Increased binding to 5-HT1A and 5-HT2A receptors is associated with large vessel infarction and relative preservation of cognition

Vascular dementia accounts for approximately 15-20% of all dementias. In addition, a significant subset of people with Alzheimer's disease have concurrent cerebrovascular disease. Vascular dementia is caused by different cerebrovascular morphological abnormalities including large artery territory infarction (multi-infarct vascular dementia) and sub-cortical ischaemic vascular dementia. Despite this distinction, there is a lack of studies examining the neurochemistry of individual vascular dementia subtypes. Serotonin is believed to play an important role in cognition, and serotonin receptors may provide a novel target for future anti-dementia therapeutics. This study aimed to determine levels of two serotonin receptors in subtypes of vascular dementia and relate any changes to cognition. We have determined, using saturation radioligand binding, the binding parameters (affinity and maximal binding) of ((3)H)-WAY 100635 binding to 5-HT(1A) receptors and ((3)H)-ketanserin binding to 5-HT(2A) receptors in post-mortem tissue from the frontal and temporal cortices of patients with either multi-infarct vascular dementia, sub-cortical ischaemic vascular dementia, mixed Alzheimer's disease/vascular dementia or stroke no dementia (SND). 5-HT(1A) and 5-HT(2A) receptor binding was significantly increased in the temporal cortex of patients with either multi-infarct vascular dementia or SND, compared to age-matched controls. 5-HT(1A) receptor maximal binding in the temporal cortex was also positively correlated with cognition as determined by Mini-Mental State Examination (MMSE) and Cambridge Assessment of Mental Health for the Elderly scores (CAMCOG). These results reveal an important distinction between the neurochemistry of multi-infarct vascular dementia/SND and sub-cortical ischaemic vascular dementia, suggesting that pharmacological manipulation of serotonin offers the possibility to develop novel therapies for stroke and multi-infarct vascular dementia patients. The results also highlight the importance of the cortical 5-HT(1A) receptor in mediating cognition.

Cortical serotonin 1A receptor levels are associated with depression in patients with dementia with Lewy bodies and Parkinson's disease dementia

BACKGROUND

Serotonin 1A receptors (5-HT(1A)) have not been studied in dementia with Lewy bodies (DLB) or Parkinson's disease dementia (PDD) patients with depression.

AIM

To examine 5-HT(1A) in DLB and PDD postmortem in relation to depression.

METHODS

[(3)H]8-hydroxy-2-dipropylaminotetralin binding to 5-HT(1A) was determined in temporal cortex (Brodmann areas, BA20 and BA36) from 10 DLB patients, 17 PDD patients and 9 controls.

RESULTS

5-HT(1A) density was significantly higher in BA36 in combined DLB/PDD patients with depression, but was unaltered in BA20.

CONCLUSION

Higher BA36 5-HT(1A) density in PDD and DLB patients than in control is dependent on whether the patient had experienced depression during life, not DLB/PDD diagnosis. A 5-HT(1A) antagonist adjuvant may improve treatment of depression in dementia.

Pharmacological profile of essential oils derived from Lavandula angustifolia and Melissa officinalis with anti-agitation properties: focus on ligand-gated channels

Both Melissa officinalis (Mo) and Lavandula angustifolia (La) essential oils have putative anti-agitation properties in humans, indicating common components with a depressant action in the central nervous system. A dual radioligand binding and electrophysiological study, focusing on a range of ligand-gated ion channels, was performed with a chemically validated essential oil derived from La, which has shown clinical benefit in treating agitation. La inhibited [35S] TBPS binding to the rat forebrain gamma aminobutyric acid (GABA)(A) receptor channel (apparent IC50 = 0.040 +/- 0.001 mg mL(-1)), but had no effect on N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or nicotinic acetylcholine receptors. A 50:50 mixture of Mo and La essential oils inhibited [3H] flunitrazepam binding, whereas the individual oils had no significant effect. Electrophysiological analyses with rat cortical primary cultures demonstrated that La reversibly inhibited GABA-induced currents in a concentration-dependent manner (0.01-1 mg mL(-1)), whereas no inhibition of NMDA- or AMPA-induced currents was noted. La elicited a significant dose-dependent reduction in both inhibitory and excitatory transmission, with a net depressant effect on neurotransmission (in contrast to the classic GABA(A) antagonist picrotoxin which evoked profound epileptiform burst firing in these cells). These properties are similar to those recently reported for Mo. The anti-agitation effects in patients and the depressant effects of La we report in neural membranes in-vitro are unlikely to reflect a sedative interaction with any of the ionotropic receptors examined here. These data suggest that components common to the two oils are worthy of focus to identify the actives underlying the neuronal depressant and anti-agitation activities reported.

Involvement of an altered 5-HT -{6} receptor function in behavioral symptoms of Alzheimer's disease

We studied the hypothesis that disturbances in 5-HT_{6} receptor function in the temporal cortex may contribute to clinical symptoms of Alzheimer's disease (AD). 5-HT_{6} density and 5-HT levels were significantly decreased in a cohort of AD patients prospectively assessed for cognitive/behavioral symptoms. cAMP formation after stimulation with the selective 5-HT_{6} receptor agonist E-6801 was significantly lower (p<0.01) in AD (170.02 +/- 27.53 pmol/mg prot.) compared to controls (823.33 +/-196.67). In addition, the ratio cAMP formation after stimulation with E-6801/5-HT_{6} receptor density was significantly lower (p< 0.01) in AD (6.67 +/- 0.83) compared to controls (16.67 +/- 3.33). Splitting these results by sex, 5-HT_{6} receptor activation was significantly lower (p< 0.01) in AD females compared to males (121.67 +/- 30.02 vs. 231.67 +/- 34.17 pmol/mg prot). 5-HT_{6} density and 5-HT levels were significantly correlated (p < or = 0.01) in both controls and AD patients, although in AD, this correlation was lost in females. Psychosis factor was the best predictor of reduced 5-HT levels or adenylate cyclase activity after E-6801 stimulation, the former result being due to females. It may be suggested that psychotic symptoms may be related to a dysregulation of 5-HT_{6} activation by 5-HT in the temporal cortex. These results are discussed in terms of purported influence of sex and therapeutical approaches to psychosis in AD.

Inflammatory mediators in the frontal lobe of patients with mixed and vascular dementia

Vascular dementia (VaD) accounts for about 20% of all dementias, and vascular risk is a key factor in more than 40% of people with Alzheimer's disease (AD). Little is known about inflammatory processes in the brains of these individuals. We have examined inflammatory mediators (interleukin (IL)-1beta, IL-1alpha, IL-6 and tumour necrosis factor alpha) and chemokines (macrophage inflammatory protein 1, monocyte chemo-attractant protein (MCP)-1 and granulocyte macrophage colony-stimulating factor) in brain homogenates from grey and white matter of the frontal cortex (Brodmann area 9) from patients with VaD (n = 11), those with concurrent VaD and AD (mixed dementia; n = 8) and from age-matched controls (n = 13) using ELISA assays. We found a dramatic reduction of MCP-1 levels in the grey matter in VaD and mixed dementia in comparison to controls (55 and 66%, respectively). IL-6 decreases were also observed in the grey matter of VaD and mixed dementia (72 and 71%, respectively), with a more modest decrease (30%) in the white matter of patients with VaD or mixed dementia. In the first study to examine the status of inflammatory mediators in a brain region severely affected by white-matter lesions, our findings highlight - in contrast to previous reports in AD - that patients at the later stage of VaD or mixed dementia have a significantly attenuated neuro-inflammatory response.

Pharmacological profile of an essential oil derived from Melissa officinalis with anti-agitation properties: focus on ligand-gated channels

A dual radioligand binding and electrophysiological study, focusing on a range of ligand-gated ion channels, was performed with a chemically-validated essential oil derived from Melissa officinalis (MO), which has shown clinical benefit in treating agitation. MO inhibited binding of [35S] t-butylbicyclophosphorothionate (TBPS) to the rat forebrain gamma-aminobutyric acid (GABA)(A) receptor channel (apparent IC50 0.040+/-0.001 mg mL(-1)), but had no effect on N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropianate (AMPA) or nicotinic acetylcholine receptors. Electrophysiological analyses with primary cultures of rat cortical neurons demonstrated that MO reversibly inhibited GABA-induced currents in a concentration-dependent manner (0.01-1 mg mL(-1)), whereas no inhibition of NMDA- or AMPA-induced currents was noted. Interestingly, MO elicited a significant dose-dependent reduction in both inhibitory and excitatory transmission, with a net depressant effect on neurotransmission (in contrast to the classical GABA(A) antagonist picrotoxinin which evoked profound epileptiform burst firing in these cells). The anti-agitation effects in patients and the depressant effects of MO in in-vitro we report in neural membranes are unlikely to reflect a sedative interaction with any of the ionotropic receptors examined here.

Glutamatergic approaches to the treatment of cognitive and behavioural symptoms of Alzheimer's disease

The glutamatergic system has long been recognised for its role in learning and memory and recent studies indicate an early loss of glutamatergic synapses in Alzheimer's disease (AD). Efforts to produce drugs which address changes in the glutamatergic system in AD are well advanced (e.g. memantine and drugs in development such as ampakines). Much less is known about the possible role of glutamate in non-cognitive behavioural changes; however, recent data from clinical trials suggest that memantine reduces agitation and aggressive behaviour in AD patients. In this context, it is important to help identify new treatment approaches to replace the use of antipsychotics in this vulnerable population.

Aggressive behavior and neuroleptic medication are associated with increased number of alpha1-adrenoceptors in patients with Alzheimer disease

OBJECTIVE

Aggressive behavior in dementia is a major clinical management problem.

METHOD

Postmortem brain tissue was obtained from 24 patients with Alzheimer disease (AD) and 25 comparison cases. [3H] Prazosin binding to alpha1-AdR was determined.

RESULTS

Aggressive behavior was significantly correlated with alpha1-adrenoceptor number in patients with AD (R(s)=0.454, N=24). Furthermore, patients receiving ongoing neuroleptics had significantly higher Bmax for [3H] prazosin (21 +/- 2, N=9) than those who were not (16 +/- 1, N=15).

CONCLUSIONS

Upregulation of alpha1-AdR is associated with aggressive behavior and chronic treatment with neuroleptic medication.

Genetic variation in the 5-HT2A receptor and altered neocortical [3H] ketanserin binding in Alzheimer's disease

A common intronic single nucleotide polymorphism (T102C) in the 5-HT2A receptor gene is associated with the development of different neuropsychiatric symptoms, including hallucinations and depressive symptoms in Alzheimer's disease (AD). Differential 5-HT2A receptor binding has also been associated with the development of these symptoms in AD. However, the relationship between 5-HT2A (T102C) genotype and 5-HT2A receptor binding in AD and control human brains has not been examined. We examined the association between different 5-HT2A (T102C) genotypes and [(3)H] ketanserin binding in the temporal and frontal cortex of 20 AD and 14 control human brains. In homozygotes, but not heterozygotes, there was a significant reduction in B(max) values for [(3)H] ketanserin binding in both areas of cortex in AD compared with control subjects. This study suggests a mechanism for the generation of different neuropsychiatric symptoms in AD from a single nucleotide polymorphism with reduced receptor binding in T102C 5-HT2A receptor gene homozygotes correlating with susceptibility to depressive symptoms, whereas the relative preservation of receptor binding in heterozygotes with AD correlating with susceptibility to hallucinations.

Abeta(1-42) modulation of Akt phosphorylation via alpha7 nAChR and NMDA receptors

Elevated Abeta and its deposition as senile plaques are pathogenic features of Alzheimer's disease. Abeta has been shown to be toxic to neurons and to inhibit long-term potentiation yet, the intracellular signalling pathways underlying these actions are unknown. We report for the first time that acute exposure of primary mouse neurons to 400nM Abeta(1-42) increased Akt phosphorylation in an alpha(7) nicotinic receptor and NMDA receptor dependant manner. However, prolonged incubation resulted in Akt phosphorylation returning to baseline consistent with the action of a physiological regulator. Analysis of an APP transgenic mouse (TAS10) revealed a significant deficit in hippocampal Akt phosphorylation at 13 months. This time point corresponds to the emergence of plaque formation and memory impairments in these mice. The present study suggests that Abeta(1-42) regulates Akt phosphorylation in a complex manner. Acutely, Abeta(1-42) stimulates Akt phosphorylation however, chronic exposure to Abeta in TAS10 mice resulted in a downregulation of Akt phosphorylation consistent with abnormalities in excitatory neurotransmission in these mice and with recent reports of Abeta(1-42) driven internalisation of NMDA receptors.

Down-regulation of vesicular glutamate transporters precedes cell loss and pathology in Alzheimer's disease

Alzheimer's disease (AD) is characterized pathologically by plaques, tangles, and cell and synapse loss. As glutamate is the principle excitatory neurotransmitter of the CNS, the glutamatergic system may play an important role in AD. An essential step in glutamate neurotransmission is the concentration of glutamate into synaptic vesicles before release from the presynaptic terminal. Recently a group of proteins responsible for uptake has been identified - the vesicular glutamate transporters (VGLUTs). The generation of antibodies has facilitated the study of glutamatergic neurones. Here, we used antibodies to the VGLUTs together with immunohistochemistry and western blotting to investigate the status of glutamatergic neurones in temporal, parietal and occipital cortices of patients with AD; these regions were chosen to represent severely, moderately and mildly affected regions at the end stage of the disease. There was no change in expression of the synaptic markers in relation to total protein in the temporal cortex, but a significant reduction in synaptophysin and VGLUT1 was found in both the parietal and occipital cortices. These changes were found to relate to the number of tangles in the temporal cortex. There were no correlations with either mental test score or behaviour syndromes, with the exception of depression.

Impaired coupling of muscarinic M1 receptors to G-proteins in the neocortex is associated with severity of dementia in Alzheimer's disease

Impaired transmission of acetylcholine-mediated signaling by postsynaptic muscarinic M1 receptors has been postulated to underlie the limited efficacy of cholinergic replacement therapies in Alzheimer's disease (AD). However, a clear relationship between the functionality of M1 receptors and dementia severity has not been demonstrated. The present study aims to measure M1 coupling to its nucleotide binding (G-) protein in the AD neocortex, and to correlate neurochemical findings with clinical features. A cohort of dementia patients was longitudinally assessed for cognitive decline, with postmortem neuropathological confirmation of AD diagnosis. Measures of M1 receptor density, M1/G-protein coupling and choline acetyltransferase (ChAT) activities were performed in the frontal and temporal cortex of 24 AD patients as well as in 12 age-matched controls. We found that M1 receptor densities were unchanged in AD, which contrasted with significantly reduced M1 coupling to G-proteins in severely demented AD patients. Loss of M1/G-protein coupling in the frontal cortex, but not the temporal cortex, also correlated with the rate of cognitive decline. Additionally, correlations between M1/G-protein coupling and ChAT activities were demonstrated in both regions. These results suggest that defective coupling of neocortical M1 receptors to G-proteins is a neurochemical substrate of cognitive decline in AD. Based on its associations with ChAT deficits and dementia severity, we propose that M1/G-protein uncoupling may have a significant role in the disease mechanism of AD and thus may be considered to be a potential therapeutic target.

Involvement of the GABAergic system in depressive symptoms of Alzheimer's disease

Cognitive and neuropsychiatric (BPSD) symptoms seen in Alzheimer's disease (AD) probably result from differential neurotransmitter alterations. The involvement of the glutamatergic and GABAergic system in cognitive and behavioral and psychological symptoms of dementia (BPSD) has been studied in post-mortem frontal and temporal cortex from AD patients who had been prospectively assessed with the Mini-Mental State Examination (MMSE) for cognitive impairment and with the Present Behavioral Examination (PBE) for BPSD. In addition to cholinergic deficits, significant decreases in gamma-amino butyric acid (GABA) content, with no changes in glutamate content, were found in frontal and temporal cortex. Both GABA levels and the glutamate/GABA ratio showed significant correlations with depression in AD. In the temporal cortex, higher densities of GABA(A)/benzodiazepine receptors also correlated with more severe depression. It can be suggested that in a situation of cholinergic deficit, such as AD, an imbalance between the excitatory glutamatergic tone and inhibitory GABAergic tone may be responsible for non-cognitive behavioral disturbances.