Tacrine, a drug with therapeutic potential for dementia: post-mortem biochemical evidence

D-cycloserine, a partial NMDA receptor-associated glycine-B site agonist, enhances reversal learning, but a cholinesterase inhibitor and nicotine has no effect

The present study examined the efficacy of single and combined treatments with an anticholinesterase, tetrahydroaminoacridine, nicotine and a glycine-B site partial agonist, D-cycloserine, in alleviating the water maze reversal learning defect induced by a medial septal lesion. D-cycloserine (3 and 10 mg/kg) improved reversal learning. Tetrahydroaminoacridine (1 and 3 mg/kg) and nicotine (0.1 and 0.3 mg/kg) had no effect on reversal learning. A combination of tetrahydroaminoacridine 3 mg/kg or nicotine 0.3 mg/kg and D-cycloserine 10 mg/kg was not more effective than D-cycloserine 10 mg/kg alone in improving reversal learning. This suggests that stimulation of NMDA mechanisms may more effectively improve in medial septal-lesioned rats reversal learning processes than stimulation of cholinergic activity.

Tacrine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in Alzheimer's disease

Tacrine is a centrally acting cholinesterase inhibitor with additional pharmacological activity on monoamine levels and ion channels. It has been postulated that some or all of these additional properties may also be relevant to the mode of action of the drug. There are wide interindividual variations in pharmacological and clinical response to tacrine, possibly related to interindividual variation in bioavailability. Tacrine appears to improve cognitive function and behavioural deficits in a proportion of patients with Alzheimer's disease, at dosages of 80 to 160 mg/day. In the best designed trials, 30 to 51% of evaluable patients showed an improvement of at least 4 points on the cognitive subscale of the Alzheimer's Disease Assessment Scale, versus 16 to 25% of placebo recipients. A similar proportion of tacrine recipients were judged to have improved when global assessment scales were used. There was a significant dose-response relationship up to 160 mg/day. However, large numbers of patients were withdrawn during the trials, many because of tacrine-associated increases in transaminase levels. Elevated liver enzyme levels occurred in about 50% of tacrine recipients (reaching clinical significance in about 25%). Cholinergic symptoms also occurred more often in tacrine recipients than in those receiving placebo. A gradual increase in tacrine dosage, at 6-week intervals, is recommended when initiating therapy, and weekly serum transaminase monitoring is required for 6 weeks after each dosage increase. Despite the limitations implied by the low proportion of responders and high incidence of hepatic adverse effects associated with therapy, tacrine appears to make a measurable difference in both cognitive and behavioural function in a proportion of patients with Alzheimer's disease--a welcome advance in an area previously devoid of acceptable treatment options.

Subclinical dementia: relevance of cognitive symptoms and signs

In 1971 and 1972, a representative sample of 70-year-old people (n = 392) from a population study was rated with regard to psychiatric symptoms and signs. Subjects showing evidence of dementia of any degree, including slight and questionable, were excluded (n = 18). The remaining 374 subjects were followed longitudinally for 9 years. Thirty-eight subjects developed severe dementia during this period. They were compared to those who did not with regard to 19 reported and 17 observed items concerning general psychopathology, seven reported items concerning sleep, and a global rating of mental health. Five items correlated with the development of severe dementia: number of remembered dreams per week, latency of speech, speed of speech, difficulties in finding words, and memory for recent events. A stepwise logistic regression procedure demonstrated that a low frequency of remembered dreams, a reduced memory for recent events, and difficulties in finding words made independent contributions to the prediction of dementia. There were no differences with regard to affective items. There were no differences between the subjects who developed senile dementia of the Alzheimer type and those with multi-infarct dementia. The results thus support the hypothesis that symptoms pertaining to cognitive functions are the first to appear in the development of dementia.

Pathology of Parkinson's disease. Changes other than the nigrostriatal pathway

In Parkinson's disease (PD), in addition to degeneration of the nigrostriatal dopaminergic pathway, a variety of neuronal systems are involved, causing multiple neuromediator dysfunctions that account for the complex patterns of functional deficits. Degeneration affects the dopaminergic mesocorticolimbic system, the noradrenergic locus ceruleus (oral parts) and motor vagal nucleus, the serotonergic raphe nuclei, the cholinergic nucleus basalis of Meynert, pedunculopontine nucleus pars compacta, Westphal-Edinger nucleus, and many peptidergic brainstem nuclei. Cell losses in subcortical projection nuclei range from 30 to 90% of controls; they are more severe in depressed and demented PD patients. Most of the lesions are region-specific, affecting not all neurons containing a specific transmitter or harboring Lewy bodies. In contrast to Alzheimer's disease (AD), subcortical system lesions in Parkinson's disease appear not to be related to cortical pathology, suggesting independent or concomitant degeneration. The pathogenesis of multiple-system changes contributing to chemical pathology and clinical course of Parkinson's disease are unknown.

Treatment of Alzheimer's disease. Molecular pathology versus neurotransmitter-based therapy

Cortical inhibitory neurotransmitters, neuropeptides, dopamine and noradrenaline are probably either not selectively or not critically affected in AD. It is, however, likely that a key change is shrinkage or loss of corticocortical pyramidal neurones, which probably use glutamate as their transmitter. This depletion appears to be circumscribed and clinically relevant.

Pyramidal neuron loss and "glycine-site therapy": a need for an animal model and study in late-life depression

Localization and other studies of glutamatergic receptors are hampered, in part, as pyramidal neurons in the neocortex cannot yet be selectively destroyed in laboratory animals. Demonstration of glutamatergic neuron dysfunction in Alzheimer's disease may allow verification of a technique suitable for the study of these cells in disorders without histopathological hallmarks. This includes Major Depressive Disorder in the elderly which has a poor prognosis.