Chronic D-amphetamine induces sexually dimorphic effects on locomotion, recognition memory, and brain monoamines

Sex differences in cognition following variations in endocrine status

Spatial memory, mediated primarily by the hippocampus, is responsible for orientation in space and retrieval of information regarding location of objects and places in an animal's environment. Since the hippocampus is dense with steroid hormone receptors and is capable of robust neuroplasticity, it is not surprising that changes in spatial memory performance occur following a variety of endocrine alterations. Here, we review cognitive changes in both spatial and nonspatial memory tasks following manipulations of the hypothalamic-pituitary-adrenal and gonadal axes and after exposure to endocrine disruptors in rodents. Chronic stress impairs male performance on numerous behavioral cognitive tasks and enhances or does not impact female cognitive function. Sex-dependent changes in cognition following stress are influenced by both organizational and activational effects of estrogen and vary depending on the developmental age of the stress exposure, but responses to gonadal hormones in adulthood are more similar than different in the sexes. Also discussed are possible underlying neural mechanisms for these steroid hormone-dependent, cognitive effects. Bisphenol A (BPA), an endocrine disruptor, given at low levels during adolescent development, impairs spatial memory in adolescent male and female rats and object recognition memory in adulthood. BPA's negative effects on memory may be mediated through alterations in dendritic spine density in areas that mediate these cognitive tasks. In summary, this review discusses the evidence that endocrine status of an animal (presence or absence of stress hormones, gonadal hormones, or endocrine disruptors) impacts cognitive function and, at times, in a sex-specific manner.

Amphetamine exposure alters behaviors, and neuronal and neurochemical activation in the brain of female prairie voles

Previous studies have shown that 3-day d-amphetamine (AMPH) treatment effectively induced conditioned place preferences (CPP) and impaired pair bonding behaviors in prairie voles (Microtus ochrogaster). Using this established animal model and treatment regimen, we examined the effects of the demonstrated threshold rewarding dose of AMPH on various behaviors and their potential underlying neurochemical systems in the brain of female prairie voles. Our data show that 3-day AMPH injections (0.2 mg/kg/day) impaired social recognition and decreased depressive-like behavior in females without affecting their locomotion and anxiety-like behaviors. AMPH treatment also decreased neuronal activation indicated by the labeling of the early growth response protein 1 (Egr-1) as well as the number of neurons double-labeled for Egr-1 and corticotrophin-releasing hormone (CRH) in the dentate gyrus (DG) of the hippocampus and paraventricular nucleus of the hypothalamus (PVN) in the brain. Further, AMPH treatment decreased the number of neurons double-labeled for Egr-1 and tyrosine hydroxylase (TH) but did not affect oxytocinergic neurons in the PVN or cell proliferation and neurogenesis markers in the DG. These data not only demonstrate potential roles of the brain CRH and dopamine systems in mediating disrupted social recognition and depressive-like behaviors by AMPH in female prairie voles, but also further confirm the utility of the prairie vole model for studying interactions between psychostimulants and social behaviors.

Androgens Enhance Recognition Memory and Dendritic Spine Density in the Hippocampus and Prefrontal Cortex of Ovariectomized Female Rats

Estrogen replacement has been repeatedly shown to enhance memory and increase dendritic spine density in the hippocampus and prefrontal cortex of ovariectomized (OVX) female rats. Given the potential deleterious effects of chronic estrogen administration, the present study assessed cognitive function using recognition memory tasks and measured dendritic spine density in the CA1 region of the hippocampus and medial prefrontal cortex after subchronic androgen replacement to adult OVX female rats. All androgens enhanced recognition memory in OVX rats, but object placement (OP) and object recognition (OR) results differed. Only testosterone enhanced OR. Testosterone had no effect on OP while dehydroepiandrosterone (DHEA), dihydrotestosterone (DHT) and androstenedione (AD) enhanced OP. Dendritic spine density was increased by both TP and DHEA in both brain areas (DHT and AD were not tested). Lastly, we used the aromatase inhibitor, letrozole, to discriminate between potential androgenic and estrogenic effects of androgens on behavior. Letrozole alone did not alter recognition memory in OVX rats and did not block the effects of either TP or DHEA on recognition memory suggesting that effects were mediated via androgenic mechanisms. The present results expand previous information on gonadal hormone actions and show that, in addition to estrogens, androgens also improve memory and increase spine density in brains of OVX female rats. While requiring further investigation, these observations provide a basis for therapeutic interventions in the treatment of menopausal, age or disease related memory loss.

Does paternal methamphetamine exposure affect the behavior of rat offspring during development and in adulthood?

Methamphetamine (MA) is one of the most abused psychostimulants in the Czech Republic and worldwide. Previous studies have demonstrated the adverse effects of maternal drug abuse. However, the father's contribution as a parent and donor of the half genetic information is unclear. The present study aimed to examine the effect of paternal MA exposure on behavioral development and locomotor activity in rat offspring. MA was administrated subcutaneously for 30 days at a dose of 5 mg/kg to adult male rats. The impact of paternal MA exposure on rat pups was investigated using behavioral tests during development and locomotor activity tests in adulthood. Prior to testing, adult offspring were exposed to an acute challenge dose of MA (1 mg/kg) to examine the possible sensitizing effect of the paternal treatment. Our results found no significant differences in behavioral development or locomotor activity in adulthood of offspring linked to paternal MA application. These results differ from the effects induced by maternal MA application. Further, our results demonstrated a significant increase in locomotor activity on the Laboras test after acute MA application. When comparing sex differences, females showed more activity than males in adulthood, whereas males were more active during development.

Sex-dependent Effects of the Drugs of Abuse Amphetamine and the Smart Drug 3,4-Methylenedioxypyrovalerone on Fear Memory Generalization in Rats

In recent years there has been an increase in the development of new synthetic drugs, among which the "bath salt" 3,4-methylenedioxypyrovalerone (MDPV), a psychostimulant with a mechanism of action similar to those of cocaine and amphetamine, stands out. Drugs of abuse have been consistently shown to affect memory function in male rodents. We have recently shown that amphetamine and MDPV induce generalization of fear memory in an inhibitory avoidance discrimination task in male rats. Although abuse of illicit drugs is more prevalent in men than in women, several studies have demonstrated that females are more vulnerable to the effects of drugs of abuse than males and the effects caused by substance dependence on memory in females are still under-investigated. Thus, we examined the effects of subchronic amphetamine or MDPV administrations on memory in a contextual fear conditioning/generalization paradigm in adult male and female rats. Animals were given daily subchronic injections of the drugs, starting 6 days prior the beginning of the behavioral procedures until the end of the paradigm. On day 1 of the experimental protocol, all rats were exposed to a safe context and, the day after, to a slightly different chamber where they received an unsignaled footshock. Twenty-four and forty-eight hours later, freezing behavior and emission of 22 kHz-ultrasonic vocalizations (USVs) were measured in the two different contexts to assess fear memory retention and generalization. Our results indicate that MDPV treatment altered freezing in both sexes, USVs were affected by amphetamine in males while by MDPV in females.

The Impact of Neonatal Methamphetamine on Spatial Learning and Memory in Adult Female Rats

The present study was aimed at evaluating cognitive changes following neonatal methamphetamine exposure in combination with repeated treatment in adulthood of female Wistar rats. Pregnant dams and their pups were used in this study. One half of the offspring were treated indirectly via the breast milk of injected mothers, and the other half of pups were treated directly by methamphetamine injection. In the group with indirect exposure, mothers received methamphetamine (5 mg/ml/kg) or saline (1 ml/kg) between postnatal days (PD) 1-11. In the group with direct exposure, none of the mothers were treated. Instead, progeny were either: (1) treated with injected methamphetamine (5 mg/ml/kg); or (2) served as controls and received sham injections (no saline, just a needle stick) on PD 1-11. Learning ability and memory consolidation were tested on PD 70-90 in the Morris Water Maze (MWM) using three tests: Place Navigation Test, Probe Test, and Memory Recall Test. Adult female progeny were injected daily, after completion of the last trial of MWM tests, with saline or methamphetamine (1 mg/ml/kg). The effects of indirect/direct neonatal methamphetamine exposure combined with acute adult methamphetamine treatment on cognitive functions in female rats were compared. Statistical analyses showed that neonatal drug exposure worsened spatial learning and the ability to remember the position of a hidden platform. The study also demonstrated that direct methamphetamine exposure has a more significant impact on learning and memory than indirect exposure. The acute dose of the drug did not produce any changes in cognitive ability. Analyses of search strategies (thigmotaxis, scanning) used by females during the Place Navigation Test and Memory Recall Test confirmed all these results. Results from the present study suggested extensive deficits in learning skills and memory of female rats that may be linked to the negative impact of neonatal methamphetamine exposure.

Chronic lithium exposure attenuates ketamine-induced mania-like behavior and c-Fos expression in the forebrain of mice

Ketamine, a dissociative anaesthetic, has been used in the treatment of major depressive disorder (MDD) as a rapid acting antidepressant drug. Recent studies have shown that ketamine may increase the potential risk of treatment-induced mania in MDD patients. Lithium is a well-known mood stabilizer and has been widely used for the treatment of mania. It is not fully understood which forebrain regions are involved in ketamine- and lithium-induced expression of c-Fos. Therefore, our aim was to investigate the effect of chronic lithium treatment on mania-like behavior and c-Fos expression in the mouse forebrain activated by a single administration of ketamine. In the open field test, our results showed that ketamine significantly increased the total distance and total cumulative duration of movement in mice, while chronic lithium could attenuate these effects of ketamine. In addition, acute ketamine induced higher c-Fos expression in the lateral septal nucleus, hypothalamus, amygdala, and hippocampus of mice in the treatment group compared to those in the control group. However, chronic lithium inhibited the significant increase in c-Fos-immunoreactive neurons following acute ketamine administration in the dentate gyrus of the hippocampus, field CA1 of the hippocampus, dorsal subiculum, ventral subiculum, ventral subiculum, central amygdaloid nucleus and basolateral amygdaloid nucleus. In summary, our research shows that pretreatment with lithium moderates the effects of acute ketamine administration on mania-like behavior and c-Fos expression in the forebrain. These findings could be helpful in better understanding the episodes of mania related to ketamine treatment for MDD and bipolar disorder.

Chronic unpredictable intermittent restraint stress disrupts spatial memory in male, but not female rats

Chronic stress leads to sex-dependent outcomes on spatial memory by producing deficits in males, but not in females. Recently it was reported that compared to daily restraint, intermittent restraint (IR) produced more robust stress and anxiety responses in male rats. Whether IR would be sufficiently robust to impair hippocampal-dependent spatial memory in both male and female rats was investigated. IR involved mixing restraint with non-restraint days over weeks before assessing spatial memory and anxiety profile on the radial arm water maze, object placement, novel object recognition, Y-maze, open field and novelty suppressed feeding. Experiments 1 and 2 used Sprague-Dawley male rats only and determined that IR for 6 h/d (IR6), but not 2 h/d, impaired spatial memory and that task order was important. In experiment 3, IR6 was extended for 6wks before spatial memory testing commenced using both sexes. Unexpectedly, an extended IR6 paradigm failed to impair spatial memory in either sex, suggesting that by 6wks IR6 may have become predictable. In experiment 4, an unpredictable IR (UIR) paradigm was implemented, in which restraint duration (30 or 60-min) combined with orbital shaking, time of day, and the days off from UIR were varied. UIR impaired spatial memory in males, but not in females. Together with other reports, these findings support the interpretation that chronic stress negatively impairs hippocampal-dependent function in males, but not in females. We interpret these findings to show that females are more resilient to chronic stress than are males as it pertains to spatial ability.

Gonadal hormones in female rats protect against dehydration-induced memory impairments in the novel object recognition paradigm

Dehydration impairs cognitive performance in humans and rodents, although studies in animal models are limited. Estrogens have both protective effects on fluid regulation and improve performance in certain cognitive tasks. We, therefore, tested whether sex and gonadal hormones influence object recognition memory during dehydration. Because past studies used fluid deprivation to induce dehydration, which is a mixture of intracellular and extracellular fluid loss, we tested the effects of osmotic (loss of intracellular fluid) and hypovolemic (loss of extracellular fluid) dehydration on object recognition memory. After training trials consisting of exposure to two identical objects, rats were either treated with hypertonic saline to induce osmotic dehydration, furosemide to induce hypovolemic dehydration, or received a control injection and then object recognition memory was tested by presenting the original and a novel object. After osmotic dehydration, regardless of group or treatment, all rats spent significantly more time investigating the novel object. After hypovolemic dehydration, regardless of treatment, both the males and estrous females spent significantly more time investigating the novel object. While the control-treated diestrous females also spent significantly more time investigating the novel object, the furosemide-treated diestrous females spent a similar amount of time investigating the novel and original object. Follow up studies determined that loss of ovarian hormones after ovariectomy, but not loss of testicular hormones after castration, resulted in impaired memory performance in the object recognition test after hypovolemic dehydration. This series of experiments provides evidence for a protective role of ovarian hormones on dehydration-induced memory impairments.

Single and Repeated Administration of Methylphenidate Modulates Synaptic Plasticity in Opposite Directions via Insertion of AMPA Receptors in Rat Hippocampal Neurons

Methylphenidate (MPH) is widely used in the treatment of Attention Deficit Hyperactivity Disorder. Several lines of evidence support that MPH can modulate learning and memory processes in different ways including improvement and impairment of test performances. A relevant factor in the efficacy of treatment is whether administration is performed once or several times. In this study we demonstrate opposite effects of MPH on performance of preadolescent rats in the Morris Water Maze test. Animals treated with a single dose (1 mg/kg) performed significantly better compared to controls, while in animals treated with repetitive administration at the same concentration performance was reduced. We found that hippocampal LTP in slices from rats treated with a single dose was increased, while LTP from rats treated with repetitive injections of MPH was lower than in controls. Using Western blot of CA1 areas from potentiated slices of rats treated with a single dose we found a significant increase of phosphorylation at Ser845 of GluA1 subunits, associated to an increased insertion of GluA1-containing AMPARs in the plasma membrane. These receptors were functional, because AMPA-dependent EPSCs recorded on CA1 were enhanced, associated to a significant increase in short-term plasticity. In contrast, CA1 samples from rats injected with MPH during six consecutive days, showed a significant decrease in the phosphorylation at Ser845 of GluA1 subunits associated to a lower insertion of GluA1-containing AMPARs. Accordingly, a reduction of the AMPA-mediated EPSCs and short-term plasticity was also observed. Taken together, our results demonstrate that single and repeated doses with MPH can induce opposite effects at behavioral, cellular, and molecular levels. The mechanisms demonstrated here in preadolescent rats are relevant to understand the effects of this psychostimulant in the treatment of ADHD.

Schizophrenia dimension-specific antipsychotic drug action and failure in amphetamine-sensitized psychotic-like rats

Schizophrenic patients suffer from various disruptions in their psyche, mood and cognition, most of which cannot be effectively treated with the available antipsychotic drugs. Some dimensions of the schizophrenia syndrome in man can be mimicked in animals by the amphetamine (AMPH)-sensitization-induced psychosis model. Using such a sensitization procedure, we induced a psychosis-like syndrome in rats, measured as a deficit in sensory information processing and memory deficits. We then investigated the possible restorative effects of continuous treatment with haloperidol (HAL), a typical antipsychotic drug, on distinct dimensions of the syndrome. We found that, continuous infusion of a clinically relevant dose of HAL (0.5 mg/kg/day) effectively ameliorated AMPH-sensitization-induced sensorimotor gating disruptions after seven days of treatment. However, the sensory information processing deficit reappeared after prolonged HAL treatment, suggesting a treatment failure in this dimension of the syndrome. HAL had at this dose little beneficial effects on the cognitive deficits. In contrast, a continuously administered low dose of HAL (0.05 mg/kg/day) successfully attenuated cognitive deficits, but aggravated the sensorimotor gating deficit under both short- or long-term treatment conditions. Post mortem neurochemical analysis revealed that the psychotic-like behavior induced by our manipulations might be explained by altered monoamine levels in distinct brain regions. These findings provide evidence for dissociating and dose-dependent HAL treatment action and failure at different dimensions of schizophrenia.

Memory and exploratory behavior impairment in ovariectomized Wistar rats

Background

Estrogen deficiency is linked to changes in several physiological processes, but the extent to which it associates with cognitive changes in menopause context is controversial.

Rationale

We evaluated the impact of ovariectomy on memory processes and normal exploratory behavior in Wistar rats.

Methods

Young adult rats (4–6 months) were either ovariectomized (OVX group) (N = 10), sham operated (N = 10), or untouched (naïve controls) (N = 8). Afterwards, they were monitored for 12 weeks during which their cognitive functions were evaluated at first week (S1), second (S2), every 3 weeks (S5, S8) and then at week 12 (S12) using: (i) object recognition test to evaluate the short-term and long-term non-spatial memory; (ii) the object placement test to assess the spatial memory; and (iii) normal exploratory behavior components like locomotor and vertical activities in an open field arena.

Results

Marked changes in ovariectomized rats were observed in long-term non-spatial memory (~ 40% change vs. naïve and sham, P < 0.001) and spatial memory (~ 30% change, P < 0.05) from S2. Instead, from S5 the exploratory behavior was affected, with decreases in line crossing and rearing episode numbers (~ 40% change, P < 0.01), and in the time spent in the center of open field arena (~ 60% change, P < 0.01).

Conclusions

Our findings support the involvement of sex hormones in cognitive functions in female rats and suggest that controversy on the importance of cognitive affections in menopause context may emerge from differences between short-term and long-term memory processes.

Role of Exogenous Progesterone in the Treatment of Men and Women with Substance Use Disorders: A Narrative Review

Substance use disorders (SUDs) remain problematic as many individuals are untreated or do not benefit from the currently available interventions. Thus, there is an urgent need to develop novel pharmacological interventions to treat SUDs. Evidence suggests that the female sex hormone, progesterone, attenuates the craving for and the euphoric effects of drugs of abuse. Research to date has demonstrated that progesterone may modulate responses to drugs of abuse and may have utility as a novel treatment for SUDs. A literature search was conducted to identify and examine studies that administered exogenous progesterone. Sixteen publications were identified, exploring the utility of exogenous progesterone or its metabolite, allopregnanolone, among a range of substances, including amphetamines (one study), benzodiazepines (one study), cocaine (nine studies), and tobacco/nicotine (five studies). Results indicated that exogenous progesterone and, its metabolite allopregnanolone, demonstrated preliminary efficacy as a treatment for substance use in both men and women. Notably, progesterone appears to target negative affect and augment cognitive functioning, especially among female substance users. Additional research is needed to explore the potential use of exogenous progesterone and allopregnanolone in the treatment of SUDs, including that associated with alcohol and opioids, but considering the current promising findings, exogenous progesterone and allopregnanolone may have utility as novel pharmacological treatments for SUDs.

Sex as a biological variable: Drug use and abuse

The study of sex as a biological variable is a necessary emphasis across a wide array of endpoints, including basic neuroscience, medicine, mental health, physiology and behavior. The present review summarizes work from clinical and preclinical populations on sex differences in drug use and abuse, ranging from initiation to escalation/dysregulation and from drug cessation/abstinence to relapse. These differences are analyzed in the context of the addiction cycle conceptualization of Koob and his colleagues and address patterns of drug use (binge/intoxication), motivation underlying its use (withdrawal/negative affect) and likelihood and causes of craving and relapse of drug taking (preoccupation/anticipation). Following this overview, an assessment of the basis for the reported sex differences is discussed in the context of the affective (rewarding and aversive) properties of drugs of abuse and how such properties and their balance vary with sex and contribute to drug intake. Finally, the interaction of sex with several experiential (drug history) and subject (age) factors and how these interactions affect reward and aversion are discussed to highlight the importance of understanding such interactions in predicting drug use and abuse. We note that sex as a biological variable remains one of critical evaluation and that such investigations of sex differences in drug use and abuse continue and be expanded to assess all facets of their mediation, including these affective properties, how their balance may be impacted by the multiple conditions under which drugs are taken and how this overall balance affects drug use and addiction vulnerability.

Hippocampus-dependent Task Improves the Cognitive Function after Ovariectomy in Rats

Objectives

Estrogen is an important hormone for cell growth, development, and differentiation by transcriptional regulation and modulation of intracellular signaling via second messengers. The reduction in the estrogen level after ovariectomy may lead to cognitive impairments associated with morphological changes in areas of the brain mediate memory. The aim of the present study was to find out the effect of tasks on the cognitive function after ovariectomy in rats.

Methods

The animals used in the experiment were 50 Sprague-Dawley female rats. This study applied a hippocampus-independent task (wheel running) and a hippocampus-dependent task (Morris water maze) after ovariectomy in rats and measured the cognitive performance (object-recognition and object-location test) and growth-associated protein 43 (GAP-43) and neurotrophin 3 (NT-3) expression in the hippocampus, which is an important center for memory and learning.

Results

There were meaningful differences between the hippocampus-independent and hippocampus-dependent task groups for the object-location test and GAP-43 and NT-3 expression in the hippocampus, but not the object-recognition test. However, the hippocampus-independent task group showed a significant improvement in the object-recognition test, compared to the control group.

Conclusion

These results suggest that hippocampus-dependent task training after ovariectomy enhances the hippocampus-related memory and cognitive function that are associated with morphological and functional changes in the cells of the hippocampus.

How methamphetamine exposure during different neurodevelopmental stages affects social behavior of adult rats?

Social behavior involves complex of different forms of interactions between individuals that is essential for healthy mental and physical development throughout lifespan. Psychostimulants, including methamphetamine (MA), have neurotoxic effect, especially, if they are targeting CNS during its critical periods of development. The present study was aimed on evaluation of changes in social interactions (SI) following scheduled prenatal/neonatal MA treatment in combination with acute application in adulthood. Eight groups of male and eight groups of female rats were tested in adulthood: rats, whose mothers were exposed to MA (5mg/ml/kg) or saline (SA, 1ml/kg) during the first half of gestation (ED 1-11), the second half of gestation (ED 12-22) and neonatal period (PD 1-11). To do this, we compared indirect neonatal applications via the exposed dams with group of rat pups that received MA or SA directly through injections. In adulthood, half animals from each group were injected with MA (1mg/kg), second half with saline 45min prior to the Social Interaction Test. Females and males were observed for social and nonsocial activities of two unfamiliar individuals of the same sex and treatment in a familiar Open field arena. The present study demonstrated that prenatal/neonatal MA exposure leads to decrease the time spent in genital investigation, following and nonsocial activity. Acute dose of MA leads to a decrease in all SI patterns and to an increase in nonsocial activities relative to acute SA. Females were more active than males. Animals exposed to prenatal/neonatal treatment during the second half of gestation (ED 12-22) and throughout lactation period (PD 1-11 indirect/direct) had fewer SI and greater exploratory behavior than animals exposed during the first half of gestation (ED 1-11).

Does effect from developmental methamphetamine exposure on spatial learning and memory depend on stage of neuroontogeny?

Psychostimulants, including methamphetamine (MA), have neurotoxic effect, especially, if they are targeting CNS during its critical periods of development. The present study was aimed to examine cognitive changes after prenatal and neonatal MA treatment in combination with chronic MA exposure in adulthood of male rats. Eight groups of male rats were tested in adulthood: males whose mothers were exposed to MA (5 mg/kg) or saline (SA, 1 ml/kg) during the first half of gestation period (GD 1-11), the second half of gestation period (GD 12-22) and neonatal period (PD 1-11). In addition, we compared indirect neonatal application via the breast milk with the group of rat pups that received MA or SA directly by injection (PD 1-11). Males were tested in adulthood for cognitive changes in the Morris Water Maze (MWM). MWM experiment lasted for 12 days: Learning (Day 1-6), Probe test (Day 8) and Retrieval Memory test (Day 12). Each day of the MWM animals were injected with MA (1 mg/kg) or SA (1 ml/kg). Prenatal MA exposure did not induce changes in learning abilities of male rats, but neonatal exposure to MA leads to an increase search errors and latencies to find the hidden platform. Prenatal and also neonatal MA exposure impaired cognitive ability to remember the position of the platform in Retrieval Memory test in adulthood. Animals exposed to the prenatal treatment within the second half of gestation (ED 12-22) swam longer, slower and spent more time to find the hidden platform in Retrieval Memory test than animals exposed throughout other periods. The present study demonstrated that stage of development is crucial for determination the cognitive deficits induced by prenatal or neonatal MA exposure.

Sex differences in the strategies of spatial learning in prenatally-exposed rats treated with various drugs in adulthood

In the present study we investigated the sex differences in the effect of adult long-term drug treatment on cognitive functions of Wistar rats, which were prenatally exposed to MA (5mg/kg) or saline. Cognitive functions were tested as an ability of spatial learning in the Morris Water Maze (MWM), which consisted of three types of tests: "Place Navigation Test"; "Probe Test", and "Memory Recall Test". Adult animals were injected daily, after completion of the last trial, either with saline or cocaine (COC; 5mg/kg), MDMA (3,4-methylenedioxy-methamphetamine; 5mg/kg), morphine (MOR; 5mg/kg), or delta-9-tetrahydrocannabinol (THC; 2mg/kg). Results revealed worsened MWM performance in female rats after drug treatment in adulthood. Not only were traditionally investigated parameters affected by drug treatment (latency of platform acquisition, search strategy, distance traveled), but also strategies used by animals (thigmotaxis, scanning). Analyses of search strategies observed in the Place Navigation Test, as well as in the Memory Recall Test, demonstrated variations in the percentage of time spent in thigmotaxis and scanning in females after treatment with COC, MDMA, MOR, and THC. Although we did not see a sensitizing effect of prenatal MA, in some cases the effect of drug treatment in adulthood differed depending on the prenatal drug exposure. The data presented in this study demonstrates that exposure to drugs with various mechanisms of action alters spatial abilities of female rats in the MWM. Alterations in the effect of adult drug treatment with reference to prenatal drug exposure were also found in the present study.

Sex differences in psychotomimetic-induced behaviours in rats

Animal model studies using equal numbers of males and females are sparse in psychiatry research. Given the marked sex differences observed in psychiatric disorders, such as schizophrenia, using both males and females in research studies is an important requirement. Thus the aim of this study was to examine sex differences in psychotomimetic-induced behavioural deficits relevant to psychosis. We therefore compared the acute effect of amphetamine or phencyclidine on locomotor activity and prepulse inhibition in adult male and female Sprague-Dawley rats. The results of this study were that: (1) amphetamine-induced distance travelled was greater in female rats than in male rats, (2) phencyclidine-induced locomotor hyperactivity was similar in male and female rats; (3) there were no sex differences in amphetamine- or phencyclidine-induced disruption of prepulse inhibition; (4) male rats had an increased startle response after amphetamine. These findings suggest that sensitivity to amphetamine, but not phencyclidine, differs between male and female rats, and that this sex difference is selective to locomotor hyperactivity and startle, but not prepulse inhibition. This study used two widely-used, validated preclinical assays relevant to psychosis; the results of this study have implications for psychiatry research, particularly for disorders where marked sex differences in onset and symptomology are observed.

Sex Differences in Animal Models: Focus on Addiction

The purpose of this review is to discuss ways to think about and study sex differences in preclinical animal models. We use the framework of addiction, in which animal models have excellent face and construct validity, to illustrate the importance of considering sex differences. There are four types of sex differences: qualitative, quantitative, population, and mechanistic. A better understanding of the ways males and females can differ will help scientists design experiments to characterize better the presence or absence of sex differences in new phenomena that they are investigating. We have outlined major quantitative, population, and mechanistic sex differences in the addiction domain using a heuristic framework of the three established stages of the addiction cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. Female rats, in general, acquire the self-administration of drugs and alcohol more rapidly, escalate their drug taking with extended access more rapidly, show more motivational withdrawal, and (where tested in animal models of "craving") show greater reinstatement. The one exception is that female rats show less motivational withdrawal to alcohol. The bases for these quantitative sex differences appear to be both organizational, in that estradiol-treated neonatal animals show the male phenotype, and activational, in that the female phenotype depends on the effects of gonadal hormones. In animals, differences within the estrous cycle can be observed but are relatively minor. Such hormonal effects seem to be most prevalent during the acquisition of drug taking and less influential once compulsive drug taking is established and are linked largely to progesterone and estradiol. This review emphasizes not only significant differences in the phenotypes of females and males in the domain of addiction but emphasizes the paucity of data to date in our understanding of those differences.

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.

Sex differences in chronic stress effects on cognition in rodents

Chronic stress causes deleterious changes in physiological function in systems ranging from neural cells in culture to laboratory rodents, sub-human primates and humans. It is notable, however, that the vast majority of research in this area has been conducted in males. In this review, we provide information about chronic stress effects on cognition in female rodents and contrast it with responses in male rodents. In general, females show cognitive resilience to chronic stressors which impair male cognitive function using spatial tasks including the radial arm maze, radial arm water maze, Morris water maze, Y-maze and object placement. Moreover, stress often enhances female performance in some of these cognitive tasks. Memory in females is not affected by stress in non-spatial memory tasks like recognition memory and temporal order recognition memory while males show impaired memory following stress. We discuss possible bases for these sex-dependent differences including the use of different strategies by the sexes to solve cognitive tasks. Whether the sex differences result from changes in non-mnemonic factors is also considered. Sex-dependent differences in alcohol and drug influences on stress responses are also described. Finally, the role of neurally derived estradiol in driving sex differences and providing resilience to stress in females is shown. The importance of determining the nature and extent of sex differences in stress responses is that such differences may provide vital information for understanding why some stress related diseases have different incidence rates between the sexes and for developing novel therapeutic treatments.

Maternal separation prior to neonatal hypoxia-ischemia: Impact on emotional aspects of behavior and markers of synaptic plasticity in hippocampus

Exposure to early-life stress is associated with long-term alterations in brain and behavior, and may aggravate the outcome of neurological insults. This study aimed at investigating the possible interaction between maternal separation, a model of early stress, and subsequent neonatal hypoxia-ischemia on emotional behavior and markers of synaptic plasticity in hippocampus. Therefore, rat pups (N=60) were maternally separated for a prolonged (MS 180min) or a brief (MS 15min) period during the first six postnatal days, while a control group was left undisturbed. Hypoxia-ischemia was applied to a subgroup of each rearing condition on postnatal day 7. Emotional behavior was examined at three months of age and included assessments of anxiety (elevated plus maze), depression-like behavior (forced swimming) and spontaneous exploration (open field). Synaptic plasticity was evaluated based on BDNF and synaptophysin expression in CA3 and dentate gyrus hippocampal regions. We found that neonatal hypoxia-ischemia caused increased levels of anxiety, depression-like behavior and locomotor activity (ambulation). Higher anxiety levels were also seen in maternally separated rats (MS180min) compared to non-maternally separated rats, but prolonged maternal separation prior to HI did not potentiate the HI-associated effect. No differences among the three rearing conditions were found regarding depression-like behavior or ambulation. Immunohistochemical evaluation of synaptophysin revealed that both prolonged maternal separation (MS180min) and neonatal hypoxia-ischemia significantly reduced its expression in the CA3 and dentate gyrus. Decreases in synaptophysin expression in these areas were not exacerbated in rats that were maternally separated for a prolonged period prior to HI. Regarding BDNF expression, we found a significant decrease in immunoreactivity only in the hypoxic-ischemic rats that were subjected to the prolonged maternal separation paradigm. The above findings suggest that early-life stress prior to neonatal hypoxia-ischemia leads to significant alterations in synaptic plasticity of the dorsal hippocampus during adulthood, but does not exacerbate HI-related changes in emotional behavior.

Memory and brain-derived neurotrophic factor after subchronic or chronic amphetamine treatment in an animal model of mania

Progression of bipolar disorder (BD) has been associated with cognitive impairment and changes in neuroplasticity, including a decrease in serum brain-derived neurotrophic factor (BDNF). However, no study could examine BDNF levels directly in different brain regions after repeated mood episodes to date. The proposed animal model was designed to mimic several manic episodes and evaluate whether the performance in memory tasks and BDNF levels in hippocampus, prefrontal cortex, and amygdala would change after repeated amphetamine (AMPH) exposure. Adult male Wistar rats were divided into subchronic (AMPH for 7 days) and chronic groups (35 days), mimicking manic episodes at early and late stages of BD, respectively. After open field habituation or inhibitory avoidance test, rats were killed, brain regions were isolated, and BDNF mRNA and protein levels were measured by quantitative real-time PCR and ELISA, respectively. AMPH impaired habituation memory in both subchronic and chronic groups, and the impairment was worse in the chronic group. This was accompanied by increased Bdnf mRNA levels in the prefrontal cortex and amygdala region, as well as reduced BDNF protein in the hippocampus. In the inhibitory avoidance, AMPH significantly decreased the change from training to test when compared to saline. No difference was observed between subchronic and chronic groups, although chronically AMPH-treated rats presented increased Bdnf mRNA levels and decreased protein levels in hippocampus when compared to the subchronic group. Our results suggest that the cognitive impairment related to BD neuroprogression may be associated with BDNF alterations in hippocampus, prefrontal cortex, and amygdala.

Sex differences in monoamines following amphetamine and social reward in adolescent rats

Interaction with social peers may increase rates of drug self-administration, but a recent study from our laboratory showed that social interaction may serve as a type of alternative reward that competes with drug taking in adolescent male rats. Based on those previous results, the current study examined sex differences in preference for social interaction compared with amphetamine (AMPH) in adolescent rats using the conditioned place preference (CPP) paradigm. Similar to previous results with males, females showed AMPH CPP regardless of whether they were individual- or pair-housed. In contrast to males, however, females failed to show social CPP, and they did not prefer a peer-associated compartment over an AMPH-associated compartment in a free-choice test. In separate experiments, dopamine (DA) and serotonin (5-HT) metabolite levels were measured in adolescent males and females that were exposed acutely to peer interaction, no peer interaction, AMPH, or saline. In amygdala, levels of the DA metabolite dihydroxyphenylacetic acid (DOPAC) were altered more in response to peer interaction in males than females; in contrast, there was a greater amygdala DOPAC response to AMPH in females. Furthermore, there were greater changes in the 5-HT metabolite hydroxyindoleacetic acid (5-HIAA) in females than in males following social interaction. These results indicate that the ability of peer interactions to reduce drug reward is greater in adolescent males than females, perhaps due to a greater ability of social cues to activate limbic reward mechanisms in males or a greater ability of AMPH cues to activate limbic reward mechanisms in females.

Effect of Amphetamine on Adult Male and Female Rats Prenatally Exposed to Methamphetamine

The aim of the present study was to examine the cross-sensitization induced by prenatal methamphetamine (MA) exposure to adult amphetamine (AMP) treatment in male and female rats. Rat mothers received a daily injection of MA (5 mg/kg) or saline throughout the gestation period. Adult male and female offspring (prenatally MA- or saline-exposed) were administered with AMP (5 mg/kg) or saline (1 ml/kg) in adulthood. Behaviour in unknown environment was examined in open field test (Laboras), active drug-seeking behaviour in conditioned place preference test (CPP), spatial memory in the Morris water maze (MWM), and levels of corticosterone (CORT) were analyzed by enzyme immunoassay (EIA). Our data demonstrate that in Laboras test, AMP treatment in adulthood increased general locomotion (time and distance travelled) regardless of the prenatal exposure and sex, while AMP increased exploratory activity (rearing) only in prenatally MA-exposed animals. AMP induced sensitization only in male rats, but not in females when tested drug-seeking behaviour in the CPP test. In the spatial memory MWM test, AMP worsened the performance only in females, but not in males. On the other hand, males swam faster after chronic AMP treatment regardless of the prenatal drug exposure. EIA analysis of CORT levels demonstrated higher level in females in all measurement settings. In males, prenatal MA exposure and chronic adult AMP treatment decreased CORT levels. Thus, our data demonstrated that adult AMP treatment affects behaviour of adult rats, their spatial memory and stress response in sex-specific manner. The effect is also influenced by prenatal drug exposure.

Estradiol and cognitive function: past, present and future

A historical perspective on estradiol's enhancement of cognitive function is presented, and research, primarily in animals, but also in humans, is reviewed. Data regarding the mechanisms underlying the enhancements are discussed. Newer studies showing rapid effects of estradiol on consolidation of memory through membrane interactions and activation of inter-cellular signaling pathways are reviewed as well as studies focused on traditional genomic mechanisms. Recent demonstrations of intra-neuronal estradiol synthesis and possible actions as a neurosteroid to promote memory are discussed. This information is applied to the critical issue of the current lack of effective hormonal (or other) treatments for cognitive decline associated with menopause and aging. Finally, the critical period hypothesis for estradiol effects is discussed along with novel strategies for hormone/drug development. Overall, the historical record documents that estradiol positively impacts some aspects of cognitive function, but effective therapeutic interventions using this hormone have yet to be realized.

Sex differences in methamphetamine pharmacokinetics in adult rats and its transfer to pups through the placental membrane and breast milk

BACKGROUND

Methamphetamine (METH) abuse is a growing health problem worldwide, and METH use during pregnancy not only endangers the mother's health but also the developing fetus. To provide better insight into these risks, we performed the following experiments.

METHOD

First, we investigated how sex influences the pharmacokinetics of METH and amphetamine (AMP) in male and female rats. Subsequently, we simulated chronic exposure of prenatal infants to METH abuse by investigating brain and plasma levels of METH and AMP in dams and pups. Finally, we modeled chronic exposure of infants to METH via breast milk and investigated sex differences in pups with regard to drug levels and possible sensitization effect of chronic prenatal METH co-treatment.

RESULTS

We observed significantly higher levels of METH and AMP in the plasma and brain of female rats compared to males. Additionally, brain concentrations of METH and AMP in pups exposed to METH prenatally were equivalent to 62.13% and 37.78% relative to dam, respectively. Plasma concentrations of AMP where equivalent to 100% of the concentration in dams, while METH was equivalent to only 36.98%. Finally, we did not observe a significant effect relative to sex with regard to METH/AMP levels or sensitization effects linked to prenatal METH exposure.

CONCLUSION

We demonstrated that female rats display higher levels of METH and AMP, thus indicating a greater risk of addiction and toxicity. Furthermore, our data show that pups are exposed to both METH and AMP following dam exposure.

Recognition memory tasks in neuroendocrine research

The recognition memory tasks, novel object and novel object location, have been beneficial to neuroendocrine research concerning the effects of gonadal and adrenal hormones on cognitive function. This review discusses the advantages of these tasks in comparison with other learning and memory tasks. Experiments conducted across a number of laboratories show that gonadal hormones, both estradiol and testosterone, promote memory while the adrenal hormone, corticosterone, impairs memory. The effects of these steroid hormones on spine density in the prefrontal cortex and hippocampus are also briefly presented. Overall, results show that these steroid hormones are potent modulators of memory consolidation in rodent models.

Gender differences in the effect of adult amphetamine on cognitive functions of rats prenatally exposed to methamphetamine

Psychostimulants have been shown to affect brain regions involved in the process of learning and memory consolidation. It has been shown that females are more sensitive to the effects of drugs than males. The aim of our study was to investigate how prenatal methamphetamine (MA) exposure and application of amphetamine (AMP) in adulthood would affect spatial learning of adult female and male rats. Mothers of the tested offspring were exposed to injections of MA (5mg/kg) or saline (SA) throughout the entire gestation period. Cognitive functions of adult rats were evaluated in the Morris Water Maze (MWM) tests. Adult offspring were injected daily with AMP (5mg/kg) or SA through the period of MWM testing. Our data from the MWM tests demonstrates the following. Prenatal MA exposure did not change the learning ability of adult male and female rats. However, AMP administration to adult animals affected cognitive function in terms of exacerbation of spatial learning (increasing the latency to reach the hidden platform, the distance traveled and the search error) only in female subjects. There were sex differences in the speed of swimming. Prenatal MA exposure and adult AMP treatment increased the speed of swimming in female groups greater than in males. Overall, the male subjects showed a better learning ability than females. Thus, our results indicate that the adult AMP treatment affects the cognitive function and behavior of rats in a sex-specific manner, regardless of prenatal exposure.

Effects of amphetamine exposure in adolescence or young adulthood on inhibitory control in adult male and female rats

Heightened impulsivity is a feature of some psychiatric disorders, including addiction, that also have sex-specific patterns of expression. The relationship between addiction and impulsivity may be driven by drug-induced changes in behavior caused by long term adaptations in signaling within the medial prefrontal cortex (mPFC). Here, we used a response inhibition task that is sensitive to changes in mPFC function to examine the effects of sex and exposure to amphetamine (AMPH) on impulsive action and vigilance. We also examined drug-induced alterations in glutamatergic and dopaminergic signaling through challenge injections with the NMDA receptor antagonist MK-801 (dizocilpine) and AMPH. Male and female Sprague Dawley rats were injected (i.p.) with saline or 3 mg/kg AMPH every other day during adolescence (postnatal day (P) 27-45) or adulthood (P85-103). Starting on P125-135, rats were tested for their ability to lever press for a food reward during periods of signaled availability and withhold responding during a "premature response" phase. In experiment 1, rats received challenge injections (i.p.) of MK-801 and AMPH followed by tests of task performance and locomotor activity. In experiment 2, rats received intra-mPFC infusion of MK-801. We found that females had better inhibitory control and poorer vigilance than males and that AMPH exposure had both sex- and age-of-exposure dependent effects on impulsivity. Systemic drug challenges disrupted task performance, particularly in females, and increased impulsivity while intra-mPFC infusions had modest effects. AMPH exposure did not affect responses to drug challenges. Together, these results suggest that sex mediates both trait and drug-induced impulsivity.

Differential effects of estrogen and testosterone on auditory sensory gating in rats

RATIONALE

Estrogen has been shown to have beneficial effects in patients with schizophrenia. However, the mechanisms involved in this protective effect are unclear. Schizophrenia is associated with deficits in sensory gating, a filtering mechanism which normally prevents sensory overload. In rodent models, acute treatment with drugs such as the dopamine D1/D2 receptor agonist, apomorphine; the dopamine releaser, amphetamine; and the glutamate NMDA receptor antagonists, phencyclidine or MK-801, can induce a phenotype similar to that seen in schizophrenia.

OBJECTIVES

Given the putative protective action of estrogen in schizophrenia, here we investigated the effect of ovariectomy (OVX) and estrogen replacement in female rats on drug-induced auditory gating deficits. For comparison, we also assessed the effects of castration (CAST) and dihydrotestosterone (DHT) replacement in male rats.

METHODS

Rats were instrumented with cortical surface electrodes. Test sessions comprised of 150 presentations of paired clicks, 500 ms apart (S1 and S2).

RESULTS

Administration of all drugs increased the ratio of responses to S2/S1 in sham-operated female and male rats. OVX reduced event-related potential amplitudes but did not alter S2/S1 ratio or drug effects. In OVX rats with 17β-estradiol implants, the effect of apomorphine was abolished, but there was no change in that of amphetamine and phencyclidine. There were no effects of CAST or DHT replacement in male rats.

CONCLUSIONS

Chronic estrogen replacement in OVX rats protected against sensory gating deficits caused by direct dopamine D1/D2 receptor stimulation. These data could indicate a possible mechanism by which estrogen exerts a protective action in schizophrenia.

Gender differences in the effect of prenatal methamphetamine exposure and challenge dose of other drugs on behavior of adult rats

The aim of the present study was to compare the response to acute application of several drugs in adult male and female rats prenatally exposed to methamphetamine (MA). Spontaneous locomotor activity and exploratory behavior of adult male and female rats prenatally exposed to MA (5 mg/kg) or saline were tested in a Laboras apparatus (Metris B.V., Netherlands) for 1 h. Challenge dose of the examined drug [amphetamine - 5 mg/kg; cocaine - 5 mg/kg; MDMA (3,4-methylenedioxymethamphetamine) - 5 mg/kg; morphine - 5 mg/kg; THC (delta9-tetrahydrocannabinol) - 2 mg/kg] or saline was injected prior to testing. Our data demonstrate that prenatal MA exposure did not affect behavior in male rats with cocaine or morphine treatment, but increased locomotion and exploration in females. Application of amphetamine and MDMA in adulthood increased activity in both sexes, while cocaine and THC only in female rats. Morphine, on the other hand, decreased the activity in the Laboras test in both sexes. As far as sex and estrous cycle is concerned, the present study shows that males were generally less active than females and also females in proestrus-estrus phase of the estrous cycle were more active than females in diestrus. In conclusion, the present study shows that the prenatal MA exposure does not induce general sensitization but affects the sensitivity to drugs dependently to mechanism of drug action and with respect to gonadal hormones.

Sex differences in baseline and drug-induced behavioural responses in classical behavioural tests

Behavioural pharmacology relies on animal models which are primarily validated using the male laboratory rat. Many researchers solely employ male animals in studies; this is primarily due to concerns about the impact of variations in the female estrous cycle on behavioural responses. The objective of the present study therefore was to examine whether sex has any effect in some commonly employed behavioural pharmacology tests. Male and female Sprague Dawley rats were examined in the following behavioural pharmacology tests: diazepam (DZP) effects on anxiolytic behaviour in the elevated plus maze (EPM); desipramine (DMI) effects on immobility time in the forced swim test (FST); amphetamine (AMP) and apomorphine (APO) effects on locomotor activity in the homecage monitoring apparatus (HCMA). Baseline investigations revealed that females were more active than males in all three tests. DZP increased open arm time and entries for males but not for females. Similarly, significant reduction in immobility time with DMI was found for males in the FST, with no effect observed in females. There was a significant effect of AMP dose on distance moved for both sexes; the peak locomotor stimulating effects were seen following 1-2 mg kg⁻¹ AMP doses for males, while 0.5 mg kg⁻¹ produced the greatest effect in females. APO impaired locomotor activity in both sexes. These results demonstrate that male and female rats respond differently to psychotropic drugs. The absence of female responses to the effects of DZP and DMI in the EPM and FST respectively was due to the high baseline activity levels seen with females; thus behavioural tests must be designed to account for sex differences in baseline behaviours to allow for unambiguous extrapolation of the results.

Gender differences in behavioral changes elicited by prenatal methamphetamine exposure and application of the same drug in adulthood

The aim of the present study was to compare the response to sub-chronic application of methamphetamine (MA) in adulthood in male and female rats prenatally exposed to the same drug. The spontaneous locomotor activity and exploratory behavior of adult male and female rats prenatally exposed to 5 mg/kg MA or saline (SAL) were tested in a Laboras apparatus (Metris B.V., Netherlands) for five consecutive days, 1 hr daily. MA 1 mg/kg or SAL were used as a challenge prior to testing. Our results showed that rats prenatally exposed to MA were more sensitive to sub-chronic administration of MA in adulthood than prenatally SAL-exposed rats. However, this sensitizing effect of prenatal MA exposure was manifested differently in males and females. In contrast, prenatal MA exposure decreased baseline locomotion in females. This study indicates that gender plays an important role in the sensitivity to MA during prenatal development and in adulthood.

Early life stress exacerbates cognitive dysfunction induced by d-amphetamine: amelioration by valproic acid

It has been demonstrated that experiences taking place early in life have a profound influence on brain development, interacting with the genetic background and determining differences in the vulnerability to the onset of bipolar disorder when the individual is exposed to a second adverse event later in life. Here, we investigated the effects of exposure to an early adverse life event (maternal deprivation) and to a later adverse life event [D-amphetamine (AMPH)] on cognition in an animal model of mania. We have previously demonstrated that that repeated AMPH exposure produces severe and persistent cognitive impairment, which was more pronounced when the animals were maternal deprived, suggesting that the early adverse life event could be potentiating the effects of the exposure to the second adverse life event later in life. Here, we show that valproic acid ameliorated the cognitive deficits induced by AMPH, but it was not effective when the animals were exposed to both stressors: maternal deprivation and AMPH treatment.

Age-related deficits in spatial memory and hippocampal spines in virgin, female Fischer 344 rats

Effects of aging on memory and brain morphology were examined in aged, 21-month-old, and young, 4-month-old, Fischer 344 female rats. Spatial memory was assessed using the object placement task, and dendritic spine density was determined on pyramidal neurons in the hippocampus following Golgi impregnation. Consistent with previous studies, aged females showed poorer object placement performance than young subjects. Young subjects significantly discriminated the location of objects with a 1.5-hour intertrial delay while aged subjects did not. Spine density of basal dendrites on CA1 pyramidal cells was 16% lower in the aged subjects as compared to the young subjects. No differences in spine density were found between young and aged subjects in basal dendrites of CA1 or in either dendritic field of CA3 pyramidal neurons. Thus, decreased hippocampal CA1 dendritic spine density in aged rats may contribute to poorer spatial memory as compared to young rats. The possibility that the neuroplastic changes observed in this study may pertain only to female subjects having had a specific set of life experiences is discussed. Different factors, such as reproductive status, diet, and handling may contribute to neuroplasticity of the brain during aging; however, this view requires further examination.

Early life stress decreases hippocampal BDNF content and exacerbates recognition memory deficits induced by repeated D-amphetamine exposure

Adverse experiences early in life may have profound influences on brain development, for example, determining alterations in response to psychostimulant drugs, an increased risk of developing a substance abuse disorder, and individual differences in the vulnerability to neuropsychiatric disorders later in life. Here, we investigated the effects of exposure to an early adverse life event, maternal deprivation, combined with repeated d-amphetamine (AMPH) administration in adulthood, on recognition memory and brain-derived neurotrophic factor (BDNF) levels in rats' brain and serum. Rats were exposed to one of the following maternal rearing conditions from postnatal days 1 to 14: non-deprived (ND) or deprived (D). In adulthood, both groups received injections of saline (SAL) or AMPH (2.0mg/kg, i.p.) for 7 days. In Experiment I (performed 24h after the last AMPH injection), AMPH induced long-term memory (LTM) impairments in ND and D groups. The D+AMPH group also presented short-term memory (STM) impairments, indicating that the effects of AMPH on memory were more pronounced when the animals where maternally deprived. The group exposed to D+SAL (SAL) showed only LTM impairments. In Experiment II (performed 8 days after the last injection), AMPH detrimental effects on memory persisted in ND and D groups. BDNF levels were decreased in the hippocampus of D+SAL rats. In conclusion, AMPH produces severe and persistent recognition memory impairments that were more pronounced when the animals were maternally deprived, suggesting that an early adverse life event may increase the vulnerability of cognitive function to exposure to a psychostimulant later in life.