Evaluation of acetylcholinesterase activity and behavioural alterations induced by ketamine in an animal model of schizophrenia.

OBJECTIVE: Cognitive deficits in schizophrenia play a crucial role in its clinical manifestation and seem to be related to changes in the cholinergic system, specifically the action of acetylcholinesterase (AChE). Considering this context, the aim of this study was to evaluate the chronic effects of ketamine in the activity of AChE, as well as in behavioural parameters involving learning and memory. METHODS: The ketamine was administered for 7 days. A duration of 24 h after the last injection, the animals were submitted to behavioural tests. The activity of AChE in prefrontal cortex, hippocampus and striatum was measured at different times after the last injection (1, 3, 6 and 24 h). RESULTS: The results indicate that ketamine did not affect locomotor activity and stereotypical movements. However, a cognitive deficit was observed in these animals by examining their behaviour in inhibitory avoidance. In addition, an increase in AChE activity was observed in all structures analysed 1, 3 and 6 h after the last injection. Differently, serum activity of AChE was similar between groups. CONCLUSION: Chronic administration of ketamine in an animal model of schizophrenia generates increased AChE levels in different brain tissues of rats that lead to cognitive deficits. Therefore, further studies are needed to elucidate the complex mechanisms associated with schizophrenia.

Increased susceptibility of brain acetylcholinesterase activity to methylmalonate in young rats with renal failure.

Tissue methylmalonic acid (MMA) accumulation is the biochemical hallmark of methylmalonic acidemia. Clinically, the disease is characterized by progressive neurological deterioration and renal failure, whose pathophysiology is still undefined. In the present study we investigated the effect of acute MMA administration on some important parameters of brain neurotransmission in cerebral cortex of rats, namely Na(+), K(+)-ATPase, ouabain-insensitive ATPases and acetylcholinesterase activities, in the presence or absence of kidney injury induced by gentamicin administration. Initially, thirty-day old Wistar rats received one intraperitoneal injection of saline or gentamicin (70 mg/kg). One hour after, the animals received three consecutive subcutaneous injections of MMA (1.67 µmol/g) or saline, with an 11 h interval between each injection. One hour after the last injection the animals were killed and the cerebral cortex isolated. MMA administration by itself was not able to modify Na(+), K(+)-ATPase, ATPases ouabain-insensitive or acetylcholinesterase activities in cerebral cortex of young rats. In rats receiving gentamicin simultaneously with MMA, it was observed an increase in the activity of acetylcholinesterase activity in cerebral cortex, without any alteration in the activity of the other studied enzymes. Therefore, it may be speculated that cholinergic imbalance may play a role in the pathogenesis of the brain damage. Furthermore, the pathophysiology of tissue damage cannot be exclusively attributed to MMA toxicity, and control of kidney function should be considered as a priority in the management of these patients, specifically during episodes of metabolic decompensation when MMA levels are higher.

Chronic exposure to cigarette smoke during gestation results in altered cholinesterase enzyme activity and behavioral deficits in adult rat offspring: potential relevance to schizophrenia.

Prenatal cigarette smoke exposure (PCSE) has been associated with physiological and developmental changes that may be related to an increased risk for childhood and adult neuropsychiatric diseases. The present study investigated locomotor activity and cholinesterase enzyme activity in rats, following PCSE and/or ketamine treatment in adulthood. Pregnant female Wistar rats were exposed to 12 commercially filtered cigarettes per day for a period of 28 days. We evaluated motor activity and cholinesterase activity in the brain and serum of adult male offspring that were administered acute subanesthetic doses of ketamine (5, 15 and 25 mg/kg), which serves as an animal model of schizophrenia. To determine locomotor activity, we used the open field test. Cholinesterase activity was assessed by hydrolysis monitored spectrophotometrically. Our results show that both PCSE and ketamine treatment in the adult offspring induced increase of locomotor activity. Additionally, it was observed increase of acetylcholinesterase and butyrylcholinesterase activity in the brain and serum, respectively. We demonstrated that animals exposed to cigarettes in the prenatal period had increased the risk for psychotic symptoms in adulthood. This also occurs in a dose-dependent manner. These changes provoke molecular events that are not completely understood and may result in abnormal behavioral responses found in neuropsychiatric disorders, such as schizophrenia.

L-tyrosine administration increases acetylcholinesterase activity in rats.

Tyrosinemia is a rare genetic disease caused by mutations on genes that codify enzymes responsible for tyrosine metabolism. Considering that tyrosinemics patients usually present symptoms associated with central nervous system alterations that ranges from slight decreases in intelligence to severe mental retardation, we decided to investigate whether acute and chronic administration of L-tyrosine in rats would affect acetylcholinesterase mRNA expression and enzymatic activity during their development. In our acute protocol, Wistar rats (10 and 30 days old) were killed one hour after a single intraperitoneal L-tyrosine injection (500 mg/kg) or saline. Chronic administration consisted of L-tyrosine (500 mg/kg) or saline injections 12 h apart for 24 days in Wistar rats (7 days old) and rats were killed 12 h after last injection. Acetylcholinesterase activity was measured by Ellman's method and acetylcholinesterase expression was carried out by a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) assay. We observed that acute (10 and 30 days old rats) and chronic L-tyrosine administration increased acetylcholinesterase activity in serum and all tested brain areas (hippocampus, striatum and cerebral cortex) when compared to control group. Moreover, there was a significant decrease in mRNA levels of acetylcholinesterase in hippocampus was observed after acute protocol (10 and 30 days old rats) and in striatum after chronic protocol. In case these alterations also occur in the brain of the patients, our results may explain, at least in part, the neurological sequelae associated with high plasma concentrations of tyrosine seen in patients affected by tyrosinemia type II.

Evaluation of behavioral and neurochemical changes induced by ketamine in rats: implications as an animal model of mania.

Bipolar disorder (BD) is a chronic, prevalent, and highly debilitating psychiatric illness characterized by recurrent manic and depressive episodes. Mood stabilizing agents such as lithium and valproate are two primary drugs used to treat BD. To develop a novel animal model of mania (hallmark of BD), it is important to assess the therapeutic and prophylactic effect of these mood stabilizers on the new candidate target animal model. The present work investigates the therapeutic and prophylactic value of lithium and valproate in a novel preclinical animal model of mania, induced by ketamine. In the prevention protocol, wistar rats were pretreated with lithium (47.5 mg/kg, i.p., twice a day), valproate (200 mg/kg, i.p., twice a day), or saline (i.p., twice a day) for 14 days. Between days 8 and 14, the rats were treated with ketamine (25 mg/kg, i.p.) or saline. In the reversal protocol, rats first received ketamine (25 mg/kg, i.p.) or saline. After, the administration of lithium, valproate, or saline was carried out for seven days. Our results indicated that lithium and valproate reversed and prevented ketamine-induced hyperlocomotion. Moreover, lithium and valproate reversed (prefrontal cortex, hippocampus, and striatum) and prevented (prefrontal cortex, hippocampus, striatum, and amygdala) the increase of the TBARS level induced by ketamine. The protein carbonyl formation, induced by ketamine, was reversed by lithium and valproate in the prefrontal cortex, hippocampus, and striatum, and prevented only in the amygdala. These findings support the notion that the administration of ketamine might be a promising pharmacological animal model of mania, which could play a role in the pathophysiology of BD.

Inhibition of acetylcholinesterase activity in brain and behavioral analysis in adult rats after chronic administration of fenproporex.

Fenproporex is an amphetamine-based anorectic and it is rapidly converted in vivo into amphetamine. It elevates the levels of extracellular dopamine in the brain. Acetylcholinesterase is a regulatory enzyme which is involved in cholinergic synapses and may indirectly modulate the release of dopamine. Thus, we investigated whether the effects of chronic administration of fenproporex in adult rats alters acquisition and retention of avoidance memory and acetylcholinesterase activity. Adult male Wistar rats received repeated (14 days) intraperitoneal injection of vehicle or fenproporex (6.25, 12.5 or 25 mg/kg i.p.). For behavioral assessment, animals were submitted to inhibitory avoidance (IA) tasks and continuous multiple trials step-down inhibitory avoidance (CMIA). Acetylcholinesterase activity was measured in the prefrontal cortex, hippocampus, hypothalamus and striatum. The administration of fenproporex (6.25, 12.5 and 25 mg/kg) did not induce impairment in short and long-term IA or CMIA retention memory in rats. In addition, longer periods of exposure to fenproporex administration decreased acetylcholinesterase activity in prefrontal cortex and striatum of rats, but no alteration was verified in the hippocampus and hypothalamus. In conclusion, the present study showed that chronic fenproporex administration decreased acetylcholinesterase activity in the rat brain. However, longer periods of exposure to fenproporex did not produce impairment in short and long-term IA or CMIA retention memory in rats.

Prenatal exposure to cigarette smoke causes persistent changes in the oxidative balance and in DNA structural integrity in rats submitted to the animal model of schizophrenia.

Epidemiological studies have indicated that prenatal exposure to environmental insults can bring an increased risk of schizophrenia. The objective of our study was to determine biochemical parameters in rats exposed to cigarette smoke (CS) in the prenatal period, evaluated in adult offspring submitted to animal model of schizophrenia induced by acute subanaesthetic doses of ketamine (5 mg/kg, 15 mg/kg and 25 mg/kg). Pregnant female Wistar rats were exposed to 12 commercially filtered cigarettes per day, daily for a period of 28 days. We evaluated the oxidative damage in lipid and protein in the rat brain, and DNA damage in the peripheral blood of male adult offspring rats. To determine oxidative damage in the lipids, we measured the formation of thiobarbituric acid reactive species (TBARS) and the oxidative damage to the proteins was assessed by the determination of carbonyl groups content. We also evaluated DNA damage using single-cell gel electrophoresis (comet assay). Our results showed that rats exposed to CS in the prenatal period presented a significant increase of the lipid peroxidation, protein oxidation and DNA damage in adult age. We can observe that the animals submitted at acute doses of ketamine also presented an increase of the lipid peroxidation and protein oxidation at different doses and structures. Finally, we suggest that exposure to CS during the prenatal period affects two essential cerebral processes during development: redox regulation and DNA integrity, evaluated in adult offspring. These effects can leads to several neurochemical changes similar to the pathophysiology of schizophrenia.

Evaluation of respiratory chain activity in lymphocytes of patients with Alzheimer disease.

Alzheimer disease (AD) is a progressive neurodegenerative disease associated with cognitive impairment in multiple domains, such as memory and executive functions. Studies reveal damage in the electron transport chain of patients with AD, suggesting that this mitochondrial dysfunction plays an important role in the pathophysiology of the disease. Blood samples were taken from patients with AD (n = 20) and older subjects without dementia (n = 40) to evaluate the activity of complexes I, II, II-III, and IV of the mitochondrial respiratory chain in isolated lymphocytes. Results from the patient and control groups were compared. The activity of complexes II and IV was increased among patients compared to the control group. No significant difference was observed between controls who were not using psychotropic medication and patients. Our findings point out a mechanism of cellular compensation in which the mitochondrial respiratory chain requires an increase in electron transport to supply the energy needed for cellular functioning. Additional studies are needed to better clarify the mechanisms involved in the mitochondrial dynamics of AD.

Reduction of acethylcolinesterase activity in the brain of mdx mice.

Lack of dystrophin in brain structures have been involved with impaired cognitive functions. Acethylcolinesterase (AChE) is implicated in many cognitive functions and probably plays important roles in neurodegenerative disorders. In the present study, we investigated AChE activity in the prefrontal cortex, hippocampus, striatum and cortex of mdx mice. To this aim, brain tissues from male dystrophic mdx and normal control mice were used. We observed that mdx mice display a reduction in AChE activity of 40-60% in all brain structures evaluated. In conclusion, dystrophin deficiency may be affecting AChE activity and contributing negatively, in part, to memory storage and restoring.

Behavioral changes and mitochondrial dysfunction in a rat model of schizophrenia induced by ketamine.

Evidence from the literature indicates that mitochondrial dysfunction occurs in schizophrenia and other psychiatric disorders. To produce an animal model that simulates psychotic symptoms analogous to those seen in schizophrenic patients, sub-anesthetic doses of N-methyl-D-aspartate (NMDA) receptor antagonists (such as ketamine) have been used. The aim of this study was to evaluate behavioral changes and mitochondrial dysfunction in rats administered ketamine for 7 consecutive days. Behavioral evaluation was performed using an activity monitor 1, 3 and 6 h after the last injection. The activities of mitochondrial respiratory chain complexes I, II, I-III and IV in multiple brain regions (prefrontal cortex, striatum and hippocampus) were also evaluated. Our results showed that hyperlocomotion occurred in the ketamine group 1 and 3 h after the last injection. Stereotypic movements were elevated only when animals were evaluated 1 h after receiving ketamine. In addition, we found that ketamine administration affects the respiratory chain, altering the activity of respiratory chain complexes in the striatum and hippocampus after 1 h, those in the prefrontal cortex and hippocampus after 3 h and those in the prefrontal cortex and striatum 6 h after the last administration of ketamine. These findings suggest that ketamine alters the behavior of rats and changes the activity of respiratory chain complexes in multiple brain regions at different time points.