Oral post-lesion administration of 5-HT(1A) receptor agonist repinotan hydrochloride (BAY x 3702) attenuates NMDA-induced delayed neuronal death in rat magnocellular nucleus basalis

Resident Astrocytes can Limit Injury to Developing Hippocampal Neurons upon THC Exposure

Cannabis legalization prompted the dilemma if plant-derived recreational drugs can have therapeutic potential and, consequently, how to address their regulation and safe distribution. In parallel, the steady worldwide decriminalization of cannabis and the enhanced content of its main psychoactive compound Δ⁹-tetrahydrocannabinol (THC), exposes populations to increasing amounts of cannabis and THC across all ages. While adverse effects of cannabis during critical stages of fetal neurodevelopment are investigated, these studies center on neurons alone. Thus, a gap of knowledge exists on how intercellular interactions between neighboring cell types, particularly astrocytes and neurons, could modify THC action. Here, we combine transcriptome analysis, transgenic models, high resolution microscopy and live cell imaging to demonstrate that hippocampal astrocytes accumulate in the strata radiatum and lacunosum moleculare of the CA1 subfield, containing particularly sensitive neurons to stressors, upon long term postnatal THC exposure in vivo. As this altered distribution is not dependent on cell proliferation, we propose that resident astrocytes accumulate in select areas to protect pyramidal neurons and their neurite extensions from pathological damage. Indeed, we could recapitulate the neuroprotective effect of astrocytes in vitro, as their physical presence significantly reduced the death of primary hippocampal neurons upon THC exposure (> 5 µM). Even so, astrocytes are also affected by a reduced metabolic readiness to stressors, as reflected by a downregulation of mitochondrial proteins. Thus, we find that astrocytes exert protective functions on local neurons during THC exposure, even though their mitochondrial electron transport chain is disrupted.

Potential Anti-Amnesic Activity of a Novel Multimodal Derivative of Salicylamide, JJGW08, in Mice

Memory impairments constitute a significant problem worldwide, and the COVID-19 pandemic dramatically increased the prevalence of cognitive deficits. Patients with cognitive deficits, specifically memory disturbances, have underlying comorbid conditions such as schizophrenia, anxiety, or depression. Moreover, the available treatment options have unsatisfactory effectiveness. Therefore, there is a need to search for novel procognitive and anti-amnesic drugs with additional pharmacological activity. One of the important therapeutic targets involved in the modulation of learning and memory processes are serotonin receptors, including 5-HT1A, 5-HT6, and 5-HT7, which also play a role in the pathophysiology of depression. Therefore, this study aimed to assess the anti-amnesic and antidepressant-like potential of JJGW08, a novel arylpiperazine alkyl derivative of salicylamide with strong antagonistic properties at 5-HT1A and D2 receptors and weak at 5-HT2A and 5-HT7 receptors in rodents. First, we investigated the compound’s affinity for 5-HT6 receptors using the radioligand assays. Next, we assessed the influence of the compound on long-term emotional and recognition memory. Further, we evaluated whether the compound could protect against MK-801-induced cognitive impairments. Finally, we determined the potential antidepressant-like activity of the tested compound. We found that JJGW08 possessed no affinity for 5-HT6 receptors. Furthermore, JJGW08 protected mice against MK-801-induced recognition and emotional memory deficits but showed no antidepressant-like effects in rodents. Therefore, our preliminary study may suggest that blocking serotonin receptors, especially 5-HT1A and 5-HT7, might be beneficial in treating cognitive impairments, but it requires further investigation.

Augmentation therapy with tandospirone citrate in vascular depression patients with mild cognitive impairment: A prospective randomized clinical trial

Cognitive impairment is a prominent clinical manifestation of vascular depression (VaDep). The current study aimed to assess the efficacy of tandospirone citrate in VaDep cases with mild cognitive impairment (VaDep-MCI) as well as the role of plasma monoamine neurotransmitters during the treatment. In this single-blind, randomized controlled study, 116 participants were randomly assigned to the tandospirone (tandospirone citrate-escitalopram) and control (escitalopram) groups. The primary endpoints were changes in cognitive test scores from baseline to Week 8, including the Rey Auditory Verbal Learning Test (RAVLT), Semantic Verbal Fluency (SVF) test, Trail Making Test (TMT), Digital Span Test (DST) and Clock Drawing Test (CDT) scores. Generalized estimating equation models were used to examine repeated measures. The results showed that compared with the changes in the control group from baseline to Week 8, the tandospirone group showed more significant changes in SVF score at Weeks 4 (p < 0.05) and 8 (p < 0.001), and TMT (B-A) score at Week 8 (p < 0.05). RAVLT, DST and DCT scores were relatively stable in both groups during the study period. Moreover, mediation analysis showed that these results were not mediated by the alleviation of depression symptoms. Partial Spearman correlation analysis showed that only plasma 5-hydroxytryptamine (5-HT) was positively correlated with Hamilton Depression Rating Scale score after Bonferroni correction (r = 0.347, p < 0.001). Augmentation therapy with tandospirone citrate improved the executive and language functions of VaDep-MCI patients. Additionally, plasma 5-HT levels may serve as a potential biomarker of VaDep severity. These findings may provide clinical insights into the treatment of vascular depression.

Immunization with Small Amyloid-β-derived Cyclopeptide Conjugates Diminishes Amyloid-β-Induced Neurodegeneration in Mice

Background: Soluble oligomeric (misfolded) species of amyloid-β (Aβ) are the main mediators of toxicity in Alzheimer’s disease (AD). These oligomers subsequently form aggregates of insoluble fibrils that precipitate as extracellular and perivascular plaques in the brain. Active immunization against Aβ is a promising disease modifying strategy. However, eliciting an immune response against Aβ in general may interfere with its biological function and was shown to cause unwanted side-effects. Therefore, we have developed a novel experimental vaccine based on conformational neo-epitopes that are exposed in the misfolded oligomeric Aβ, inducing a specific antibody response.

Objective: Here we investigate the protective effects of the experimental vaccine against oligomeric Aβ_1-42-induced neuronal fiber loss in vivo.

Methods: C57BL/6 mice were immunized or mock-immunized. Antibody responses were measured by enzyme-linked immunosorbent assay. Next, mice received a stereotactic injection of oligomeric Aβ_1-42 into the nucleus basalis of Meynert (NBM) on one side of the brain (lesion side), and scrambled Aβ_1-42 peptide in the contralateral NBM (control side). The densities of choline acetyltransferase-stained cholinergic fibers origination from the NBM were measured in the parietal neocortex postmortem. The percentage of fiber loss in the lesion side was determined relative to the control side of the brain.

Results: Immunized responders (79%) showed 23% less cholinergic fiber loss (p = 0.01) relative to mock-immunized mice. Moreover, fiber loss in immunized responders correlated negatively with the measured antibody responses (R² = 0.29, p = 0.02).

Conclusion: These results may provide a lead towards a (prophylactic) vaccine to prevent or at least attenuate (early onset) AD symptoms.

Yokukansan and Yokukansankachimpihange Ameliorate Aggressive Behaviors in Rats with Cholinergic Degeneration in the Nucleus Basalis of Meynert

Yokukansan (YKS) and yokukansankachimpihange (YKSCH) are traditional Japanese Kampo medicines. The latter comprises YKS along with the medicinal herbs Citrus unshiu peel and Pinellia tuber. Both of these Kampo medicines are indicated for the treatment of night crying and irritability in children and for neurosis and insomnia in adults. In recent clinical trials, YKS exhibited ameliorative effects on the behavioral and psychological symptoms of dementia, such as aggressiveness, excitement, and irritability. In the present study, we aimed to clarify the involvement of cholinergic degeneration in the nucleus basalis of Meynert (NBM) in the development of aggressiveness in rats. Subsequently, using this animal model, the effects of YKS and YKSCH on aggressiveness were compared and the mechanisms underlying these effects were investigated. L-Glutamic acid (Glu) was injected into the right NBM of rats to induce deterioration of cholinergic neurons. On day 8 after Glu injection, aggressive behaviors were evaluated using resident–intruder tests. After the evaluation, YKS or YKSCH was administered to rats with aggressive behaviors daily for 7 days. In some groups, the 5-HT_1A receptor antagonist WAY-100635 was coadministered with YKS or YKSCH over the same period. In other groups, locomotor activity was measured on days 12–14 after Glu injection. On day 15, immunohistochemistry was then performed to examine choline acetyltransferase (ChAT) activities in the NBM. Aggressive behaviors had developed on day 8 after Glu injection and were maintained until day 15. YKS and YKSCH significantly ameliorated the aggressive behaviors. These suppressive effects were entirely abolished following coadministration of WAY-100635. Finally, the number of ChAT-positive cells in the right NBM was significantly reduced on day 15 after Glu injection, and treatment with YKS or YKSCH did not ameliorate these reduced cell numbers. Our results show that unilateral Glu injections into the NBM of rats leads to the development of aggressive behaviors, which is thought to reflect cholinergic degeneration. YKS and YKSCH treatments ameliorated Glu-induced aggressive behaviors, and these effects were suggested to be mediated by 5-HT_1A receptor stimulation, but not by improvement of cholinergic degeneration.

5-hydroxytryptamine1A (5-HT1A) receptor agonists: A decade of empirical evidence supports their use as an efficacious therapeutic strategy for brain trauma

Traumatic brain injury (TBI) is a significant and enduring health care issue with limited treatment options. While several pre-clinical therapeutic approaches have led to enhanced motor and/or cognitive performance, the benefits of these treatments have not translated to the clinic. One plausible explanation is that the therapies may not have been rigorously evaluated, thus rendering the bench-to-bedside leap premature and subsequently unsuccessful. An approach that has undergone considerable empirical research after TBI is pharmacological targeting of 5-HT1A receptors with agonists such as repinotan HCl, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), and buspirone. The goal of this review is to integrate and interpret the findings from a series of studies that evaluated the efficacy of 5-HT1A receptor agonists on functional, histological, and molecular outcome after acquired brain injury. The overwhelming consensus of this exhaustive review is that a decade of empirical evidence supports their use as an efficacious therapeutic strategy for brain trauma. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Early onset of cognitive impairment is associated with altered synaptic plasticity and enhanced hippocampal GluA1 expression in a mouse model of depression

Memory deficit is a common manifestation of age-related cognitive impairment, of which depression is a frequently occurring comorbidity. Previously, we developed a submissive (Sub) mouse line, validated as a model of depressive-like behavior. Using learning paradigms testing hippocampus-dependent spatial and nonspatial memory, we demonstrate here that Sub mice developed cognitive impairments at earlier age (3 months), compared with wild-type mice. Furthermore, acute hippocampal slices from Sub animals failed to display paired-pulse facilitation, whereas primed burst stimulation elicited significantly enhanced long-term potentiation in region CA1, relative to control mice. Changes in synaptic plasticity were accompanied by markedly reduced hippocampal messenger RNA expression of insulin-like growth factor and brain-derived neurotrophic factor. Finally, we identified markedly elevated protein levels of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA1 in the hippocampi of Sub mice, which was exacerbated with age. Taken together, the results point to a linkage between depressive-like behavior and the susceptibility to develop age-related cognitive impairment, potentially by hippocampal α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated glutamatergic signaling.

A combined therapeutic regimen of buspirone and environmental enrichment is more efficacious than either alone in enhancing spatial learning in brain-injured pediatric rats

Buspirone, a 5-HT1A receptor agonist, and environmental enrichment (EE) enhance cognition and reduce histopathology after traumatic brain injury (TBI) in adult rats, but have not been fully evaluated after pediatric TBI, which is the leading cause of death in children. Hence, the aims of this study were to assess the efficacy of buspirone alone (Experiment 1) and in combination with EE (Experiment 2) in TBI postnatal day-17 male rats. The hypothesis was that both therapies would confer cognitive and histological benefits when provided singly, but their combination would be more efficacious. Anesthetized rats received a cortical impact or sham injury and then were randomly assigned to receive intraperitoneal injections of buspirone (0.08 mg/kg, 0.1 mg/kg, and 0.3 mg/kg) or saline vehicle (1.0 mL/kg) 24 h after surgery and once daily for 16 days (Experiment 1). Spatial learning and memory were assessed using the Morris water maze (MWM) on post-operative days 11-16, and cortical lesion volume was quantified on day 17. Sham controls for each condition were significantly better than all TBI groups. In the TBI groups, buspirone (0.1 mg/kg) enhanced MWM performance versus vehicle and buspirone (0.08 mg/kg and 0.3 mg/kg) (p<0.05) and reduced lesion volume relative to vehicle (p=0.038). In Experiment 2, buspirone (0.1 mg/kg) or vehicle was combined with EE after TBI, and the data were compared to the standard (STD)-housed groups from Experiment 1. EE lead to a significant enhancement of spatial learning and a reduction in lesion size versus STD. Moreover, the combined treatment group (buspirone+EE) performed markedly better than the buspirone+STD and vehicle+EE groups, which suggests an additive effect and supports the hypothesis. The data replicate previous studies assessing these therapies in adult rats. These novel findings may have important rehabilitation-relevant implications for clinical pediatric TBI.

The role of serotonin in memory: interactions with neurotransmitters and downstream signaling

Serotonin, or 5-hydroxytryptamine (5-HT), is found to be involved in many physiological or pathophysiological processes including cognitive function. Seven distinct receptors (5-HT1-7), each with several subpopulations, have been identified for serotonin, which are different in terms of localization and downstream signaling. Because of the development of selective agonists and antagonists for these receptors as well as transgenic animal models of cognitive disorders, our understanding of the role of serotonergic transmission in learning and memory has improved in recent years. A large body of evidence indicates the interplay between serotonergic transmission and other neurotransmitters including acetylcholine, dopamine, γ-aminobutyric acid (GABA) and glutamate, in the neurobiological control of learning and memory. In addition, there has been an alteration in the density of serotonergic receptors in aging and Alzheimer's disease, and serotonin modulators are found to alter the process of amyloidogenesis and exert cognitive-enhancing properties. Here, we discuss the serotonin-induced modulation of various systems involved in mnesic function including cholinergic, dopaminergic, GABAergic, glutamatergic transmissions as well as amyloidogenesis and intracellular pathways.

Traumatic brain injury-induced cognitive and histological deficits are attenuated by delayed and chronic treatment with the 5-HT1A-receptor agonist buspirone

The aim of this study was to evaluate the potential efficacy of the serotonin(1A) (5-HT(1A)) receptor agonist buspirone (BUS) on behavioral and histological outcome after traumatic brain injury (TBI). Ninety-six isoflurane-anesthetized adult male rats were randomized to receive either a controlled cortical impact or sham injury, and then assigned to six TBI and six sham groups receiving one of five doses of BUS (0.01, 0.05, 0.1, 0.3, or 0.5 mg/kg) or saline vehicle (VEH, 1.0 mL/kg). Treatments began 24 h after surgery and were administered intraperitoneally once daily for 3 weeks. Motor function (beam-balance/beam-walk tests) and spatial learning/memory (Morris water maze) were assessed on post-operative days 1-5 and 14-19, respectively. Morphologically intact CA1/CA3 cells and cortical lesion volume were quantified at 3 weeks. No differences were observed among the BUS and VEH sham groups in any end-point measure and thus the data were pooled. Regarding the TBI groups, repeated-measures ANOVAs revealed that the 0.3 mg/kg dose of BUS enhanced cognitive performance relative to VEH and the other BUS doses (p<0.05), but did not significantly impact motor function. Moreover, the same dose conferred selective histological protection as evidenced by smaller cortical lesions, but not greater CA1/CA3 cell survival. No significant behavioral or histological differences were observed among the other BUS doses versus VEH. These data indicate that BUS has a narrow therapeutic dose response, and that 0.3 mg/kg is optimal for enhancing spatial learning and memory in this model of TBI. BUS may have potential as a novel pharmacotherapy for clinical TBI.

Evaluation of a combined therapeutic regimen of 8-OH-DPAT and environmental enrichment after experimental traumatic brain injury

When provided individually, both the serotonin (5-HT(1A))-receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and environmental enrichment (EE) enhance behavioral outcome and reduce histopathology after experimental traumatic brain injury (TBI). The aim of this study was to determine whether combining these therapies would yield greater benefit than either used alone. Anesthetized adult male rats received a cortical impact or sham injury and then were randomly assigned to enriched or standard (STD) housing, where either 8-OH-DPAT (0.1 mg/kg) or vehicle (1.0 mL/kg) was administered intraperitoneally once daily for 3 weeks. Motor and cognitive assessments were conducted on post-injury days 1-5 and 14-19, respectively. CA1/CA3 neurons and choline acetyltransferase-positive (ChAT(+)) medial septal cells were quantified at 3 weeks. 8-OH-DPAT and EE attenuated CA3 and ChAT(+) cell loss. Both therapies also enhanced motor recovery, acquisition of spatial learning, and memory retention, as verified by reduced times to traverse the beam and to locate an escape platform in the water maze, and a greater percentage of time spent searching in the target quadrant during a probe trial in the TBI + STD + 8-OH-DPAT, TBI + EE + 8-OH-DPAT, and TBI + EE + vehicle groups versus the TBI + STD + vehicle group (p ≤ 0.0016). No statistical distinctions were revealed between the TBI + EE + 8-OH-DPAT and TBI + EE + vehicle groups in functional outcome or CA1/CA3 cell survival, but there were significantly more ChAT(+) cells in the former (p = 0.003). These data suggest that a combined therapeutic regimen of 8-OH-DPAT and EE reduces TBI-induced ChAT(+) cell loss, but does not enhance hippocampal cell survival or neurobehavioral performance beyond that of either treatment alone. The findings underscore the complexity of combinational therapies and of elucidating potential targets for TBI.

Repinotan, a selective 5-HT1A-R-agonist, antagonizes morphine-induced ventilatory depression in anesthetized rats

BACKGROUND

Spontaneous breathing during mechanical ventilation improves arterial oxygenation and cardiovascular function, but is depressed by opioids during critical care. Opioid-induced ventilatory depression was shown to be counteracted in anesthetized rats by serotonin(1A)-receptor (5-HT(1A)-R)-agonist 8-OH-DPAT, which cannot be applied to humans. Repinotan hydrochloride is a selective 5-HT(1A)-R-agonist already investigated in humans, but the effects on ventilation and nociception are unknown. In this study, we sought to establish (a) the effects of repinotan on spontaneous breathing and nociception, and (b) the interaction with the standard opiate morphine.

METHODS

The dose-dependent effects of repinotan, given alone or in combination with morphine, on spontaneous minute ventilation (MV) and nociceptive tail-flick reflex latencies (TFLs) were measured simultaneously in spontaneously breathing anesthetized rats. An additional series with NaCl 0.9% and the 5-HT(1A)-R-antagonist WAY 100 135 served as controls.

RESULTS

(a) Repinotan dose-dependently activated spontaneous breathing (MV, mean [95% confidence interval]; 53% [29%-77%]) of pretreatment level) and suppressed nociception (TLF, 91% maximum possible effect [68%-114%]) with higher doses of repinotan (2-200 μg/kg). On the contrary, nociception was enhanced with a small dose of repinotan (0.2 μg/kg; TFL, -47% maximum possible effect [-95% to 2%]). Effects were prevented by 5-HT(1A)-antagonist WAY 100 135. (B) Morphine-induced depression of ventilation (MV, -72% [-100% to -44%]) was reversed by repinotan (20 μg/kg), which returned spontaneous ventilation to pretreatment levels (MV, 18% [-40% to 77%]). The morphine-induced complete depression of nociception was sustained throughout repinotan and NaCl 0.9% administration. Despite a mild decrease in mean arterial blood pressure, there were no serious cardiovascular side effects from repinotan.

CONCLUSIONS

The 5-HT(1A)-R-agonist repinotan activates spontaneous breathing in anesthetized rats even in morphine-induced ventilatory depression. The potency of 5-HT(1A)-R-agonists to stimulate spontaneous breathing and their antinociceptive effects should be researched further.

Calpain inhibition prevents amyloid-beta-induced neurodegeneration and associated behavioral dysfunction in rats

Amyloid-beta (Abeta) is toxic to neurons and such toxicity is - at least in part - mediated via the NMDA receptor. Calpain, a calcium dependent cystein protease, is part of the NMDA receptor-induced neurodegeneration pathway, and we previously reported that inhibition of calpain prevents excitotoxic lesions of the cholinergic nucleus basalis magnocellularis of Meynert. The present study reveals that inhibition of calpain is also neuroprotective in an in vivo model of Abeta oligomer-induced neurodegeneration in rats. Abeta-induced lesions of the nucleus basalis induced a significant decrease in the number of cholinergic neurons and their projecting fibers, as determined by analysis of choline-acetyltransferase in the nucleus basalis magnocellularis and cortical mantle of the lesioned animals. Treatment with the calpain inhibitor A-705253 significantly attenuated cholinergic neurodegeneration in a dose-dependent manner. Calpain inhibition also significantly diminished the accompanying neuroinflammatory response, as determined by immunohistochemical analysis of microglia activation. Administration of beta-amyloid markedly impaired performance in the novel object recognition test. Treatment with the calpain inhibitor, A-705253, dose-dependently prevented this behavioral deficit. In order to determine whether pre-treatment with the calpain inhibitor is necessary to exhibit its full protective effect on neurons we induced Abeta toxicity in primary neuronal cultures and administered A-705253 at various time points before and after Abeta oligomer application. Although the protective effect was higher when A-705253 was applied before induction of Abeta toxicity, calpain inhibition was still beneficial when applied up to 1h post-treatment. We conclude that inhibition of calpains may represent a valuable strategy for the prevention of Abeta oligomer-induced neuronal decline and associated cognitive deterioration.

Effect of selective serotonin re-uptake inhibitors (SSRIs) on functional outcome in patients with acute ischemic stroke treated with tPA

BACKGROUND

Selective serotonin re-uptake inhibitors (SSRIs) may have therapeutic potential in the treatment of ischemic stroke by effects on neuronal cell survival and the plasticity of brain processes. In the present study, we investigated whether prior treatment with a SSRI is associated with more favorable functional outcome in a cohort of patients with acute ischemic stroke treated with tissue plasminogen activator (tPA).

METHODS

In a prospective observational cohort study of 476 acute ischemic stroke patients treated with tPA we investigated the relationship between prior SSRI treatment and functional outcome at 3 months. Ischemic stroke subtypes were defined according to the Oxfordshire Community Stroke Project Classification. Favorable outcome was defined as a modified Rankin Scale score <or=2.

RESULTS

In the cohort of 476 patients, 22 (5%) patients used a SSRI at stroke onset. At 3 months, 217 (46%) patients had a favorable outcome of whom 9 (41%) on SSRI treatment and 208 (46%) not using SSRIs (p=0.65). In a multivariable analysis SSRI treatment showed a trend to association with unfavorable outcome (OR 0.4, 95% CI 0.14-1.13, p=0.08). In the 376 patients with cortical stroke, SSRI treatment was associated with an unfavorable outcome (OR 0.17, 95% CI 0.04-0.73, p=0.017).

CONCLUSION

Our data suggest that in patients with acute ischemic stroke treated with tPA, prior SSRI use may be associated with a less favorable outcome, especially in cortical stroke.

Anticonvulsive effects of the dopamine agonist lisuride maleate after experimental traumatic brain injury

Traumatic brain injury is a heterogeneous disease, encompassing a wide range of pathologies. The dopamine agonist lisuride is well established in the therapy of Parkinson's disease. Additionally to its dopaminergic effects it decreases prolactine release, reducing the amount of inflammatory mediators such as TNF-alpha or Il-6. Lisuride has strong binding affinity to serotonergic and histaminergic receptors on neuronal and glial cells leading to scavenging of highly reactive free radicals. Due to its interaction with dopaminergic D2 and D4 receptors as well as 5-HT-1A receptors, NMDA-receptor signaling and glutamate-mediated excitotoxicity can be modulated beneficially. Despite of these promising neuroprotective effects, experimental data scrutinizing the effects of lisuride after acute brain injury are sparse. We therefore investigated the effect of lisuride after controlled cortical impact injury (CCII) in rats. 70 male Sprague-Dawley rats were randomized to lisuride or to placebo treatment by an initial s.c. loading dose (0.3mg/kg BW) and following continuous application (0.5mg/kg/d) by s.c. implanted osmotic pumps. In three experimental groups we determined (sub)acute neuro-physiological changes after trauma. Mean arterial blood pressure, intracranial pressure, and electrical brain activity were monitored acutely for up to 3h after trauma. Brain edema formation was assessed 24h after CCII. Furthermore, contusion volumes were quantified by magnetic resonance tomography and neurological testing was performed for up to 7 days after injury. Associated with the administration of lisuride there was a significant reduction in duration and number of post-traumatic seizures. Despite of a sustained arterial hypotension following the initial bolus administration in the treatment group, contusion volumes and neurological function tests did not differ significantly in comparison to the control group. Overall, lisuride seems to have significant anticonvulsive effects but seems not to influence secondary brain damage in this experimental model.

Neither in vivo MRI nor behavioural assessment indicate therapeutic efficacy for a novel 5HT(1A) agonist in rat models of ischaemic stroke

Background

5HT_1A agonists have previously been shown to promote recovery in animal models of stroke using ex vivo outcome measures which have raised the hopes for a potential clinical implementation. The purpose of this study was to evaluate the potential neuroprotective properties of a novel 5HT_1A agonist DU123015 in 2 different models of transient focal ischaemic stroke of varying severities using both in vivo neuroimaging and behavioural techniques as primary outcome measures. For these studies, the NMDA receptor antagonist MK-801 was also utilized as a positive control to further assess the effectiveness of the stroke models and techniques used.

Results

In contrast to MK-801, no significant therapeutic effect of DU123015 on lesion volume in either the distal MCAo or intraluminal thread model of stroke was found. MK-801 significantly reduced lesion volume in both models; the mild distal MCAo condition (60 min ischaemia) and the intraluminal thread model, although it had no significant impact upon the lesion size in the severe distal MCAo condition (120 min ischaemia). These therapeutic effects on lesion size were mirrored on a behavioural test for sensory neglect and neurological deficit score in the intraluminal thread model.

Conclusion

This study highlights the need for a thorough experimental design to test novel neuroprotective compounds in experimental stroke investigations incorporating: a positive reference compound, different models of focal ischaemia, varying the duration of ischaemia, and objective in vivo assessments within a single study. This procedure will help us to minimise the translation of less efficacious compounds.

5-HT(1A) receptor function in major depressive disorder

Dysfunction of the serotonin 1A receptor (5-HT(1A)) may play a role in the genesis of major depressive disorder (MDD). Here we review the pharmacological, post-mortem, positron emission tomography (PET), and genetic evidence in support of this statement. We also touch briefly on two MDD-associated phenotypes, cognitive impairment and somatic pain. The results of pharmacological challenge studies with 5-HT(1A) receptor agonists are indicative of blunted endocrine responses in depressed patients. Lithium, valproate, selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs), and other treatment, such as electroconvulsive shock therapy (ECT), all increase post-synaptic 5-HT(1A) receptor signaling through either direct or indirect effects. Reduced somatodendritic and postsynaptic 5-HT(1A) receptor numbers or affinity have been reported in some post-mortem studies of suicide victims, a result consistent with well-replicated PET analyses demonstrating reduced 5-HT(1A) receptor binding potential in diverse regions such as the dorsal raphe, medial prefrontal cortex (mPFC), amygdala and hippocampus. 5-HT(1A) receptor knockout (KO) mice display increased anxiety-related behavior, which, unlike in their wild-type counterparts, cannot be rescued with antidepressant drug (AD) treatment. In humans, the G allele of a single nucleotide polymorphism (SNP) in the 5-HT(1A) receptor gene (HTR1A; rs6295), which abrogates a transcription factor binding site for deformed epidermal autoregulatory factor-1 (Deaf-1) and Hes5, has been reported to be over-represented in MDD cases. Conversely, the C allele has been associated with better response to AD drugs. We raise the possibility that 5-HT(1A) receptor dysfunction represents one potential mechanism underpinning MDD and other stress-related disorders.

A delayed and chronic treatment regimen with the 5-HT1A receptor agonist 8-OH-DPAT after cortical impact injury facilitates motor recovery and acquisition of spatial learning

An early (i.e., 15min) single systemic administration of the 5-HT(1A) receptor agonist 8-OH-DPAT enhances behavioral recovery after experimental traumatic brain injury (TBI). However, acute administration of pharmacotherapies after TBI may be clinically challenging and thus the present study sought to investigate the potential efficacy of a delayed and chronic 8-OH-DPAT treatment regimen. Forty-eight isoflurane-anesthetized adult male rats received either a controlled cortical impact or sham injury and beginning 24h later were administered 8-OH-DPAT (0.1 or 0.5mg/kg) or saline vehicle (1.0mL/kg) intraperitoneally once daily until all behavioral assessments were completed. Neurobehavior was assessed by motor and cognitive tests on post-operative days 1-5 and 14-19, respectively. The lower dose of 8-OH-DPAT (0.1mg/kg) enhanced motor performance, acquisition of spatial learning, and memory retention vs. both the higher dose (0.5mg/kg) and vehicle treatment (p<0.05). These data replicate previous findings from our laboratory showing that 8-OH-DPAT improves neurobehavior after TBI, and extend those results by demonstrating that the benefits can be achieved even when treatment is withheld for 24h. A delayed and chronic treatment regimen may be more clinically feasible.

Serotonin 5-hT1A receptor activation prevents phosphorylation of NMDA receptor NR1 subunit in cerebral ischemia

The mechanisms involved in the neuroprotective effect of serotonin 5-HT1A receptor agonists on brain damage induced by ischemia remain 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, this study 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 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. 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-HT1A receptor agonist. The results suggest that NR1 subunit phosphorylation plays a role in the neuroprotective effect of 8-OH-DPAT on cell damage induced by global cerebral ischemia in the gerbil hippocampus and support the potential interest of 5-HT1A receptor activation in the search for neuroprotective strategies.

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.

Brain-derived neurotrophic factor selectively regulates dendritogenesis of parvalbumin-containing interneurons in the main olfactory bulb through the PLCgamma pathway

Molecular mechanisms of neurotrophin signaling on dendrite development and dynamics are only partly understood. To address the role of brain-derived neurotrophic factor (BDNF) in the morphogenesis of GABAergic neurons of the main olfactory bulb, we analyzed mice lacking BDNF, mice carrying neurotrophin-3 (NT3) in the place of BDNF, and TrkB signaling mutant mice with a receptor that can activate phospholipase Cgamma (PLCgamma) but is unable to recruit the adaptors Shc/Frs2. BDNF deletion yielded a compressed olfactory bulb with a significant loss of parvalbumin (PV) immunoreactivity in GABAergic interneurons of the external plexiform layer. Dendrite development of PV-positive interneurons was selectively attenuated by BDNF since other Ca2+ -binding protein-containing neuron populations appeared unaffected. The deficit in PV-positive neurons could be rescued by the NT3/NT3 alleles. The degree of PV immunoreactivity was dependent on BDNF and TrkB recruitment of the adaptor proteins Shc/Frs2. In contrast, PLCgamma signaling from the TrkB receptor was sufficient for dendrite growth in vivo and consistently, blocking PLCgamma prevented BDNF-dependent dendrite development in vitro. Collectively, our results provide genetic evidence that BDNF and TrkB signaling selectively regulate PV expression and dendrite growth in a subset of neurochemically-defined GABAergic interneurons via activation of the PLCgamma pathway.

Targeting cell death in dementia

Neuronal degeneration is a key feature of both Alzheimer disease (AD) and vascular dementia (VaD). Although the exact cause(s) of neurodegeneration in AD is uncertain, strong candidates are beta-amyloid and neurofibrillary tangles (NFT) within neurons. VaD arises as a consequence of ischemic insults such as hemorrhage and hypoperfusion that trigger neurodegeneration by depriving the cells of oxygen and glucose. The initial insults in AD and VaD result in regional differences in the pattern of neurodegeneration, with cholinergic and glutamatergic neurons being particularly vulnerable in AD, and neurons of whatever neurochemical phenotype close to the vascular insult being more at risk of death in VaD. Although the initial trigger of neurodegeneration and the population of neurons affected differ in AD and VaD, there is considerable overlap in the downstream pathways that mediate cell death. As a consequence there are, therefore, a number of levels in the cytotoxic pathway common to AD and VaD at which a neuroprotective agent might be targeted.

Possible Mechanisms of Neurodegeneration in Schizophrenia

Brain morphological alterations in schizophrenic patients have led to the neurodevelopmental hypothesis of schizophrenia. On the other hand, a progressive neurodegenerative process has also been suggested and some follow-up studies have shown progressive morphological changes in schizophrenic patients. Several neurotransmitter systems have been suggested to be involved in this disorder and some of them could lead to neuronal death under certain conditions. This review discusses some of the biochemical pathways that could lead to neurodegeneration in schizophrenia showing that neuronal death may have a role in the etiology or natural course of this disorder.

A review of the neuroprotective properties of the 5-HT1A receptor agonist repinotan HCl (BAYx3702) in ischemic stroke

Repinotan HCl (repinotan, BAYx3702), a highly selective 5-HT1A receptor agonist with a good record of safety was found to have pronounced neuroprotective effects in experimental models that mimic various aspects of brain injury. Repinotan caused strong, dose-dependent infarct reductions in permanent middle cerebral artery occlusion, transient middle cerebral artery occlusion, and traumatic brain injury paradigms. The specific 5-HT1A receptor antagonist WAY 100635 blocked these effects, indicating that the neuroprotective properties of repinotan are mediated through the 5-HT1A receptor. The proposed neuroprotective mechanisms of repinotan are thought to be the result of neuronal hyperpolarization via the activation of G protein-coupled inwardly rectifying K+ channels upon binding to both pre- and post-synaptic 5-HT1A receptors. Hyperpolarization results in inhibition of neuron firing and reduction of glutamate release. These mechanisms, leading to protection of neurons against overexcitation, could explain the neuroprotective efficacy of repinotan per se, but not necessarily the efficacy by delayed administration. The therapeutic time window of repinotan appeared to be at least 5 h in in vivo animal models, but may be even longer at higher doses of the drug. Experimental studies indicate that repinotan affects various mechanisms involved in the pathogenesis of brain injury. In addition to the direct effect of repinotan on neuronal hyperpolarization and suppression of glutamate release this compound affects the death-inhibiting protein Bcl-2, serotonergic glial growth factor S-100beta and Nerve Growth Factor. It also suppresses the activity of caspase-3 through MAPK and PKCalpha; this effect may contribute to its neuroprotective efficacy. The dose- and time-dependent neuroprotective efficacy of repinotan indicates that the drug is a promising candidate for prevention of secondary brain damage in brain-injured patients suffering from acute ischemic stroke. Unfortunately, however, the first, randomized, double blind, placebo-controlled clinical trial did not demonstrate the efficacy of repinotan in acute ischemic stroke.

5-HT1A receptor agonist-mediated protection from MPTP toxicity in mouse and macaque models of Parkinson's disease

Excitotoxicity-mediated cell death is involved in Parkinson's disease (PD). 5-HT1A receptor agonists can protect from such mechanisms. The current study demonstrates that the 5-HT1A agonists BAY 639044 and repinotan have neuroprotective effects in a subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. In addition, we also show that both compounds delay the appearance of parkinsonian motor abnormalities in a MPTP monkey model that recapitulates the progressive nature of PD. Thus, BAY 639044 or repinotan treatment was initiated when there was 30% neuronal death in the substantia nigra pars compacta, and nerve terminal loss in the striatum was 40%, i.e., compatible with the clinical situation where early symptomatic patients would receive such a treatment. The delay in appearance of parkinsonian motor abnormalities is a consequence of partial neuroprotection of nigrostriatal dopamine neurons, both at neuronal and terminal levels as shown for BAY 639044. These results suggest that 5-HT1A agonists, such as BAY 639044, may protect from neurodegeneration and delay the worsening of motor symptoms in Parkinson patients.

Functional Pharmacology in Human Brain

Most neurological and psychiatric disorders involve selective or preferential impairments of neurotransmitter systems. Therefore, studies of functional transmitter pathophysiology in human brain are of unique importance in view of the development of effective, mechanism-based, therapeutic modalities. It is well known that central nervous system functional proteins, including receptors, transporters, ion channels, and enzymes, can exhibit high heterogeneity in terms of structure, function, and pharmacological profile. If the existence of types and subtypes of functional proteins amplifies the possibility of developing selective drugs, such heterogeneity certainly increases the likelihood of interspecies differences. It is therefore essential, before choosing animal models to be used in preclinical pharmacology experimentation, to establish whether functionally corresponding proteins in men and animals also display identical pharmacological profiles. Because of evidence that scaffolding proteins, trafficking between plasma membrane and intracellular pools, phosphorylation and allosteric modulators can affect the function of receptors and transporters, experiments with human clones expressed in host cells where the environment of native receptors is rarely reproduced should be interpreted with caution. Thus, the use of neurosurgically removed fresh human brain tissue samples in which receptors, transporters, ion channels, and enzymes essentially retain their natural environment represents a unique experimental approach to enlarge our understanding of human brain processes and to help in the choice of appropriate animal models. Using this experimental approach, many human brain functional proteins, in particular transmitter receptors, have been characterized in terms of localization, function, and pharmacological properties.

Neuroprotective efficacy of repinotan HCl, a 5-HT1A receptor agonist, in animal models of stroke and traumatic brain injury

Repinotan is a highly potent 5-HT1A receptor agonist with strong neuroprotective efficacy in animal models of middle cerebral artery occlusion and traumatic brain injury. In this study, we characterized the time window for neuroprotective effects of repinotan in animal models. In the permanent middle cerebral artery occlusion model, repinotan showed neuroprotective efficacy when administered as a triple bolus injection (0.3-100 microg/kg) or an intravenous infusion (0.3-100 microg/kg per hour). A 73% reduction in infarct volume was observed with a 3 microg/kg intravenous bolus, and a 65% reduction was observed with a 3 and 10 microg/kg per hour intravenous infusion. When delayed until 5 hours after occlusion, repinotan (10 microg/kg per hour) reduced infarct volume by 43%. In the transient middle cerebral artery occlusion model, repinotan (10 microg/kg per hour) administered immediately after occlusion reduced infarct volume by 97%, and a delay to 5 hours reduced infarct volume by 81%. In the acute subdural hematoma model, repinotan (3 and 10 microg/kg per hour) reduced infarct volume by 65%. In this model, repinotan (3 microg/kg per hour) administered 5 hours after occlusion reduced infarct volume by 54%. The favorable neuroprotective efficacy, broad dose-response curve, and prolonged therapeutic window observed in all models strongly suggest that repinotan is a promising candidate for treating acute ischemic stroke in humans.

Effects of Lesopitron on the Central Nervous System Arising from Its Interaction with 5-HT1A Receptors

Lesopitron acts as a ligand for central serotonin 5-HT1A receptors. Ki obtained from [3H]8-OH-DPAT competition studies was 104.8 +/- 10.6 nmol/l. As lesopitron did not affect the binding of [3H]paroxetine, involvement of the serotonin reuptake system in the effects of lesopitron is rejected. Lesopitron inhibits haloperidol-induced catalepsy that is the consequence of its action on 5-HT1A autoreceptors. The ability of lesopitron to induce 5-HT syndrome reflects post-synaptic 5-HT1A receptor activation and the reversion of 8-OHDPAT-induced 5-HT syndrome by lesopitron suggests a partial agonist effect on this receptor-type. Lesopitron induced a hypothermic effect due to the enhanced activation of post-synaptic 5-HT1A receptors. The agonist effect of lesopitron on 5-HT1A receptors and its marked hypothermic effect is an added value for this drug and a stimulus to the study of its possible neuroprotective action.

Synthesis and structure–activity relationships of a new model of arylpiperazines. Part 7: Study of the influence of lipophilic factors at the terminal amide fragment on 5-HT1A affinity/selectivity

The influence of lipophilic factors at the amide fragment of a new series of (+/-)-7a-alkyl-2-[4-(4-arylpiperazin-1-yl)butyl]-1,3-dioxoperhydropyrrolo[1,2-c]imidazoles 2 and of (+/-)-7a-alkyl-2-[(4-arylpiperazin-1-yl)methyl]-1,3-dioxoperhydropyrrolo[1,2-c]imidazoles 3 has been studied. Variations of logP have been carried out by introducing different hydrocarbonated substituents (R(1)) at the position 7a of the bicyclohydantoin, namely the non-pharmacophoric part. All the new compounds exhibit high potency for the 5-HT(1A) receptor; however, affinities for the alpha(1) receptor are high for compounds 2a-l while compounds 3a-f are selective over this adrenergic receptor. On the other hand, differences in logP do not notably affect the K(i) values for the above receptors.

p-Chloroamphetamine blocks physostigmine-induced memory enhancement in rats with unilateral nucleus basalis lesions

The present experiment examined whether p-chloroamphetamine (PCA), a serotonergic releasing/depleting agent, would block the memory-enhancing effect of physostigmine in rats with N-methyl-D-aspartic acid (NMDA)-induced unilateral lesions of the nucleus basalis of Meynert (uni-nbM). Six groups of subjects with uni-nbM lesions in addition to an isolated sham-operated control group were included. Subjects were trained and tested 72 h later on a one-trial passive avoidance task. Thirty minutes before training, rats with uni-nbM lesions were injected with either 1.0 or 5.0 mg/kg PCA or saline. Immediately after training, approximately half the subjects in each group were injected with either saline or 0.06 mg/kg physostigmine. Animals in the sham group received saline injections. Saline-injected animals with uni-nbM lesions performed poorly at test, a deficit that was reversed with physostigmine. Pretraining injections of PCA blocked physostigmine's memory-enhancing effect, although motor impairment during training may have contributed to decrements in test performance in animals injected with 5.0 mg/kg. Subjects were killed about 10 days later and their frontal cortices examined for choline acetyltransferase (ChAT). Results from the neurochemical analysis revealed that the lesion decreased ChAT levels and that the injection of 1.0 mg/kg PCA exaggerated this lesion-induced depletion. Implications for the interaction between acetylcholine and serotonin are discussed.

Enantioselective synthesis of 2- and 3-substituted 2,3-dihydro[1,4]dioxino[2,3-b]pyridine derivatives and enantiomeric purity control by capillary electrophoresis

A rapid and simple procedure for enantioselective preparation of 2- and 3-substituted 2,3-dihydro[1,4]dioxino[2,3-b]pyridine derivatives (A and B, respectively) is described. The enantiomeric purity of each isomer was determined by capillary electrophoresis using a dual-cyclodextrin system (S-beta-CD/beta-CD) dissolved in formic acid-ammonia buffer (pH 4, ionic strength 50 mM).

Synthesis of 3-Aminochroman Derivatives by Radical Cyclization

[reaction: see text] Enantiomerically pure 5-acetyl-3-amino-3,4-dihydro-2H-1-benzopyran and methyl 3-amino-3,4-dihydro-2H-1-benzopyran-5-carboxylate were successfully synthesized starting from d- or l-serine. The formation of the benzopyran ring involved a radical cyclization step. The enantiomeric purities of the final aminochroman derivatives were determined by capillary electrophoresis using beta-cyclodextrins as a chiral selector.

Rabbit forebrain cholinergic system: morphological characterization of nuclei and distribution of cholinergic terminals in the cerebral cortex and hippocampus

Although the rabbit brain, in particular the basal forebrain cholinergic system, has become a common model for neuropathological changes associated with Alzheimer's disease, detailed neuroanatomical studies on the morphological organization of basal forebrain cholinergic nuclei and on their output pathways are still awaited. Therefore, we performed quantitative choline acetyltransferase (ChAT) immunocytochemistry to localize major cholinergic nuclei and to determine the number of respective cholinergic neurons in the rabbit forebrain. The density of ChAT-immunoreactive terminals in layer V of distinct neocortical territories and in hippocampal subfields was also measured. Another cholinergic marker, the low-affinity neurotrophin receptor (p75(NTR)), was also employed to identify subsets of cholinergic neurons. Double-immunofluorescence labeling of ChAT and p75(NTR), calbindin D-28k (CB), parvalbumin, calretinin, neuronal nitric oxide synthase (nNOS), tyrosine hydroxylase, or substance P was used to elucidate the neuroanatomical borders of cholinergic nuclei and to analyze the neurochemical complexity of cholinergic cell populations. Cholinergic projection neurons with heterogeneous densities were found in the medial septum, vertical and horizontal diagonal bands of Broca, ventral pallidum, and magnocellular nucleus basalis (MBN)/substantia innominata (SI) complex; cholinergic interneurons were observed in the caudate nucleus, putamen, accumbens nucleus, and olfactory tubercule, whereas the globus pallidus was devoid of cholinergic nerve cells. Cholinergic interneurons were frequently present in the hippocampus and to a lesser extent in cerebral cortex. Cholinergic projection neurons, except those localized in SI, abundantly expressed p75(NTR), and a subset of cholinergic neurons in posterior MBN was immunoreactive for CB and nNOS. A strict laminar distribution pattern of cholinergic terminals was recorded both in the cerebral cortex and in CA1-CA3 and dentate gyrus of the hippocampus. In summary, the structural organization and chemoarchitecture of rabbit basal forebrain may be considered as a transition between that of rodents and that of primates.

Design and synthesis of S-(-)-2-[[4-(napht-1-yl)piperazin-1-yl]methyl]-1,4-dioxoperhydropyrrolo[1,2-a]pyrazine (CSP-2503) using computational simulation. A 5-HT1A receptor agonist

Based on a computational model for 5-HT(1A)R-ligand interaction and QSAR studies, we have designed and synthesized a new series of arylpiperazines 2-8 which exhibit high 5-HT(1A)R affinity and selectivity over alpha(1)-adrenergic receptors. Among them, compound CSP-2503 (4) has been pharmacologically characterized as a 5-HT(1A)R agonist at somatodendritic and postsynaptic sites, endowed with anxiolytic properties.

5-hydroxytryptamine 1A receptor activation protects against N-methyl-D-aspartate-induced apoptotic cell death in striatal and mesencephalic cultures

Apoptosis and glutamate-mediated excitotoxicity may play a role in the pathogenesis of many neurodegenerative disorders, including Parkinson's disease (PD). In the present study, we investigated whether stimulation of the 5-hydroxytryptamine 1A (5-HT1A) receptor attenuates N-methyl-D-aspartate- (NMDA) and 1-methyl-4-phenylpyridinium (MPP(+))-induced apoptotic cell death in cell culture models. A brief exposure (20 min) of M213-2O striatal cells to NMDA and glutamate produced a delayed increase in caspase-3 activity and DNA fragmentation in a dose- and time-dependent manner. NMDA-induced caspase-3 activity and DNA fragmentation were almost completely blocked by the 5-HT1A agonists 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and (R)-5-fluoro-8 hydroxy-2-(dipropylamino)-tetralin (R-UH-301). Additionally, the protective effects of 8-OH-DPAT and R-UH-301 on NMDA-induced caspase-3 activation and apoptosis were reversed by pretreatment with the 5-HT1A antagonists N-[2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl]-N-(2-pyridinyl) cyclohexane carboxamide (WAY 100635) and S-UH-301, respectively. Similarly, dose- and time-dependent increases in caspase-3 activity and DNA fragmentation were observed in rat primary mesencephalic neurons after a brief exposure to NMDA and glutamate. Caspase-3 activation and DNA fragmentation in primary mesencephalic neurons were almost completely inhibited by 8-OH-DPAT. This neuroprotective effect of 8-OH-DPAT was reversed by WAY 100635. Additionally, 8-OH-DPAT blocked tyrosine hydroxylase (TH)-positive cell death after NMDA exposure and also almost completely attenuated the NMDA-induced Ca(2+) influx in primary mesencephalic cultures. Furthermore, 8-OH-DPAT and R-UH-301 blocked apoptotic cell death in the primary mesencephalic neurons that were exposed to the Parkinsonian toxin MPP(+). Together, these results suggest that 5-HT1A receptor stimulation may be a promising pharmacological approach in the development of neuroprotective agents for PD.

Functional recovery of cholinergic basal forebrain neurons under disease conditions: old problems, new solutions?

Recognition of the involvement of cholinergic neurons in the modulation of cognitive functions and their severe dysfunction in neurodegenerative disorders, such as Alzheimer's disease, initiated immense research efforts aimed at unveiling the anatomical organization and cellular characteristics of the basal forebrain (BFB) cholinergic system. Concomitant with our unfolding knowledge about the structural and functional complexity of the BFB cholinergic projection system, multiple pharmacological strategies were introduced to rescue cholinergic nerve cells from noxious attacks; however, a therapeutic breakthrough is still awaited. In this review, we collected recent findings that significantly contributed to our better understanding of cholinergic functions under disease conditions, and to the design of effective means to restore lost or damaged cholinergic functions. To this end, we first provide a brief survey of the neuroanatomical organization of BFB nuclei with emphasis on major evolutionary differences among mammalian species, in particular rodents and primates, and discuss limitations of the translation of experimental data to human therapeutic applications. Subsequently, we summarize the involvement of cholinergic dysfunction in the pathogenesis of severe neurological conditions, including stroke, traumatic brain injury, virus encephalitis and Alzheimer's disease, and emphasize the critical role of pro-inflammatory cytokines as common mediators of cholinergic neuronal damage. Moreover, we review leading functional concepts on the limited recovery of cholinergic neurons and their impaired plastic re-modeling, as well as on the hampered interplay of the ascending cholinergic and monoaminergic projection systems under neurodegenerative conditions. In addition, recent advances in the dynamic labeling of living cholinergic neurons by fluorochromated antibodies, referred to as in vivo labeling, and novel neuroimaging approaches as potential diagnostic tools of progressive cholinergic decline are surveyed. Finally, the potential of cell replacement strategies using embryonic and adult stem cells, and multipotent neural progenitors, as a means to recover damaged cholinergic functions, is discussed.

Post-lesion administration of 5-HT1A receptor agonist 8-OH-DPAT protects cholinergic nucleus basalis neurons against NMDA excitotoxicity

Recent evidence indicates that serotonin (5-HT)1A receptor agonists may abrogate excitotoxic brain damage. We investigated whether a single i.p. injection of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), at a dose of 2.5 mg/kg, protects cholinergic neurons of the rat magnocellular nucleus basalis (MBN) against NMDA excitotoxicity when administered at post-injury intervals ranging from 6 to 96 h. Drug effects on passive avoidance learning and on the density of cortical cholinergic innervation, a measure of neuronal survival in the damaged MBN, were analyzed. Our results demonstrate that 8-OH-DPAT, when administered up to 24 h post-lesion, significantly attenuates both behavioral and neuroanatomical consequences of NMDA excitotoxicity on cholinergic MBN neurons; and support the hypothesis that 5-HT1A receptor agonists may interfere with delayed neuronal death in vivo that is of significance in the pharmacological treatment of neurological disorders associated with excitotoxic neuronal damage.

Distinct subsets of nucleus basalis neurons exhibit similar sensitivity to excitotoxicity

Excitotoxic lesions in the magnocellular nucleus basalis (MBN) lead to a significant damage of cholinergic neurons concomitant with increased amyloid precursor protein (APP) expression in the cerebral cortex. However, the sensitivity of non-cholinergic neurons to excitotoxicity, and changes of APP expression in the damaged MBN are still elusive. Hence, we performed multiple-labeling immunocytochemistry for choline-acetyltransferase (ChAT), neuron-specific nuclear protein (NeuN) and APP 4, 24, and 48 h after NMDA infusion in the MBN. Whereas all cholinergic neurons were immunoreactive for NeuN, this neuronal marker also labeled a population of ChAT-immunonegative non-cholinergic neurons. Both neuron populations exhibited a similar degree of sensitivity to NMDA excitotoxicity that became evident as early as 4 h post-lesion. Cholinergic MBN neurons showed abundant APP immunoreactivity (approximately 90%), while only a fraction (approximately 20-30%) of non-cholinergic neurons expressed the protein. Remarkably, cholinergic but not non-cholinergic neurons retained their APP immunoreactivity after NMDA infusion. In conclusion, cholinergic MBN neurons are not preferentially sensitive to short-term excitotoxicity, but are one of the major sources of APP in the basal forebrain.