptic targeting of AMPA receptors in rat hippocampus by antidepressant drugs

Recent data suggest that the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor subtype plays a pivotal role in the pathogenesis of effective disorders and in the action of antidepressant drugs. After chronic treatment with the antidepressants desipramine or paroxetine, we measured by immunoprecipitation and Western blotting, the changes in the interaction of AMPA receptor subunits with proteins involved in trafficking and/or stabilization of the subunits into synaptic membranes of the hippocampus. Both antidepressants increased the interaction of GluR1 subunit with stargazin and of GluR2/3 with NSF. Paroxetine increased the interaction of GluR1 with Rab4A, and desipramine markedly increased the interaction of GluR1 with SAP97. Paroxetine, but not desipramine, also increased membrane levels of CaMKII, autophosphorylated CaMKII and GluR1 phosphorylated at the CaMKII site. Interactions of GluR1 and GluR2/3 with proteins implicated in AMPA receptor trafficking and with scaffolding proteins appear to account for the enhanced membrane expression of AMPA receptors in the hippocampus after antidepressant treatment.

The neuroprotective activity of GPE tripeptide analogues does not correlate with glutamate receptor binding affinity

The influence of several modifications on the GPE tripeptide structure upon the binding to GluRs and on their neuroprotective effects has been studied. The results indicated that the prevention of neuronal death showed by GPE and some analogues is not directly related to their affinity at glutamate receptors.

Differential effects of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") on BDNF mRNA expression in rat frontal cortex and hippocampus

The serotonergic neurotoxin 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") produces rapid serotonin (5-HT) depletion in different areas of the forebrain after acute administration to rats and other animal species. We previously found that 5-HT depletion induced by acute MDMA treatment was transient in the frontal cortex, but not in the hippocampus, and recovery of cortical 5-HT levels correlated with an induction of CRE-binding activity and increased expression of tryptophan-hydroxylase (TPH), the rate-limiting enzyme in 5-HT biosynthesis. As the brain-derived neurotrophic factor (BDNF) stimulates the growth and sprouting of serotonergic neurons, we sought the possible involvement of this neurotrophin in the region-specific increase in TPH mRNA expression induced by MDMA. We here report that, 24-48 h after acute MDMA treatment, the expression of BDNF in the frontal cortex is increased by approximately 33-70%, and the levels of the transcription factor phospho-CREB are also increased. In the hippocampus, however, a time-dependent decrease in BDNF mRNA expression (maximal decrease of approximately 73%) is found in all subfields examined 2-7 days after treatment in spite of increased phospho-CREB levels, perhaps as a consequence of corticosterone release by the serotonergic neurotoxin. The differential regulation of BDNF mRNA expression in the two brain regions examined appears to account for the enhanced TPH expression and the recovery of 5-HT levels in the frontal cortex, but not in the hippocampus, after neurotoxin treatment.

Opposing effects of AMPA and 5-HT1A receptor blockade on passive avoidance and object recognition performance: correlation with AMPA receptor subunit expression in rat hippocampus

It has been suggested that antagonists at serotonin 5-HT1A receptors may exert a procognitive effect by facilitating glutamatergic neurotransmission. Here we further explored this issue by looking for the ability of a 5-HT1A antagonist to prevent the learning deficit induced by AMPA receptor blockade in two behavioural procedures in rats, and for concomitant molecular changes presumably involved in memory formation in the hippocampus. Pretraining administration of the competitive AMPA receptor antagonist, NBQX, produced a dose-related retention impairment in a passive avoidance task 24h later, and also impaired retention in a novel object recognition test when an intertrial interval of 3h was selected. Pretreatment with the selective 5-HT1A receptor antagonist, WAY-100635, prevented the learning deficit induced by NBQX in the two behavioural procedures. In biochemical studies performed on rat hippocampus after the retention tests, we found that learning increased the membrane levels of AMPA receptor GluR1 and GluR2/3 subunits, as well as the phosphorylated forms of GluR1, effects that were abolished by NBQX administration before the training session. Pretreatment with WAY-100635 counteracted the NBQX effects and restored the initial learning-specific increase in Ca2+/calmodulin-dependent protein kinase II (CaMKII) function and the later increase in GluR2/3 and phosphorylated GluR1 surface expression. Moreover, administration of WAY-100635 before object recognition training improved recognition memory 24h later and potentiated the learning-associated increase in AMPA receptor subunits. The results support the proposed utility of 5-HT1A antagonists in the treatment of cognitive disorders.

New Gly-Pro-Glu (GPE) analogues: expedite solid-phase synthesis and biological activity

A suitable solid-phase approach, based on Fmoc/(t)Bu methodology and on the use of 2-chlorotrityl resin, allowed a rapid and efficient preparation of new GPE analogues. Most of the synthesized tripeptides displayed glutamate receptor binding affinity comparable to that of GPE, but only a few derivatives showed significant neuroprotective activity.

Sequential changes in BDNF mRNA expression and synaptic levels of AMPA receptor subunits in rat hippocampus after chronic antidepressant treatment

Increased expression of brain-derived neurotrophic factor (BDNF) appears to be involved in the mechanism of action of antidepressant drugs. It has also been proposed that potentiation of the AMPA receptor (AMPAR) function may be useful in the treatment of depression. Here we looked for the time course of the effect of different doses of two antidepressants, desipramine (DMI) and paroxetine (PAR), which differentially affect monoamine reuptake, on BDNF mRNA expression in hippocampal subfields (CA1, CA3 and dentate gyrus) and levels of AMPAR subunits in total and membrane-enriched extracts from rat hippocampus. Acute antidepressant treatment changed neither BDNF mRNA expression nor AMPAR subunit levels. In chronic treatments, rats were treated daily with the antidepressants for 7-21 days. PAR produced a time- and dose-dependent increase of BDNF expression in the three hippocampal subfields examined. On the contrary, the effect of DMI on BDNF mRNA was neither dose- nor time-dependent. In rats receiving the same chronic antidepressant treatments, PAR produced a dose-dependent increase of GluR1 and GluR2/3 levels in the membrane fraction after a 3-week treatment, and not at earlier times. DMI increased the membrane levels of AMPAR subunits after a 3-week treatment with the lower dose tested. However, a higher dose, 15 mg/kg, did not produce any change in AMPAR subunits and reduced membrane levels of alpha-tubulin and PSD-95, possibly indicating a disorganization of membrane scaffolding proteins. The results suggest that paroxetine, but not desipramine, enhances synaptic plasticity in the hippocampus by increasing BDNF mRNA expression, which determines a later AMPAR subunit trafficking to synaptic membranes.

Acute and chronic effects of MDMA on molecular mechanisms implicated in memory formation in rat hippocampus: Surface expression of CaMKII and NMDA receptor subunits

Acute 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") treatment induces learning deficits in different animal models. In a passive avoidance learning task in rats, previous studies suggested a role for Ca2+/calmodulin-dependent protein kinase II (CaMKII) and N-methyl-D-aspartate (NMDA) receptors in the acute learning impairment. As cognitive deficits by "ecstasy" in humans have been only reported in frequent recreational users, we examined whether a repeated MDMA treatment could induce in rats lasting molecular changes related to memory consolidation of passive avoidance. In rats with a pronounced 5-HT depletion by MDMA, the effect of another drug challenge was also examined. The surface expression in the hippocampus of NMDA receptor subunits, the scaffolding postsynaptic density protein PSD-95, phosphorylated CaMKII and protein phosphatase 1 (PP1) was measured. In rats repeatedly treated with MDMA (10 mg/kg) twice daily for 4 consecutive days, hippocampal 5-HT levels were markedly reduced 1 week later. At this time, neither learning performance was affected nor changes in membrane levels of NMDA receptor subunits, PSD-95, CaMKII and PP1 were found. In these rats, however, another drug challenge produced a rapid reduction in PSD-95 immunoreactivity and prevented the learning-specific increase in the NMDA receptor NR1 subunit and phosphorylated CaMKII. The results show no lasting change in learning-associated molecular events after a neurotoxic MDMA treatment. This drug only produces transient effects on early molecular events involved in memory consolidation, which do not appear to depend on endogenous 5-HT levels.

Serotonin 5-HT1A receptor blockade enhances Ca2+/calmodulin-dependent protein kinase II function and membrane expression of AMPA receptor subunits in the rat hippocampus: implications for memory formation

Stimulation of hippocampal 5-HT(1A) receptors impairs memory retention. The highly selective 5-HT(1A) antagonist, WAY-100635, prevents the cognitive deficits induced not only by 5-HT(1A) stimulation but also by cholinergic or NMDA receptor blockade. On this basis, the effects of WAY-100635 on molecular events associated with memory storage were explored. In rat hippocampus, WAY-100635 produced a rapid increase in phosphorylated Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and in Ca(2+)-independent CaMKII and protein kinase A (PKA) enzyme activity. This increase was followed a few hours later by an enhanced membrane expression of AMPA receptor subunits, especially of the GluR1 subunit phosphorylated at the CaMKII site, pGluR1(Ser831). The same qualitative effects were found with the weaker 5-HT(1A) antagonist NAN-190. The effects of both antagonists were no longer apparent in rats with a previous 5-HT depletion induced by the tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA), suggesting that 5-HT(1A) receptor blockade removes the tonic inhibition of 5-HT through 5-HT(1A) receptor stimulation on excitatory hippocampal neurons, with the consequent increase in PKA activity. In addition, administration of WAY-100635 potentiated the learning-specific increase in the hippocampus of phospho-CaMKII, Ca(2+)-independent CaMKII activity, as well as the phosphorylation of either the CaMKII or the PKA site on the AMPA receptor GluR1 subunit. This study suggests that blockade of hippocampal 5-HT(1A) receptors favours molecular events critically involved in memory formation, and provides an in vivo molecular basis for the proposed utility of 5-HT(1A) receptor antagonists in the treatment of cognitive disorders.

Analogues of the neuroprotective tripeptide Gly-Pro-Glu (GPE): synthesis and structure–activity relationships

A series of GPE analogues, including modifications at the Pro and/or Glu residues, was prepared and evaluated for their NMDA binding and neuroprotective effects. Main results suggest that the pyrrolidine ring puckering of the Pro residue plays a key role in the biological responses, while the preference for cis or trans rotamers around the Gly-Pro peptide bond is not important.

Role of hippocampal CaMKII in serotonin 5-HT(1A) receptor-mediated learning deficit in rats

The serotonin 5-HT(1A) receptor agonist, 8-OH-DPAT (8-hydroxy-2-di-n-propylamino-tetralin), impairs retention performance in a passive avoidance learning task in rats. In the hippocampus of rats trained on this procedure and killed 1 h after the acquisition trial, an increase in the membrane levels of both Ca2+/calmodulin-dependent protein kinase II (CaMKII) and phosphorylated CaMKII, as well as in total and Ca2+-independent enzyme activity in tissue lysates was found. These effects were learning-specific as no changes in CaMKII levels or activity were found in rats receiving a footshock identical to the trained rats. The effect of training on CaMKII was prevented by a low 8-OH-DPAT dose. The 5-HT(1A) agonist also reduced protein kinase A (PKA) activity and increased the membrane levels of phosphatase 1 (PP1) and PP1 enzyme activity in the hippocampus. All of the changes induced by 8-OH-DPAT were reversed by the selective 5-HT(1A) antagonist WAY-100635, indicating receptor-specific effects. We suggest that 5-HT(1A) receptor-mediated disruption of retention performance is a consequence of the reduced PKA activity and the ensuing enhancement in PP1 activity, possibly through decreased phosphorylation/activation of endogenous PP1 inhibitors, that cause a reduced activity of phosphorylated CaMKII, a key enzyme in early stages of memory formation. This study provides an in vivo molecular basis for the cognitive deficits induced by stimulation of hippocampal 5-HT(1A) receptors.

Increased CRE-binding activity and tryptophan hydroxylase mRNA expression induced by 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") in the rat frontal cortex but not in the hippocampus

A single administration of either 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") or p-chloroamphetamine (PCA) produced a rapid and marked reduction of serotonin (5-HT) content in rat frontal cortex and hippocampus. In the cortex of MDMA-treated rats, 5-HT levels returned to control values 48 h after drug administration. This recovery was correlated with an induction of CRE-binding activity and an enhanced expression of tryptophan hydroxylase (TPH) mRNA, the rate-limiting enzyme in 5-HT biosynthesis, suggesting that MDMA may up-regulate the TPH gene through a CREB-dependent mechanism. In the cortex of PCA-treated rats, neither a recovery of 5-HT levels nor changes in DNA-binding or TPH mRNA were found at the same time point. In the hippocampus of rats receiving either PCA or MDMA a decrease in TPH mRNA levels was found at all times, along with a reduced CRE-binding at the 8-h time point. The results show region-specific effects of MDMA. In the frontal cortex, the increased TPH expression suggests a compensatory response to MDMA-induced loss of serotonergic function.

NMDA receptor subunit and CaMKII changes in rat hippocampus induced by acute MDMA treatment: a mechanism for learning impairment

RATIONALE

Cognitive deficits have been reported in recreational 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") users. In rats and other animal species, acute MDMA administration produces an impairment in passive avoidance and other learning tasks. Different studies have shown that this learning deficit is not strictly related to the pronounced serotonin (5-HT) depletion induced by the drug.

OBJECTIVES

This study was aimed at determining if acute MDMA administration induces in the rat hippocampus early molecular changes related to memory impairment in a passive avoidance task. The membrane expression of key molecules in memory consolidation, such as the NR1 and NR2B subunits of the N-methyl-D-aspartate (NMDA) receptor, Ca2+/calmodulin-dependent protein kinase II (CaMKII) and protein phosphatase 1 (PP1) was measured. Some of these studies were also performed after 5-HT depletion induced by the 5-HT synthesis inhibitor p-chlorophenylalanine (PCPA).

METHODS

Neurochemical studies were performed in rats treated with MDMA and killed 90 min later and also in rats subjected to passive avoidance 30 min after MDMA treatment. Western blotting was used for measuring the levels of NMDA receptor subunits, CAMKII and PP1. Enzyme activity assays were also performed.

RESULTS

In hippocampal membrane extracts, passive avoidance training increased NMDA receptor NR1 subunit expression as well as CaMKII levels and phosphorylated CaMKII. In untrained rats, MDMA reduced NR1 and NR2B protein levels, membrane CaMKII levels and enzyme activity, and enhanced PP1 levels and activity. In trained rats, MDMA prevented the learning-specific increase in NR1 subunit expression and membrane CaMKII/pCaMKII levels. After pronounced 5-HT depletion by PCPA, MDMA impaired passive avoidance retention to a similar extent and also prevented the training-associated changes in NR1 levels and CaMKII activity.

CONCLUSIONS

Diminished function of hippocampal CaMKII and reduced levels of synaptic NMDA receptor subunits appear to be involved in the impairment of passive avoidance learning induced in rats by acute MDMA treatment.

Design and synthesis of new benzimidazole-arylpiperazine derivatives acting as mixed 5-HT1A/5-HT3 ligands

A series of new benzimidazole-arylpiperazine derivatives III were designed, synthesized and evaluated for binding affinity at serotoninergic 5-HT(1A) and 5-HT(3) receptors. Compound IIIc was identified as a novel mixed 5-HT(1A)/5-HT(3) ligand with high affinity for both serotonin receptors and excellent selectivity over alpha(1)-adrenergic and dopamine D(2) receptors. This compound was characterized as a partial agonist at 5-HT(1A)Rs and a 5-HT(3)R antagonist, and was effective in preventing the cognitive deficits induced by muscarinic receptor blockade in a passive avoidance learning test.

Reduced basal and phencyclidine-induced expression of heat shock protein-70 in rat prefrontal cortex by the atypical antipsychotic abaperidone

The effect of antipsychotic treatment on basal and phencyclidine (PCP)-induced heat shock protein-70 (hsp70) mRNA expression was studied in the rat striatum and in the prefrontal cortex. Abaperidone, a novel drug with an atypical antipsychotic profile, was compared, at pharmacologically equivalent doses, with the atypical antipsychotics clozapine and risperidone and also with haloperidol, a classical antipsychotic. Abaperidone and clozapine reduced basal hsp70 mRNA expression in the rat striatum and in the prefrontal cortex. No change in either region was found after haloperidol, whereas risperidone reduced hsp70 mRNA in the striatum but not in the prefrontal cortex. The N-methyl-D-aspartate (NMDA) receptor antagonist PCP significantly elevated hsp70 mRNA levels in the prefrontal cortex, an elevation that was potentiated by haloperidol and prevented by all of the atypical antipsychotics tested. Since hsp70 has been associated to some schizophrenia symptoms, we suggest that reduced hsp70 in the prefrontal cortex, a cortical area that plays a critical role in the etiology of many schizophrenia symptoms, may be linked to an atypical profile of antipsychotics, such as clozapine, and possibly also abaperidone.

Chronic antidepressant treatment increases the membrane expression of AMPA receptors in rat hippocampus

It has been proposed that potentiation of AMPA receptor (AMPAR) function may be useful in the treatment of depression. Here we studied the acute and chronic effect of the antidepressants desipramine and paroxetine, which differentially affect monoamine reuptake, on the expression of the AMPAR subunits GluR1 and GluR2/3, analyzed by Western blot, both in total and in membrane-enriched extracts from rat hippocampus. Acute antidepressant treatment did not produce any change in the expression of AMPAR subunits. In chronic treatments, rats were daily treated with the antidepressants (10 mg/kg/day) for 7, 14, or 21 days. In rats receiving either of the two antidepressant treatments for 21 consecutive days and killed 24 h after the last injection, an increase in GluR1 and GluR2/3 levels was found in the membrane fraction, with no significant change in the total extract, suggesting a trafficking of the AMPAR subunits from intracellular pools to synaptic sites in the hippocampus. This appeared to be a region-specific effect since no change in AMPAR subunit expression was found in the frontal cortex. Previously reported modifications in phosphorylating enzymes by chronic antidepressants could perhaps play a role in hippocampal membrane insertion of AMPAR subunits. When the survival time after the 21-day-treatment was longer - 72 instead of 24 h - the hippocampal membrane expression of GluR1, but not of GluR2/3 subunits, was still increased, as could be expected from the distinct mechanisms operating in synaptic delivery of GluR1 and GluR2/3 subunits. The antidepressant-induced increase in the number of GluR1- and GluR2/3-containing AMPARs at the synapses may indicate an enhanced AMPAR-mediated synaptic transmission which could help to counteract the alterations in neuronal connectivity which appear to underlie the pathophysiology of mood disorders.

Conformationally restricted PACAP27 analogues incorporating type II/II' IBTM beta-turn mimetics. Synthesis, NMR structure determination, and binding affinity

To probe the importance of a proposed beta-turn within residues S9-R12 of PACAP for recognition by VIP/PACAP receptors, compounds 1 and 2, two conformationally restricted analogues of PACAP27 incorporating respectively (S)- or (R)-IBTM as type II or II' beta-turn dipeptide mimetic at the Y10-S11 position, were synthesized. According to 1H NMR conformational analyses in aqueous solution and 30% TFE, both PACAP27 and the [S-IBTM(10,11)]PACAP27 analogue 1 adopt similar ordered structures. PACAP27 shows an N-terminal disordered region (residues H1-F6) and an alpha-helical conformation within segment T7-L27. For residues S9-R12, our data seem more compatible with a segment of the alpha-helix than with the beta-turn previously proposed for this fragment. In compound 1 the alpha-helix, also spanning T7-L27 residues, appears slightly distorted at the N-terminus relative to the native peptide. Although this distortion could lead to the marked decrease in binding affinity of this compound at the VIP/PACAP receptors, the lack of the Y10 side chain in analogues 1 and 2 could also significantly affect the binding of these compounds.

BDNF mediates the neuroprotective effect of PACAP-38 on rat cortical neurons

In primary cultures from rat cerebral cortex, pituitary adenylate cyclase-activating polypeptide (PACAP-38) exerted a protective effect on cell death induced by the excitotoxin NMDA in neuron-enriched cultures and also on apoptotic cell death induced by serum deprivation in mixed neuronal-glial cultures. The neuroprotective effect was already observed at subnanomolar concentrations of PACAP and was slightly more pronounced against excitotoxic cell death. BDNF protein expression was reduced by NMDA and much more markedly by serum deprivation (approximately 28 and 93% reduction respectively). In both cellular injury conditions, the diminished BDNF expression was significantly prevented by PACAP. When purified neuronal cultures were preincubated with an antiserum anti-BDNF, at a concentration without any intrinsic effect on cell viability, the neuprotective effect of PACAP was no longer observed. The results suggest that the neuroprotective effect of PACAP-38 is mediated, at least in part, by preventing the suppressed expression of a neurotrophin essential for cortical neuron survival.

Serotonin 5-HT(1A) receptor expression is selectively enhanced in the striosomal compartment of chronic parkinsonian monkeys

Cynomolgus monkeys (Macaca fascicularis) were chronically treated with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) until stable parkinsonism was reached. Two months later, monkeys were sacrificed and monoamine content was measured in different brain regions of the lesioned monkeys and of age-matched controls. 5-HT(1A) serotonin receptor density was measured in coronal sections labeled with [(3)H]8-OH-DPAT. As expected, dopamine was virtually nonexistent in the caudate nucleus and putamen of MPTP-treated monkeys. Serotonin levels were significantly reduced in different brain regions, particularly in the raphe nuclei. 5-HT(1A) receptor density of control animals was high in the hippocampus, notably in the CA1 field and also in the raphe nuclei, and much lower in the striatum, where 5-HT(1A) receptors showed a patchy distribution which corresponded to striosomes with poor calbindin immunostaining. 5-HT(1A) receptor density was reduced in hippocampal fields and in the raphe nuclei of parkinsonian monkeys. Conversely, in the severely lesioned striatal nuclei 5-HT(1A) receptor density was increased at caudal levels of the striatum, particularly in the putamen. The results tend to support the possibility of an increased synthesis of 5-HT(1A) receptors in brain regions with higher neuronal cell death. Upregulation of this 5-HT receptor subtype in the limbic compartment of the striatum may represent a compensatory event for the serotonergic dysfunction and associated mental disorders in neurodegenerative diseases such as Parkinson disease.

Effect of p-chloroamphetamine on 5-HT1A and 5-HT7 serotonin receptor expression in rat brain

The aim of this study was to investigate if p-chloroamphetamine (PCA), which is neurotoxic to serotonin (5-HT) nerve terminals, was able to induce, like 3,4-methylenedioxymethamphetamine, a region-specific regulation of 5-HT1A receptor mRNA expression. The effect of PCA on the expression of 5-HT7 receptors, which share some pharmacological properties with 5-HT1A receptors, was comparatively studied. PCA (2 x 5 mg/kg) produced a lasting depletion of 5-HT content in the rat frontal cortex and hippocampus. In the hippocampus, the maximal 5-HT depletion was found on day 21 (-70%), whereas in the cortex, the highest 5-HT depletion was found on day 14 (-73%), with a partial but significant recovery on day 21. At the latter time point, 5-HT1A receptor mRNA expression was increased by 80% in the cortex and decreased by 50% in the hippocampus. The 5-HT1A receptor mRNA expression was also enhanced after exposure to PCA of rat cortical but not of hippocampal primary cultures. In regard to 5-HT7 receptor mRNA expression, the most remarkable change after PCA was the great increase (+200%) in the brain-stem. Binding studies to 5-HT1A receptors matched the changes in receptor mRNA expression. Gel shift assays revealed enhanced nuclear protein binding to the KB sequence with use of cortical but not hippocampal extracts of PCA-treated rats. Overall, the data show region-specific changes in 5-HT receptor-type expression that may not be entirely dependent on the neurotoxic effect of PCA on 5-HT terminals.

Implanted BDNF-producing fibroblasts prevent neurotoxin-induced serotonergic denervation in the rat striatum

Degeneration of serotonergic fibers in the rat striatum was produced by local administration of the serotonergic neurotoxin 5, 7-dihydroxytryptamine (5,7-DHT) or the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)), which is also toxic to serotonergic neurons. One week before neurotoxin administration, fibroblasts engineered to express the human BDNF gene were grafted into the mesencephalon, dorsal to the substantia nigra. Rats implanted with fibroblasts expressing the LacZ gene were used as controls, as well as sham-operated animals (not injected with any neurotoxin). After a survival period of 1 week, the serotonergic innervation of the striatum was assessed by measuring serotonin (5-HT) content and by immunohistochemical detection of 5-HT positive fibers. BDNF-producing cells prevented the striatal 5-HT loss induced by local administration of either 5,7-DHT or MPP(+), as well as the striatal dopamine (DA) loss induced by the latter neurotoxin. Grafting of fibroblasts carrying the BDNF or the Lac-Z gene did not modify striatal 5-HT or DA content in sham-operated animals. In 5, 7-DHT-lesioned rats, implanted or not with control Lac-Z fibroblasts, a striking reduction in the density of 5-HT immunoreactive fibers was observed. By contrast, the density of 5-HT fibers was similar in rats implanted with BDNF-producing fibroblasts as compared to sham-operated controls. The protective effect of BDNF on the damage to serotonergic terminals induced by the two neurotoxins suggests the interest of this neurotrophin in the treatment of behavioral disorders associated to neurodegenerative diseases.

Facilitation by 8-OH-DPAT of passive avoidance performance in rats after inactivation of 5-HT(1A) receptors

1. Pretraining administration of 8-hydroxy-2-di-n-propylamino-tetralin (8-OH-DPAT 0.1 mg kg(-1)), a 5-HT(1A) receptor agonist, or buspirone (1 mg kg(-1)), a 5-HT(1A) receptor partial agonist, markedly impaired passive avoidance retention in rats 24 h later. The effect of 8-OH-DPAT was prevented by the 5-HT(1A) receptor antagonists, NAN-190 and WAY-100635, at doses without any intrinsic effect. 2. N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ 10 mg kg(-1)), an alkylating agent that inactivates different G-protein coupled receptors, impaired retention performance when given 48 h pretraining. The disruptive effect of EEDQ was reversed by 8-OH-DPAT or buspirone, given 30 min before training. 3. Non-specific actions did not account for 8-OH-DPAT-induced reversal of the EEDQ effect since no significant difference in locomotor activity or in pain threshold was found between rats receiving EEDQ or EEDQ+8-OH-DPAT. 4. When NAN-190 (1 mg kg(-1)) or WAY-100635 (0.5 mg kg(-1)) were given before 8-OH-DPAT to EEDQ-pretreated animals, the reversal by 8-OH-DPAT of EEDQ-induced retention impairment was still more pronounced. However, no EEDQ reversal by 8-OH-DPAT was found when 5-HT(1A) receptors were protected by WAY-100635 (10 mg kg(-1)) 30 min before EEDQ. 5. In the hippocampus of EEDQ-treated rats, 5-HT(7) receptors were less inactivated than 5-HT(1A) receptors and significant increases were found in 5-HT(1A) but not in 5-HT(7) receptor mRNA levels. Ritanserin and methiothepin (10 mg kg(-1) each), antagonists with higher affinity at 5-HT(7) than at 5-HT(1A) receptors, prevented the retention impairment induced by EEDQ but did not significantly protect against 5-HT(7) receptor inactivation. 6. The results indicate that the facilitatory effect of 8-OH-DPAT is not mediated through 5-HT(1A) receptors and suggest that other 8-OH-DPAT-sensitive receptors could be involved in the dual effect of 8-OH-DPAT on passive avoidance performance in rats.

Antibodies and antisense oligonucleotide for probing the distribution and putative functions of central 5-HT6 receptors

Among the recently cloned serotonin (5-hydroxytryptamine, 5-HT) receptors, the 5-HT6 subtype is of special interest for at least two reasons: 1) it is abundant in limbic areas which participate in the control of mood and emotion; and 2) some antidepressants and antipsychotics are potent 5-HT6 receptor antagonists. Studies using polyclonal anti-5-HT6 receptor antibodies and an antisense oligonucleotide were performed in order to investigate further the function(s) of 5-HT6 receptors in the rat brain. Immunocytochemistry at the light and electron microscope levels showed that 5-HT6 receptors are mainly confined to the dendritic compartment, suggesting that they could mediate 5-HT actions on neuronal firing. In some limbic areas, 5-HT6 receptor-like immunoreactivity is also associated with neuronal cilia with yet unknown functions. Continuous i.c.v. infusion with an antisense oligonucleotide for 3-4 days resulted in decreased 5-HT6 receptor-like immunostaining of the nucleus accumbens and anxiogenic behaviours in the social interaction and elevated plus maze tests. Selective 5-HT6 receptor ligands are eagerly expected to investigate further the potential implication of these receptors in limbic-dependent behaviours.

Anxiogenic-like effects and reduced stereological counting of immunolabelled 5-hydroxytryptamine6 receptors in rat nucleus accumbens by antisense oligonucleotides

The physiological role of 5-hydroxytryptamine6 receptors in the central nervous system has not yet been elucidated. The high affinity of various psychotropic drugs for 5-hydroxytryptamine6 receptors has led to the suggestion that this receptor type may be a novel target in neuropsychiatry. We have found that continuous intracerebroventricular administration of a 5-hydroxytryptamine6 receptor antisense oligonucleotide, but not of a missense oligonucleotide, produced an anxiogenic-like response in rats using two different models of anxiety, the social interaction test and the elevated plus-maze. Neither oligonucleotide treatment modified locomotor activity, rectal temperature or food intake, suggesting a low or null neurotoxicity. The effectiveness of the treatment with the designed antisense oligonucleotide to block the synthesis of the protein encoded by the target mRNA was assessed by immunolabelling 5-hydroxytryptamine6 receptors in the nucleus accumbens, where this receptor is highly expressed, using previously characterized specific antibodies. The density of the immunostaining was quantified by means of an unbiased three-dimensional stereologic procedure, which revealed a significant reduction (-25%) in the number of immunolabelled neuronal elements. These results suggest that, in addition to other 5-hydroxytryptamine receptor subtypes, 5-hydroxytryptamine6 receptors in the nucleus accumbens may participate in anxiety-related neurobiological mechanisms.

Effect of chronic antidepressant treatment on transcription factor binding activity in rat hippocampus and frontal cortex

1. The effect of chronic antidepressant administration on CRE-, SP1- and GRE-binding activity was studied in rat hippocampus and frontal cortex. 2. Fluoxetine and desipramine (3 and 10 mg/kg/day respectively) were given to rats for 21 consecutive days. The animals were killed 3 hr after the last injection and nuclear extracts were prepared to perform the DNA-protein reaction with consensus CRE, SP1 and GRE oligonucleotides. 3. Gel-shift assays showed that CRE-binding activity was increased in both frontal cortex and hippocampus by chronic fluoxetine treatment. Desipramine, however, only enhanced this activity in the frontal cortex. 4. Chronic fluoxetine decreased SP1-binding activity in the two selected brain regions. Again, desipramine only produced a significant reduction in the frontal cortex. 5. GRE-binding in the hippocampus was only enhanced by desipramine. Since chronic desipramine, and not fluoxetine, is able to increase hippocampal glucocorticoid receptor (GR) expression, interactions of GR with CREB and SP1 may determine the lack of effect of desipramine on binding activity of the two latter transcription factors in this brain region. 6. Overall, the results show a differential and region-specific effect of chronic, and not acute, antidepressant treatment on the DNA-binding activities studied and are consonant with the possible role of changes in gene expression in the mechanism of antidepressant action.

Differential regulation by methylenedioxymethamphetamine of 5-hydroxytryptamine1A receptor density and mRNA expression in rat hippocampus, frontal cortex, and brainstem: the role of corticosteroids

The present study examined the effects of repeated administration to rats of 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") on 5-hydroxytryptamine1A (5-HT1A) receptor density and mRNA expression in the hippocampus, frontal cortex, and brainstem. As expected, 7 days after subacute MDMA administration (20 mg/kg i.p. twice daily for 4 consecutive days) 5-HT content was markedly reduced (-70%) in the hippocampus and the frontal cortex. 5-HT1A receptor density was increased in the frontal cortex by 23% and decreased in the hippocampus and the brainstem by 25%. These changes correlated with an enhanced or diminished 5-HT1A receptor mRNA expression in the three regions studied. To examine the influence of corticosteroids on these changes, adrenalectomized (ADX) rats received the same dosage regimen as above. Adrenalectomy by itself did not modify 5-HT content in the brain regions examined and increased 5-HT1A receptor density in the hippocampus (+20%) but produced no change in the frontal cortex and brainstem. Adrenalectomy also prevented MDMA-induced changes in receptor number in the hippocampus and brainstem but not in the frontal cortex. Dexamethasone (1 mg/kg/day i.p.) administered for 7 consecutive days reversed the effects of adrenalectomy in the hippocampus but not in the frontal cortex. In the brainstem, MDMA no longer reduced 5-HT1A receptor number in ADX rats, but a significant reduction was restored when ADX animals received the glucocorticoid treatment. The present data show that MDMA may affect 5-HT1A receptors in a regionally dependent manner, notably through a drug effect on corticosterone release, which attenuates 5-HT1A receptor gene transcription selectively in the hippocampus.

Inotropic and chronotropic effects of 4-(4'-n-butylaniline)-7,8- dimethoxy-5H-pyrimido[5,4-b]indole in guinea-pig atria

Cardiotonic effect of 4-(4'-n-butylaniline)-7,8-dimethoxy- 5H-pyrimido[5,4-b]indole (B11) was investigated in isolated cardiac tissue preparations. The action of this agent on force of contraction, beating frequency and cyclic nucleotide phosphodiesterase (PDE) activity was studied. Amrinone was used for comparison. B11 produced concentration-dependent (5 x 10(6)-1 x 10(-4)M) positive inotropic and positive chronotropic responses in guinea-pig atrial tissues. The potency of B11 was greater than that of amrinone. The cardiotonic effects of B11 were not modified by beta-adrenoceptor blockade. Carbachol inhibited the positive inotropic effect of B11. The activity of B11 was increased in desensitized left atrial tissues. B11 inhibited the activities of PDE isoenzymes (type I, II, IV and V) from dog heart ventricle and PDE type IV from guinea-pig heart ventricle nonselectively. It is concluded that B11 possesses potent positive inotropic activity in guinea-pig atria, and the effect is probably mediated by a non-selective inhibition of PDE activity.

Inhibition of inflammation and gastric damage in rats by copper (II) complexes

Anti-inflammatory activity and the effect on gastric damage of some copper(II) complexes has been investigated. In a preliminary screening the compounds were studied on the carrageenin paw edema model and two complexes showed inhibitory action on acute as well as subacute models of inflammation. This activity does not seem to be related to an inhibitory effect on prostaglandin biosynthesis or with leukocyte migration into inflamed tissue. These complexes showed an inhibitory effect on volume exudate in experimental pleurisy and on the production of superoxide anions. These inhibitory effects could explain, at least in part, their anti-inflammatory activity. Also, these complexes protected gastric mucosa against the damage induced by HCl and by oral administration of indometacin.

VIP suppression in the intestine and cerebral cortex following administration of VIP antiserum to newborn rats

The administration of vasoactive intestinal peptide (VIP) antiserum to newborn rats significantly reduced the VIP content, both in the cerebral cortex and in intestinal epithelial cells. The decrease was observed at postnatal days 14 and 21 and also in 90 day-old animals. The neonatal treatment produced a significant increase in the density of high- and low-affinity binding sites for VIP in the cerebral cortex at post-natal days 14 and 21 whereas in the intestinal epithelial cells only the low-affinity binding sites were up-regulated at the same time points. VIP suppression induced by neonatal administration of the corresponding antiserum may represent a useful approach to further characterize the physiological role of this neuropeptide.

Differential effects of the novel analgesic, S 12813-4, on the spinal release of substance P- and calcitonin gene-related peptide-like materials in the rat

The possible inhibitory control by the novel analgesic S 12813-4 (3-(2-(4-phenylpiperazine-1-yl)-ethyl)-2-oxo-2,3- dihydrooxazolo(b)pyridine) of spinal neurones containing substance P (SP) and/or calcitonin gene-related peptide (CGRP) was assessed in vitro and in vivo in the rat. S 12813-4 (10 nM-0.1 mM) did not affect the spinal release of CGRP-like material (CGRPLM) but inhibited in a concentration dependent manner the K(+)-evoked overflow of SP-like material (SPLM) from slices of the dorsal half of the rat lumbar enlargement. The inhibitory effect of 10 microM S 12813-4 on SPLM release was not additive with that of Na (0.1 mM), and could be prevented by the alpha 2-adrenoceptor antagonist idazoxan (10 microM). Similarly, idazoxan (10 microM) suppressed the inhibition by intrathecally administered S 12813-4 (10 microM) of the spinal outflow of SPLM in halothane anaesthetized rats whose intrathecal space was perfused with an artificial cerebrospinal fluid. These data suggest that the analgesic effect of S 12813-4 might involve some alpha 2-adrenoreceptor-mediated control of SPLM release within the spinal cord. Whether this control concerns SP-containing primary afferent fibres (presynaptic inhibition) or SP-containing interneurones and/or bulbo-spinal SP-ergic pathways (postsynaptic inhibition) deserves further investigations.

New pyridazino[4,5-b]indole derivatives with inodilator and antiaggregatory activities

Some 4-(3,5-dimethylpyrazol) 5H-pyridazino [4,5-b]indoles (7), 1,2,4-triazolo [4,3-b]pyridazino [4,5-b]indoles (9) and 1,2,4-tetrazolo [4,5-b]pyridazino [4,5-b] indoles (11) substituted in position 1 by amino groups have been synthesized and tested as inotropic agents and inhibitors of platelet aggregation. 6-Imidazolyl-11H-1,2,4-triazolo [4,3-b]pyridazino [4,5-b]indole (9) shows an activity superior to that of amrinone, with a notable selectivity towards phosphodiesterase (PDE) IV and PDEV, vasodilator activity and a good effect on blood platelet aggregation.

Increased in vivo release of calcitonin gene-related peptide-like material from the spinal cord in arthritic rats

Possible alterations in spinal systems containing calcitonin gene-related peptide (CGRP) due to polyarthritis were assessed in rats 3-4 weeks after an intradermal injection of Freund's adjuvant in the low back. The tissue levels of CGRP-like material (CGRPLM) were approximately 50% higher in the dorsal zone of the spinal cord and dorsal root ganglia at both the cervical and lumbar (but not thoracic) segments in polyarthritic rats than in age-paired control animals. In addition the rate of the spinal release of CGRPLM determined through an intrathecal perfusion procedure in halothane-anaesthetized animals was approximately 15-fold higher in polyarthritic rats than in controls. The blockade of mu-opioid receptors by intrathecal perfusion with 10 microM naloxone produced a larger increase in the spontaneous CGRPLM outflow in polyarthritic rats than in age-paired controls. Furthermore, the stimulation of mu-opioid receptors by intrathecal perfusion with 10 microM DAGO significantly inhibited the spinal outflow of CGRPLM only in polyarthritic rats. These data indicate that CGRP-containing primary afferent fibres are markedly activated in chronic suffering polyarthritic rats. This activation occurs in spite of an increased tonic inhibitory control by endogenous opioids acting at mu receptors.

A novel class of cardiotonic agents: synthesis and biological evaluation of pyridazino[4,5-b]indoles with cyclic AMP phosphodiesterases inhibiting properties

Some fused pyridazino[4,5-b]indoles (7) were synthesized. These new compounds present a planar topography and some resemblance to carbazeram, imadozan, and other pyridazino agents with cardiotonic activity. These compounds also possess a complementary effect as inhibitors of platelet aggregation. 6-(3,5-Dimethylpyrazolyl)-1,2,4-triazolo[4,3-b]pyridazino[4, 5-b]indole (7a) has a good profile as an inodilatador with antiaggregate activity due to the inhibition of phosphodiesterase.

Opioid control of the release of calcitonin gene-related peptide-like material from the rat spinal cord in vivo

The possible control by opioids of the spinal release of calcitonin gene-related peptide-like material (CGRPLM) was investigated in halothane-anaesthetized rats whose intrathecal space was perfused with an artificial cerebrospinal fluid. Morphine (20 mg/kg i.v.; or at 10-100 microM added to the perfusing fluid), the mu selective agonist DAGO (10 microM) and the kappa selective agonist U 50488 H (10 microM) did not affect the spontaneous outflow of the CGRPLM. In contrast, the selective delta agonist DTLET (10 microM) significantly increased CGRPLM release. The latter effect could be prevented by the selective delta antagonist naltrindole (10 microM) as expected from the involvement of this class of opioid receptors. However, the addition of naltrindole alone to the perfusing fluid did not modify CGRPLM outflow, indicating that endogenous opioids do not exert a tonic control of CGRP-containing fibers through the stimulation of delta receptors. In contrast, intrathecal perfusion with naloxone (10 microM) or nor-binaltorphimine (10 microM), a selective antagonist of kappa receptors, produced a marked increase in spinal CGRPLM release, suggesting that endogenous opioids acting at mu and kappa receptors, respectively, exert a tonic inhibitory control of CGRP-containing fibers. Indeed, a significant decrease in the spinal release of CGRPLM release could be evoked by the combined addition of U 50488 H (10 microM) plus DAGO (10 microM) to the perfusing medium, indicating that the simultaneous stimulation of both kappa and mu receptors is required for this negative control to occur. This could notably be achieved with morphine (10 microM) in the presence of naltrindole (10 microM) which also produced a significant reduction in the spinal release of CGRPLM. In conclusion, morphine per se did not change CGRPLM release because this drug triggers opposite positive (through the stimulation of delta receptors) and negative (through the concomitant stimulation of both kappa and mu receptors) control mechanisms within the rat spinal cord.