Fernando Sánchez-Santed

Impulsivity Characterization in the Roman High- and Low-Avoidance Rat Strains: Behavioral and Neurochemical Differences

The selective breeding of Roman high- (RHA) and low-avoidance (RLA) rats for rapid vs extremely poor acquisition of active avoidance behavior in a shuttle-box has generated two phenotypes with different emotional and motivational profiles. The phenotypic traits of the Roman rat lines/strains (outbred or inbred, respectively) include differences in sensation/novelty seeking, anxiety/fearfulness, stress responsivity, and susceptibility to addictive substances. We designed this study to characterize differences between the inbred RHA-I and RLA-I strains in the impulsivity trait by evaluating different aspects of the multifaceted nature of impulsive behaviors using two different models of impulsivity, the delay-discounting task and five-choice serial reaction time (5-CSRT) task. Previously, rats were evaluated on a schedule-induced polydipsia (SIP) task that has been suggested as a model of obsessive-compulsive disorder. RHA-I rats showed an increased acquisition of the SIP task, higher choice impulsivity in the delay-discounting task, and poor inhibitory control as shown by increased premature responses in the 5-CSRT task. Therefore, RHA-I rats manifested an increased impulsivity phenotype compared with RLA-I rats. Moreover, these differences in impulsivity were associated with basal neurochemical differences in striatum and nucleus accumbens monoamines found between the two strains. These findings characterize the Roman rat strains as a valid model for studying the different aspects of impulsive behavior and for analyzing the mechanisms involved in individual predisposition to impulsivity and its related psychopathologies.

Spatial delayed alternation of rats in a T-maze: effects of neurotoxic lesions of the medial prefrontal cortex and of T-maze rotations.

The medial prefrontal cortex (mPFC) is usually considered to be a brain area important for working memory processes. In rats this statement is evidenced by their diminished performance in delay-type tasks following mPFC damage, notably in spatial delayed alternation (SDA) in a T-maze. This study has addressed two questions. First, to examine whether the functional deficiency in SDA, observed in rats with (usually large) mPFC damage, can be ascribed to an anatomically defined subarea of mPFC, the dorsal anterior cingulate area (ACd). Small, bilateral, NMDA-induced lesions were made, restricted to the dorsal part of mPFC. The performance of such animals in a T-maze paradigm, using delays of 0 and 15 s, was compared with sham-operated animals. Although these small lesions resulted in an increased number of perseverative errors, this effect was not delay-dependent, and, moreover, by the end of the training group differences had disappeared. The second aim was to study whether or not spatial (extra-maze) cues are important for the performance of this task. This was achieved by subjecting the well-trained sham-operated animals to a series of systematic trial-to-trial variations in the position of the maze in the experimental room. These spatial manipulations severely impaired the performance of the SDA task, indicating that extra-maze information is required to solve this task. In animals with ACd lesions, subjected to the same manipulations, the deficiency was comparable to that of the sham-operated animals.

Impulsivity differences in recreational cannabis users and binge drinkers in a university population

BACKGROUND Recreational cannabis use and alcohol binge drinking are the most common drug consumption patterns in young adults. Impulsivity and several psychopathological signs are increased in chronic drug users, but the implications of recreational use are still poorly understood. METHODS We evaluated impulsivity, sensation-seeking traits, impulsive decision-making, inhibitory control and possible symptoms of depression, anxiety and psychosis in three groups of young university adults: recreational cannabis users (N=20), alcohol binge drinkers (N=22) and non-drug users (N=26). RESULTS The cannabis and binge drinking groups had increased scores for impulsivity and sensation-seeking traits. Both groups also exhibited increased impulsive decision-making on the two-choice task and the Iowa gambling task; however, only the cannabis group was significantly different from the non-drug group regarding inhibitory control (go/no-go and stop tasks). The cannabis and binge drinking groups did not show differences in the psychopathological symptoms evaluated. CONCLUSIONS Our observations of this population of non-dependent drug users are consistent with the increased impulsivity traits and behaviors that have been described previously in chronic drug abusers. In this study, compared to no drug use, the recreational use of cannabis was associated with a major dysfunction of the different facets of impulsive behaviors. However, alcohol binge drinking was related only to impulsive decision-making. These results suggest that impulsivity traits and behaviors are present not only in chronic drug abusers but also in recreational drug users. Future work should continue to investigate the long-term effects of these common consumption patterns on various impulsive behaviors and psychopathological symptoms.

Long-term monoamine changes in the striatum and nucleus accumbens after acute chlorpyrifos exposure.

This study examined the time-course effects (2, 7, 14 and 30 days) of acute chlorpyrifos (CPF) intoxication (250 mg/kg, s.c.) on monoamine systems and acetylcholinesterase (AChE) activity in the striatum and nucleus accumbens of adult male rats. We show that CPF produced significant long-term inhibition of AChE activity in the striatum and nucleus accumbens. In the striatum, CPF intoxication resulted in changes in dopamine (DA) metabolism after 2 days and changes in serotonin (5-HT) turnover after 7 and 15 days. Significant decreases in monoamine content including norepinephrine (NE), DA, 5-HT and their metabolites were found in the nucleus accumbens 30 days after CPF intoxication. These results suggest that acute exposure to CPF induces long-term changes in the monoamine systems (NE, DA and 5-HT) in adult animals. The lack of correlation between regional AChE activity and neurochemical outcomes points to independent mechanisms.

Organophosphate pesticide exposure and neurodegeneration.

Organophosphate pesticides (OPs) are used extensively throughout the world. The main sources of contamination for humans are dietary ingestion and occupational exposures. The major concerns related to OP exposure are delayed effects following high level exposures as well as the impact of low level exposures during the lifespan which are suggested to be a risk factor for nervous system chronic diseases. Both high and low level exposures may have a particularly high impact in population subgroups such as aged or genetically vulnerable populations. Apart from the principle action of OPs which involves inhibition of the acetylcholinesterase (AChE) enzyme, several molecular targets, such as hormones; neurotransmitters; neurotrophic factors; enzymes related to the metabolism of beta amyloid protein as well as inflammatory changes have been identified for OP compounds. Here we review the main neurological and/or cognitive deficits described and the experimental and epidemiological relationships found between pesticide exposure and Alzheimers, Parkinsons, and Amyotrophic Lateral Sclerosis (ALS) diseases. This report also focuses on possible individual differences making groups resilient or vulnerable to these toxicants. A critical discussion of the evidence obtained from experimental models and possible sources of bias in epidemiological studies is included. In particular this review aims to discuss common targets and pathways identified which may underlie the functional deficits associated with both pesticide exposure and neurodegeneration.

Cholinergic receptor blockade in prefrontal cortex and lesions of the nucleus basalis: implications for allocentric and egocentric spatial memory in rats.

In this study we have examined the involvement of the prefrontal cortex (PFC) along with the Nucleus basalis magnocellularis (NBM) in two types of spatial navigation tasks. We evaluated the effects of excitotoxic (ibotenate-induced) lesions of the NBM in an allocentric and an egocentric task in the Morris water maze, using sham operations for a comparison. In both cases we also assessed the effects of local cholinergic receptor blockade in the PFC by infusing the muscarinic receptor antagonist scopolamine (4 or 20 microg). Anatomically, the results obtained showed that this lesion produced a profound loss of acetylcholinesterase (AChE) positive cells in the NBM, and a loss of AChE positive fibres in most of the neocortex, but hardly in the medial PFC. Behaviourally, such lesions led to a severe impairment in the allocentric task. Intraprefrontal infusions of scopolamine led to a short-lasting impairment in task performance when the high dose was used. In the second experiment, using the same surgical manipulations, we examined the performance in the egocentric task. Like in the allocentric task animals with NBM lesions were also impaired, but with continued training they acquired a level of performance similar to the sham-operated ones. This time, infusions of scopolamine in the medial PFC led to a severe disruption of performance in both groups of animals. We conclude that acetylcholine in the medial PFC is important for egocentric but not allocentric spatial memory, whereas the NBM is involved in the learning of both tasks, be it to a different degree.

Amyloid β peptide levels increase in brain of AβPP Swedish mice after exposure to chlorpyrifos.

Chlorpyrifos (CPF) is an organophosphate pesticide widely used in intensive agriculture. Various studies have demonstrated delayed neurotoxic effects in adult mammals after acute CPF exposure. This pesticide induces oxidative stress and neuronal damage, which suggests a possible relationship between CPF exposure and Alzheimers disease (AD). In the present study, we examined in a mice model of AD, long-term changes in the behavior and brain levels of amyloid β after acute CPF exposure. Fifty mg/kg of CPF were subcutaneously injected to Tg2576 (Tg) mice carrying the Swedish amyloid-β protein precursor (AβPP) mutation for AD. General status, body weight, acetyl cholinesterase (AChE) inhibition, and behavioral changes were assessed. Amyloid β fragment (1-40 and 1-42) levels were also measured in the cortical and hippocampal brain regions. A significant and transient decrease in body weight was observed 72 hr after treatment, while no autonomic effects were noted. Motor activity was decreased in Tg mice seven months after CPF treatment. Acquisition learning in a water maze task was not affected, but retention was ameliorated in CPF-exposed Tg mice. Amyloid β levels increased in the brains of treated Tg mice eight months after CPF exposure. The results of this study show that some behavioral changes persisted or emerged months after acute CPF exposure, while amyloid β levels increased. These findings raise concern about the risk of developing neurodegenerative diseases following moderate exposure to CPF in vulnerable subjects.

Chlorpyrifos-, Diisopropylphosphorofluoridate- and Parathion-induced behavioral and oxidative stress effects: Are they mediated by analogous mechanisms of action?

Exposure to organophosphates (OPs) can lead to cognitive deficits and oxidative damage. Little is known about the relationship between behavioral deficits and oxidative stress within the context of such exposures. Accordingly, the first experiment was carried out to address this issue. Male Wistar rats were administered 250 mg/kg of chlorpyrifos (CPF), 1.5 mg/kg of diisopropylphosphorofluoridate (DFP), or 15 mg/kg of parathion (PTN). Spatial learning in the water maze task was evaluated, and F(2)-isoprostanes (F(2)-IsoPs) and prostaglandin (PGE(2)) were analyzed in the hippocampus. A second experiment was designed to determine the degree of inhibition of brain acetylcholinesterase (AChE) activity, both the soluble and particulate forms of the enzyme, and to assess changes in AChE gene expression given evidence on alternative splicing of the gene in response to OP exposures. In addition, brain acylpeptide hydrolase (APH) activity was evaluated as a second target for OP-mediated effects. In both experiments, rats were sacrificed at various points to determine the time course of OPs toxicity in relation to their mechanism of action. Results from the first experiment suggest cognitive and emotional deficits after OPs exposure, which could be due to, at least in part, increased F(2)-IsoPs levels. Results from the second experiment revealed inhibition of brain AChE and APH activity at various time points post OP exposure. In addition, we observed increased brain read-through splice variant AChE (AChE-R) mRNA levels after 48 h PTN exposure. In conclusion, this study provides novel data on the relationship between cognitive alterations and oxidative stress, and the diverse mechanisms of action along a temporal axis in response to OP exposures in the rat.

Cognitive and histological disturbances after chlorpyrifos exposure and chronic Aβ(1–42) infusions in Wistar rats

Exposure to pesticides has been linked to an increased vulnerability to neurodegenerative diseases. In order to study whether the exposure to the organophosphate chlorpyrifos renders the brain prone to amyloid-beta peptide deposition and accelerates its neuropathological and behavioural effects, Wistar rats were injected a single subcutaneous dose of chlorpyrifos (250 mg/kg) and subsequently infused with Aβ(1-42) peptide (i.c.v.) for 15 days. No effects of either treatment were noted in the classic water maze test. The animals infused with Aβ peptide showed worse performance when the platform was both hidden and moved from trial to trial. Both groups showed worse performance when the platform was visible and moved from trial to trial. No amyloid deposition was observed in hippocampus or cerebral cortex after the infusion period, although microtubule-associated protein 1A (MAP1A) immunoreactivity was significantly reduced in hippocampus and prefrontal cortex, whereas chlorpyrifos exposure produced a significant reduction of microtubule-associated protein 2 (MAP2) in the prefrontal cortex. Therefore, behavioural deficits could be related to a loss of dendrite and spine processes in these brain regions.

Impaired retention in AβPP Swedish mice six months after oral exposure to chlorpyrifos

Chlorpyrifos (CPF) is an organophosphate pesticide. This pesticide induces cognitive impairments, oxidative stress and neuronal damage, which suggests a possible relationship between CPF exposure and Alzheimers disease. In this study we examined long-term changes in behavior and brain levels of the amyloid beta (Aβ) protein after repeated CPF exposure in a mouse model of Alzheimers disease. Tg2576 male mice between four and six months of age carrying the human Swedish mutation for Alzheimers disease were exposed to eight doses of 25 mg/kg of CPF distributed over four weeks. Five months after exposure, general activity was measured in an open-field, while learning and memory were assessed in a Morris water maze task six months after treatment with CPF. Levels of the Aβ fragments (1-40 and 1-42) were also measured in the frontal cortex and hippocampal brain regions. Motor activity was increased in CPF-exposed mice. Although acquisition learning in a water maze task was not affected, retention was worsened in CPF-exposed mice. There were no significant increases of Aβ levels in the brains of CPF-treated mice six months after exposure. These findings raise concerns about the risk of developing neurodegenerative diseases in vulnerable subjects following repeated exposure to CPF.