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Biomedical subjects

I C Reid

Publications and source records attributed to I C Reid.

At least 19 recordsLinked to original sources
PubMed2005

Behavioural and neurochemical responses evoked by repeated exposure to an elevated open platform.

Increased psychophysiological resistance to chronic stress has been related to increased 5-HT release in the dorsal hippocampus. This study investigated the changes in 5-HT release and turnover in the hippocampus evoked by acute and repeated exposure to an inescapable stressor, an elevated open platform, and compared them to the changes evoked in the frontal cortex. Repeated exposure to this stressor results in habituation of the plasma corticosterone response to the test, with full habituation being observed after 20 trials. Repeated exposure to the stressor for 5 or 10 occasions increased 5-HT turnover in the hippocampus. By contrast, 5-HT turnover in frontal cortex was increased by acute exposure to the stressor. Microdialysis studies showed that acute stress increased 5-HT overflow in prefrontal cortex but not dorsal hippocampus whereas repeated daily (10 days) exposure to the stressor increased basal extracellular 5-HT in the dorsal hippocampus, but not the prefrontal cortex. Prior exposure to the stressor on up to 10 occasions enhanced the plasma corticosterone response to a challenge in an elevated plus-maze performed 24h later whereas repeated, but not acute, exposure to the stressor, elicited anxiolytic-like behavioural responses in this test. It is concluded that acute exposure to this form of inescapable stress selectively stimulates the 5-HT projections to the frontal cortex; repeated stress elicits a sustained increase in 5-HT release and turnover in the hippocampus. The data are consistent with the hypothesis that increased 5-HT release in the hippocampus may be implicated in the mechanisms underlying habituation to inescapable stress.

Animals↗
PubMed2005

Regulation of corticosteroid receptors in the rat brain: the role of serotonin and stress.

It has been suggested that physiological resistance to repeated stress is associated with increased 5-hydroxytryptamine (5-HT) release in the dorsal hippocampus and that dysregulation of this neuroadaptation may be implicated in the psychopathology of depression. This study used 5,7-dihydroxytryptamine lesions to investigate the role of 5-HT projections to the hippocampus in physiological responses to repeated stress and putative changes in corticosteroid receptor immunoreactivity in the brain. Repeated exposure to elevated open platform stress (1 h/day) caused regionally selective changes in glucocorticoid and mineralocorticoid receptor immunoreactivity in the dorsal hippocampus that were not observed in ventral hippocampus, frontal cortex, hypothalamus or parietal cortex. Glucocorticoid receptor immunoreactivity in the dorsal hippocampus was decreased after 5 days but increased after 20 days of stress. Mineralocorticoid receptor immunoreactivity was increased after 5 or 10 days of stress. The increases in glucocorticoid and mineralocorticoid receptor immunoreactivity, evoked by repeated stress, were abolished by lesions of the principal 5-HT projections to the hippocampus. The lesions abolished the increased defecation observed in stressed animals, but had no effects on the plasma corticosterone response to the stressor or the habituation of this response observed following repeated stress. The experiments have revealed a dissociation in the regulation of corticosteroid receptor expression in the dorsal and ventral hippocampus by repeated stress and 5-HT. The data suggest that adaptation to inescapable stress is associated with regionally selective changes in corticosteroid receptor expression in dorsal hippocampus that are largely 5-HT-dependent, although these changes do not mediate habituation of the pituitary adrenocortical response to the stressor.

Animals↗
PubMed2002

Antidepressant mechanisms: functional and molecular correlates of excitatory amino acid neurotransmission.

Specific targeting of the serotonergic and noradrenergic systems for the development of antidepressant compounds has resulted in drugs with more favourable side-effect profiles but essentially no greater efficacy than those compounds discovered more than 40 years ago. Alternative targets are now being considered in the hope that they will have a faster onset of action and be useful for those patients currently unresponsive to conventional treatments. Excitatory amino acid neurotransmission has been attributed various roles in both normal and abnormal brain function. The N-methyl-D-aspartate receptor in particular has long been postulated to play a role in the formation of memories. Major depressive disorder is characterised by alterations in cognitive function, as well as affect. Although there is evidence that early adverse events and stress can have a causal influence on depression, the underlying neurobiology of the disorder is poorly understood. This review will document current evidence for the involvement of excitatory amino acid neurotransmission in the pathophysiology of the affective disorders. The preclinical literature suggests that both electroconvulsive stimulation and antidepressant drugs can affect hippocampal long-term potentiation and the expression of excitatory amino acid receptor subtypes. Exposing animals to stress, including the kind that produces learned helplessness, can also affect synaptic plasticity in the hippocampus. There is clinical evidence that patients with chronic depression have structural brain abnormalities, including hippocampal atrophy, and a preliminary study has shown that an N-methyl-D-aspartate receptor antagonist may have antidepressant efficacy.

Animals↗
PubMed2001

How antidepressants work: new perspectives on the pathophysiology of depressive disorder.

BACKGROUND: New research in animals is beginning to change radically our understanding of the biology of stress and the effects of antidepressant agents. AIMS: To relate recent findings from the basic neurosciences to the pathophysiology of depressive disorder. METHOD: Drawing together findings from molecular and physiological studies in rats, social studies in primates and neuropsychological studies in humans, we review the neurotrophic and neuroplastic effects of antidepressants and stress. RESULTS: Stress and antidepressants have reciprocal actions on neuronal growth and vulnerability (mediated by the expression of neurotrophins) and synaptic plasticity (mediated by excitatory amino acid neurotransmission) in the hippocampus and other brain structures. Stressors have the capacity to progressively disrupt both the activities of individual cells and the operating characteristics of networks of neurons throughout the life cycle, while antidepressant treatments act to reverse such injurious effects. CONCLUSIONS: We propose a central role for the regulation of synaptic connectivity in the pathophysiology of depressive disorder.

Animals↗
PubMed2000

Repeated ECS and fluoxetine administration have equivalent effects on hippocampal synaptic plasticity.

RATIONALE: Recent studies have implicated intracellular transduction pathways and neurotrophic factors in the action of antidepressants. Adaptation in these pathways may ultimately affect electrophysiological and morphological properties of neurones. We have previously shown that repeated electroconvulsive stimulation, a safe and effective antidepressant treatment, has profound effects on hippocampal synaptic connectivity and plasticity in the rat. Here, we investigated whether these electrophysiological properties were shared by the chemical antidepressant, fluoxetine. OBJECTIVES: To compare the electrophysiological and cognitive effects of two very different antidepressant treatments: repeated electroconvulsive stimulation (rECS); and chronic administration of the serotonin specific re-uptake inhibitor (SSRI), fluoxetine. METHODS: Rats were exposed to either rECS or daily fluoxetine administration for 15 days. The animals were then anaesthetised and dentate field excitatory post-synaptic potential (fEPSP) characteristics were measured before and after the induction of long-term potentiation (LTP) by high frequency perforant path stimulation. In a separate experiment, the effects of rECS and chronic fluoxetine administration on acquisition and retention of a spatial learning task in the Morris watermaze were determined. RESULTS: Chronic fluoxetine administration and rECS produced equivalent increases in dentate fEPSP compared to respective control groups. LTP induction was attenuated in both groups. Spatial learning was, in contrast, unaffected by fluoxetine treatment but significantly impaired following rECS. CONCLUSIONS: Given that fluoxetine and rECS share antidepressant properties, but differ in their effects on learning and memory, we propose that the common effects on dentate connectivity and synaptic plasticity described here are more likely to relate to affective rather than cognitive function. This result is consistent with other experiments showing that a reduction in dentate connectivity correlates with stress susceptibility in animals.

Animals↗
PubMed2000

The N-methyl-D-aspartate receptor, synaptic plasticity, and depressive disorder. A critical review.

The roles of the N-methyl-D-aspartate (NMDA) receptor and NMDA receptor-mediated synaptic plasticity are reviewed in the context of depressive disorder and its treatment. The mode of action of antidepressant treatment is poorly understood. Animal studies have suggested that many antidepressant drugs show activity at the NMDA receptor and that NMDA antagonists have antidepressant profiles in preclinical models of depression. A post-mortem study in humans has suggested that certain binding characteristics of the NMDA receptor may be down-regulated in the brains of suicide victims. "Depressogenic" stressors in animals and chronic administration of antidepressant agents perturb NMDA-dependent synaptic plasticity in the hippocampus.

Animals↗
PubMed1999

The views and outcomes of consenting and non-consenting patients receiving ECT.

BACKGROUND: Current mental health legislation in the UK makes provision for the use of certain treatments in severely ill patients who are unable, or unwilling, to give informed consent. Under the terms of this legislation, electroconvulsive therapy (ECT) may be used, usually to treat severely depressed patients. A number of organizations have challenged this practice, stating that ECT should only be given with fully informed consent: it has been implied that patients receiving compulsory ECT (given without the patient's consent, under the terms of mental health legislation) find the treatment damaging and unhelpful. METHODS: A series of 150 patients receiving ECT in Aberdeen was studied. A proportion of the series (approximately 7%) received compulsory ECT. The views and treatment outcomes of compulsory patients were compared with those of patients giving informed consent for treatment. RESULTS: More than 80% of patients in both consenting and compulsory groups considered ECT to have helped them. Clinical outcome did not differ between the groups. Patients' views showed marked concordance with independent medical evaluation of outcome. CONCLUSIONS: Outcome following ECT in non-consenting patients is equivalent to that seen in consenting patients whether rated by the patients themselves or by clinicians. Overall outcome is good, with more than 80% of patients benefiting from treatment. A ban on compulsory ECT would deny the access of seriously ill patients to an effective and acceptable treatment.

Adult↗
PubMed1998

Association of road-traffic accidents with benzodiazepine use.

BACKGROUND: Psychomotor studies suggest that commonly prescribed psychoactive drugs impair driving skills. We have examined the association between the use of psychoactive drugs and road-traffic accidents. METHODS: We used dispensed prescribing as a measure of exposure in a within-person case-crossover study of drivers aged 18 years and over, resident in Tayside, UK, who experienced a first road-traffic accident between Aug 1, 1992, and June 30, 1995, and had used a psychoactive drug (tricyclic antidepressant, benzodiazepine, selective serotonin-reuptake inhibitor, or other psychoactive drug [mainly major tranquillisers]) between Aug 1, 1992, and the date of the accident. For each driver, the risks of having a road-traffic accident while exposed and not exposed to a drug were compared. FINDINGS: 19386 drivers were involved in a first road-traffic accident during the study period. 1731 were users of any study drug. On the day of the accident, 189 individuals were taking tricyclic antidepressants (within-patient exposure odds ratio for an accident 0.93 [95% CI 0.72-1.21]), 84 selective serotonin-reuptake inhibitors (0.85 [0.55-1.33]), 235 benzodiazepines (1.62 [1.24-2.12]), and 47 other psychoactive drugs (0.88 [0.62-1.25]). The risk associated with benzodiazepine use decreased with increasing driver's age and was greater when the breath test for alcohol was positive. A dose-response relation was evident with benzodiazepines. The increased risk with benzodiazepines was significant for long-half-life drugs, used as anxiolytics, and for short-half-life hypnotics (all zopiclone). INTERPRETATION: Users of anxiolytic benzodiazepines and zopiclone were at increased risk of experiencing a road-traffic accident. Users of anxiolytic benzodiazepines and zopiclone should be advised not to drive.

Accidents, Traffic↗
PubMed1997

Seizures, memory and synaptic plasticity.

Electrophysiological studies of the rodent hippocampus show that repeated seizure activity has a profound, deleterious effect on an important form of synaptic plasticity (long-term potentiation, LTP) which has been suggested to underlie memory formation. It appears that seizure activity incrementally causes an indiscriminate and widespread induction of long-term potentiation, consuming and thereby reducing overall hippocampal plasticity available for information processing. Consistent with this finding, severe deficits in a form of learning known to be mediated by hippocampal function are observed in rat subjected to repeated electroconvulsive seizures (ECS). The effect on synaptic function gradually resolves over a period of around 40 days, paralleling the time course of the transitory cognitive impairment seen following electrical seizure induction (ECT) in humans being treated for severe affective disorder. The effect is likely to be mediated by NMDA receptor activation during seizure activity, as the phenomenon can be prevented by the administration of a non-competitive NMDA receptor associated channel blocker (ketamine) immediately before seizure induction. The mechanisms described may account for the inter-ictal cognitive disturbance observed in patients suffering from poorly controlled epilepsy.

Animals↗
PubMed1997

Modifiable neuronal connections: an overview for psychiatrists.

Synaptic plasticity is currently the target of much neurobiological research, because it is thought to play an important role in brain function (particularly memory formation). However, it has attracted little attention from psychiatrists to date despite accumulating evidence that links it to various clinical syndromes, including amnesia and possibly psychosis. The purpose of this article is to present an overview of the two major arms of synaptic plasticity research-theoretical (the field of neural network modeling) and neurobiological (long-term potentiation). Artificial neural networks are a class of theoretical model that has been developed with the aim of understanding how information could, in principle, be represented by large numbers of interconnected and relatively simple units. Over the past few decades, several theoretical accounts of information-processing mechanisms have been developed, and these are briefly reviewed. The principle common to representation formation in nearly all neural networks is that of "associability"-the idea that streams of information are combined by forming, strengthening, or pruning connections between them to form new representations that can later be retrieved. Associability also lies at the heart of psychological theories of information storage in the brain. Research into associability has directed the attention of many experimenters toward the possible biological correlates of such mechanisms. Of particular interest is the recent discovery that some neurons appear to possess connections of modifiable strength. The implications of this finding for psychiatry are discussed in relation to representational disorders such as delusions and amnesia.

Amnesia↗
PubMed1996

Repeated ECS induces GluR1 mRNA but not NMDAR1A-G mRNA in the rat hippocampus.

The neural basis underlying the cognitive side effects of ECT is unknown. Recent studies suggest that the memory dysfunction may be caused by alterations in hippocampal synaptic efficacy [20]. In situ hybridisation was used to examine the possible receptor mechanisms responsible for this effect. Repeated ECS markedly increased mRNA expression for the GluR1 subunit of the AMPA receptor, but not the NMDAR1A-G subtypes of the NMDA receptor, relative to control treatments. This effect was present 24 h after the last seizure and may be responsible for the expression of the ECS-induced increase in synaptic efficacy.

Animals↗
PubMed1996

Chronic mild stress and sucrose consumption: validity as a model of depression.

Sucrose consumption and preference were examined in rats subjected to a 6-week regimen of unpredictable mild stressors, after Willner et al. (11). These subjects were compared with groups exposed to: 1. only the food deprivation element of the stress protocol; or 2. the stress protocol without the food deprivation element. A control group was not exposed to stressors. Body weight and sucrose consumption were significantly reduced in stressed and food-deprived animals compared to the other 2 groups. These variables therefore appeared dependent on food deprivation and independent of other elements of the stress protocol. Neither sucrose consumption per gram body weight nor sucrose preference differed significantly among the 4 groups. These results indicate that food deprivation is not only necessary, but sufficient, to produce sucrose consumption deficits in rats. It is, therefore, likely that reduced sucrose consumption in stressed rats results solely from diminished body weight rather than exposure to the series of stressors. We conclude that sucrose consumption is not a valid index of reward responsiveness. Other measures (such as place-preference conditioning or intracranial self-stimulation threshold) should be evaluated also with respect to body weight change when considering the validity of stressor-based models of depressive disorder.

Animals↗
PubMed1995

Sucrose consumption as an hedonic measure following chronic unpredictable mild stress.

The consumption of, and preference for, a rewarding 0.9% sucrose solution was examined in rats subjected chronically (8 wk) to a regimen of unpredictable mild stressors. Intake of sucrose was reduced in stressed animals compared to controls after 3 wk. However, correction for body weight changes revealed no significant difference in sucrose consumption between the groups. A comparison of the mean sucrose intakes of matched low-weight rats, with low weight a function of either immaturity or stress, failed to differentiate between the groups. Total sucrose consumption and total fluid intake correlated significantly with body weight of stressed animals and controls. Percentage preference for sucrose solution did not differ between controls and stressed animals. It is concluded that the validity and reliability of sucrose consumption as an hedonic measure within the context of exposure to chronic unpredictable mild stress must be questioned.

Animals↗
PubMed1994

Ketamine prevents ECS-induced synaptic enhancement in rat hippocampus.

Electrical induction of seizure activity profoundly impairs hippocampal long-term potentiation (LTP) in rats. A similar effect may account for the memory dysfunction observed after electroconvulsive stimulation in humans and other species. The co-administration of ketamine with the induction of electroconvulsive seizures (ECS) was evaluated as a possible method for reducing the impact of ECS on hippocampal synaptic plasticity in rats. Electrophysiological studies in vivo showed that both the enhancement of the EPSP slope and the subsequent reduction of experimentally induced LTP in the dentate gyrus by repeated, spaced ECS were significantly attenuated by ketamine anaesthesia. The findings suggest that ketamine may protect against ECS-induced memory impairment and thus prove useful in reducing the transient cognitive impairment following electroconvulsive therapy (ECT).

Animals↗
PubMed1993

The enigma of olfactory learning.

It has been suggested, on the basis of neuroanatomical and behavioural data, that olfactory discrimination in the rat provides privileged access to higher cognitive processes, involves the acquisition of a learning-set and, importantly, can be used to model human hippocampal function and dysfunction. In this article, Ian C. Reid and Richard G. M. Morris question the assumptions upon which these claims have been based and criticize the application of odour discrimination learning in the rat to the study of human memory.

Animals↗
PubMed1992

Effects of intraventricular infusion of the N-methyl-D-aspartate (NMDA) receptor antagonist AP5 on spatial memory of rats in a radial arm maze.

Rats were trained to asymptotic performance in an 8-arm radial maze. They then received chronic intraventricular infusion of either artificial CSF or the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5- phosphonopentanoic acid (AP5), at a concentration (30 mM) that has been shown previously to prevent the induction of long-term potentiation in the dentate gyrus of the hippocampus in vivo. Subsequently the rats received another 9 trials in the maze in a quasi-random order, 3 uninterrupted trials, and another 6 trials each with mid-trial delays of 5, 20 or 60 min during which the animals were placed in their home cage. The mean number of errors for the AP5 rats did not differ significantly from that of the controls in the uninterrupted trials throughout the experiment, nor did it differ from that of the controls in any of the 3 delayed trials when these were first introduced. However, the control animals performed better at the longer delays when these were introduced for the second time, whilst there was no such improvement (but rather a deterioration) for the AP5 animals. The impairment of performance in the AP5 rats during the second block of delayed trials was significant, and independent of the length of the delay. These results show that NMDA receptor blockade does not impair working memory in the radial maze per se, but that it does prevent an improvement of working memory persistence with further training.

2-Amino-5-phosphonovalerate↗