Comparison of neurokinin SP with diazepam in effects on memory and fear parameters in the elevated T-maze free exploration paradigm.

The elevated T-maze was combined with a free exploration protocol, which, in contrast to the conventional procedure, dispenses with handling of the animals during the experimental sessions. This allows measurement of fear indexes derived from the elevated plus-maze as well as assessment of acquisition of open arm avoidance and open arm escape in one continuous session. Retention of the different fear-responses is measured 72 h later without drug treatment. In order to assess the effects of two known anxiolytics in this paradigm, rats received an IP injection of diazepam (1 to 4 mg/kg), substance P (5 to 500 microg/kg) or vehicle (1 ml/kg) and were tested on the T-maze for 5 min. Diazepam elevated open arm activity, indicative of an anxiolytic effect. The drug also increased the latency to escape from the open arms, but did not significantly affect acquisition of open arm avoidance. During the retention trial, diazepam in higher doses impaired the performance of both fear-responses, suggestive of an anterograde amnesic effect. Substance P did not influence acquisition and retention of open arm avoidance and escape. However, in high doses, the peptide increased the sojourn time in the central arena of the maze, indicating reduced fear and, hence, a dissociation between anxiolytic and amnesic effects. The present findings demonstrate that the elevated T-maze free exploration paradigm is sensitive to anxiolytic and memory-modulating effects of drugs.     

Influence of the estrous cycle on the behavior of rats in the elevated T-maze

The elevated T-maze is an animal anxiety model which can discriminate between anxiety-like and fear-like behaviors. The estrous cycle is an important variable of the response in animal anxiety tests and is known to affect other models. The aim of the present study was to investigate the influence of the estrous cycle on behavior displayed in the elevated T-maze test. Seventeen male and 60 female rats were submitted to one session in this test, with the females being screened for the estrous cycle and divided into groups according to the various phases. The elevated T-maze had three arms of equal dimensions ( 50 cm x 10 cm), one enclosed by 40-cm high walls and perpendicular to the others, the apparatus being elevated 50 cm above the floor. Each rat was placed in the end of the enclosed arm and the latency for it to leave this arm was recorded. These measurements were repeated three times separated by 30-s intervals (passive avoidance). After trial 3, each rat was placed at the distal end of the right open arm and the latency to exit this arm was recorded. Whenever latencies were greater than 300 s the trial was finished. The results demonstrated females in diestrus exhibited anxiety-like behaviors while females in metaestrus behaved in a similar way as the males. There were no differences between groups in fear-like behaviors. The results also indicate the elevated T-maze to be a sensitive test to measure anxiety.     

Systemic and intra-dorsal periaqueductal gray injections of cholecystokinin sulfated octapeptide (CCK-8s) induce a panic-like response in rats submitted to the elevated T-maze

The neuropeptide cholecystokinin (CCK) has been implicated in fear and anxiety. CCK is found in the CNS in several molecular forms such as the tetrapeptide (CCK-4) and, mainly, the sulfated octapeptide (CCK-8s) fragments. Administration of CCK-4 induces panic attacks in humans and increases the expression of different anxiety-related behaviors in laboratory animals. The effects of CCK-8s on fear and anxiety are less straightforward and seem to be influenced, among other factors, by the route of the peptide administration and the animal model employed. In other to further investigate the role of CCK-8s in fear and anxiety, in the present study we analyzed the effect of CCK-8s in male Wistar rats submitted to the elevated T-maze. This animal model of anxiety was developed in order to separate generalized anxiety (inhibitory avoidance) and panic-like (escape) responses in the same rat. The effect of CCK-8s in this test was also investigated after injection of the peptide into the dorsal periaqueductal gray (DPAG). This brainstem area is rich in CCK receptors and has consistently been implicated in the mediation of fear and anxiety responses. The results showed that both the intraperitoneal and intra-DPAG injections of CCK-8s potentiated one-way escape behavior, suggesting a panicogenic action. In contrast, the injection of the CCK2 receptor antagonist CR2945 inhibited the expression of this behavior, a panicolytic-like effect. Therefore, the elevated T-maze, in contrast to other animal models of anxiety, can detect the anxiety-eliciting effects of CCK-8s both after its systemic and central administration. Also, the results provide further evidence about the involvement of a CCK-mediated mechanism within the DPAG in the regulation of panic-related defensive behaviors.     

Involvement of the lateral habenula in the regulation of generalized anxiety- and panic-related defensive responses in rats

Recently obtained evidence points to the involvement of the lateral habenular nuclei (LHb) in the mediation of coping defensive responses to threatening/stressful stimuli. Nevertheless, the role of this brain area in the regulation of defensive responses that have been associated with specific subtypes of anxiety disorders recognized in clinical settings is presently unknown. To address this question, we investigated the effects of either electrolytic lesions or chemical stimulation of the LHb on the defensive behaviors generated in rats by the elevated T-maze. This experimental model allows the measurement, in a same rat, of two defensive behaviors, inhibitory avoidance and escape, that have been related in terms of psychopathology to generalized anxiety and panic disorders, respectively. Bilateral electrolytic lesions of the LHb (1 mA, 10 s) impaired inhibitory avoidance acquisition and facilitated escape performance. On the other hand, chemical stimulation of the LHb by bilateral microinjection of kainic acid (30-60 pmol/0.2 microL) had the opposite effect, i.e., facilitated inhibitory avoidance and impaired escape. The present results indicate that the LHb exerts an opposed regulatory control on generalized anxiety- and panic-related defensive responses in rats.     

Assessment of anxiolytic and panicolytic effects of dichloromethane fraction from stems of Kielmeyera coriacea

Kielmeyera coriacea Mart. (Calophyllaceae) is known popularly as "Pau Santo". The hydroethanolic extract (HE) of Kielmeyera coriacea stems and its semi-pure dichloromethane (DCM) constituent produced an antidepressant-like effect in rats. The purpose of this study was to investigate the effects of repeated administration (21 days) by gavage of the DCM fraction (5, 10 or 15mg/kg) in rats submitted to the elevated T-maze (ETM), a model of generalized anxiety and panic disorders. The tricyclic antidepressant imipramine (15mg/kg) was used as a positive control. Rat locomotion was assessed using the open field test (OFT) following each drug treatment. The 2-hydroxy-1-methoxyxanthone (1), aucuparin (2), swertinin (3), 1,3,7-trihydroxy-2-(3-methylbut-2-enyl)-xanthone (4) and 1,3,5-trihydroxy-2-(3-methylbut-2-enyl)-xanthone (5) were identified in DCM fraction, and suggest that the xanthone (4) is related with the antidepressant-like profile of this plant. Pharmacological evaluation showed that DCM fraction (10 and 15 mg/kg) decreased the inhibitory avoidance latency from the closed arm and increased the one-way escape latency from the open arm in the ETM, which is indicative of anxiolytic and panicolytic effects, respectively, as occurs with the positive control, imipramine (15 mg/kg), when compared to their control group (vehicle). Locomotor activity was not significantly altered by the different treatments. This study suggests that the DCM fraction from stems of Kielmeyera coriacea can be an important therapeutic alternative in the treatment of anxiety disorders, such as generalized anxiety and panic disorders.     

Serotonin transporter deficient mice are vulnerable to escape deficits following inescapable shocks

Modulation of serotonin transporter (5-HTT) function causes changes in affective behavior, both in humans and rodents. Stressful life events likewise affect emotional behavior. In humans, a low-expressing genetic 5-htt variant, the s allele of the 5-htt linked promoter region, has been associated with increased risk for depression only where there was a history of stressful life events. To investigate this gene by environment interaction in mice, we compared the effects of inescapable shocks on the behavior of wild-type (5-htt+/+), heterozygote (5-htt+/-) and serotonin transporter deficient (5-htt-/-) mice. Inescapable shocks induce behavioral changes including a shock escape deficit, in a subsequent test when escape is possible. Confirming a gene by environment interaction, we found that stress increases escape latencies in a gene-dose dependent manner (5-htt-/->5-htt+/->5-htt +/+), where as there were no differences among the genotypes in the unstressed condition. The vulnerability to increased escape latency could not be accounted for by enhanced fear learning, as 5-htt-/- mice did not show heightened fear conditioning. The interaction of 5-htt genotype and stress appeared to produce a selective behavioral vulnerability, because no interaction of 5-htt genotype and stress was observed in other measures of anxiety and depression-linked behavior, including the open field, novelty suppressed feeding, and forced swim tests. We replicated prior findings that the 5-htt-/- displays heightened anxiety and depression-like behavior at baseline (unstressed condition). In conclusion, our data offer the possibility for future investigation of the neural basis underlying 5-htt genotype-by-stress interaction shown here.     

Effects of short- and long-term neuroleptic treatment on brain serotonin synthesis and turnover: focus on the serotonin hypothesis of schizophrenia

Short-term (90 min) administration of haloperidol (2 mg/kg), or chlorpromazine (10 mg/kg) increased the activity of tryptophan hydroxylase as well as the levels of 5-hydroxytryptamine (serotonin) and 5-hydroxyindoleacetic acid in mid-brain of rats. The chronic neuroleptic treatment (21 days) produced more pronounced changes in all parameters related to serotonin synthesis and turnover. The activity of tryptophan hydroxylase in mid-brain was further augmented; the levels of 5-hydroxytryptamine and 5-hydroxyindole-acetic acid were significantly elevated not only in mid-brain, but also in several other discrete regions examined. These data suggest that neuroleptics enhance the synthesis and utilization of brain serotonin. The role of brain serotonergic neurons in the pathophysiology of schizophrenia is further considered.     

Effects of Milnacipran in Animal Models of Anxiety and Memory

Serotonin (5-HT) and noradrenaline (NA) are involved in both pathogenesis and recovery from depression and anxiety. We examined the effects of acute and chronic treatment with milnacipran, a serotonin/noradrenaline reuptake inhibitors (SNRIs) antidepressant, on anxiety and memory retention in rats. Male Wistar rats received acute or chronic administration of milnacipran (12.5, 25 or 50 mg/kg) or saline (control group). The animals were separately submitted to elevated plus-maze, inhibitory avoidance and open-field tasks 1 h after injection, in the acute group, or 23 h after last injection, in the chronic group. Our results showed an anxiolytic-like effect after chronic administration of milnacipran at doses of 25 and 50 mg/kg. The treatment does not interfere in memory retention and habituation to a novel environment at any doses studied. These findings support that milnacipran, an established SNRIs antidepressant, can also be useful in the treatment of anxiety disorders.     

Emotional state variations in rats during recall of passive avoidance reactions after neurotensin administration into nucleus accumbens of the brain

Behavioral effects of neurotensin administration into the nucleus accumbens were studied in rats with neurotoxic lesions of serotoninergic structures of the dorsal raphe nucleus or periaqueductal grey matter. Changes in recall of passive avoidance conditioned reactions and aftereffects of painful stimulation in the locomotor activity were studied in the "open field" and elevated plus-maze and T-maze tests. The toxin administration into the dorsal raphe nucleus did not impair the recall of the passive avoidance reactions, but enhanced the oppressive aftereffects of painful stimulation, which can specify the development of anxiety in rats. The toxin administration into the periaqueductal grey matter had an opposite effect, which can be considered as a manifestation of the panic state. Neurotensin weakened the above mentioned effects of the toxin and, depending on the evoked emotional disorders, produced the anxiolytic or antipanic effects.     

Effects of leptin on memory processing

Leptin is a peptide hormone secreted by adipose tissue. Studies have shown that leptin crosses the blood-brain barrier (BBB) by a saturable transport system where it acts within the hypothalamus to regulate food intake and energy expenditure. Leptin also acts in the hippocampus where it facilitates the induction of long-term potentiation and enhances NMDA receptor-mediated transmission. This suggests that leptin plays a role in learning and memory. Obese mice and rats, which have leptin receptor deficiency, have impaired spatial learning. In disease states such as diabetes, humans and animals develop leptin resistance at the BBB. This suggests that low leptin levels in the brain may be involved in cognitive deficits associated with diabetes. In the current study, the effects of leptin on post-training memory processing in CD-1 mice were examined. Mice were trained in T-maze footshock avoidance and step down inhibitory avoidance. Immediately after training, mice received bilateral injections of leptin into the hippocampus. Retention was tested 1 week later in the T-maze and 1 day later in step down inhibitory avoidance. Leptin administration improved retention of T-maze footshock avoidance and step down inhibitory avoidance. Leptin administered 24 h after T-maze training did not improve retention when tested 1 week after training. SAMP8 mice at 12 months of age have elevated amyloid-beta protein and impaired learning and memory. We examined the effect of leptin on memory processing in the hippocampus of 4 and 12 months old SAMP8 mice. Leptin improved retention in both 4 and 12 months old SAMP8 mice; 12 month SAMP8 mice required a lower dose to improve memory compared to 4 months SAMP8 mice. The current results indicate that leptin in the hippocampus is involved in memory processing and suggests that low levels of leptin may be involved in cognitive deficits seen in disease states where leptin transport into the CNS is compromised.     

Behavioral and IL-2 responses to diosgenin in ovariectomized rats

Neuroimmune system is involved in communication between the endocrine and nervous systems, which may take part in the effects of dioscorea, reversing changes of anxiety-like behavior and interleukin (IL)-2 levels in the brains of ovariectomized (OVX) rats. This study was aimed at evaluating administration of diosgenin, an ingredient of dioscorea, on neuroimmune and behavioral functions in OVX animals. One month after ovariectomy, female Wistar rats were fed daily with diosgenin (0, 10, 50 or 100 mg/kg/day) and the elevated plus-maze and learned helplessness tests were used to measure anxiety-like and depressive behaviors after 23 and 24 days of diosgenin treatment, respectively. In the learned helplessness test, the rats needed to cross from one compartment of the shuttle box to the opposite compartment to avoid or escape the shock. If the rat failed to escape the shock in 10 sec, a "failure" was recorded. Two days after the behavioral tests, the brain was removed to measure levels of IL-2 which was used as an indicator of neuroimmune function. Anxiety-like behavior in the OVX rats was not affected by diosgenin treatment. However, avoidance behavior in the learned helplessness test in the OVX rats with high anxiety (HA) levels was improved by treatment with diosgenin at the dosage of 10mg/kg/day. Interestingly, the number of failures in the same test was increased when the dosage of diosgenin was increased to 50 mg/kg/day, and this was accompanied by an increase in IL-2 levels in the pituitary gland. In addition, treatment with 100 mg/kg/day of diosgenin resulted in decreased IL-2 levels in the amygdala and prefrontal cortex of the OVX rats with low anxiety levels, and in increased IL-2 levels in the amygdala of OVX HA rats. These results show that chronic diosgenin treatment influences IL-2 levels in the brain of OVX rats and affects depressive behavior in OVX HA rats, but not OVX low anxiety rats.     

Effects of citalopram on cognitive performance in passive avoidance, elevated plus-maze and three-panel runway tasks in naïve rats

Recent studies have shown that learning and memory capacity is disturbed in depressive patients, and it is important to reveal the effects of antidepressant drugs on cognitive function in depressive patients with memory problems. Citalopram, a selective serotonin reuptake inhibitor (SSRI), is one of the most widely used drugs for the treatment of disorders related to serotonergic dysfunction like depression and anxiety. Contradictory findings exist regarding the effects of SSRIs on memory. The aim of this study is to investigate whether citalopram affects memory in various models of learning and memory tasks in rats. Citalopram (at 20 and 50 mg/kg) significantly shortened the retention latency in the passive avoidance test and prolonged the transfer latency on the second day at 10 and 50 mg/kg doses in the elevated plus-maze test. Citalopram also significantly increased the number of errors (at the 10 mg/kg dose) and prolonged the latency values compared to the control group in both reference and working memory trials in the three-panel runway test. Citalopram also impaired reference memory trials of animals at the 20 mg/kg dose. In conclusion, citalopram impaired cognitive performance in passive avoidance, elevated plus-maze and three-panel runway tasks in naive rats. These effects might be related to serotonergic and nitrergic mechanisms, which need to be investigated in further studies.     

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 250 ng/0.2 μl, experiment 1) or with the CRFR1 antagonist antalarmin (25 ng/0.2 μl, experiment 2) and 10 min 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 (250 ng/0.2 μl) and antalarmin (25 ng/0.2 μl) (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.     

Effects of chronic Semax administration on exploratory activity and emotional reaction in white rats

Effects of chronic intranasal administration of ACTH(4-10) analog Semax (MEHFPGP) on exploratory activity, anxiety level, and depression-like behaviour were studied in white rats. The peptide was injected daily in dose 0.05 mg/kg during 10 or 14 days. It was shown that chronic Semax administration at 1-2 weeks induced anxiolytic and antidepressant effects but did not influenced the exploratory activity in non-stressogenic environment. The Semax effects may be the results of activation of the brain serotoninergic system as well as increased BDNF expression in the rat hippocampus.     

Behavioural phenotyping of sodium-myo-inositol cotransporter heterozygous knockout mice with reduced brain inositol

Inositol plays a key role in dopamine, serotonin, noradrenaline and acetylcholine neurotransmission, and inositol treatment is reported to have beneficial effects in depression and anxiety. Therefore, a reduction in brain intracellular inositol levels could be a cause of some psychiatric disorders, such as depression or anxiety. To determine the behavioural consequences of inositol depletion, we studied the behaviour of sodium-dependent myo-inositol cotransporter-1 heterozygous knockout mice. In heterozygous mice, free inositol levels were reduced by 15% in the frontal cortex and by 25% in the hippocampus, but they did not differ from their wild-type littermates in cholinergic-mediated lithium-pilocarpine seizures, in the apomorphine-induced stereotypic climbing model of dopaminergic system function, in the Porsolt forced-swimming test model of depression, in amphetamine-induced hyperactivity, or in the elevated plus-maze model of anxiety. Reduction of brain inositol by more than 25% may be required to elicit neurobehavioural effects.     

Study on the optimum number of trials and intensity of unconditioned stimulants and strain difference in the two-way shuttle-box avoidance test using rats

In order to determine the optimun conditions suitable for a number of trials and the intensity of unconditioned stimulant (US) in the two-way shuttle-box avoidance test in Sprague-Dawley strain rats, which are used most frequently in reproduction studies, conditioned avoidance response was observed under various conditions for 30 and 60 trials and the low and high US levels. Investigation was also conducted in Wistar rats under a high US level with 30 and 60 trials. Latency time of the escape response in Sprague-Dawley rats was shortened with increasing trials. Body weight gains of both strains of rats in the high US level with the 60-trial group decreased during the observation period. These findings suggest that the high US level with the 60-trial group is not suitable for the two-way shuttle-box avoidance test. The rate and latency time of the avoidance response were lower in Wistar rats than in Sprague-Dawley rats, although those of the escape response were higher. Significant changes in the following were observed, mainly from first to third sessions: the avoidance rate of all groups in strains of rats, escape rate of 60-trial group in Sprague-Dawley rats, avoidance and escape latency time of the 60-trial groups in both strains of rats and escape latency time of the 30-trial group in Sprague-Dawley strain rats.     

Effects of oxytocin and vasopressin on retrieval of passive avoidance response in melatonin-treated and/or pinealectomized male rats

The role of the pineal gland and its hormone-melatonin-as to the impact of vasopressin (VP) and/or oxytocin (OT) on the regulation of behavior was studied, the passive avoidance task being chosen as an experimental model. The results showed that VP facilitated the avoidance latency during the first retention trial; after pinealectomy, however, VP was ineffective in this regard. Intraperitoneal application of OT was ineffective in modifying the passive avoidance latency when compared with respective saline-treated animals. Melatonin alone, when injected to shamoperated animals 30 min before behavioral experiment, did not affect the passive avoidance response in SA- or OT-treated rats, but blocked the VP-induced lengthening of the passive avoidance latency in the first retention trial. In pinealectomized and OT-treated animals the passive avoidance latency during the second retention trial was severely diminished by melatonin when compared to respective control. We conclude that: a) VP needs a regulated pineal function for developing short-term effects on the passive avoidance response and b) the effect of OT on the avoidance latency in pinealectomized rats develops after melatonin treatment as a long-term effect.     

Comparative studies of somatostatin-14 and some of its fragments on passive avoidance behavior, open field activity and on barrel rotation phenomenon in rats

Behavioral effects of somatostatin-14, and some of its fragments [somatostatin(3–8), somatostatin(9–14), somatostatin(7–10)] after intracerebroventricular (ICV) administration have been investigated in male rats. In a passive avoidance learning test, somatostatin-14 (0.6 nM) given immediately after the learning session increased the avoidance latency at 24 hr after the injection, when compared to a somatostatin(3–8) (0.6 nM)-treated group. However, compared to a saline-treated group, the peptides did not significantly influence the avoidance latency. Somatostatin-14 administered in higher dose (6.0 nM) decreased the avoidance latency compared to the saline-treated group, while its fragments did not influence it. In an open field behavioral test, immediately after the 24-hr passive avoidance test, 6 nM of somatostatin-14 decreased the rearing activity, while the fragments did not influence this behavior. Somatostatin-14 produced barrel rotation in a dose-related manner, but after the injection of a high dose of the peptide (12 nM) all of the animals died in cardiorespiratory failure (apnea, pulmonary oedema). The fragments did not produce barrel rotation.     

Effects of orexin-A on memory processing

Orexin-A is an endogenous peptide with receptors present throughout the brain. Here, we examined the effect of post-training administration of orexin-A on retention in active and passive avoidance. Orexin-A administered by intracerebroventricular (i.c.v.) injection to CD-1 mice post-training improved retention in both T-maze footshock avoidance and one trial step-down passive avoidance. SAMP8 mice have age-related deficits in learning and memory, which correlate with an increase in brain levels of beta amyloid (Abeta) and an impaired response to memory-enhancing compounds. Orexin-A at 3nmol improved retention in young and old SAMP8 mice. These findings show that orexin-A can improve memory even with overproduction of Abeta.     

Estrogen receptor alpha influences socially motivated behaviors

Male mice lacking estrogen receptor alpha (ERalphaKO) show reduced social behaviors. We hypothesized that this might be due to either socially elicited or generalized anxiety. Male ERalphaKOs and wild type (WT) mice were given a series of behavioral tests: elevated plus maze, T-maze, and social recognition. Each test included a social dimension by exposing males to ovariectomized (OVX) females. In addition plasma concentrations of corticosterone were measured, and open field activity was assessed. In the elevated plus maze, WT males exposed to an OVX female 1 min prior to the test were more anxious than WT controls. ERalphaKO males showed anxiety in this test whether or not they were preexposed to a female. In the T-maze, WT males increased exploration of a novel arm when it contained an OVX female. The presence or absence of a female in a novel arm did not affect behavior of ERalphaKO males. In social recognition tests, ERalphaKO males spent less time than WT littermates investigating an OVX female that was repeatedly introduced into their home cage. On the final trial, when a novel female was introduced, WT males increased their chemo-investigation but ERalphaKOs did not. Plasma corticosterone levels were lower in ERalphaKO than in WT males when plasma was taken directly after a brief (control) cage disturbance. In the open field WT and ERalphaKO males behaved essentially the same. Taken together, the results of these experiments suggest the ERalphaKO males avoid contact with other conspecifics, perhaps due to an inability to be aroused by social cues.