Peter Knott

Neurochemical correlates of dementia severity in Alzheimer's disease: relative importance of the cholinergic deficits.

Abstract: Cholinergic markers, neuropeptides, and amines and their metabolites were sampled from identical specimens across 10 neocortical regions in a large sample of Alzheimers disease (AD) cases and controls. Levels of choline acetyltransferase, acetylcholinesterase, somatostatin, corticotropin‐releasing factor, serotonin, and 5‐hydroxyindoleacetic acid were significantly reduced in AD versus controls. After data reduction, the most descriptive neurochemical indices were used to examine the relationship of neurochemical measures and dementia severity within the AD sample, controlling for age effects. Dementia severity ratings were based on antemortem assessments (46.9% of AD sample) and postmortem chart review (53.1% of the AD sample). Choline acetyltransferase activity was highly correlated with clinical dementia ratings across the neocortex of the AD cases. Somatostatin and corticotropin‐releasing factor levels were correlated with dementia severity only when control cases were included in the analyses. None of the amines, their metabolites, or the neuropeptides quantified related significantly to dementia severity in the AD cohort. These data (a) confirm the strong association of cholinergic deficits with functional impairment in AD and show that this association is independent of age and (b) suggest that of all the neurochemical species quantified, the cholinergic indices may be unique in their association with dementia severity.

Blinded, multi-center validation of EEG and rating scales in identifying ADHD within a clinical sample

Previous validation studies of attention deficit/hyperactivity disorder (ADHD) assessment by rating scales or EEG have provided Class-IV evidence per standards of the American Academy of Neurology. To investigate clinical applications, we collected Class-I evidence, namely from a blinded, prospective, multi-center study of a representative clinical sample categorized with a clinical standard. Participating males (101) and females (58) aged 6 to 18 had presented to one of four psychiatric and pediatric clinics because of the suspected presence of attention and behavior problems. DSM-IV diagnosis was performed by clinicians assisted with a semi-structured clinical interview. EEG (theta/beta ratio) and ratings scales (Conners Rating Scales-Revised and ADHD Rating Scales-IV) were collected separately in a blinded protocol. ADHD prevalence in the clinical sample was 61%, whereas the remainder had other childhood/adolescent disorders or no diagnosis. Comorbidities were observed in 66% of ADHD patients and included mood, anxiety, disruptive, and learning disorders at rates similar to previous findings. EEG identified ADHD with 87% sensitivity and 94% specificity. Rating scales provided sensitivity of 38-79% and specificity of 13-61%. While parent or teacher identification of ADHD by rating scales was reduced in accuracy when applied to a diverse clinical sample, theta/beta ratio changes remained consistent with the clinicians ADHD diagnosis. Because theta/beta ratio changes do not identify comorbidities or alternative diagnoses, the results do not support the use of EEG as a stand-alone diagnostic and should be limited to the interpretation that EEG may complement a clinical evaluation for ADHD.

Excessive serotonin release, not depletion, leads to memory impairments in rats

Eight experiments compared and contrasted the effects of serotonin release and depletion on performance by rats in two tests of memory. Most experiments (Experiments 1-5) examined the effects of the serotonergic releasing/depleting agent p-chloroamphetamine on passive avoidance performance. Additional experiments explored p-chloroamphetamines effects on retention performance by animals trained in an 8-arm radial maze (Experiment 6), and the effects of dorsal raphe nucleus lesions on passive avoidance in animals treated with (Experiment 8) or not treated with (Experiment 7) p-chloroamphetamine. In general, acute increases in serotonin release produced consistent and extensive retention performance deficits in both passive avoidance and radial arm maze. Results from an ancillary control experiment indicated that the p-chloroamphetamine-induced passive avoidance impairment was not related to drug-induced alterations in pain sensitivity. Other experiments ruled out the possibility that p-chloroamphetamine was disrupting passive avoidance retention performance by affecting post-trial consolidation processes, producing state-dependent retention, having direct effects at postsynaptic receptors, or indirectly by affecting non-serotonergic neurotransmitter systems. Depletion of serotonin resulting from either the long-term residual effects of p-chloroamphetamine or lesions of the dorsal raphe nucleus failed to alter passive avoidance retention scores although it produced extensive depletion (45-85%) of serotonin and 5-hydroxyindoleacetic acid in the cortex and hippocampus. These data contribute to the growing body of literature indicating an important role of serotonin in cognitive processes by demonstrating that excessive release, but not depletion, of serotonin produces profound retention performance impairment.

Treatment with clozapine and its effect on plasma homovanillic acid and norepinephrine concentrations in schizophrenia

Measurement of plasma concentrations of the dopamine metabolite, homovanillic acid (pHVA), is an indirect tool to assess changes in dopamine turnover. Levels of pHVA have been reported to decrease during treatment with conventional antidopaminergic, neuroleptics, with the decrement correlating with symptomatic improvement in schizophrenic symptoms. Clozapine, an atypical neuroleptic, is the only drug proved to be effective in treatment-refractory patients. However, the mechanism mediating this unique efficacy has not been fully elucidated. This study examined the effect of clozapine on pHVA concentrations in schizophrenic patients. Since clozapine potently binds to alpha 2-adrenergic receptors, plasma norepinephrine (pNE) concentrations were also measured. Twenty-eight treatment-refractory schizophrenic patients (24 men, 4 women) were treated with clozapine (up to 600 mg/day) for 5 weeks, after a minimum 1-week drug-free period. Symptomatology and pHVA and pNE concentrations were measured at the last drug-free day and weekly for 5 weeks. Fourteen patients responded to clozapine treatment, while an equal number did not. Mean pHVA concentrations did not significantly change during treatment with clozapine. Although clozapine tended to lower pHVA concentrations in treatment responders, the effect was small and not significant. Clozapine treatment significantly raised pNE concentrations, but this did not differentiate responders from nonresponders to clozapine. These findings suggest that clozapines effect on DA turnover is small and that clozapine may be effective in treatment-refractory schizophrenia by mechanisms other than, or in addition to, dopamine receptor blockade. However, since about one-third of NE is metabolized into HVA, the clozapine-induced increase in pNE may have overshadowed a possible lowering effect of clozapine on pHVA.

Relationship between 3-Methoxy-4-Hydroxyphenylglycol and Homovanillic Acid in Saliva and Plasma of Healthy Volunteers

Plasma 3-methoxy-4-hydroxyphenylglycol (MHPG) and homovanillic acid (HVA) levels may reflect changes in central noradrenergic and dopaminergic activity, respectively. The relationship between MHPG and HVA in saliva and plasma was investigated to evaluate the utility of salivary metabolite measurement as a relatively noninvasive and useful alternative to plasma analysis. MHPG and HVA in saliva and plasma, collected concurrently, from 12 healthy volunteers, were measured by high-performance liquid chromatography. Concentration of free MHPG in saliva correlated significantly with plasma free MHPG. Salivary free MHPG was significantly higher than in plasma. Enzymatic hydrolysis of conjugated MHPG corroborated other work that plasma free MHPG, MHPG-glucuronide, and MHPG-sulfate were in roughly equal proportions. Unpredictably, in saliva, free MHPG was greater than 80% of the total. Salivary and plasma free HVA concentrations also correlated significantly, but salivary HVA levels were significantly lower than in plasma. Conjugated HVA was consistently less than 10% of total both in saliva and plasma. These findings suggest that salivary MHPG and HVA can reflect plasma metabolite levels. Although local factors may influence their formation and concentration in saliva, large changes in plasma free MHPG or HVA could be reflected by parallel changes in saliva.

Correlations post-mortem between ventricular CSF and cortical tissue concentrations of MHPG, 5-HIAA and HVA in Alzheimer's disease

Alzheimer’s disease, characterized by plagues and tangles in hippocampal and cortical areas, is also associated with reduced choline acetylase and choline esterase, noradrenergic cell loss in the locus ceruleus and serotonergic impairment. We confirm the reported cholinergic, noradrenergic and serotonergic deficits in Alzheimer’s brain tissue. Furthermore, we find that concentrations of the norepinephrine metabolite , MHPG , of the serotonin metabolite, 5-HIAA and of the dopamine metabolite, HVA in most cerebral cortical regions correlate significantly with concentration of these substances in ventricular CSF post-mortem. Brains from 13 subjects (eight Alzheimer’s disease; two multi-infarct dementia control; one normal control and two other non-AD dementia) were divided into ten Brodman areas and a corresponding sample of ventricular CSF was also obtained at autopsy. All samples were assayed for amine metabolite concentration by HPLC with electrochemical detection. Regression analysis of tissue and CSF values of MHPG, 5-HIAA and HVA of all 13 subjects are shown in the table below. These data suggest that post-mortem ventricular CSF concentrations of MHPG , 5-HIAA and HVA are meaningful indicators of their concentrations in cortical tissue.

Diurnal neuroendocrine and autonomic function in acute and remitted depressed male patients

This study evaluated diurnal data gathered hourly (1000 to 1800 hours) in males during acute depression and during remission of depression and in age-range/gender-matched normal controls. Mean, peak, variability, and time-course of the noradrenergic metabolite, plasma 3-methoxy, 4-hydroxyphenylglycol [MHPG]), plasma cortisol, and autonomic (mean arterial blood pressure [MAP] and heart rate) variables were examined. Compared to controls, acutely depressed, but not remitted depressed, patients had 1) an earlier plasma MHPG peak, 2) a greater intragroup variability of plasma MHPG, 3) a higher plasma cortisol concentration, 4) a lower MAP, and 5) tended to increase MAP more slowly than did the normal controls. The time course of diurnal heart rate also differed in acutely depressed patients from controls: acutely depressed patients started higher and converged by midday to normal levels. These diurnal data lend limited support to the dysregulation hypotheses of depression that suggest normal circadian rhythmicities are altered or disrupted in acute depression and that peripheral manifestations of central dysregulation normalize in remission of depression.

Genetic antecedents of dopamine dysfunction in schizophrenia

BACKGROUND Relatives of schizophrenic probands frequently manifest attenuated features of this illness including the negative symptoms and the milder positive psychotic symptoms. These two symptom dimensions are hypothesized to be associated with decreased and increased brain dopamine (DA) functions, respectively, raising the possibility that DA abnormalities may be present in the relatives of schizophrenic probands. METHODS Plasma homovanillic acid (HVA), the major DA metabolite and an indicator of brain DA activity, was measured in nonpsychotic, physically healthy first-degree relatives (n = 55) of schizophrenic probands and in normal subjects (n = 20) without a family history of schizophrenia. RESULTS Plasma HVA inversely correlated with negative symptoms and positively correlated with attenuated positive symptoms. Also, relatives had decreased plasma HVA compared to normal subjects, consistent with the fact that these relatives are characterized by negative symptoms. These findings were not related to major peripheral factors that could affect plasma HVA suggesting that the findings may reflect changes in brain DA activity. CONCLUSIONS Negative symptoms indicating a genetic diathesis to schizophrenia in relatives may have a biologic basis in reduced DA activity and the DA dysfunction of schizophrenia may have genetic antecedents. This opens an important new avenue for further study of DA in this illness.

Noradrenergic responses to clonidine in acute and remitted depressed male patients

To investigate noradrenergic function in depression, plasma 3-methoxy-4-hydroxyphenylglycol (MHPG), plasma norepinephrine (NE), mean arterial pressure (MAP), and heart rate responses to intravenous clonidine (2 micrograms/kg), an alpha 2-adrenergic agonist, were measured in 27 acutely depressed patients, 18 remitted depressed patients, and 27 normal control subjects; a placebo infusion was administered to a subgroup. Clonidine compared with placebo, over a 150-minute time course, decreased plasma NE, MAP, and heart rate, but not plasma MHPG, in the control subjects. Plasma MHPG, plasma NE, MAP, and heart rate at baseline or in response to clonidine and placebo over 150 minutes did not indicate any group differences. The only significant plasma MHPG response to clonidine in the normal control subjects occurred 60 minutes after the infusion. A significantly diminished plasma MHPG response to clonidine at 60 minutes was found in the acutely depressed group compared with the normal control subjects. These results suggest that peripheral inhibitory noradrenergic responses to clonidine are normal in depressed patients, while plasma MHPG responses to clonidine, which have a limited central contribution, appear to be a weak reflection of central noradrenergic function and appear insufficiently robust for a meaningful evaluation of hypothetical group differences in central inhibitory alpha 2-adrenergic activity in this population.

Effect of m-Chlorophenylpiperazine on plasma homovanillic acid concentrations in healthy subjects

In view of the abundant anatomical and functional interactions between serotonin and dopamine systems, this study examined the effect of the serotonin agonist, m-chlorophenylpiperazine (mCPP) on plasma concentrations of the dopamine metabolite, homovanillic acid. Plasma prolactin levels, body temperature, and mCPP blood level were also measured. mCPP (0.35 mg/kg) and placebo were administered orally to 10 healthy men in a randomized double-blind design. Variables were measured for 210 min after administration of capsules. mCPP raised prolactin and temperature as compared to placebo, but did not affect plasma homovanillic acid concentrations. Results suggest that mCPP does not alter dopamine function.