Comparison of exploratory behavior of male and female woodlice (Armadillidium vulgare).

There are several studies in the literature showing that male and female rats explore novel environments and exhibit different exploration patterns when submitted to different apparatuses. In general, female rats spend more time moving and exploring the apparatuses than males do. A previous study showed that male woodlice (Armadillidium vulgare) explore novel environments in a very similar way to male rats (Rattus norvegicus) when tested in apparatuses analogous to the open-field test and light/dark box. Since that study was conducted only with male rats and woodlice, and since they exhibited very similar patterns of behavior, the present experiment aimed at investigating whether male and female woodlice explore novel environments with different behavioral patterns. Female and male woodlice were tested in the open-field and in the dry/moist box. Results obtained in the open-field test showed that both males and females remained longer in the corners than along the walls and avoided staying in the center. However, females remained longer along the walls and less in the corners. In the dry/moist box, there were no significant differences between the sexes: both females and males remained significantly longer in the moist compartment.

Comparison of exploratory behavior of male and female woodlice (Armadillidium vulgare)

There are several studies in the literature showing that male and female rats explore novel environments and exhibit different exploration patterns when submitted to different apparatuses. In general, female rats spend more time moving and exploring the apparatuses than males do. A previous study showed that male woodlice (Armadillidium vulgare) explore novel environments in a very similar way to male rats (Rattus norvegicus) when tested in apparatuses analogous to the open-field test and light/dark box. Since that study was conducted only with male rats and woodlice, and since they exhibited very similar patterns of behavior, the present experiment aimed at investigating whether male and female woodlice explore novel environments with different behavioral patterns. Female and male woodlice were tested in the open-field and in the dry/moist box. Results obtained in the open-field test showed that both males and females remained longer in the corners than along the walls and avoided staying in the center. However, females remained longer along the walls and less in the corners. In the dry/moist box, there were no significant differences between the sexes: both females and males remained significantly longer in the moist compartment.

Bidirectional genetic selection of behaviors involved in social interaction of Wistar rats.

Bidirectional selection is a procedure in which an arbitrary characteristic is chosen as a selection criterion and animals exhibiting more of this characteristic are bred in one group and animals exhibiting less are bred in another group. The procedure is repeated along generations until the selected characteristic becomes stable, resulting in two strains that are opposite in relation to the chosen characteristic. The present study aimed at selectively breeding rats exhibiting either a high or a low tendency to socialize by using the proximity test. We tested male and female Wistar rats in a square open field with a communicating birdcage, separated by a grid, containing a co-specific rat and coupled on the outside. Subjects that remained more time in front of the birdcage, interacting with the co-specific rat were bred in a group considered of high sociability (SOC+). Likewise, subjects that remained little time in front of the birdcage, with little interaction with the co-specific rat, were bred in a second group considered of low sociability (SOC-). By the 10th generation, the bidirectional selection resulted in SOC+ rats that spent a large amount of time in front of the cage sniffing and rearing in interaction with the co-specific rat and spent less time in the corners, exploring and grooming. It also resulted in SOC- rats that spent a small amount of time in front of the cage sniffing and rearing in interaction with the co-specific rat and spent more time in the corners and used most of their time grooming.

Comparison of female and male behavior in the elevated gradient of aversion.

The elevated gradient of aversion (EGA) is an apparatus for investigating the exploratory behavior of rats in 3-min sessions, consisting of three different sections of the same size: tunnel, closed arm, and open arm. Factorial analyses have defined three factors: exploration, impulsivity, and self-protection. In general, male rats are placed in the tunnel end and tend to hesitate leaving this starting point. Then, they hesitate leaving the tunnel and entering the closed arm, which they explore and tend to avoid entering the open arm or even just stick their head in and not enter it at all. Since females were not used for this test and are reported to be more explorative than male rats, the present work aimed to compare the behavior of male and female rats in the EGA. Thirty male and 34 female Wistar rats were submitted to 3-min sessions in the EGA. In general, results indicated that females were different from males: they explored more (Factor 1 - Exploration), are more impulsive (Factor 2 - Impulsivity), and are less anxious/fearful (Factor 3 - Self-protection). These results confirmed the results of other studies obtained with other apparatuses and show that females exhibit higher locomotion than males and are less anxious/fearful.

Bidirectional genetic selection of behaviors involved in social interaction of Wistar rats

Bidirectional selection is a procedure in which an arbitrary characteristic is chosen as a selection criterion and animals exhibiting more of this characteristic are bred in one group and animals exhibiting less are bred in another group. The procedure is repeated along generations until the selected characteristic becomes stable, resulting in two strains that are opposite in relation to the chosen characteristic. The present study aimed at selectively breeding rats exhibiting either a high or a low tendency to socialize by using the proximity test. We tested male and female Wistar rats in a square open field with a communicating birdcage, separated by a grid, containing a co-specific rat and coupled on the outside. Subjects that remained more time in front of the birdcage, interacting with the co-specific rat were bred in a group considered of high sociability (SOC+). Likewise, subjects that remained little time in front of the birdcage, with little interaction with the co-specific rat, were bred in a second group considered of low sociability (SOC-). By the 10th generation, the bidirectional selection resulted in SOC+ rats that spent a large amount of time in front of the cage sniffing and rearing in interaction with the co-specific rat and spent less time in the corners, exploring and grooming. It also resulted in SOC- rats that spent a small amount of time in front of the cage sniffing and rearing in interaction with the co-specific rat and spent more time in the corners and used most of their time grooming.

Comparison of female and male behavior in the elevated gradient of aversion

The elevated gradient of aversion (EGA) is an apparatus for investigating the exploratory behavior of rats in 3-min sessions, consisting of three different sections of the same size: tunnel, closed arm, and open arm. Factorial analyses have defined three factors: exploration, impulsivity, and self-protection. In general, male rats are placed in the tunnel end and tend to hesitate leaving this starting point. Then, they hesitate leaving the tunnel and entering the closed arm, which they explore and tend to avoid entering the open arm or even just stick their head in and not enter it at all. Since females were not used for this test and are reported to be more explorative than male rats, the present work aimed to compare the behavior of male and female rats in the EGA. Thirty male and 34 female Wistar rats were submitted to 3-min sessions in the EGA. In general, results indicated that females were different from males: they explored more (Factor 1 - Exploration), are more impulsive (Factor 2 - Impulsivity), and are less anxious/fearful (Factor 3 - Self-protection). These results confirmed the results of other studies obtained with other apparatuses and show that females exhibit higher locomotion than males and are less anxious/fearful.

The elevated gradient of aversion: a new apparatus to study the rat behavior dimensions of anxiety, fear, and impulsivity.

Few behavioral tests allow measuring several characteristics and most require training, complex analyses, and/or are time-consuming. We present an apparatus based on rat exploratory behavior. Composed of three different environments, it allows the assessment of more than one behavioral characteristic in a short 3-min session. Factorial analyses have defined three behavioral dimensions, which we named Exploration, Impulsivity, and Self-protection. Behaviors composing the Exploration factor were increased by chlordiazepoxide and apomorphine and decreased by pentylenetetrazole. Behaviors composing the Impulsivity factor were increased by chlordiazepoxide, apomorphine, and both acute and chronic imipramine treatments. Behaviors composing the Self-protection factor were decreased by apomorphine. We submitted Wistar rats to the open-field test, the elevated-plus maze, and to the apparatus we are proposing. Measures related to exploratory behavior in all three tests were correlated. Measures composing the factors Impulsivity and Self-protection did not correlate with any measures from the two standard tests. Also, compared with existing impulsivity tests, the one we proposed did not require previous learning, training, or sophisticated analysis. Exploration measures from our test are as easy to obtain as the ones from other standard tests. Thus, we have proposed an apparatus that measured three different behavioral characteristics, was simple and fast, did not require subjects to be submitted to previous learning or training, was sensitive to drug treatments, and did not require sophisticated data analyses.

The elevated gradient of aversion: a new apparatus to study the rat behavior dimensions of anxiety, fear, and impulsivity

Few behavioral tests allow measuring several characteristics and most require training, complex analyses, and/or are time-consuming. We present an apparatus based on rat exploratory behavior. Composed of three different environments, it allows the assessment of more than one behavioral characteristic in a short 3-min session. Factorial analyses have defined three behavioral dimensions, which we named Exploration, Impulsivity, and Self-protection. Behaviors composing the Exploration factor were increased by chlordiazepoxide and apomorphine and decreased by pentylenetetrazole. Behaviors composing the Impulsivity factor were increased by chlordiazepoxide, apomorphine, and both acute and chronic imipramine treatments. Behaviors composing the Self-protection factor were decreased by apomorphine. We submitted Wistar rats to the open-field test, the elevated-plus maze, and to the apparatus we are proposing. Measures related to exploratory behavior in all three tests were correlated. Measures composing the factors Impulsivity and Self-protection did not correlate with any measures from the two standard tests. Also, compared with existing impulsivity tests, the one we proposed did not require previous learning, training, or sophisticated analysis. Exploration measures from our test are as easy to obtain as the ones from other standard tests. Thus, we have proposed an apparatus that measured three different behavioral characteristics, was simple and fast, did not require subjects to be submitted to previous learning or training, was sensitive to drug treatments, and did not require sophisticated data analyses.

A combined study of behavior and Fos expression in limbic structures after re-testing Wistar rats in the elevated plus-maze.

The elevated plus-maze is an animal model used to study anxiety. In a second session, rats show a reduction in the exploratory behavior even when the two sessions are separated by intervals as large as 7 days. The aim of the present study was to investigate whether the reduction in the exploratory behavior is maintained after intervals larger than 7 days. Additionally, we aimed at investigating eventual correlations between behaviors in the plus-maze and activation of limbic structures as measured by Fos protein expression after the second session. Rats were tested for 5 min in the elevated plus-maze and re-tested 3, 9 or 33 days later. Other groups were tested only once. The rat brains were processed for immunohistochemical detection of Fos protein. The results show a decrease in the open arms exploration in the second trial with intervals of 3, 9 and 33 days. The expression of Fos protein in the piriform cortex, septal nucleus and paraventricular hypothalamic nucleus in the groups tested with intervals of 9 and 33 days were statistically different from the other groups. The alterations observed in exploratory behavior in the second session in the plus-maze did not correlate with Fos expression. In conclusion, although the specific test conditions were sufficient to evoke behavioral alterations in exploration in the elevated plus-maze, they were enough to induce significant Fos protein expression in piriform cortex, septal nucleus and thalamic and hypothalamic paraventricular nuclei but not in other areas such as dorsomedial nucleus of the hypothalamus and amygdala nuclei, known to be also active participants in circuits controlling fear and anxiety.

Thigmotactic responses in an open-field.

The goal of the present study was to investigate the role of thigmotaxis (the tendency to remain close to vertical surfaces) in rat exploratory behavior in an open-field. Thigmotaxis was investigated in a parametric way, using 24 experimentally adult naive male Wistar rats (210-230 g). Exploratory behavior was studied in an open-field (N = 12) in 5-min sessions and behavior was analyzed in terms of where it occurred: in areas surrounded by two, one, or no walls. Another group of rats (N = 12) was studied in an open-field with blocks placed near two of the corners so as to make these corner areas surrounded by three walls. The floor of the open-fields was divided into 20-cm squares in order to locate the exact place of occurrence of each behavior. The following behaviors were recorded: entries into the squares, rearings, and groomings. In both types of open-field the rats chose to remain longer in the squares surrounded by the largest possible number of walls. In one of the open-fields, the mean time (seconds) spent in squares surrounded by two walls was longer than the time spent in squares surrounded by one or no walls (37.2, 7.7, and 1.8 s, respectively). In the other open-field, the mean time spent in squares surrounded by three walls was longer than the time spent in squares surrounded by two, one or no walls (41.7, 20.4, 7.0, and 2.6 s, respectively). Other measures presented a similar profile. These results indicate that rats are sensitive to the number of walls in an environment and prefer to remain close to them.

Thigmotactic responses in an open-field

The goal of the present study was to investigate the role of thigmotaxis (the tendency to remain close to vertical surfaces) in rat exploratory behavior in an open-field. Thigmotaxis was investigated in a parametric way, using 24 experimentally adult naive male Wistar rats (210-230 g). Exploratory behavior was studied in an open-field (N = 12) in 5-min sessions and behavior was analyzed in terms of where it occurred: in areas surrounded by two, one, or no walls. Another group of rats (N = 12) was studied in an open-field with blocks placed near two of the corners so as to make these corner areas surrounded by three walls. The floor of the open-fields was divided into 20-cm squares in order to locate the exact place of occurrence of each behavior. The following behaviors were recorded: entries into the squares, rearings, and groomings. In both types of open-field the rats chose to remain longer in the squares surrounded by the largest possible number of walls. In one of the open-fields, the mean time (seconds) spent in squares surrounded by two walls was longer than the time spent in squares surrounded by one or no walls (37.2, 7.7, and 1.8 s, respectively). In the other open-field, the mean time spent in squares surrounded by three walls was longer than the time spent in squares surrounded by two, one or no walls (41.7, 20.4, 7.0, and 2.6 s, respectively). Other measures presented a similar profile. These results indicate that rats are sensitive to the number of walls in an environment and prefer to remain close to them.

Thermal stress decreases general motor activity of rats in the elevated plus-maze but does not alter aversion to the open arms.

Environmental temperature is known to affect a variety of biological processes ranging from simple chemical reactions up to ecological distribution of animal species. To our knowledge, however, there are no studies relating environmental temperature and exploration in the elevated plus-maze. The present study was aimed at investigating the influence of animal house temperature on the exploration of an elevated plus-maze. Fifty-seven male Wistar-derived rats were divided into five groups which were kept for 96-h in an animal house with different temperatures (18, 22, 26, 30 or 34 degrees C) and then tested in the elevated plus-maze. Results showed that the animals submitted to the higher temperatures decreased body weight, frequency of entries into both the open and closed arm, time spent in the open arm extremities, distance run in the closed arms and frequency of rearing while increasing the mean duration of each entry into both the open and closed arms. There were no significant effects on the time spent in the open arms and the percentage of entries into the open arms. These effect are probably due to thermal stress and do not relate to emotional changes but rather to modifications in general activity. The frequency of stretching and head-dipping exhibited different profile reactions to temperature when compared to the above measures. These behavioral modifications are also consistent with the effects of thermal stress rather than alterations in emotionality.

Effects of under- and overcrowding on exploratory behavior in the elevated plus-maze.

The present work investigated whether the number of rats housed in a cage affects exploration of an elevated plus-maze. Male Wistar-derived rats were kept 1, 2, 3, 4, 6, 8, 12, 16, or 24 to same size cages either for 1 or 14 days and tested in the elevated plus-maze. Rats kept 6 to a cage were arbitrarily considered controls because this is the housing condition adopted in many laboratories, ours included. In comparison to controls, 1-day housed rats kept 1, 2, 16, and 24 to a cage decreased the percentage of entries into the open arms. Similar decreases were also found in the time spent in the open arms, the only exception being the group with rats kept 16 to a cage which failed to show significant differences from the control group. Fourteen-day housed rats kept 1, 2, 16, or 24 to a cage decreased the percentage of entries and time spent in the open arms. We found plus-maze exploration to be similar in groups in which rats were kept from 4 to 12 to a cage. The present data indicate that anxiogenic effects resulting from under- and overcrowding should be taken into consideration in behavioral studies.

Effect of the blockade of mu1-opioid and 5HT2A-serotonergic/alpha1-noradrenergic receptors on sweet-substance-induced analgesia.

RATIONALE: Sweet-substance-induced analgesia has been widely studied, and the investigation of the neurotransmitters involved in this antinociceptive process is an important way for understanding the involvement of the neural system controlling this kind of antinociception. OBJECTIVE: The aim of this study was to investigate the involvement of opioid and monoaminergic systems in sweet-substance-induced analgesia. METHODS: The present work was carried out in an animal model with the aim of investigating whether acute (24 h) or chronic (14 days) intake of a sweet substance, such as sucrose (250 g/l), is followed by antinociception. Tail withdrawal latencies in the tail-flick test were measured before and immediately after this treatment. Immediately after the recording of baseline values, independent groups of rats were submitted to sucrose or tap-water intake and, after chronic treatment, they were pretreated with intraperitoneal administration of (1) naltrexone at 0.5, 1, 2 or 3 mg/kg; (2) naloxonazine at 5, 10, 20 or 30 mg/kg; (3) methysergide at 0.5, 1, 2 or 3 mg/kg; (4) ketanserin at 0.5, 1, 2 or 3 mg/kg; or (5) physiological saline. RESULTS: Naltrexone and methysergide at two major doses decreased sweet-substance-induced analgesia after chronic intake of a sweet substance. These effects were corroborated by peripheral administration of naloxonazine and ketanserin. CONCLUSIONS: These data give further evidence for: (a) the involvement of endogenous opioids and a mu1-opioid receptor in the sweet-substance-induced antinociception; (b) the involvement of monoamines and 5HT2A serotonergic/alpha1-noradrenergic receptors in the central regulation of the sweet-substance-produced analgesia.

Profile of wild Neotropical spiny rats (Trinomys, Echimyidae) in two behavioral tests.

The performance of three closely related species of spiny rats was compared in the elevated plus-maze and in the open-field tests. Laboratory rats were also evaluated. It was hypothesized that such tests should reveal differences in anxiety and exploratory profile among the wild species, which differ with respect to habitat, type of social organization and locomotion pattern. No consistent differences were found among the spiny rats, as assessed by conventional parameters, while such differences were detected between the domesticated lines. The social spiny rats (Trinomys yonenagae), which live in dunes, differed from the solitary sylvan species (T. iheringi and T. albispinus) in only one index of anxiety (open arms end-exploring). Nevertheless, thigmotaxis in novel environments exists in these spiny rats just as it does in the laboratory rats. During the tests, the sylvan species relied on erratic movements and T. iheringi was the most active species, whereas T. yonenagae employed vigilance and direct escape locomotion. This latter feature may be due to challenges imposed by open environments. Defecation score was reduced for all wild rats: it may represent a predation avoidance response. Concerning ethological measures, T. iheringi presented the highest scores of grooming, in both test situations, and T. albispinus the highest scores of rearing in the open-field. The great within-species variability found in the spiny rats may have concealed anxiety differences among them, despite the ability of both tests to reveal plesiomorphic behavioral characteristics, such as thigmotaxis. Our results also support the use of ethological approach in these tests.

Effects of septal cholinergic lesion on rat exploratory behavior in an open-field.

The medial septum participates in the modulation of exploratory behavior triggered by novelty. Also, selective lesions of the cholinergic component of the septohippocampal system alter the habituation of rats to an elevated plus-maze without modifying anxiety indices. We investigated the effects of the intraseptal injection of the cholinergic immunotoxin 192 IgG-saporin (SAP) on the behavior of rats in an open-field. Thirty-nine male Wistar rats (weight: 194-230 g) were divided into three groups, non-injected controls and rats injected with either saline (0.5 microl) or SAP (237.5 ng/0.5 microl). Twelve days after surgery, the animals were placed in a square open-field (120 cm) and allowed to freely explore for 5 min. After the test, the rats were killed by decapitation and the septum, hippocampus and frontal cortex were removed and assayed for acetylcholinesterase activity. SAP increased acetylcholinesterase activity in the septum, hippocampus and frontal cortex and decreased the total distance run (9.15 +/- 1.51 m) in comparison to controls (13.49 +/- 0.91 m). The time spent in the center and at the periphery was not altered by SAP but the distance run was reduced during the first and second minutes (2.43 +/- 0.36 and 1.75 +/- 0.34 m) compared to controls (4.18 +/- 0.26 and 3.14 +/- 0.25 m). SAP-treated rats showed decreased but persistent exploration throughout the session. These results suggest that septohippocampal cholinergic mechanisms contribute to at least two critical processes, one related to the motivation to explore new environments and the other to the acquisition and storage of spatial information (i.e., spatial memory).

Effects of septal cholinergic lesion on rat exploratory behavior in an open-field

The medial septum participates in the modulation of exploratory behavior triggered by novelty. Also, selective lesions of the cholinergic component of the septohippocampal system alter the habituation of rats to an elevated plus-maze without modifying anxiety indices. We investigated the effects of the intraseptal injection of the cholinergic immunotoxin 192 IgG-saporin (SAP) on the behavior of rats in an open-field. Thirty-nine male Wistar rats (weight: 194-230 g) were divided into three groups, non-injected controls and rats injected with either saline (0.5 æl) or SAP (237.5 ng/0.5 æl). Twelve days after surgery, the animals were placed in a square open-field (120 cm) and allowed to freely explore for 5 min. After the test, the rats were killed by decapitation and the septum, hippocampus and frontal cortex were removed and assayed for acetylcholinesterase activity. SAP increased acetylcholinesterase activity in the septum, hippocampus and frontal cortex and decreased the total distance run (9.15 ± 1.51 m) in comparison to controls (13.49 ± 0.91 m). The time spent in the center and at the periphery was not altered by SAP but the distance run was reduced during the first and second minutes (2.43 ± 0.36 and 1.75 ± 0.34 m) compared to controls (4.18 ± 0.26 and 3.14 ± 0.25 m). SAP-treated rats showed decreased but persistent exploration throughout the session. These results suggest that septohippocampal cholinergic mechanisms contribute to at least two critical processes, one related to the motivation to explore new environments and the other to the acquisition and storage of spatial information (i.e., spatial memory)

Vibrissal sense is not the main sensory modality in rat exploratory behavior in the elevated plus-maze.

Four groups of male Wistar rats were submitted to acute bilateral removal of mystacial vibrissae at different lengths from the follicle. Each group was divided into two subgroups, tested under high (150 Lux) and low environmental illumination (2 Lux). All the subjects were allowed to freely explore an elevated plus-maze for 5 min. Results indicated that rats tested under low illumination tended to explore the open arms more frequently and longer then rats tested under high illumination. When tested under low illumination, rats in the group that suffered whole vibrissa removal stayed longer in the open arms than those in the other groups but did not differ in the number of entries. The average increase in the length of open arm entries, rather than a decrease in aversion to the open arms, may be due to the need of more time to obtain information about the environment since there is no light and the vibrissae were removed. This effect was not seen with rats tested under high illumination, possibly because vision could be used to obtain relevant information.

Facilitatory effect of substance P on learning and memory in the inhibitory avoidance test for goldfish.

The aim of this study was to investigate if substance P (SP) can improve learning and memory processes in goldfish, using an inhibitory avoidance test. A two-compartment aquarium with a central sliding door was used. The animals were placed in the white compartment, and after 20 s the door was opened. As they entered the dark compartment, a weight was dropped in front of them. This procedure was repeated three times. After training, the animals were injected intraperitoneally with SP or vehicle. Twenty-four hours after training, the animals were tested and their latency was recorded. The group injected with SP showed an increase in the latency on the test day as compared with the vehicle group. These results suggest SP can facilitate memory in goldfish in an inhibitory avoidance test.

Dissociation of memory and anxiety in a repeated elevated plus maze paradigm: forebrain cholinergic mechanisms.

The effect of intraseptal injection of the cholinergic immunotoxin 192-IgG-saporin on behavior in the elevated plus maze was investigated. A 5-min test-retest paradigm, with minute-by-minute analysis of the first session, was used to evaluate both anxiety and memory in this task. Biochemical analyses revealed a decrease in acetylcholinesterase (AChE) activity in the hippocampus (HPC), septum, and frontal cortex of animals injected with IgG-192 saporin (237.5 ng) when compared with controls. No statistical differences were found between groups in terms of behaviors associated with locomotor activity, conventional measures of anxiety, or ethological behaviors during either session 1 or 2. During test session 2 the controls exhibited decreased exploratory activity and increased indices of anxiety. In contrast, the saporin-treated rats did not exhibit these experience-dependent behavioral changes from session 1 to 2. The minute-by-minute analysis showed a significant decrease in exploratory as well in anxiety associated behaviors during the first session for the control group, but not for the saporin-treated group. These results suggest that the cholinergic innervation of the HPC, the frontal cortex, or both forebrain structures, modulate the initiation of exploratory activity which, results in the acquisition and retention of spatial information, but does not affect the expression of anxiety in the elevated plus-maze.