Inhibitory Avoidance Response Research Articles

Oxytocin-Cholinergic Central Interaction: Implications for Non-Social Memory Formation

Oxytocin (OT) and vasopressin (AVP) are two closely related neuropeptides implicated in learning and memory processes, anxiety, nociception, addiction, feeding behavior and social information processing. Regarding learning and memory, OT has induced long-lasting impairment in different behaviors, while the opposite was observed with AVP. We have previously evaluated the effect of peripheral administration of OT or its antagonist (AOT) on the inhibitory avoidance response of mice and on the modulation of cholinergic mechanisms. Here, we replicate and validate those results, but this time through central administration of neuropeptides, considering their poor passage through the blood–brain barrier (BBB). When we delivered OT (0.10 ng/mouse) and its antagonist (0.10 ng/mouse) through intracerebroventricular (ICV) injections, the neuropeptide impaired and AOT enhanced the behavioral performance on an inhibitory avoidance response evaluated 48 h after training in a dose-dependent manner. On top of that, we investigated a possible central interaction between OT and the cholinergic system. Administration of anticholinesterases inhibitors with access to the central nervous system (CNS), the activation of muscarinic acetylcholine (Ach) receptors and the increase of evoked ACh release using linopirdine (Lino) (3–10 µg/kg, IP), reversed the impairment of retention performance induced by OT. Besides, either muscarinic or nicotinic antagonists with unrestricted access to the CNS reduced the magnitude of the performance-facilitating effect of AOT’s central infusion. We suggest that OT might induce a cholinergic hypofunction state, resulting in an impairment of IA memory formation, a process for which the cholinergic system is crucially necessary.

Epinephrine modulates memory of latent learning in an inhibitory avoidance task

The present study examined the memory modulatory effect of epinephrine on latent learning of an inhibitory avoidance task. Male Sprague-Dawley rats on the first day were subjected to one of three conditions (no, short or long) in pre-exposure to the task apparatus. One day or several days later, they received the typical inhibitory avoidance training with a 0.5 mA/0.5 s foot shock. Memory of the inhibitory avoidance response was tested one day after the foot-shock training. The long pre-exposure group showed better memory than the no or short pre-exposure group, and this latent memory could last for 6 days: Retention scores of the long pre-exposure group were significantly better than those of the no pre-exposure group if the shock training was given 3 or 6 days, but not 12 or 21 days, after the pre-exposure. Epinephrine injected after the pre-exposure training modulated the latent memory in a dose- and time-dependent manner: 0.01 mg/kg given shortly after the short pre-exposure enhanced the memory, but 0.5 mg/kg given shortly after the long pre-exposure impaired it. Epinephrine injected 4 h after the pre-exposure had no effect, neither did that given to rats pre-exposed to a different context. Epinephrine (0.01 mg/kg) also made the latent memory lasting longer as the rats treated with it showed significant avoidance behavior when they had the shock training at 12 or 21 days after the pre-exposure. These findings suggest that epinephrine could modulate memory formed in the latent learning.

Critical role of hippocampal muscarinic acetylcholine receptors on memory reconsolidation in mice

Over the years, experimental and clinical evidence has given support to the idea that acetylcholine (Ach) plays an essential role in mnemonic phenomena. On the other hand, the Hippocampus is already known to have a key role in learning and memory. What is yet unclear is how the Ach receptors may contribute to this brain region role during memory retrieval.The Ach receptors are divided into two broad subtypes: the ionotropic nicotinic acetylcholine receptors and the metabotropic muscarinic acetylcholine receptors. Back in 2010, we demonstrated for the first time the critical role of hippocampal α7 nicotinic acetylcholine receptors in memory reconsolidation process of an inhibitory avoidance response in mice. In the present work, we further investigate the possible implication of hippocampal muscarinic Ach receptors (mAchRs) in this process using a pharmacological approach. By specifically administrating agonists and antagonists of the different mAchRs subtypes in the hippocampus, we found that M1 and M2 but not M3 subtype may be involved in memory reconsolidation processes in mice.

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL PROPERTIES OF NEW CODEINE FE(III) COMPLEX

ABSTRACT The reaction of FeCl 3 hexahydrate with C 18 H 20 NO 3 .PO 4 in acetonitrile produced new complex with general formula [Fe(L)]Cl 2 , (L= codeine). Characterization of the ligand and its complex were made by elemental analysis, FT-IR, 1 H-NMR, Raman and UV–visible spectroscopy. This new complex showed antitumor activity against two kinds of cancer cell lines: AGS (Stomach) and MCF-7 (Breast). Cell cytotoxic effects of the ligand and its complex were assayed by MTT and Natural-red tests. The antibacterial activity of ligand and complex against Pseudomonas aeruginosa , Staphylococcus aureus , Streptococcus pyogenes and Escherichia coli were also examined. Keywords: Codeine; Fe(III) complex; Synthesis; Anti-tumor; AGS and MCF-7; Antibacterial. e-mail: mojdeh.golzani@gmail.com INTRODUCTION Natural products play an important role in diseases control and treatment. The plants extracts are used in the treatment of human diseases all the time. From the last century, a scientific interest for phototherapy increased in several medical fields such as immunology, hematology and oncology [1-5].Currently there are three major ways of treating cancer: radiation therapy, surgery and cytotoxic drugs. Application of plants in medicine has affected the identification of natural compounds such as cocaine, morphine, vinblastine, tax land codeine [5-8].Many different coordination compounds and the mechanism of cytotoxic action have been discussed with regard to the development of new antitumor agents [8-15]. Numerous medicinal plants have been screened extensively for their antimicrobial potential worldwide [1, 11]. Morphine and its derivatives have received considerable attention as narcotic and used in lenitive drudge products. Morphine plays an important role in the therapy of acute and chronic pain. Exogenously delivered morphine acts in the body by activating different subtypes of opioid receptors [14].Over the last decades, proposals have accumulated that morphine present in mammalian tissues and fluids comes not only from an exogenous or dietary origin, but may also be biosynthesized de novo. Latest studies have unequivocally proven the existence of a mammalian morphine biosynthetic pathway [15], which consists of at least 19 steps and is different in its primary steps from that occurring in plants [16]. Meanwhile the endogenous morphine biosynthesis takes place in mammals, their cells and tissues are constantly exposed to certain amounts of morphine and its precursors [17].Investigation of lithium effect in opioid receptors on inhibitory avoidance response in mice has been reported. The results suggest that the opioid receptors in the central nervous system may be involved in the retrieval of lithium state dependent learning [18]. The lithium efficacy in controlling behaviors related with dopamine stimulants and manic states has been proposed [19]. Thus, it may be suggested that lithium‘s action may be mediated through dopamine receptors [20].Furthermore interactions between lithium and opioids have been reported. There is evidence that lithium is able to affect some actions of morphine. In particular, it has been shown that lithium inhibits morphine withdrawal signs in morphine-dependent mice [21], reduces the self-stimulation facilitated by morphine and the expression of tolerance to morphine [22] and alters the morphine induced analgesia in mice [23]. Both drugs produce a conditioned taste avoidance response and suppress schedule-induced polydipsia [24]. Another morphine precursor codeine, which stands in the biosynthetic pathway after salutaridinol, had a higher partial agonist efficacy. Their metal chelates are of interest due to their fascinating chemistry as well as antimicrobial and anti-cancer activities. The other natural ligand from plants such as phenolic compound of mono and sesquiterpenoid, flavonoids also can be used in synthesis of metal complex [25].Codeine is generally named codeine phosphate (Cod.P), morphine-3-methyl ether phosphate, methyl-morphine phosphate, or morphine monomethyl ether phosphate. It takes the general formulae of C

Protein malnutrition during pregnancy alters maternal behavior and anxiety-like behavior in offspring

Objective: The aim of this study was to evaluate the effects of protein malnutrition during pregnancy on maternal behavior, on the early behavior in pups by ultrasonic vocalizations (USVs) emission, and on the behavior of offspring in adulthood in an elevated T-maze.Methods: Pregnant female rats were fed a normal protein-powdered diet (22% casein; control) or a low-protein (hypoproteic) diet (6% casein; protein restriction) during the first 2 weeks of pregnancy. On the fifth postpartum day (PND5), the number of USV was rated. On PND7, maternal behavior was assessed. Male offspring in adulthood were evaluated for behavioral performance in an elevated T-maze.Results: Our results demonstrated that a hypoproteic diet during early pregnancy increased the maternal behavior, increased the number of USV by pups, and reduced the inhibitory avoidance responses in an elevated T-maze during adulthood. In addition, there was a reduction in weight gain of rats during pregnancy and of offspring during lactation.Conclusion: In conclusion, the data found in our study suggest that the increase in USV emitted by pups due to hypoproteic diet during pregnancy accentuated maternal behavior. In addition, an increase in maternal care promoted the reduction in anxiety-like behavior in adult male offspring.

Brain Angiotensin II AT1 receptors are involved in the acute and long-term amphetamine-induced neurocognitive alterations.

Angiotensin II, by activation of its brain AT1-receptors, plays an active role as neuromodulator in dopaminergic transmission. These receptors participate in the development of amphetamine-induced behavioral and dopamine release sensitization. Dopamine is involved in cognitive processes and provides connectivity between brain areas related to these processes. Amphetamine by its mimetic activity over dopamine neurotransmission elicits differential responses after acute administration or after re-exposure following long-term withdrawal periods in different cognitive processes. The purpose of this study is to evaluate the AT1-receptor involvement in the acute and long-term amphetamine-induced alterations in long-term memory and in cellular-related events. Male Wistar rats (250-300g) were used in this study. Acute effects: Amphetamine (0.5/2.5mg/kgi.p.) was administered after post-training in the inhibitory avoidance (IA) response. The AT1-receptor blocker Losartan was administered i.c.v. before a single dose of amphetamine (0.5mg/kgi.p.). Long-term effects: The AT1-receptors blocker Candesartan (3mg/kg p.o.) was administered for 5days followed by 5 consecutive days of amphetamine (2.5mg/kg/day, i.p.). The neuroadaptive changes were evidenced after 1week of withdrawal by an amphetamine challenge (0.5mg/kgi.p.). The IA response, the neuronal activation pattern, and the hippocampal synaptic transmission were evaluated. The impairing effect in the IA response of post-training acute amphetamine was partially prevented by Losartan. The long-term changes induced by repeated amphetamine (resistance to acute amphetamine interference in the IA response, neurochemical altered response, and increased hippocampal synaptic transmission) were prevented by AT1-receptors blockade. AT1-receptors are involved in the acute alterations and in the neuroadaptations induced by repeated amphetamine associated with neurocognitive processes.

Intrauterine Exposure to Chronic 22 kHz Sound Affects Inhibitory Avoidance and Serotonergic Parameters in Forebrain Areas of Dams and Rat Offspring

In the present study we evaluated the effects of chronic exposure to sounds at 22 kHz during pregnancy on the central serotonergic and behavioral parameters in Wistar rat dams after the suckling period and on their male rat offspring. In addition, we also assessed the effects of an acute 22 kHz sound, associated with the chronic intrauterine exposure, on the emotional responses of adult offspring. The primary hypothesis was that experiencing 22 kHz stimuli during an early stage of development would interfere with brain serotonergic parameters and, later, with the adult rat’s defensive responses. The corollary question was whether a 22 kHz sound exposure would differentially affect inhibitory avoidance and escape responses and central serotonergic parameters. Female rats were divided into four groups: non-pregnant control; non-pregnant chronic exposure; pregnant control; and pregnant chronic exposure. Male offspring were divided into four groups: chronic intrauterine sound exposure; acute sound exposure in adulthood; chronic intrauterine exposure with acute exposure in adulthood; and no exposure. Chronic sound exposure affected inhibitory avoidance and serotonergic parameters in female rats. For offspring, there was an interaction between chronic and acute sound exposure effects on inhibitory avoidance response but not on escape response. There were significant effects of chronic intrauterine exposure on serotonin turnover in the hippocampus and PFC of females. For offspring, the turnover was increased by chronic exposure only in PFC, and in amygdala it was increased by acute exposure. These results illuminate the potential of an early acoustic sound exposure for causing central serotonergic and emotional behavioral changes that can persist into later periods of life.

Dorsomedial hypothalamus CRF type 1 receptors selectively modulate inhibitory avoidance responses in the elevated T-maze

Corticotropin-releasing factor (CRF) plays a critical role in the mediation of physiological and behavioral responses to stressors. In the present study, we investigated the role played by the CRF system within the dorsomedial hypothalamus (DMH) in the modulation of anxiety- and panic-related responses. Male Wistar rats were administered into the DMH with CRF (125 and 250ng/0.2μl, experiment 1) or with the CRFR1 antagonist antalarmin (25ng/0.2μl, experiment 2) and 10min later tested in the elevated T-maze (ETM) for inhibitory avoidance and escape measurements. In clinical terms, these responses have been respectively related to generalized anxiety and panic disorder. To further verify if the anxiogenic effects of CRF were mediated by CRFR1 activation, we also investigated the effects of the combined treatment with CRF (250ng/0.2μl) and antalarmin (25ng/0.2μl) (experiment 3). All animals were tested in an open field, immediately after the ETM, for locomotor activity assessment. Results showed that 250ng/0.2μl of CRF facilitated ETM avoidance, an anxiogenic response. Antalarmin significantly decreased avoidance latencies, an anxiolytic effect, and was able to counteract the anxiogenic effects of CRF. None of the compounds administered altered escape responses or locomotor activity measurements. These results suggest that CRF in the DMH exerts anxiogenic effects by activating type 1 receptors, which might be of relevance to the physiopathology of generalized anxiety disorder.

CRF type 1 receptors of the medial amygdala modulate inhibitory avoidance responses in the elevated T-maze

Corticotropin-releasing factor (CRF) plays a critical role in the mediation of physiological and behavioral responses to stressors. In the present study, we investigated the role played by the CRF system within the medial amygdala (MeA) in the modulation of anxiety and fear-related responses. Male Wistar rats were bilaterally administered into the MeA with CRF (125 and 250ng/0.2μl, experiment 1) or with the CRFR1 antagonist antalarmin (25ng/0.2μl, experiment 2) and 10min later tested in the elevated T-maze (ETM) for inhibitory avoidance and escape measurements. In clinical terms, these responses have been respectively related to generalized anxiety and panic disorder. To further verify if the anxiogenic effects of CRF were mediated by CRFR1 activation, we also investigated the effects of the combined treatment with CRF (250ng/0.2μl) and antalarmin (25ng/0.2μl) (experiment 3). All animals were tested in an open field, immediately after the ETM, for locomotor activity assessment. Results showed that CRF, in the two doses administered, facilitated ETM avoidance, an anxiogenic response. Antalarmin significantly decreased avoidance latencies, an anxiolytic effect, and was able to counteract the anxiogenic effects of CRF. None of the compounds administered altered escape responses or locomotor activity measurements. These results suggest that CRF in the MeA exerts anxiogenic effects by activating type 1 receptors, which might be of relevance to the physiopathology of generalized anxiety disorder.

Repeated asenapine treatment produces a sensitization effect in two preclinical tests of antipsychotic activity

Among several commonly used atypical antipsychotic drugs, olanzapine and risperidone cause a sensitization effect in the conditioned avoidance response (CAR) and phencyclidine (PCP)-induced hyperlocomotion paradigms – two well established animal tests of antipsychotic drugs, whereas clozapine causes a tolerance effect. Asenapine is a novel antipsychotic drug recently approved for the treatment of schizophrenia and manic disorders. It shares several receptor binding sites and behavioral features with other atypical antipsychotic drugs. However, it is not clear what type of repeated effect (sensitization or tolerance) asenapine would induce, and whether such an effect is transferrable to other atypicals. In this study, male adult Sprague-Dawley rats were first repeatedly tested with asenapine (0.05, 0.10 or 0.20 mg/kg, sc) for avoidance response or PCP (3.20 mg/kg, sc)-induced hyperlocomotion daily for 5 consecutive days. After 2–3 days of retraining/drug-free recovery, they were then challenged with asenapine (0.10 mg/kg, sc), followed by olanzapine (0.50 mg/kg, sc) and clozapine (2.50 mg/kg, sc). During the 5-day drug test period (the induction phase), repeated asenapine treatment progressively increased its inhibition of avoidance response and PCP-induced hyperlocomotion in a dose-dependent fashion. On the asenapine and olanzapine challenge tests (the expression phase), rats previously treated with asenapine still showed significantly lower avoidance response and lower PCP-induced hyperlocomotion than those previously treated with vehicle. An increased reactivity to clozapine challenge in prior asenapine-treated rats was also found in the PCP-induced hyperlocomotion test. These findings suggest that asenapine is capable of inducing a sensitization effect and a cross-sensitization to olanzapine and clozapine (to a lesser extent). Because the behavioral profile of asenapine in both tests is similar to that of olanzapine, but different from that of clozapine, we suggest that asenapine resembles olanzapine to a greater extent than clozapine in its therapeutic and side effect profiles.

Effects of compounds that interfere with the endocannabinoid system on behaviors predictive of anxiolytic and panicolytic activities in the elevated T-maze

An extensive literature has implicated the endocannabinoid system in the modulation anxiety-related responses. Nonetheless, it remains uncertain what would be the effects of endocannabinoid-related compounds against responses related to specific subtypes of anxiety disorders, particularly generalized anxiety and panic. In this context, the elevated T maze (ETM) has been developed to evaluate two distinct tasks in the same rat, inhibitory avoidance and escape response from an open arm, predictive of anxiolytic and panicolytic effects, respectively. Thus, the present study tested the hypothesis that drugs that facilitate endocannabinoid-signaling would inhibit both types of aversive responses in this model. As positive controls, diazepam attenuated only inhibitory avoidance (anxiolytic-like effect), whereas alprazolam was effective against both avoidance and escape (anxiolytic- and panicolytic like effects). The synthetic cannabinoid WIN55,212-2 (1.0mg/kg) promoted an anxiolytic-like effect, which was prevented by pre-treatment with the CB1 receptor antagonist, AM 251 (1.0mg/kg). At the higher dose (3.0mg/kg), this antagonist promoted an anxiogenic-like effect. None of these drugs interfered with the escape task. The endocannabinoid (anandamide) hydrolysis inhibitor, URB 597 at doses of 0.3 and 1.0mg/kg, induced, respectively, panicolytic- and anxiolytic-like effects, which were reversed by pretreatment with AM 251. These results suggest that drugs that act on the endocannabinoid system have different effects on the behaviors assessed in the ETM.

Differential effects of environmental enrichment and isolation housing on the hormonal and neurochemical responses to stress in the prefrontal cortex of the adult rat: relationship to working and emotional memories

The present study was designed to investigate the modulation of the stress responses by the environmental conditions and its putative neurobiological mechanisms. For that an integrative study on the effects of environmental enrichment and isolation housing on (1) the corticosterone, dopamine and acetylcholine responses to acute restraint stress in the prefrontal cortex (PFC) of the awake rat; (2) the mRNA levels of glucocorticoid receptors (GRs) in the PFC, and (3) the behavioral responses to stress, related to the PFC (habituation to a novel environment, spatial-working memory and inhibitory avoidance response) was performed. Male Wistar rats were maintained from 3 to 6months of age in two different conditions: enriched (EC) or impoverished (IC). Animals were stereotaxically implanted with bilateral guide cannulae in the PFC to perform microdialysis experiments to evaluate the concentrations of corticosterone, dopamine and acetylcholine. EC animals showed lower increases of corticosterone and dopamine but not of acetylcholine than IC animals in the PFC in response to acute restraint stress (20min). In the PFC, GR mRNA levels showed a trend towards an enhancement in EC animals. EC reduced the days to learn the spatial working memory task (radial-water maze). Spatial working memory, however, was not different between groups in either basal or stress conditions. Inhibitory avoidance response was reduced in EC rats. The changes produced by EC in the neurochemical, neuroendocrine and behavioral parameters evaluated suggest that EC rats could show a better coping during an acute stress challenge.

Effect of the acute and chronic estrogen on anxiety in the elevated T-maze

Despite the extensive studies on the influences of estrogen (E2) on anxiety-like behaviors, there is still conflicting evidence regarding the specific effects of E2 on anxiety. These discrepancies may be a result of different replacement regimens. The goals of this study were to evaluate anxiety-like behavior in ovariectomized rats (Ovx) using the elevated T-maze (ETM) test for the following variables: (1) the effects of acute versus chronic E2 dosing, (2) the effects of chronic E2 at different doses and, (3) the effects of Tamoxifen (Tam) co-administered with E2. Rats in the acute E2 dosing group (aE2) showed reduced inhibitory avoidance responses with prolong escape latencies compared to Ovx; while rats in the chronic E2 dosing group (cE2) showed reduced inhibitory avoidance responses only. These results suggest that E2 contains anxiolytic effects when given once or repeatedly. Moreover, when various doses of E2 (1–100μg/kg) were chronically given to the Ovx rats, all doses produced impaired inhibitory avoidance responses compared to Ovx, suggesting that chronic replacement of E2 had no dose-dependent effect on anxiety-like behavior. Interestingly, in the 3-week delay replacement regimen, the low dose E2 (1μg/kg, s.c.) group displayed no anxiolytic effects as their inhibitory avoidance responses in the ETM were not different from their Ovx counterparts. On the contrary, the Ovx group that received Tam+E2 (Tam 1mg/kg, PO and E2 1μg/kg, s.c.) had reduced inhibitory avoidance responses compared to other groups. These findings indicate that when Tam is co-administered with chronic low dose estrogen, it can act as an estrogen receptor agonist and result in anti-anxiety effects. Therefore, it is likely that the anxiolytic-like behavior relative to generalized anxiety disorder can be conserved when estrogen is given acutely or chronically; while the anxiolytic-like behavior relative to panic disorder can be conserved only when estrogen is given acutely.

Distinct behavioral consequences of stress models of depression in the elevated T-maze

Animals exposed to inescapable stress develop behavioral consequences that are similar to symptoms of depression. Therefore, most of the animal models of depression are based on animal exposure to such stressors. The stress-induced behavioral consequences induced by pre-exposure to shock in the learned helplessness model of depression have been proposed to be a consequence of excessive activation of fear/anxiety related structures which would lead to inhibitory avoidance and impaired escape performance. However, this hypothesis has not yet been investigated in a test that is able to generate these different defense strategies in a same rat, such as the elevated T-maze (ETM). Therefore, the objective of the present study was to test the effects of footshock pre-exposure (inescapable-IS or escapable-ES) on both inhibitory avoidance and escape responses of rats submitted to the ETM 24 h later. Moreover, since it is not known whether these effects would be a common feature to other inescapable stressors used as animal models of depression, we have also investigated the behavior of rats previously exposed to forced swimming or restraint. All stressed groups displayed anxiogenic-like behavior when compared to control groups (non-stressed), evidenced by facilitated acquisition of inhibitory avoidance in the ETM. However, only rats exposed to IS showed impaired escape performance. These results support the hypothesis that the facilitated inhibitory avoidance is a common behavioral consequence of distinct stressful stimuli. However, the impaired escape response is likely to be particularly involved in the mediation of the helpless behavior observed in rats pre-exposed to IS. The neurobiological mechanisms involved in these responses are discussed in the manuscript.

Aging impairs the control of prefrontal cortex on the release of corticosterone in response to stress and on memory consolidation

This study investigated the role of the dorsomedial prefrontal cortex (dmPFC) on the activity of the hypothalamus-pituitary-adrenal axis and memory consolidation in young and aged rats. The messenger RNA (mRNA) expression of several gamma-aminobutyric acid (GABA) and glutamate receptor subunits were also evaluated in the prefrontal cortex (PFC) of young and aged rats. Microinjections of picrotoxin (GABAA antagonist), muscimol (GABAA agonist), or vehicle were performed into the dmPFC of young adult (3 months) and aged (27 months) male Wistar rats. Plasma corticosterone was measured under acute stress (30-minute restraint) conditions following microinjections. The retention of an inhibitory avoidance response was also evaluated in response of the same treatments. Picrotoxin microinjections into the dmPFC reduced the stress-induced corticosterone concentrations on young but not on aged animals. Aging did not modify the mRNA content of any of the receptor subunits analyzed. Picrotoxin into the dmPFC reduced inhibitory avoidance response in young but not aged animals. Muscimol treatment did not modify any of the parameters evaluated. These results suggest that prefrontal cortex loses its capacity to control hypothalamo-pituitary-adrenal (HPA) axis activity and the consolidation of emotional memory during aging.

Facilitation of 5-HT 2A/2C-mediated neurotransmission in the ventromedial hypothalamic nucleus decreases anxiety in the elevated T-maze

Previous evidence has shown that facilitation of GABA/benzodiazepine-mediated neurotransmission in the ventromedial hypothalamus (VMH) inhibits both escape and inhibitory avoidance responses generated in the elevated T-maze test of anxiety (ETM). These defensive behaviors have been associated with panic and generalized anxiety, respectively. Aside from GABA/benzodiazepine receptors, the VMH also contains a significant number of serotonin (5-HT) receptors, including 1A, 2A and 2C subtypes. The purpose of the present study was to investigate the effect of the activation of 5-HT 1A and 5-HT 2A/2C receptors in the VMH on defensive behavioral responses in rats submitted to the ETM. For that, male Wistar rats were treated intra-VMH with the 5-HT 1A agonist 8-OH-DPAT, with the 5-HT 2A/2C agonist DOI, with the 5-HT 2C selective agonist MK-212, or with the 5-HT 2A/2C antagonist ketanserin and 10 min after were submitted to the ETM. Results showed that both DOI and MK-212 significantly decreased avoidance measurements, an anxiolytic-like effect, without altering escape. 8-OH-DPAT and ketanserin were without effect, although the last drug attenuated the effects of DOI. None of the drugs altered locomotor activity in an open field. These results suggest that 5-HT 2A/2C receptors of the VMH are involved in the regulation of inhibitory avoidance and might be of relevance to the physiopathology of generalized anxiety.

5-HT2C receptor regulation of defensive responses in the rat dorsal periaqueductal gray

Activation of 5-HT2C receptors in limbic structures such as the amygdala and hippocampus increases anxiety. Indirect evidence obtained with non-selective 5-HT2C-interacting drugs suggests that the same may occur in the dPAG, a brainstem region consistently implicated in the genesis/regulation of panic attacks. In this study we used more selective agonists and antagonists to unveil the role played by dPAG 5-HT2C receptors in the regulation of anxiety- and panic-related defensive behaviors. Our results showed that intra-dPAG microinjection of the endogenous agonist 5-HT (20 nmol) or the 5-HT2C receptor agonists MK-212 (1 and 10 nmol) and RO-600175 (40 nmol) significantly increased inhibitory avoidance acquisition in rats tested in the elevated T-maze, suggesting an anxiogenic effect. 5-HT, but not the two 5-HT2C receptor agonists, inhibited escape performance. In the elevated T-maze, inhibitory avoidance and escape responses have been related to generalized anxiety and panic attacks, respectively. The behavioral effects caused by 5-HT and MK-212 were fully blocked by previous local microinjection of the 5-HT2C receptor antagonist SB-242084. Intra-dPAG injection of MK-212 also failed to affect escape expression in another test relating this behavior to panic, the electrical stimulation of the dPAG. Overall, the results indicate that 5-HT2C receptors in the dPAG are preferentially involved in the regulation of defensive behaviors related to anxiety, but not panic. This finding extends to the dPAG the prominent role that has been attributed to 5-HT2C receptors in anxiety generation.

Hippocampal alpha7 nicotinic receptors modulate memory reconsolidation of an inhibitory avoidance task in mice

CF-1 male mice were trained in an inhibitory avoidance (IA) task using either a mild or a high footshock (0.8 or 1.2 mA, 50 Hz, 1 s). A retention test was given 48 h later. Immediately after the retention test, mice were given intra-dorsal hippocampus infusions of either choline (Ch, an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, 0.08–1.30 μg/hippocampus), or methyllycaconitine (MLA, an α7nAChR antagonist, 1.0–30.0 μg/hippocampus). Memory retention was tested again 24 h later. Methyllycaconitine impaired retention performance regardless of footshock intensity and its effects were long lasting. Ch impaired retention performance only in those mice trained with a high footshock. On the contrary, Ch enhanced retention performance when mice were trained with a mild footshock. These effects were long lasting and dose- and time-dependent. Retention performance was not affected in drug-treated mice that were not subjected to memory reactivation, suggesting that the performance effects could not be attributable to non-specific effects of the drugs. Methyllycaconitine effects were dose-dependently reversed by choline, suggesting that MLA and Ch interact at the α7nAChR. Altogether, results suggest that hippocampal α7nAChRs play a critical role in reconsolidation of an IA response in mice, and may also have important implications for dynamic memory processes. This is the first presentation, to our knowledge, indicating that a specific receptor (α7nAChR) is able to modulate consolidated memories after retrieval.

The Ameliorating Effects of Luteolin on Beta-Amyloid-Induced Impairment of Water Maze Performance and Passive Avoidance in Rats

The present study investigated the effects of luteolin on Abeta (1-40)-induced impairment of Morris water maze (MWM) spatial performance, reference memory, and passive avoidance (PA) behavior in rats. Luteolin treatment was started 4 days before the initiation of behavioral testing (passive avoidance on treatment day of 4-5; MWM spatial performance memory testing on treatment day of 5-7 and MWM reference memory testing on treatment day of 7) and continued until the end of the study. We also measured the activity of Mn-SOD, copper/zinc (Cu/Zn)-SOD and glutathione (GSH) levels in rat cortex and hippocampus to understand the ameliorating effect of luteolin on Abeta (1-40) induced memory impairment. The present results showed that luteolin (5, 10 mg/kg) has a protective effect on Abeta (1-40)-induced memory dysfunction in spatial performance, reference memory, and inhibitory avoidance response impairment. Finally, luteolin also increases the level of Mn-SOD, (Cu/Zn)-SOD and glutathione (GSH) in the cortex and hippocampus to reduce the oxidative stress by Abeta (1-40). Taken together, the results in this study suggest that luteolin (5, 10 mg/kg) treatment improves the learning and memory in Abeta (1-40)-induced cognition deficit in rats. The ameliorating mechanisms of luteolin on Abeta (1-40)-induced amnesia may be related to activating the anti-oxidation system.

Nicotine improves ethanol-induced memory impairment: The role of dorsal hippocampal NMDA receptors

Aims The current study was undertaken to determine the role of dorsal hippocampal N-methyl- d-aspartate (NMDA) receptors in nicotine's effect on impairment of memory by ethanol. Main methods Adult male mice were cannulated in the CA1 regions of dorsal hippocampi and trained on a passive avoidance learning task for memory assessment. Key findings We found that pre-training intraperitoneal (i.p.) administration of ethanol (0.5 and 1 g/kg) decreased memory retrieval when tested 24 h later. Pre-test administration of ethanol reversed the decrease in inhibitory avoidance response induced by pre-training ethanol. Similar to ethanol, pre-test administration of nicotine (0.125–0.75 mg/kg, s.c.) prevented impairment of memory by pre-training ethanol. In the animals that received ethanol (1 g/kg, i.p) before training and tested following intra-CA1 administration of different doses of NMDA (0.0005–0.005 µg/mouse), no significant change was observed in the retrieval latencies. Co-administration of the same doses of NMDA with an ineffective dose of nicotine (0.125 mg/kg, s.c.) significantly improved the memory retrieval and mimicked the effects of pre-test administration of a higher dose of nicotine. Pre-test intra-CA1 microinjection of MK-801 (0.25–1 µg/mouse), which had no effect alone, in combination with an effective dose of nicotine (0.75 mg/kg, s.c.) prevented the improving effect of nicotine on memory impaired by pre-training ethanol. Moreover, intra-CA1 microinjection of MK-801 reversed the NMDA-induced potentiation of the nicotine response. Significance The results suggest the importance of NMDA glutamate system(s) in the CA1 regions of dorsal hippocampus for improving the effect of nicotine on the ethanol-induced amnesia.