Dynamics of cholinergic synaptic mechanisms in rat hippocampus after stress

Distinct synaptic mechanisms drive the behavioral response to acute stress and rapid correction by ketamine

Prevailing hypotheses on the mechanisms of antidepressant action posit that antidepressants directly counteract deficiencies in major neurotransmitter signaling systems that underlie depression. The rapidly acting antidepressant ketamine has been postulated to correct excess glutamatergic signaling via glutamatergic antagonism leading to the rescue of neuronal structural deficits and reversal of behavioral symptoms. We studied this premise using systemic administration of the acetylcholinesterase inhibitor physostigmine, which has been shown to rapidly elicit a shorter-term period of depressed mood in humans via cholinergic mechanisms. We observed that physostigmine induces acute stress in tandem with long term depression of glutamate release in the hippocampus of mice. However, ketamine rapidly acts to re-establish glutamatergic synaptic efficacy via postsynaptic signaling and behaviorally masks the reduction in passive coping induced by physostigmine. These results underscore the divergence of synaptic signaling mechanisms underlying mood changes and antidepressant action and highlight how distinct synaptic mechanisms may underlie neuropsychiatric disorders versus their treatment.

Substances of health concern in home-distilled and commercial alcohols from Texas

Objective

Poor distillation practices in the production of spirits have historically resulted in many instances of adverse health outcomes including death. Concern has focused on lead and copper contamination as well as unhealthy levels of methanol and glyphosate. This study assesses home-distilled and commercially distilled alcohols from Texas for these substances of concern, highlighting their potential risks to public health.

Methods

Atomic absorption spectroscopy, gas chromatography, and enzyme-linked immunosorbent assay were employed to determine lead and copper, methanol, and glyphosate levels in 12 commercial and 36 home-distilled alcohol samples.

Results

Our findings showed that 11 % of the home-distilled alcohols exceeded the U.S. Alcohol and Tobacco Tax and Trade Bureau's copper safety limits of 0.5 mg/L for wine. Additionally, 36 % of these samples surpassed the European Commission (EC)'s lead legal threshold of 0.15 mg/L set for wine products. Results from commercial alcohols indicated that no samples exceeded the same safety limits for copper, and 33 % exceeded the same legal threshold for lead. Both commercial and home-distilled alcohols exhibited methanol concentrations remarkably below the 0.35 % limit for brandy set by the U.S. Food and Drug Administration. Only two home-distilled samples contained detectable glyphosate concentrations well below 100 μg/L, the maximum residue level in beer and wine established by the EC.

Conclusions

Our findings suggested that consumption of alcohol in Texas may pose potential health risks associated with the elevated content of lead and copper. There is a need for increased focus on alcohol as a potential source of exposure to heavy metals.

Modulation of Muscarinic Signalling in the Central Nervous System by Steroid Hormones and Neurosteroids

Muscarinic acetylcholine receptors expressed in the central nervous system mediate various functions, including cognition, memory, or reward. Therefore, muscarinic receptors represent potential pharmacological targets for various diseases and conditions, such as Alzheimer's disease, schizophrenia, addiction, epilepsy, or depression. Muscarinic receptors are allosterically modulated by neurosteroids and steroid hormones at physiologically relevant concentrations. In this review, we focus on the modulation of muscarinic receptors by neurosteroids and steroid hormones in the context of diseases and disorders of the central nervous system. Further, we propose the potential use of neuroactive steroids in the development of pharmacotherapeutics for these diseases and conditions.

Blood Pressure Regulation Evolved from Basic Homeostatic Components

Blood pressure (BP) is determined by several physiological factors that are regulated by a range of complex neural, endocrine, and paracrine mechanisms. This study examined a collection of 198 human genes related to BP regulation, in the biological processes and functional prisms, as well as gene expression in organs and tissues. This was made in conjunction with an orthology analysis performed in 19 target organisms along the phylogenetic tree. We have demonstrated that transport and signaling, as well as homeostasis in general, are the most prevalent biological processes associated with BP gene orthologs across the examined species. We showed that these genes and their orthologs are expressed primarily in the kidney and adrenals of complex organisms (e.g., high order vertebrates) and in the nervous system of low complexity organisms (e.g., flies, nematodes). Furthermore, we have determined that basic functions such as ion transport are ancient and appear in all organisms, while more complex regulatory functions, such as control of extracellular volume emerged in high order organisms. Thus, we conclude that the complex system of BP regulation evolved from simpler components that were utilized to maintain specific homeostatic functions that play key roles in existence and survival of organisms.

Navigating Alzheimer's Disease via Chronic Stress: The Role of Glucocorticoids

Alzheimer's disease (AD) is a chronic intensifying incurable progressive disease leading to neurological deterioration manifested as impairment of memory and executive brain functioning affecting the physical ability like intellectual brilliance, common sense in patients. The recent therapeutic approach in Alzheimer's disease is only the symptomatic relief further emerging the need for therapeutic strategies to be targeted in managing the underlying silent killing progression of dreaded pathology. Therefore, the current research direction is focused on identifying the molecular mechanisms leading to the evolution of the understanding of the neuropathology of Alzheimer's disease. The resultant saturation in the area of current targets (amyloid β, τ Protein, oxidative stress etc.) has led the scientific community to rethink of the mechanistic neurodegenerative pathways and reprogram the current research directions. Although, the role of stress has been recognized for many years and contributing to the development of cognitive impairment, the area of stress has got the much-needed impetus recently and is being recognized as a modifiable menace for AD. Stress is an unavoidable human experience that can be resolved and normalized but chronic activation of stress pathways unsettle the physiological status. Chronic stress mediated activation of neuroendocrine stimulation is generally linked to a high risk of developing AD. Chronic stress-driven physiological dysregulation and hypercortisolemia intermingle at the neuronal level and leads to functional (hypometabolism, excitotoxicity, inflammation) and anatomical remodeling of the brain architecture (senile plaques, τ tangles, hippocampal atrophy, retraction of spines) ending with severe cognitive deterioration. The present review is an effort to collect the most pertinent evidence that support chronic stress as a realistic and modifiable therapeutic earmark for AD and to advocate glucocorticoid receptors as therapeutic interventions.

Remodeling of cholinergic input to the hippocampus after noise exposure and tinnitus induction in Guinea pigs

Here, we investigate remodeling of hippocampal cholinergic inputs after noise exposure and determine the relevance of these changes to tinnitus. To assess the effects of noise exposure on the hippocampus, guinea pigs were exposed to unilateral noise for 2 hr and 2 weeks later, immunohistochemistry was performed on hippocampal sections to examine vesicular acetylcholine transporter (VAChT) expression. To evaluate whether the changes in VAChT were relevant to tinnitus, another group of animals was exposed to the same noise band twice to induce tinnitus, which was assessed using gap-prepulse Inhibition of the acoustic startle (GPIAS) 12 weeks after the first noise exposure, followed by immunohistochemistry. Acoustic Brainstem Response (ABR) thresholds were elevated immediately after noise exposure for all experimental animals but returned to baseline levels several days after noise exposure. ABR wave I amplitude-intensity functions did not show any changes after 2 or 12 weeks of recovery compared to baseline levels. In animals assessed 2-weeks following noise-exposure, hippocampal VAChT puncta density decreased on both sides of the brain by 20-60% in exposed animals. By 12 weeks following the initial noise exposure, changes in VAChT puncta density largely recovered to baseline levels in exposed animals that did not develop tinnitus, but remained diminished in animals that developed tinnitus. These tinnitus-specific changes were particularly prominent in hippocampal synapse-rich layers of the dentate gyrus and areas CA3 and CA1, and VAChT density in these regions negatively correlated with tinnitus severity. The robust changes in VAChT labeling in the hippocampus 2 weeks after noise exposure suggest involvement of this circuitry in auditory processing. After chronic tinnitus induction, tinnitus-specific changes occurred in synapse-rich layers of the hippocampus, suggesting that synaptic processing in the hippocampus may play an important role in the pathophysiology of tinnitus.

Enhanced cholinergic-tone during the stress induce a depressive-like state in mice

Major depressive disorder has a heterogeneous etiology, since it arises from the interaction of multiple factors and different pathophysiological mechanisms are involved in the symptomatology. This study aimed to investigate the role of the cholinergic system in the susceptibility to stress and, consequently, in the depression-like behavior. C57BL/6 mice were treated with Physostigmine (PHYS), an acetylcholinesterase (AChE) inhibitor, and were submitted to the social defeat stress. For the behavioral evaluation of the locomotor activity, anxiety-like and depression-like behaviors the open field, elevated plus maze, sucrose preference, social interaction and forced swim were used. Hippocampus and prefrontal cortex samples were collected for evaluation of AChE activity, as well as blood samples for analysis of serum cortisol levels. Our results showed that 15 min after the injection of PHYS there was a significant inhibition of AChE activity in the hippocampus and in the prefrontal cortex. On the other hand, in the end of the experimental design, day 12, there was no difference in AChE activity levels. Inhibition of AChE and exposure to the stress led to an increase in cortisol levels. Animals that received PHYS and were exposed to stress showed less social interaction and greater learned helplessness, anhedonia and anxious-like behavior. Taken together, our findings suggest that increasing the cholinergic tone shortly before stress induction impacts on the ability to cope with upcoming stressful situations, leading to a depressive-like state.

Impairments in laterodorsal tegmentum to VTA projections underlie glucocorticoid-triggered reward deficits

Ventral tegmental area (VTA) activity is critical for reward/reinforcement and is tightly modulated by the laterodorsal tegmentum (LDT). In utero exposure to glucocorticoids (iuGC) triggers prominent motivation deficits but nothing is known about the impact of this exposure in the LDT-VTA circuit. We show that iuGC-rats have long-lasting changes in cholinergic markers in the LDT, together with a decrease in LDT basal neuronal activity. Interestingly, upon LDT stimulation, iuGC animals present a decrease in the magnitude of excitation and an increase in VTA inhibition, as a result of a shift in the type of cells that respond to the stimulus. In agreement with LDT-VTA dysfunction, we show that iuGC animals present motivational deficits that are rescued by selective optogenetic activation of this pathway. Importantly, we also show that LDT-VTA optogenetic stimulation is reinforcing, and that iuGC animals are more susceptible to the reinforcing properties of LDT-VTA stimulation.

Brain nicotinic acetylcholine receptors are involved in stress-induced potentiation of nicotine reward in rats

The aim of the present study was to examine the possible role of nicotinic acetylcholine receptors of the dorsal hippocampus (CA1 regions), the medial prefrontal cortex or the basolateral amygdala in the effect of acute or sub-chronic stress on nicotine-induced conditioned place preference. Our results indicated that subcutaneous administration of nicotine (0.2 mg/kg) induced significant conditioned place preference. Exposure to acute or sub-chronic elevated platform stress potentiated the response of an ineffective dose of nicotine. Pre-conditioning intra-CA1 (0.5-4 µg/rat) or intra-medial prefrontal cortex (0.2-0.3 µg/rat) microinjection of mecamylamine (a non-selective nicotinic acetylcholine receptor antagonist) reversed acute stress-induced potentiation of nicotine reward as measured in the conditioned place preference paradigm. By contrast, pre-conditioning intra-basolateral amygdala microinjection of mecamylamine (4 µg/rat) potentiated the effects of acute stress on nicotine reward. Our findings also showed that intra-CA1 or intra-medial prefrontal cortex, but not intra-basolateral amygdala, microinjection of mecamylamine (4 µg/rat) prevented the effect of sub-chronic stress on nicotine reward. These findings suggest that exposure to elevated platform stress potentiates the rewarding effect of nicotine which may be associated with the involvement of nicotinic acetylcholine receptors. It seems that there is a different contribution of the basolateral amygdala, the medial prefrontal cortex or the CA1 nicotinic acetylcholine receptors in stress-induced potentiation of nicotine-induced conditioned place preference.

Interaction of basal forebrain cholinergic neurons with the glucocorticoid system in stress regulation and cognitive impairment

A substantial number of studies on basal forebrain (BF) cholinergic neurons (BFCN) have provided compelling evidence for their role in the etiology of stress, cognitive aging, Alzheimer’s disease (AD), and other neurodegenerative diseases. BFCN project to a broad range of cortical sites and limbic structures, including the hippocampus, and are involved in stress and cognition. In particular, the hippocampus, the primary target tissue of the glucocorticoid stress hormones, is associated with cognitive function in tandem with hypothalamic-pituitary-adrenal (HPA) axis modulation. The present review summarizes glucocorticoid and HPA axis research to date in an effort to establish the manner in which stress affects the release of acetylcholine (ACh), glucocorticoids, and their receptor in the context of cognitive processes. We attempt to provide the molecular interactive link between the glucocorticoids and cholinergic system that contributes to BFCN degeneration in stress-induced acceleration of cognitive decline in aging and AD. We also discuss the importance of animal models in facilitating such studies for pharmacological use, to which could help decipher disease states and propose leads for pharmacological intervention.

Comparison of operant escape and reflex tests of nociceptive sensitivity

Testing of reflexes such as flexion/withdrawal or licking/guarding is well established as the standard for evaluating nociceptive sensitivity and its modulation in preclinical investigations of laboratory animals. Concerns about this approach have been dismissed for practical reasons - reflex testing requires no training of the animals; it is simple to instrument; and responses are characterized by observers as latencies or thresholds for evocation. In order to evaluate this method, the present review summarizes a series of experiments in which reflex and operant escape responding are compared in normal animals and following surgical models of neuropathic pain or pharmacological intervention for pain. Particular attention is paid to relationships between reflex and escape responding and information on the pain sensitivity of normal human subjects or patients with pain. Numerous disparities between results for reflex and operant escape measures are described, but the results of operant testing are consistent with evidence from humans. Objective reasons are given for experimenters to choose between these and other methods of evaluating the nociceptive sensitivity of laboratory animals.

Neonatal stress affects vulnerability of cholinergic neurons and cognition in the rat: involvement of the HPA axis

Adverse experiences early in life may sensitize specific neurocircuits to subsequent stressors. We have evaluated in maternal separation (MS) rats, an animal paradigm of early-life stress, the effects of a selective cholinergic lesion on cognitive function as well as susceptibility of cholinergic neurons to the lesion. MS rats subjected to a cholinergic lesion by administration of the immunotoxin 192 IgG-saporin, showed significant decreases in both choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity compared to control lesioned rats. Morris water maze results revealed a significant impairment in learning and memory function in MS adult rats and further cognitive deficits after the lesion. The lesion of cholinergic neurons induced a significant decrease in glucocorticoid receptor density in MS rats, accompanied by increases in CRF mRNA expression. Decreases in NGF and increases in NGF-p75NTR expression have also been found in MS rats. Our results suggest that vulnerability of basal forebrain cholinergic nerve cells might be affected by the HPA axis. The present data are discussed not only in terms of conditions that occur during ageing or Alzheimer disease, but also regarding a purported involvement of the cholinergic system in the regulation of HPA axis activity.

Differential effects of chronic partial sleep deprivation and stress on serotonin-1A and muscarinic acetylcholine receptor sensitivity

Disrupted sleep and stress are often linked to each other, and considered as predisposing factors for psychopathologies such as depression. The depressed brain is associated with reduced serotonergic and enhanced cholinergic neurotransmission. In an earlier study, we showed that chronic sleep restriction by forced locomotion caused a gradual decrease in postsynaptic serotonin-1A receptor sensitivity, whilst chronic forced activity alone, with sufficient sleep time, did not affect receptor sensitivity. The first aim of the present study was to examine whether the sleep loss-induced change in receptor sensitivity is mediated by adrenal stress hormones. The results show that the serotonin-1A receptor desensitization is independent of adrenal hormones as it still occurs in adrenalectomized rats. The second aim of the study was to establish the effects of sleep restriction on cholinergic muscarinic receptor sensitivity. While sleep restriction affected muscarinic receptor sensitivity only slightly, forced activity significantly hypersensitized the muscarinic receptors. This hypersensitization is because of the stressful nature of the forced activity protocol as it did not occur in adrenalectomized rats. Taken together, these data confirm that sleep restriction may desensitize the serotonin-1A receptor system. This is not a generalized effect as sleep restriction did not affect the sensitivity of the muscarinic cholinergic receptor system, but the latter was hypersensitized by stress. Thus, chronic stress and sleep loss may, partly via different pathways, change the brain into a direction as it is seen in mood disorders.

Changes in pain behavior induced by formalin, substance P, glutamate and pro-inflammatory cytokines in immobilization-induced stress mouse model

In the present study, we examined the change of pain behaviors induced by formalin injected subcutaneously (s.c.) into the hind paw, or substance P (SP), glutamate, and pro-inflammatory cytokines (TNF-alpha, IL-1beta, and IFN-gamma) injected intrathecally (i.t.) in the mouse immobilization stress model. The mouse was restrained either once for 1h or five times for 5 days (once/day). In the formalin test, a single immobilization stress attenuated pain behaviors (licking, biting or scratching) in the second phase, while it had no effect on the pain behaviors revealed during the first phase. In addition, repeated immobilization stress attenuated pain behaviors revealed during the second phase but not in the first phase. A single as well as repeated immobilization stress decreased pain behaviors induced by substance P i.t. injection, but there were no significant changes in the glutamate test. In the pro-inflammatory cytokine pain model, a single immobilization stress decreased the pain behaviors induced by TNF-alpha, IL-1beta administered i.t. but not by IFN-gamma administered i.t. Moreover, a mouse applied with repeated immobilization stress did not show any changes in pain behaviors elicited by pro-inflammatory cytokines (TNF-alpha, IL-1beta and IFN-gamma) compared to the control group. These results suggest that a single and repeated immobilization stress differentially affects such nociceptive processing induced by formalin, SP, glutamate and pro-inflammatory cytokines in different manners.

Nature of stress: differential effects on brain acetylcholinesterase activity and memory in rats

Effect of acute, chronic-predictable and chronic-unpredictable stress on memory and acetylcholinesterase (AChE) was investigated in rats. The animals were subjected to 3 type of stressors--(1) acute immobilization stress, (2) chronic-predictable stress i.e., immobilization daily for 5 consecutive days and (3) chronic-unpredictable stress that included reversal of light/dark cycle, over-night fasting, forced-swimming, immobilization and forced exercise in random unpredictable manner daily for 5 consecutive days. Learning and memory function was studied by single trial Passive avoidance test. AChE activity was assayed spectrophotometrically in the detergent (DS) and salt (SS) soluble fractions in different brain regions. Learning was obtained in acute and chronic-predictable stress groups but not in chronic-unpredictable group. Acute, chronic-predictable and chronic-unpredictable stress caused significant decrease in AChE activity in the DS fraction of cortex, hippocampus and hypothalamus as compared to control. Results indicate that AChE in DS fraction is predominantly affected in stressed and stressed-trained group but cognition is affected only by chronic-unpredictable stress. In acute and chronic-predictable groups the decreased AChE activity in the hippocampal DS fraction during learning may be responsible to maintain cognitive function by enhancing the cholinergic activity.

Repeated Restraint Stress Reduces Opioid Receptor Binding in Different Rat CNS Structures

Different effects of exposure to acute or to repeated stress have been observed upon the nociceptive response in rats. In the present study, we repeatedly submitted Wistar rats to restraint for 40 days, a treatment known to induce an increase in the nociceptive response in the tail-flick test. Afterwards, the effect of repeated restraint stress on the density of opioid receptors in rat spinal cord, frontal cortex, and hippocampus was investigated. Results showed that repeatedly stressed rats displayed a significant decrease in opioid receptors density in all structures studied; cortex (141.3 +/- 5.7 for control and 103.3 +/- 15.9 for stressed rats), hippocampus (92.4 +/- 7.2 for control and 64.8 +/- 7.7 for stressed rats), and spinal cord (122.2 +/- 12.8 for control and 79.7 +/- 9.7 for stressed rats). These findings suggest opioid mediation of the altered responses observed in these repeatedly-stressed animals, although the participation of non-opioid mechanisms in this phenomenon cannot be ruled out.

Effects of different kinds of acute stress on nerve growth factor content in rat brain

Nerve growth factor (NGF) has several effects on the central nervous system; on the one hand NGF fosters survival and function of cholinergic neurons of the basal forebrain, on the other hand this protein is implicated in the stress response of the hypothalamic-pituitary-adrenocortical axis (HPAA). In this study we tested the influence of threatening and painful stress treatments in three different intensities as well as forced motoric activity on NGF content in different brain areas in adult rats. We found that threatening treatment with or without painful stimuli was followed by a significant decrease of NGF concentration in the amygdala (44.5%; P=0.03) and the frontal cortex (-45.5%; P=0.02). We also observed that after stress of forced motoric activity NGF content in the frontal cortex (-32%; P=0.01) and the hippocampus (-32%; P=0.006) was significantly reduced. Thus, NGF content in distinct brain regions is decreased, following different forms of acute stress. This might be relevant for the pathophysiological understanding of psychiatric diseases, such as depression, which are associated with stress.

Diet restriction in mice causes a decrease in hippocampal choline uptake and muscarinic receptors that is restored by administration of tyrosine: interaction between cholinergic and adrenergic receptors influencing cognitive function

We have studied the effects of diet restriction (DR) to 60% and 40% of daily requirements, and tyrosine administration on cognitive function in mice, to define the nutritional-neurochemical interactions on autonomic tone involved in behavior and energy regulation. Cognitive function in the Morris Water maze was significantly impaired after 40% DR compared to both control and 60% DR. It was restored after tyrosine in association with increased M1 cholinergic and beta-adrenergic receptor function, and decreased alpha-adrenergic function. DR to 40% significantly decreased choline uptake (p <.05) and M1 receptor number (Bmax) (p <.05), without changes in affinity (Kd), choline acetyl transferase (ChAT) or acetyl cholinesterase (AChE) activity. Tyrosine administration significantly increased choline uptake (Bmax) (p <.05) and M1 density in the 40% DR (p <.01) without changes in affinity. ChAT activity was decreased after tyrosine--significantly after 40% DR (p <.05) while AChE was not affected. Both M1 mRNA and protein were not influenced by DR or tyrosine administration. Tyrosine hydroxylase mRNA was decreased significantly by 40% DR (p <.01). The effect of DR and tyrosine appeared to be both pre- and post-synaptic, indicating modulation of cholinergic activity by adrenergic tone. Nutritional effect on behavior and autonomic tone may have implications for the treatment of mood changes associated with weight loss and semi-starvation.

The influence of phosphatidylserine supplementation on mood and heart rate when faced with an acute stressor

There have been previous reports that supplements of phosphatidylserine (PS) blunted the release of cortisol in response to exercise stress and that it improved mood. The present study extended these observations by considering whether PS supplementation influenced subjective feelings of stress and the change in heart rate when a stressful mental arithmetic task was performed. In young adults, with neuroticism scores above rather than below the median, the taking of 300mg PS each day for a month was associated with feeling less stressed and having a better mood. The study for the first time reports an improvement in mood following PS supplementation in a sub-group of young healthy adults.

Effects of chlorpyrifos in the plus-maze model of anxiety

The purpose of the present study was to determine the effect of two different doses of the organophosphate insecticide O,O'-diethyl-O-3,5,6-trichloro-2-pyridylphosphorothionate [chlorpyrifos (CPF)], a cholinesterase (ChE) inhibitor, in the plus-maze test of anxiety in the rat, as well as on acetylcholinesterase (AChE) activity in the brain. In a first experiment, the behavioural methodology was validated by showing the anxiolytic and anxiogenic effects of diazepam and pentylenetetrazole (PTZ), respectively. Acute exposure to CPF (166 mg/kg and 250 mg/kg, s.c.) produced significant dose-dependent inhibition (54% and 71%, respectively) of whole-brain AChE 48 hours after treatment. Neither dose produced signs of acute cholinergic toxicity at any time following treatment, as was verified by a functional observational battery. Both doses of CPF were injected 48 h before testing in the plus-maze and were shown to have anxiogenic effects as demonstrated by the significant decrease in the percentage of time spent and percentage of entries into open arms. This report thus shows clear behavioural alteration as an acute effect of an organophosphate in the absence of any classic sign of cholinergic toxicity. Our results are relevant to the understanding of both the pharmacology of anxiety and the behavioural toxicology of cholinesterase inhibitors.

Immobilization stress-induced changes in brain acetylcholinesterase activity and cognitive function in mice

In the present study, the effect of acute and chronic immobilization stress on brain acetylcholinesterase (AChE) enzyme activity and cognitive function in mice was investigated. Mice were immobilized by strapping for 150 min. One group of mice were only immobilized once (acute stress) while in another group mice were immobilized (150 min) daily for 5 consecutive days (chronic stress). Specific AChE enzyme activity (micromol min(-1)mg(-1)) was estimated by a spectrophotometric method in the whole brain of mice subjected to acute and chronic stress. In the acute stress group, AChE activity (0.24922 +/- 0.011) in the detergent-soluble fraction was found to be significantly decreased in comparison to the control group (0.33561 +/- 0.022). Chronic stress did not cause any significant change in AChE activity in the detergent-soluble fraction. In the salt-soluble fraction, AChE activity was significantly decreased only in the chronic stress group (0.08791 +/- 0.011) as compared to the control group (0.12051 +/- 0.011). A passive avoidance test was used to assess cognitive function. The transfer latency time (TLT) from a light to dark chamber was recorded in the control and acute stress groups (30 min after immobilization is over) on day 1 (Trial I) and the following day (Trial II). The acute stress group showed an increase (178%) in TLT from Trial I to Trial II, which was significantly higher than that of the non-stress control group (75%). In the chronic stress group, Trial I was undertaken 30 min after the last immobilization, i.e. on day 5 and 24 hr later, Trial II. However, the chronically stressed mice showed an increase (70%) in TLT similar to the control group. Thus this study shows that acute immobilization stress may enhance cognitive function in mice which may be attributed to a decrease in AChE activity leading to an increase in cholinergic activity in the brain.

Accumbens cholinergic interneurons play a role in the regulation of body weight and metabolism

The aims of the present study were (1) to determine whether selective lesions of the accumbens cholinergic interneurons impair feeding and body weight regulation, and (2) to characterize the nature of disturbances using motivational and metabolic challenges. Rats with bilateral cholinotoxic (AF64A) lesions in the nucleus accumbens showed a significant and lasting lag in body weight gain in comparison to the sham-operated controls. This failure to gain weight was not due to a decrease in feeding because lesioned rats actually ate more food and drank more water than controls under basal conditions. Lesion-induced deficits were also exposed when the rats were challenged with food deprivation or cold exposure. Lesioned rats ate less than controls when 24 h food deprived and maintained both a higher core temperature and a higher metabolic rate than controls following either 24-h food deprivation or exposure to cold. Thyroid hormones, insulin, and blood glucose levels were, however, within the physiological range, and no sensory and motor disturbances were observed. The results suggest that the altered body weight regulation is partly due to the enhanced metabolic responsiveness to stress. Possible explanations for the effects of the lesions are also discussed in the context of motivational alterations, including possible dopamine-acetylcholine interactions.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Cortical spreading depression reduces paraventricular activation induced by hippocampal neostigmine injection

The firing rate of the neurons of the hypothalamic paraventricular nucleus, the temperatures of the interscapular brown adipose tissue and of the colon (TIBAT and Tc) were monitored in 24 urethane-anesthetized male Sprague-Dawley rats divided into four groups. These variables were measured before and after hippocampal injection of neostigmine (5x10(-7) mol) in the 1st and 2nd groups or of saline in the 3rd and 4th groups. The hippocampal injection was preceded by cortical spreading depression in the 1st and 3rd groups, while the cortical depression was not induced in the 2nd and 4th groups. The results show an increase of firing rate, TIBAT and Tc after neostigmine injection in the rats without cortical depression. Cortical spreading depression significantly reduces these enhancements. These findings demonstrate that: (1) the paraventricular nucleus plays a significant role in the hyperthermia induced by neostigmine injection into the hippocampus; and (2) the cerebral cortex is involved in the control of the paraventricular activity.

Restriction of environmental space attenuates locomotor activity and hippocampal acetylcholine release in male rats

We examined the effects of the restriction of environmental space on hippocampal acetylcholine release and spontaneous locomotor activity. Four days after the housing in a large or small cage, sampling for microdialysis study was begun. The locomotor activity counts exhibited significant daily changes in all rats in either the large or small cage. But, the mean locomotor activity counts in rats in the small cage was significantly less than that in the large cage. In contrast, the amount of acetylcholine collected per 20-min sample exhibited significant diurnal changes in all six rats in the large cage and in 5 of 6 rats in the small cage. The mean acetylcholine release in the rat in the small cage was significantly lower than that in the rat in the large cage during the dark phase, but not during the light phase. In addition, during the dark phase, hippocampal acetylcholine release was closely associated with spontaneous activity in all six rats in the large cage but not in 3 of 6 rats in the small cage. The present study suggests that the restriction of environmental space somehow interfere with the spontaneous locomotor activity and hippocampal acetylcholine release during the dark phase.

Glucocorticoid facilitation of cholinergic development in the rat hippocampus

The role of endogenous glucocorticoids in facilitating the postnatal innervation of septohippocampal cholinergic projections was examined. Septohippocampal cholinergic innervation was determined using two methods. One method involved measuring the optical density of acetylcholinesterase, a marker of cholinergic fibres in the hippocampus. In the other method, acetylcholinesterase-positive fibre counts were made in the hippocampus. Both methods revealed that 14-day-old rats adrenalectomized at 10 days of age have significantly lower densities of acetylcholinesterase in the hippocampal dentate gyrus molecular layer and in the regio inferior when compared to sham-operated control rats. This reduction in hippocampal acetylcholinesterase did not occur when 10-day-old adrenalectomized rats were either injected daily with exogenous corticosterone (0.3 mg/100 g body weight) or when adrenalectomy was conducted at later postnatal ages. In addition, unlike the developing hippocampus, the basolateral nucleus of the amygdala, which is also highly innervated by cholinergic fibres, showed no significant changes in acetylcholinesterase density after adrenalectomy. These observations suggest that glucocorticoids play an important role in supporting the development of cholinergic projections to the hippocampus. Cholinergic innervation of the hippocampus appears especially sensitive to the action of glucocorticoids occurring before the conclusion of the second postnatal week. Furthermore, this glucocorticoid influence is directed rather specifically to the hippocampus in comparison to the basolateral amygdala.

The effects of acute and repeated restraint stress on the nociceptive response in rats

The effects of acute and repeated restraint stress on nociception, as measured by the tail-flick latency, were studied in adult male and female rats. After the exposure to a single restraint session, both male and female rats presented an increased latency in the tail-flick test. On the other hand, chronically stressed females presented a performance similar to the control group, whereas chronically stressed male rats responded to restraint with a decrease in the tail-flick latency. This response could be determined by the chronic treatment itself or by the restraint done just before the measurement. Thus, the effect of chronic stress upon basal tail-flick latency was evaluated. In male rats, this latency was significantly decreased in the stressed animals compared with the control group. In female rats, no difference between those groups was observed. Therefore, the results suggest that: (a) acute restraint stress induces an analgesic response in both male and female rats, and (b) there is a gender-specific nociceptive response induced by repeated restraint stress with a hyperalgesic effect in response to stress only in males.

In Vivo Hippocampal Acetylcholine Release During Exposure to Acute Stress

Hippocampal extracellular acetylcholine (ACh) and choline levels were evaluated using in vivo microdialysis in male Fischer 344 rats before, during, and following an 80-min exposure to two different stress conditions. Measurements were taken in rats restrained and immersed in a water bath containing either 37 degreesC (normothermic-restraint) or 20 degreesC (cold-restraint) water. Results were compared to normothermic-freely-moving rats. Cold-restrained rats displayed decreased ACh levels during cold exposure relative to both normothermic-restrained and normothermic-freely-moving rats. By the end of the cold exposure period and following removal from cold, ACh levels had returned to near-baseline values. Normothermic-restrained rats had levels similar to those of normothermic-freely-moving rats, except for a marked increase in ACh following removal from restraint. Cold-restrained rats displayed a gradual elevation in choline levels during cold stress, followed by a gradual decline after stress termination, whereas both normothermic-restrained and normothermic-freely-moving rats displayed gradual decreases during the microdialysis session. These findings demonstrate that central cholinergic neurotransmission can be altered by the application of, and removal from, acute stressors. In addition, the results suggest a possible relationship between the magnitudes of both the stressor and its cholinergic consequences.

Effects of novelty, pain and stress on hippocampal extracellular acetylcholine levels in male rats

In vivo microdialysis was used to assess the effects of Novelty, persistent pain (Formalin test) and stress (Restraint) on hippocampal acetylcholine (ACh) release. Experiments were carried out during the dark phase, i.e. during the active period of the animal, and consisted of four experimental phases: Baseline (30 min), Novelty (30 min), Formalin test (90 min) and Restraint (30 min); each animal was consecutively exposed to all phases. The extracellular levels of ACh in the dorsal hippocampus were estimated by measurement of its concentration in the perfusion fluid by high-performance liquid chromatography with electrochemical detection. The introduction to a new environment (Novelty) induced in all rats higher ACh levels than Baseline. Formalin treatment decreased ACh release only in animals considered 'Inactive' during the Novelty phase while no modification in ACh release was observed in the 'Active' ones. Restraint did not produce any modification of ACh release but increased Corticosterone plasma levels both in sham- and formalin-treated animals. Results indicate that Novelty, but not Formalin or Restraint, increases ACh release in the hippocampus and that the type of behavioral state displayed by the animal at the time of formalin injection determines the response of the septo-hippocampal cholinergic pathway.

Neuroimmunomodulation via limbic structures--the neuroanatomy of psychoimmunology

During the last 20 years, mutual communications between the immune, the endocrine and the nervous systems have been defined on the basis of physiological, cellular, and molecular data. Nevertheless, a major problem in the new discipline "Psychoneuroimmunology" is that controversial data and differences in the interpretation of the results make it difficult to obtain a comprehensive overview of the implications of immunoneuroendocrine interactions in the maintenance of physiological homeostasis, as well as in the initiation and the course of pathological conditions within these systems. In this article, we will first discuss the afferent pathways by which immune cells may affect CNS functions and, conversely, how neural tissues can influence the peripheral immune response. We will then review recent data, which emphasize the (patho)physiological roles of hippocampal-amygdala structures and the nucleus accumbens in neuroimmunomodulation. Neuronal activity within the hippocampal formation, the amygdaloid body, and the ventral parts of the basal ganglia has been examined most thoroughly in studies on neuroendocrine, autonomic and cognitive functions, or at the level of emotional and psychomotor behaviors. The interplay of these limbic structures with components of the immune system and vice versa, however, is still less defined. We will attempt to review and discuss this area of research taking into account recent evidences for neuroendocrine immunoregulation via limbic neuronal systems, as well as the influence of cytokines on synaptic transmission, neuronal growth and survival in these brain regions. Finally, the role of limbic structures in stress responses and conditioning of immune reactivity will be commented. Based on these data, we propose new directions of future research.

Time-related effects of stress on cholinergic sensitivity

The effect of the administration of the muscarinic cholinergic agonist oxotremorine on locomotor activity was investigated in DBA/2 mice subjected to chronic restraint stress of different durations (120 min daily for 10, 14 or 18 days). Oxotremorine induced a depressant effect on locomotion, which was reduced after 10 and 14 days of restraint, but not after a 18-day restraint stress. Acetylcholine (ACh) content was significantly reduced in prefrontal cortex after 10 and 14 days of stress but returned to control values after 18 days of restraint. No changes in ACh content were observed in nucleus accumbens and striatum. These results are discussed in terms of possible changes in muscarinic receptor sensitivity.

Glucocorticoids and the hippocampus. Developmental interactions facilitating the expression of behavioral inhibition

When threatened, the rapid induction of fear and anxiety responses is adaptive. This article summarizes the current knowledge of the neurobiological development of behavioral inhibition, a prominent response occurring in fear and anxiety-provoking situations. In the rat, behavioral inhibition as exemplified by freezing first appears near the end of the second postnatal week. This emergence of freezing coincides with the developmental period marked by the rapid increase in plasma concentrations of glucocorticoids. Studies show that removal of glucocorticoids at this time severely impairs the age-dependent appearance of freezing. This behavioral impairment produced by adrenalectomy, however, is prevented by exogenous glucocorticoid administration. The effectiveness of glucocorticoids in facilitating the development of freezing appears to be caused by its actions in the hippocampus. In particular, glucocorticoids appear to play a vital role in the postnatal cellular development of the hippocampal dentate gyrus. Doses of glucocorticoids shown to reverse the behavioral inhibitory deficits occurring after adrenalectomy are ineffective when hippocampal dentate granule neurons are destroyed by neurotoxins. Notably, site-specific administration of glucocorticoids to the dorsal hippocampus is successful in promoting the occurrence of freezing in the adrenalectomized rat pup. It is hypothesized that glucocorticoids exert their behavioral inhibitory effects by influencing the development of the septohippocampal cholinergic system. Support for this hypothesis is derived from work demonstrating the importance of glucocorticoids on nerve growth factor systems that play a critical role in septohippocampal cholinergic survival.

Ethanol alone or with dexamethasone alters the kinetics of choline acetyltransferase

Choline acetyltransferase activity was measured in rats treated with daily injections of ethanol (0.1 g/kg body wt) and or dexamethasone (1 mg/kg body wt) for 5 consecutive days. Ethanol produced a biphasic reduction of choline acetyltransferase activity in rat cerebral cortex, which at most time points was further decreased by simultaneous injection of dexamethasone. Kinetic studies of cortex choline acetyltransferase activity in rats that had received 5 daily injections of ethanol or ethanol and dexamethasone indicated that the observed reduction in enzyme activity was due to an apparent reduction in affinity (K(m)) of the enzyme for acetyl coenzyme A with no significant change in the total amount of enzyme present (Vmax). This finding has implications with respect to the use of choline acetyltransferase as a marker for cholinergic neurons, and for the understanding of the regulation of choline acetyltransferase activity in the brain.

Inescapable stress enhances extracellular acetylcholine in the rat hippocampus and prefrontal cortex but not the nucleus accumbens or amygdala

A number of experimental results has pointed to a cholinergic involvement in the stress response. Recently, analytical techniques have become available to measure acetylcholine release in vivo during exposure to various stressors. In these experiments, microdialysis was used to monitor acetylcholine output every 15 min in the dorsal hippocampus, amygdala, nucleus accumbens and prefrontal cortex before, during and after 1 h of restraint, including a 15-min session of intermittent tail-shock (1/min, 1 mA, 1-s duration) in rats. In response to the stressful event, acetylcholine release was significantly increased in the prefrontal cortex (186%; p < 0.01) and hippocampus (168%; P < 0.01) but not in the amygdala or nucleus accumbens. The sole effects observed in the amygdala and nucleus accumbens occurred upon release from the restrainer, at which point acetylcholine levels were significantly elevated in both areas (amygdala: 150%; P < 0.05; nucleus accumbens: 13%; P < 0.05). An enhanced acetylcholine release was also evident during this sample period in the hippocampus and prefrontal cortex. These data demonstrate an enhancement of cholinergic activity in response to stress in two acetylcholine projection systems (hippocampus and prefrontal cortex) but not in the intrinsic acetylcholine system of the nucleus accumbens or the extrinsic innervation of the amygdala. Moreover, the data showed that relief from stress was accompanied by a more ubiquitous acetylcholine response that extended to each site tested.

Presynaptic muscarinic cholinergic receptors in the dorsal hippocampus regulate behavioral inhibition of preweanling rats

The aim of this research was to determine whether early maturation of the dorsal hippocampal cholinergic system mediates behavior exhibited by preweanling rats in the presence or absence of an unfamiliar adult male rat, a threatening stimulus. The behavioral responses that were examined included behavioral inhibition or freezing which emerges at 2 weeks of age and ultrasonic vocalizations. Prior to behavioral testing, oxotremorine, an M2 muscarinic receptor agonist that reduces cholinergic release from presynaptic terminals, was infused into the dorsal hippocampal dentate gyrus. Results demonstrated that 14-day-old rats with bilateral hippocampal infusions of a 1 microgram dose of oxotremorine exhibited significant deficits in freezing when exposed to the adult male rat. Importantly, oxotremorine had no significant effects on ultrasound emission and ambulatory activity when rat pups were tested in social isolation. Thus, effects of oxotremorine in the hippocampal dentate gyrus do not produce global changes in behavior. Results suggest that cholinergic release into the dorsal hippocampus facilitates the display of behavioral inhibition at the end of the second postnatal week. Behavioral deficits in freezing may reflect an oxotremorine-induced disruption of hippocampal cholinergic function underlying the processing of biologically relevant olfactory stimuli as well as mechanisms associated with attention.

Cholinergic Responsiveness of Rat CA1 Hippocampal Neurons In Vitro: Modulation by Corticosterone and Stress

Corticosterone can activate two corticosteroid receptor types in rat hippocampus: low doses activate mineralocorticoid receptors (MR) while high doses additionally activate glucocorticoid receptors (GR). We found that corticosterone, administered to adrenalectomized rats in vivo, dose-dependently modulates carbachol responsiveness of CA1 hippocampal neurons, recorded subsequently in vitro. Thus, the carbachol (3 µM) induced membrane depolarization in CA1 neurons was relatively large in hippocampal slices where either (almost) no corticosteroid receptors were activated (0-1 µg corticosterone/100g body weight) or where both MRs and GRs were occupied by high corticosterone doses (100-1000 µg/100g). Slices from rats that received intermediate doses of corticosterone (10-30 µg/100g) resulting in predominant MR occupation, displayed significantly suppressed carbachol responses. In adrenally intact rats with MRs and GRs fully activated by a very high dose of corticosterone (1 mg/100g), carbachol responses were increased compared to rats that received only the vehicle or that were untreated. When endogenous corticosterone levels were elevated by ether stress, carbachol responses were not increased. These findings suggest that a shift in the relative occupation of MRs and GRs occurring under physiological conditions is associated with modulation of acetylcholine sensitivity in CA1 neurons. After stress, however, the sensitivity to acetylcholine is rather low, although MRs and GRs are fully activated by endogenous corticosterone; this may point to the involvement of additional stress-induced factors modulating the cholinergic responses.

Immobilization stress-induced increase of hippocampal acetylcholine and of plasma epinephrine, norepinephrine and glucose in rats

We investigated the role of the hippocampal cholinergic neurons during immobilization stress in rats using a microdialysis technique. Blood levels of glucose, epinephrine and norepinephrine during immobilization stress were also determined. Acetylcholine release was initially increased by immobilization stress, then gradually decreased. Plasma level of epinephrine increased gradually and reached significance at 30 min after the start of immobilization and remained at the elevated level during immobilization. Plasma level of norepinephrine initially increased and reached significance at 30 min after the start of immobilization and remained at the elevated level during immobilization. Plasma level of glucose increased gradually and reached maximum and significance 45 min after the start of immobilization, then decreased. Fifteen min after immobilization, acetylcholine release increased again, while concentrations of epinephrine and norepinephrine were still elevated. Thus the response of acetylcholine and the other responses to immobilization stress were not parallel.

Central nicotinic receptor blockade inhibits emotionally conditioned pressor responses in rats

A conditioned stimulus previously paired with electric footshock produced an increase in blood pressure in conscious, freely moving rats. The conditioned pressor response was reproducible. Intracerebroventricular injection of the nicotinic receptor antagonists hexamethonium (1-10 micrograms) or pentolinium (10 micrograms) but not the muscarinic receptor antagonist methylatropine (3 micrograms) produced an inhibition of the conditioned pressor response, whereas intraarterial injection of hexamethonium (10 micrograms) did not affect the response. Intraventricular injection of the cholinesterase inhibitor physostigmine (3-10 micrograms) produced an enhancement of the conditioned pressor response. These results are consistent with the possibility that central nicotinic receptors play a role in the expression of the emotionally conditioned pressor response in rats.

Tail pinch increases acetylcholine release in rat striatum even after toluene exposure

The effect of tail pinch on acetylcholine release in the striatum of freely moving rats was studied by microdialysis immediately after inhalation exposure to toluene (2000 ppm, 2 h) or exposure to air only. It has recently been found that toluene increases extracellular dopamine levels while decreasing acetylcholine release, and that dopamine uptake inhibition increases both extracellular dopamine levels and acetylcholine release, suggesting that toluene decreases acetylcholine release by a dopamine-independent mechanism. The present experiment was an attempt to study if a behaviourally induced increase of extracellular dopamine differs from that induced by toluene in affecting striatal acetylcholine release. Acetylcholine released increased during tailpinch in the unexposed as well as the toluene exposed group. No difference between the two groups in the acetylcholine release response to tailpinch was demonstrated. The result supports the conclusion that acute toluene exposure decreases acetylcholine release via a dopamine independent mechanism, and suggests that toluene exposure does not affect the striatal acetylcholine response to an acute stressful stimulus.

Long-term control of neuronal excitability by corticosteroid hormones

Hippocampal CA1 neurons express both mineralocorticoid and glucocorticoid receptors. Due to the difference in affinity of the two receptor types for corticosterone and variations in endogenous steroid levels, occupation of the receptors will range between a situation of predominant mineralocorticoid receptor activation and conditions where both receptor types are occupied. It was observed that local signal transduction is regulated by activation of the corticosteroid receptors. Particularly, transmission mediated by biogenic amines appears to be sensitive to steroid control. The data indicate that cholinergic and serotonergic responses are small with predominant mineralocorticoid receptor activation, while additional glucocorticoid receptor activation results in large responses; the reverse has been found for noradrenalin. The steroid-dependent control over transmission by biogenic amines will influence local excitability and therefore functional processes in which the hippocampal system is involved.

Alteration of brain nicotinic receptors induced by immobilization stress and nicotine in rats

Immobilization stress (2 h.day-1, for 2 weeks) caused downregulation of the nicotinic receptors ([3H]cytisine binding sites) in the rat brain (cerebral cortex and midbrain). However, chronic nicotine treatment abrogated stress induced downregulation of the [3H]cytisine binding sites, suggesting that chronic nicotine treatment may block stress activated nicotinic receptor-mediated neurotransmission.