Infrared thermography is a method that detects thermal radiation energy and can measure the body surface temperature of animals from a distance. While rectal temperature has traditionally been used ...to measure animals' core temperature, thermal imaging can avoid the stress and potential rise of body temperature deriving from handling of the animals. Additionally, being non-invasive and contactless, thermal imaging allows free movement of the animals. The validity of this technique as a psychophysiological method has been proven in a series of stress-induced hyperthermia (SIH) studies of mice under social inequality conditions. Restraint in a holder elicits SIH in mice. A restrained mouse surrounded by freely moving cage mates displays increased SIH suggesting that social inequality enhances the stress. Social inequality can be examined also in unrestrained mice, in particular through unequal distribution of food. In this protocol, a food-deprived mouse is given a small piece of cheese, while its cage mate is given a large piece of cheese. This inequity causes SIH, suggesting social inequality aversion in mice. Thus, social inequality in different situations similarly increased SIH. Importantly, in future studies infrared thermography could also be used to evaluate emotional arousal states different from stress (for example to assess reactivity to rewards or in social and sexual preference tests). Moreover, the technique could be used to investigate also cognitive arousal induced by novelty. Indeed, infrared thermography could be a particularly useful tool for animal-friendly studies of cognition and emotion in rodents.
Abstract Stress-induced hyperthermia (SIH) was examined in three different social conditions in mice by thermographic measurement of the body surface temperature. Placing animals in cylindrical ...holders induced restraint stress. I examined the effect of the social factors in SIH using the thermograph (body surface temperature). Mice restrained in the holders alone showed SIH. Mice restrained in the holders at the same time as other similarly restrained cage mates (social equality condition) showed less hyperthermia. Interestingly, restrained mice with free moving cage mates (social inequality condition) showed the highest hyperthermia. These results are consistent with a previous experiment measuring the memory-enhancing effects of stress and the stress-induced elevation of corticosterone, and suggest that social inequality enhances stress.
Japanese eels (
) were trained on a spatial-learning paradigm in a pool placed in an experimental room where several extra-maze cues were present. Four tubes were placed in the pool, of which one was ...open and could be entered by the eels. The open tube was placed at a fixed position in the pool and contained a triangular block that served as an intra-maze cue. The eels learned to identify the open tube, and their performance was maintained when the pool was rotated. However, they were unable to maintain their performance in a dark room, which suggests that spatial learning is based on visual cues. To determine the influence of the extra- and intra-maze cues, the tube with the triangle was moved to a new position and another open tube was kept in its place. The eels chose either the tube at the original position or the tube with the triangle at its new position, suggesting that spatial discrimination may be based on either extra- or intra-maze cues. We thus conclude that the eels employed an adjunctive strategy of multiple cues. In the next experiment, the eels were trained to visually discriminate the position of the stimulus (triangle), which changed in every trial. After the training, the eels were submitted to a test in which, in addition to the triangular pattern, a rectangular pattern was introduced. The eels discriminated between the tubes with the triangular and rectangular patterns, suggesting that they had the ability to discriminate visual patterns.
Eels migrate long distances and their spatial learning ability based on extra-maze visual cues has been examined in the laboratory. Here, I examine the discriminative properties of water flow in ...their spatial cognition. Individuals of the Japanese eel (Anguilla japonica) were trained in a circular pool containing four pipes. One pipe was open where the eels could enter, and the other pipes were closed. A small motor-driven water screw was placed beside each pipe. The water screw close to the open pipe was active to allow water flow, whereas the other screws were inactive. The position of the open pipe with the active screw was randomly changed, and the eels could learn the position of the open pipe after approximately 15 trials. Overall, five tests were conducted. Test 1: A generalization test showed a generalization gradient along the distance from the open pipe and the active screw. Test 2: A test using a screw with no blades (i.e., no water flow but possible vibration or sound by a motor is present) resulted in chance level performance, suggesting that the eels needed water flow to find the open pipe. Test 3: A test with a water pump that produced water flow by a mechanism different from that of the original motor-driven screw showed that the eels maintained the detection of water flow under this condition. Test 4: The eels also located the open pipe in a dark room test; therefore, visual cues were not used for the detection of the open pipe. To confirm that the water flow was detected by the lateral organ, streptomycin sulfate was dissolved in a home tank to impair the hair cells in the lateral line organ in Test 5, and the eels were not able to detect the open pipe under these conditions. This observation suggests that the detection of water flow depends on the lateral-line organ. In summary, the data show that eels can detect water flow to find hiding locations.
I measured preference for paintings (Renoir vs. Picasso or Kandinsky vs. Mondrian) in mice. In general mice did not display a painting preference except for two mice: one preferred Renoir to Picasso, ...and the other preferred Kandinsky to Mondrian. Thereafter, I examined discrimination of paintings with new mice. When exposure to paintings of one artist was associated with an injection of morphine (3.0 mg/kg), mice displayed conditioned preference for those paintings, showing discrimination of paintings by Renoir from those by Picasso, and paintings by Kandinsky from those by Mondrian after the conditioning. They also exhibited generalization of the preference to novel paintings of the artists. After conditioning with morphine for a set of paintings consisting of two artists, mice showed discrimination between two sets of paintings also from the two artists but not in association with morphine. These results suggest that mice can discriminate not only between an artist's style but also among paintings of the same artist. When mice were trained to discriminate a pair of paintings by Kandinsky and Renoir in an operant chamber equipped with a touch screen, they showed transfer of the discrimination to new pairs of the artists, but did not show transfer of discrimination of paintings by other artists, suggesting generalization.
Empathy is an emotional response to display of distress in others and reversed-empathy is an emotional response to non-distressed others in distressed subjects. Stress has memory enhancing effect on ...aversive experience. Here, I examine empathy and reversed empathy using the memory enhancing effects of stress in mice. Restrain stress enhanced aversive memory of a floor with electric shock, but restrain stress, with cage mates also restrained, reduced the enhancing effect. On the other hand, restrain stress with free-moving cage mates increased the memory enhancing effect, suggesting the stronger stress. This is the reversed-empathy. Level of corticosterone is the highest after the restrain with free-moving mates and lowest after the restrain with restrained mates.
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Mouse showed category-like learning in Kandinsky vs. Mondrian discrimination but not in Renoir vs. Picasso discrimination
•The mice employ different strategies for different painting ...discrimination tasks.•They display category-like discrimination for Kandinsky vs. Mondrian task.•But they display item-to-item discrimination for Renoir vs. Picasso task.
C57BL/6 mice were trained on simultaneous discrimination of paintings with multiple exemplars, using an operant chamber with a touch screen. The number of exemplars was successively increased up to six. Those mice trained in Kandinsky/Mondrian discrimination showed improved learning and generalization, whereas those trained in Picasso/Renoir discrimination showed no improvements in learning or generalization. These results suggest category-like discrimination in the Kandinsky/Mondrian task, but item-to-item discrimination in the Picasso/Renoir task. Mice maintained their discriminative behavior in a pixelization test with various paintings; however, mice in the Picasso/Renoir task showed poor performance in a test that employed scrambling processing. These results do not indicate that discrimination strategy for any Kandinsky/Mondrian combinations differed from that for any Picasso/Monet combinations but suggest the mice employed different strategies of discrimination tasks depending upon stimuli.
•This study examined the social preference of mice for a conspecific in pain.•Subordinate mice preferred a dominant mate in pain to a mid-status mate not in pain.•Dominant mice did not display a ...social preference.•The relationship between observer and demonstrator modifies social preference.
Many species display approach behavior to conspecifics. This study evaluated approach behavior exhibited by mice toward a cage mate in pain according to the social relationship between the mice. The relative dominant/subordinate relationship among three cage mates was determined using a competitive food retrieval test. Social preference of the subordinate mouse for the mid-status or dominant cage mate was tested with and without pain induced in the dominant cage mate. Social preference of the dominant mouse was similarly tested with and without pain induced in the subordinate cage mate. Subordinate mice spent more time with the dominant cage mate in pain than with the mid-status cage mate but spent a similar amount of time with dominant and mid-status cage mates that were not in pain. Dominant mice spent a similar amount of time with subordinate and mid-status cage mates regardless of pain. The time that subordinate mice spent with the dominant cage mate in pain inversely correlated with dominancy distance between the two mice. These results demonstrate that social relationship can modify perception of the pain of others.
We propose a simple index of brain volume (D*L index), calculated using two-dimensional photographs of the brain, captured from the dorsal and lateral views. Here, D and L represent the dorsal and ...lateral brain areas in the images, respectively. Two distantly related species were assessed. The D*L indices of 11 Japanese eels,
Anguilla japonica
and 11 yellowfin gobies,
Acanthogobius flavimanus
were calculated. High correlation coefficients of D*L index with brain weights were obtained from both species, suggesting the validity and reliability of the index. The relative profiles of the olfactory bulb, telencephalon, optic tectum, and cerebellum were calculated using this index. Eels had a larger olfactory bulb and telencephalon, whereas gobies had a larger optic tectum. Principal component analysis showed two separate clusters for eels and gobies. Published images of two Anguilliformes species and four Gobiidae species were used to test the D*L index. Principal component analysis showed separate clusters for Anguilliformes and Gobiidae species. The D*L index is a suitable tool for data collection because it is simple, low-cost, and has reliability and validity.
Japanese eels (
Anguilla japonica
) were trained on a Morris-type spatial learning task. There were four tubes in a pool, but the eels could hide in only one of these. The eels learned the position ...of the open tube, and maintained their performance when the pool was rotated to remove possible intra-maze cues. The eels could not maintain their performance in a dark room, suggesting that spatial learning involved extra-maze visual cues. When the position of the open tube was randomly changed every day, the performance of the eels in finding the open tube did not improve.
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