Methyl-laudanosine: A new pharmacological tool to investigate the function of small-conductance Ca2+-activated K+ channels

ABSTRACT Small-conductance Ca 2ϩ -activated K ϩ channels (SK channels) underlie the prolonged postspike afterhyperpolarization (AHP) observed in many central neurons and play an important role in modulating neuronal activity. However, a lack of specific and reversible blockers of these channels hampers their study in various experimental conditions. Because previous work has shown that bicuculline salts block these channels, we examined whether related alkaloids, namely laudanosine quaternary derivatives, would produce similar effects. Intracellular recordings were performed on rat midbrain dopaminergic neurons and hippocampus CA1 pyramidal cells. Binding experiments were performed on rat cerebral cortex membranes. Laudanosine, methyl-laudanosine, and ethyl-laudanosine blocked the apamin-sensitive AHP of dopaminergic neurons with mean IC 50 values of 152, 15, and 47 M, respectively. The benzyl and butyl derivatives were less potent. Methyl-laudanosine had no effect on the I h current, action potential parameters, or membrane resistance of dopaminergic cells, or on the decrease in input resistance induced by muscimol, indicating a lack of antagonism at GABA A receptors. Interestingly, 100 M methyllaudanosine induced a significant increase in spiking frequency of dopaminergic neurons but not of CA1 pyramidal cells, suggesting the possibility of regional selectivity. Binding experiments on laudanosine derivatives were in good agreement with electrophysiological data. Moreover, methyl-laudanosine has no affinity for voltage-gated potassium channels, and its affinity for SK channels (IC 50 4 M) is superior to its affinity for muscarinic (IC 50 114 M) and neuronal nicotinic (IC 50 Ն367 M) receptors . Methyl-laudanosine may be a valuable pharmacological tool to investigate the role of SK channels in various experimental models. Other than neurotransmitter receptors and transporters, ion channels constitute an attractive target to develop new drugs that will be active on the central nervous system. Currently, the only ion channel that is well established as a central nervous system target is the voltage-gated Na ϩ channel, which is blocked by antiepileptic drugs such as phenytoin, carbamazepine, and lamotrigine Evidence suggests that SK-channel modulation may be interesting in a range of central nervous system disorders, This work was supported in part by Grant 3.4525.98 from the National Fund for Scientific Research (Brussels, Belgium). This work has been presented in meeting abstract form: Scuvée-Moreau J, Liégeois JF, and Seutin V (2002) Effect of laudanosine derivatives on the apamin-sensitive afterhyperpolarization of rat dopaminergic neurons-identification of methyl-laudanosine as a new specific blocker (Abstract). Fundam Clin Pharmacol 16:67

Prevalence of dementia and Alzheimer's disease in elders of nursing homes and a senior center of Durango City, Mexico

BACKGROUND: Epidemiological reports about dementia and Alzheimer's disease (AD) in elderly people from developing countries are scarce. Therefore, we sought to determine the prevalences of dementia and AD in a population of nursing home residents and senior center attendees of Durango City, Mexico, and to determine whether any socio-demographic characteristics from the subjects associated with dementia or AD exist. METHODS: One hundred and fifty-five residents of two nursing homes and 125 attendees of a senior center were examined for dementia and Alzheimer's disease. All subjects were tested by the mini-mental state examination, and those who scored twenty-four or less underwent psychiatric and neurological evaluations. Diagnosis of dementia, AD and vascular dementia (VaD) was based on the DSM-IV criteria. Socio-demographic characteristics from each participant were also obtained. RESULTS: Residents of nursing homes found to suffer from dementia were 25 out of 155 (16.1%). Eighteen of them (11.6%) had AD, and seven (4.5%) had VaD. None of the attendees of the senior center suffered from dementia. Dementia (pooled AD and VaD cases) correlated with white ethnicity (OR = 3.2; 95%CI = 1.28–8.31), and a history of unemployment (OR = 6.46; 95%CI = 1.42–25.97), while AD correlated with journeymen occupations (OR = 4.55; 95%CI = 1.00–19.29). CONCLUSION: Prevalence of dementia in residents of nursing homes found in this study is much lower than reported from more industrialized countries. AD was more frequent than VaD. Ethnicity and occupation showed effects on the prevalence figures. The prevalence of dementia found has implications for the optimum kind of health care that nursing homes should provide to their residents

Role of Kv1 Potassium Channels in Regulating Dopamine Release and Presynaptic D2 Receptor Function

Dopamine (DA) release in the CNS is critical for motor control and motivated behaviors. Dysfunction of its regulation is thought to be implicated in drug abuse and in diseases such as schizophrenia and Parkinson's. Although various potassium channels located in the somatodendritic compartment of DA neurons such as G-protein-gated inward rectifying potassium channels (GIRK) have been shown to regulate cell firing and DA release, little is presently known about the role of potassium channels localized in the axon terminals of these neurons. Here we used fast-scan cyclic voltammetry to study electrically-evoked DA release in rat dorsal striatal brain slices. We find that although G-protein-gated inward rectifying (GIRK) and ATP-gated (KATP) potassium channels play only a minor role, voltage-gated potassium channels of the Kv1 family play a major role in regulating DA release. The use of Kv subtype-selective blockers confirmed a role for Kv1.2, 1.3 and 1.6, but not Kv1.1, 3.1, 3.2, 3.4 and 4.2. Interestingly, Kv1 blockers also reduced the ability of quinpirole, a D2 receptor agonist, to inhibit evoked DA overflow, thus suggesting that Kv1 channels also regulate presynaptic D2 receptor function. Our work identifies Kv1 potassium channels as key regulators of DA release in the striatum

Cognitive impairment, dementia and quality of life in patients and caregivers.

OBJECTIVE: To study the impact of cognitive impairment and severity of dementia on the quality of life (QoL) of patients and their caregivers. DESIGN: Descriptive cross-sectional study within the NAtional Dementia Economic Study. SETTING: 231 general practices and 15 specialist clinics in Belgium. SUBJECTS: 605 patients aged > or = 65 years: 106 referent subjects without cognitive impairment (R), 113 subjects with cognitive impairment and no dementia (CIND), 386 subjects with mild (83), mild/moderate (108), moderate (62) or severe (133) dementia (D1 to D4). OUTCOME MEASURES: QoL of patients: COOP/WONCA charts, Katz's Activities of Daily Living (ADL) scale, Lawton's Instrumental Activities of Daily Living (IADL) scale. QoL of caregivers: COOP/WONCA charts, SF-36 questionnaire, short-form Beck Depression Inventory, Sense of Competence questionnaire (SCQ). MAIN RESULTS: QoL of patients: For R, CIND and D1 to D4 patients, dependence for ADL reached 5%, 6%, 16%, 20%, 48% and 79%, respectively, and mean IADL scores were 5.6, 5.0, 3.4, 2.0, 0.6 and 0.1, respectively. QoL of caregivers: The main impact of caregiving was on mental health, with SF-36 MCS scores of 51.3, 47.7 and 45.4 for R, CIND and all D patients and respectively 32.6%, 31.3% and 42.5% depression prevalence. Sense of competence decreased with severity of patient's cognitive impairment. Caregivers of CIND patients always rated intermediate between R and D1 patients. Caregivers of D3 patients were the most affected ones. CONCLUSION: The data suggest that improving the cognitive status of patients and providing assistance to caregivers would be complementary ways of action to support caregiving of patients living at home

[The measurement of sense of competence in caregivers of patients with dementia]

BACKGROUND: In the context of a cohort study on the socio-economic consequences of dementia in Belgium, we evaluated the validity, reliability and feasibility of the French version of the Dutch Sense of Competence questionnaire (SCQ), and of its short version (the SSCQ), in caregivers of demented patients The questionnaire was based on Zarit's burden interview and on a theoretical family-crisis model. METHODS: Construct validity was evaluated by factor analysis and by comparison of the results with those of the original SCQ study. Reliability was evaluated by Cronbach's alpha and by item-total correlations. Feasibility was assessed by a standardized index of missing values. RESULTS: The three domains found in the original SCQ were identified by factor analysis: consequences of involvement in care for the personal life of the caregiver, satisfaction with one's own performance as a caregiver and satisfaction with the elderly person as a recipient of care. The mean scores were similar to those in the original study, except for the consequences for personal life. Cronbach's alpha for both the SCQ and the SSCQ exceeded the 0.70 criterion. Two of the 27 items did not meet the item-total correlation criterion; the SSCQ items all met the criterion. The standardised index of missing values was deemed acceptable. CONCLUSIONS: The French versions of the SCQ and the SSCQ are valid and reliable. Like the Dutch version, the French version of the SCQ can be a useful outcome measure for the evaluation of intervention studies and the SSCQ is suitable for the daily practice

Cognitive impairment, dementia and quality of life in patients and caregivers.

Item does not contain fulltextOBJECTIVE: To study the impact of cognitive impairment and severity of dementia on the quality of life (QoL) of patients and their caregivers. DESIGN: Descriptive cross-sectional study within the NAtional Dementia Economic Study. SETTING: 231 general practices and 15 specialist clinics in Belgium. SUBJECTS: 605 patients aged > or = 65 years: 106 referent subjects without cognitive impairment (R), 113 subjects with cognitive impairment and no dementia (CIND), 386 subjects with mild (83), mild/moderate (108), moderate (62) or severe (133) dementia (D1 to D4). OUTCOME MEASURES: QoL of patients: COOP/WONCA charts, Katz's Activities of Daily Living (ADL) scale, Lawton's Instrumental Activities of Daily Living (IADL) scale. QoL of caregivers: COOP/WONCA charts, SF-36 questionnaire, short-form Beck Depression Inventory, Sense of Competence questionnaire (SCQ). MAIN RESULTS: QoL of patients: For R, CIND and D1 to D4 patients, dependence for ADL reached 5%, 6%, 16%, 20%, 48% and 79%, respectively, and mean IADL scores were 5.6, 5.0, 3.4, 2.0, 0.6 and 0.1, respectively. QoL of caregivers: The main impact of caregiving was on mental health, with SF-36 MCS scores of 51.3, 47.7 and 45.4 for R, CIND and all D patients and respectively 32.6%, 31.3% and 42.5% depression prevalence. Sense of competence decreased with severity of patient's cognitive impairment. Caregivers of CIND patients always rated intermediate between R and D1 patients. Caregivers of D3 patients were the most affected ones. CONCLUSION: The data suggest that improving the cognitive status of patients and providing assistance to caregivers would be complementary ways of action to support caregiving of patients living at home

Mechanisms of caffeine-induced diuresis

Caffeine is an alkaloid which belongs to the family of methylxanthines and is present in beverages, food and drugs. Caffeine competitively antagonizes the adenosine receptors (AR), which are G protein-coupled receptors largely distributed throughout the body, including brain, heart, vessels and kidneys. Caffeine consumption has a well-known diuretic effect. The homeostasis of salt and water involves different segments of the nephron, in which adenosine plays complex roles depending on the differential expression of AR. Hence, caffeine increases glomerular filtration rate by opposing the vasoconstriction of renal afferent arteriole mediated by adenosine via type 1 AR during the tubuloglomerular feedback. Caffeine also inhibits Na(+) reabsorption at the level of renal proximal tubules. In addition, caffeine perturbs the hepatorenal reflex via sensory nerves in Mall's intrahepatic spaces. Here, we review the physiology of caffeine-induced natriuresis and diuresis, as well as the putative pathological implications