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Biomedical subjects

M A Mehta

Publications and source records attributed to M A Mehta.

10 recordsLinked to original sources
PubMed2003

Aftercare of depressed inpatients--service delivery and unmet needs.

BACKGROUND: In contrast to acute treatment, delivery of aftercare to depressed patients has not been well studied. Poor care may contribute to poor outcomes for treated depression. METHODS: One hundred and two patients discharged from hospital with unipolar depression were followed up 18 months later and were interviewed in detail regarding aftercare and treatment received. Unmet needs were assessed on the community version of the MRC Needs for Care Assessment. RESULTS: In the first month after discharge approximately 70 % of subjects received contacts with mental health services and in the first 3 months over 80 % received at least one contact. About 40 % were in contact with mental health services at 18 months. Needs assessment found comparatively low unmet needs, reaching highest levels (around 25 % in any 6-month period) for medication. Two-thirds of unmet needs for medication and psychotherapy were due to patient refusal or non-compliance. Aftercare levels were higher in those with more previous admissions and were unrelated to presence of personality disorder. CONCLUSIONS: There were some deficiencies in service aftercare for depressed patients in a British NHS setting, although unmet need was not high. Some aftercare failures reflect patient reluctance to receive further treatment, representing a challenge to overcome in patients entitled to autonomous choices.

Adolescent↗
PubMed2001

Improved short-term spatial memory but impaired reversal learning following the dopamine D(2) agonist bromocriptine in human volunteers.

RATIONALE: Studies in humans of cognitive effects of dopaminergic drugs have largely focused on tasks of working memory, with a few studies also examining executive function. OBJECTIVES: This study was designed to investigate the effects of 1.25 mg of the dopamine D(2) agonist bromocriptine on spatial working memory, planning and discrimination reversal learning in young healthy volunteers. METHODS: Twenty volunteers were tested in a double-blind, placebo-controlled, cross-over design. The cognitive assessment included tests taken from the Cambridge Neuropsychological Test Automated Battery (CANTAB) designed to test visuo-spatial recognition memory and spatial working memory. In addition, tests of spatial planning and discrimination reversal learning were used to assess the more general effects of bromocriptine. Tests of subjective feelings and motivation were also incorporated into the battery. RESULTS: Bromocriptine enhanced the spatial memory span of subjects, whilst impairing their ability to reverse a learned probabilistic discrimination. Tests of recognition memory and planning were unaffected by the drug. The findings were not explained by changes in subjective mood or motivational measures. CONCLUSIONS: The pattern of findings observed here mirror medication-dependent observations seen in Parkinson's disease. The results are discussed with reference to the different anatomical networks known to subserve performance of the differentially affected tasks.

Adult↗
PubMed2001

Acute dietary tryptophan depletion impairs maintenance of "affective set" and delayed visual recognition in healthy volunteers.

RATIONALE: Altered serotonergic transmission in affective disorders and Alzheimer's disease has prompted research aimed at defining the precise cognitive effects of depleting central serotonin in humans, using acute dietary tryptophan depletion. OBJECTIVE: We examined the effects of tryptophan depletion on mood and cognition in healthy volunteers. Cognitive tests of memory and attentional processing were employed to test hypotheses of central 5-hydroxytryptamine (5-HT) function related to cortical processing. METHODS: A double-blind, parallel design, placebo control study was employed with 15 subjects in each group. Mood rating scales were performed at the start and 5 h after ingestion of the drink. Cognitive tests were also performed at 5 h, after completion of the subjective rating scales. RESULTS: A robust reduction in total tryptophan was achieved in the test group. Subjects receiving the placebo drink showed the expected effect of shift on the affective shifting task, that is, more errors in the more difficult shift versus the non-shift condition. The tryptophan-depleted group made a similar number of errors in the shift trials but failed to reduce the number of errors in the non-shift trials. The tryptophan-depleted group showed a significant impairment on the delayed pattern recognition task. No significant effects on the subjective mood measures were found. CONCLUSIONS: Tryptophan depletion abolished the normal tendency to improve error scores on non-shift trials in response to affective cues on a go/no-go task. We suggest that this inability to "maintain set" in the non-shift condition may be due to a disruption of semantic retrieval processes concerned with affect. The novel finding of impairment on a delayed visual pattern recognition task confirms and extends previous studies where selective effects on memory and learning have been found following acute tryptophan depletion.

Adult↗
PubMed2000

Neuroscience. Boosting working memory.

Working out which areas of the brain become activated during the formation of working (short-term) memory has been greatly helped by functional magnetic resonance imaging (fMRI). In a Perspective, Robbins et al. discuss new findings (Furey et al.) with fMRI that reveal how working memory is enhanced by the drug physostigmine, which increases cholinergic function in the brain.

Acetylcholine↗
PubMed2000

Methylphenidate enhances working memory by modulating discrete frontal and parietal lobe regions in the human brain.

The indirect catecholamine agonist methylphenidate (Ritalin) is the drug treatment of choice in attention deficit/hyperactivity disorder (AD/HD), one of the most common behavioral disorders of childhood (DSM-IV), although symptoms may persist into adulthood. Methylphenidate can enhance cognitive performance in adults and children diagnosed with AD/HD (Kempton et al., 1999; Riordan et al., 1999) and also in normal human volunteers on tasks sensitive to frontal lobe damage, including aspects of spatial working memory (SWM) performance (Elliott et al., 1997). The present study investigated changes in regional cerebral blood flow (rCBF) induced by methylphenidate during performance of a self-ordered SWM task to define the neuroanatomical loci of the beneficial effect of the drug. The results show that the methylphenidate-induced improvements in working memory performance occur with task-related reductions in rCBF in the dorsolateral prefrontal cortex and posterior parietal cortex. The beneficial effects of methylphenidate on working memory were greatest in the subjects with lower baseline working memory capacity. This is to our knowledge the first demonstration of a localization of a drug-induced improvement in SWM performance in humans and has relevance for understanding the treatment of AD/HD.

Adrenergic Uptake Inhibitors↗
PubMed2000

Amelioration of specific working memory deficits by methylphenidate in a case of adult attention deficit/hyperactivity disorder.

Cognitive neuroscience has provided an extensive literature on the neuroanatomy and psychopharmacology of working memory. However, while it has been shown that children with attention deficit/hyperactivity disorder (AD/HD) have deficits in working memory, relatively little is known about working memory functions in adults diagnosed with AD/HD. Furthermore, it remains to be seen whether methylphenidate (Ritalin), which is used in the treatment of childhood AD/HD can improve performance deficits in adult AD/HD patients. We have used three paradigms of spatial working memory validated in cortical lesion patients, and psychopharmacological and neuroimaging studies, in order to examine the effects of methylphenidate administration in a case of an adult diagnosed with AD/HD. In the AD/HD patient at baseline testing, performance on a test of spatial recognition memory and on a task of self-ordered spatial working memory was shown to be impaired. Importantly, the impairments on the self-ordered spatial working memory task were ameliorated by an acute oral dose of methylphenidate (0.5 mg/kg). These findings provide insights into the possible neurochemical and neuroanatomical substrates of the action of methylphenidate in AD/HD and suggest a useful methodology for further research into this potentially debilitating disorder.

Adult↗
PubMed1999

Systemic sulpiride in young adult volunteers simulates the profile of cognitive deficits in Parkinson's disease.

RATIONALE: The mesotelencephalic dopamine system has been implicated in cognitive processes dependent on an intact prefrontal cortex. Most previous research in humans has focused on dopaminergic agonists and their effects on tasks of working memory. OBJECTIVES: The present study was designed to investigate the cognitive and subjective effects of two doses (200 mg and 400 mg) of the dopaminergic D(2) receptor antagonist, sulpiride on a broad range of well-validated neuropsychological tasks in a group of 34 young healthy male volunteers. METHODS: Cognitive tasks were administered to subjects after ingestion of either drug or placebo within a double-blind, placebo-controlled, cross-over design. The cognitive tests included tasks from the Cambridge Neuropsychological Test Automated Battery (CANTAB) and were designed to assess visuospatial recognition memory, planning ability, working memory, strategy learning, sustained attention and attentional set-shifting. In addition, the National Adult Reading Test (NART) was used to assess verbal IQ, and visual analogue scales to assess subjective effects of the drug. RESULTS: Subjects on sulpiride were impaired on the tasks of spatial recognition, spatial working memory (sequence generation), planning (one-touch Tower of London) and attentional set-shifting. Only the spatial working memory task demonstrated a dose dependent effect. The impairments were not due to generalised sedative or motoric influences of sulpiride. CONCLUSIONS: All of the tasks impaired following sulpiride are known to be sensitive to frontal lobe damage and the precise pattern of deficits seen is consistent with the anatomical distribution of central dopamine receptors. The results are discussed with particular reference to their close simulation of the impairments seen in idiopathic Parkinson's disease.

Adult↗
PubMed1999

Medication received by patients with depression following the acute episode: adequacy and relation to outcome.

BACKGROUND: The adequacy of pharmacotherapy received in practice by patients after an acute episode of depression has been little studied. AIMS: To describe and assess adequacy of drug continuation and maintenance in patients with depression. METHOD: Patients with depression were interviewed 18 months after discharge from hospital. Quantitative assessments of drug treatment doses and compliance were made monthly over this period, and qualitative ratings in continuation and maintenance phases. RESULTS: About 20% of patients were prescribed low drug doses after discharge and 10% were prescribed no drugs at all. Reported compliance was around 70%. About 30% failed to receive adequate longer-term treatment, mostly due to the continuation phase being too short. Deficiencies of dosage and compliance were greater in patients who never achieved full recovery. Patient refusal was the most common reason for not using antidepressants. Further episodes of depression were not particularly associated with inadequate treatment. CONCLUSIONS: There were deficiencies in drug treatment that did not appear to be the principal cause of further episodes but may be important in non-recovery. Patient fears require discussion.

Acute Disease↗
PubMed1996

Distance measurements in nucleic acids using windowless dipolar recoupling solid state NMR.

A windowless, homonuclear dipolar recoupling pulse sequence (DRAWS) is described and a theoretical basis for describing its recoupling performance is developed using numerical techniques. It is demonstrated that DRAWS recouples weak dipolar interactions over a broad range of experimental and molecular conditions. We discuss two spectroscopic control experiments, which help to take into account effects due to insufficient proton decoupling, relaxation, and static dipolar couplings to nearby 13C spins at natural abundance. Finally DRAWS is used in combination with selective 13C labeling to measure 13C-13C distances in five doubly labeled DNA dodecamers, [d(CGCGAAT*T*CGCG)]2, which contain the binding site for the restriction enzyme EcoRI. The longest distance reported is 4.8 A. In most cases the distances agree well with those derived from X-ray crystallographic data, although small changes in hydration level can result in relatively large changes in internuclear distances.

Carbon Isotopes↗