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At least 1,747 records · Page 97Linked to original sources

PubMed1975

Comparative aggression in Sceloporus virgatus, S. undulatus consobrinus, and S. u. tristichus (Sauria: iguanidae).

Aggressive behaviour in both sexes of Sceloporus virgatus, S. undulatus consobrinus, and S. u. tristichus were compared by introducing a conspecific to a resident lizard in the field. Males of S. u. consobrinus exhibited high intensity aggression more commonly than did males of the other forms. Of the females, S. u. tristichus showed the greatest propensity for aggressive behaviour; S. u. consobrinus showed the least. In males, degree of aggression was correlated positively with degree of sexual dichromatism. The high degree of aggression in male S. u. consobrinus may be selectively advantageous because of (1) low density increasing space between females, (2) low density reducing selection against a relatively high frequency of violent fighting, and (3) high predation favouring lizards that do not leave their sites upon intrusion of another male. High aggression in female S. u. tristichus may be selectively advantageous because of (1) higher density leading to reduced food supply and fewer egg-laying sites, and (2) lower predation reducing selection against mobility and fighting in females.

Aggression↗

PubMed1991

Sex differences in opioid and non-opioid mediated predator-induced analgesia in mice.

The present study compared the nociceptive responses of male and female mice exposed to a predator, an ecologically relevant threatening stimulus. After 15 min of exposure to the presence of an experienced predatory cat, mice displayed a naloxone (1.0 mg/kg)-sensitive opioid mediated analgesic response, while after a brief 30-s exposure to the cat mice displayed a lower amplitude, relatively brief, non-opioid analgesia that was insensitive to naloxone and blocked by the serotonin-1A (5-HT1A) agonist, 8-hydroxy-2-(di-n-propylamino)tetralin. Male mice displayed a significantly greater opioid mediated predator-induced analgesia than females, whereas female mice showed a significantly greater non-opioid, 5-HT1A sensitive, analgesia than males. These results indicate that there are significant sex differences in both the opioid and non-opioid analgesic responses arising from exposure to a natural aversive stimulus.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1992

Behavioural and neurohistological changes in aging Sepia.

The life cycle of the cuttlefish in the English Channel is characterized by a succession of homogeneous population cohorts. These conditions provide an excellent opportunity for the study of aging in this cephalopod. In a first longitudinal study, we considered the oldest animals and compared their success rates at the first capture attempt. During the first weeks of the study, the results remained constant and then, during the weeks immediately preceding the natural death, a dramatic drop was observed. This deterioration may be due to defects of visuomotor coordination. In a second study, we used an associative learning protocol with negative reinforcement and the performances of young and old animals were compared. The most striking results showed that the performances of the oldest animals during the retention test were very mediocre. Such results suggest that the long-term memory process is affected. Finally, a modification of the Fink-Heimer silver stain enabled us to draw a map of spontaneous terminal degeneration in the central nervous system of the oldest animals. The structures which are characterized by the presence of multimodal inputs (the spine of the peduncle lobe and the basal lobes) present the most obvious signs of degeneration.

Aging↗

PubMed1993

Predator-induced opioid and non-opioid mediated analgesia in young meadow voles: sex differences and developmental changes.

The present study examined developmental changes in the nociceptive responses of male and female meadow voles, Microtus pennsylvanicus, exposed to a garter snake, a natural predator of young voles. After 15 min of exposure to the presence of a garter snake, neonatal-juvenile voles (5-20 days of age) displayed naloxone (1.0 mg/kg)-sensitive opioid mediated analgesic responses, while after a brief 30-s exposure to the snake, voles displayed a higher amplitude, non-opioid analgesia that was insensitive to naloxone and blocked by the serotonin-1A (5-HT1A) agonist, 8-hydroxy-2-(di-n-propylamino)tetralin. The levels of opioid and non-opioid mediated analgesia declined during development as the threat presented by the snake decreased. Young female voles also displayed a significantly greater non-opioid, 5-HT1A sensitive analgesia than males, with no significant sex differences in the lower amplitude opioid analgesia. These results indicate that young (neonatal) meadow voles that are exposed to a naturally threatening stimulus display sexually dimorphic analgesic responses. These findings also illustrate the need to consider the ecological context when examining environmentally-induced analgesia.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1994

Reduction of predator odor-induced anxiety in mice by the neurosteroid 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP).

The effects of the centrally produced allylic neurosteroid, 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP), on the responses of male mice to an aversive, anxiety-inducing, predator (cat) odor were examined in an odor preference test. Control untreated mice displayed an anxiogenic response to the cat odor, spending a minimal amount of time in a Y-maze in the vicinity of the cat odor. Intracerebroventricular (i.c.v.) administrations of 3 alpha HP had an anxiolytic action, resulting in significant dose-related (0.01-1.0 micrograms) increases in the amount of time spent in the proximity of the cat odor. These anxiolytic effects of 3 alpha HP were stereospecific, with the stereoisomer, 3 beta-hydroxy-4-pregnen-20-one (3 beta HP) having no significant effects on odor preferences. The analgesic, morphine, also had no significant effects on the response to cat odor indicating that the anxiolytic actions of 3 alpha HP were unlikely to be related to any analgesic effects. The effects of 3 alpha HP were significantly reduced by peripheral administrations of the GABAA antagonists, bicuculline and picrotoxin, but were unaffected by either the benzodiazepine antagonist, Ro 15-1788, or the opiate antagonist, naloxone. These results indicate that the allylic neurosteroid 3 alpha HP has anxiolytic actions involving interactions with the GABAA receptor.

20-alpha-Dihydroprogesterone↗

PubMed1989

A view of the world through the bat's ear: the formation of acoustic images in echolocation.

Echolocating bats perceive objects as acoustic images derived from echoes of the ultrasonic sounds they emit. They can detect, track, identify, and intercept flying insects using sonar. Many species, such as the big brown bat, Eptesicus fuscus, emit frequency-modulated sonar sounds and perceive the distance to targets, or target range, from the delay of echoes. For Eptesicus, a point-target's image has a sharpness along the range axis that is determined by the acuity of echo-delay perception, which is about 10 ns under favorable conditions. The image as a whole has a fine range structure that corresponds to the cross-correlation function between emissions and echoes. A complex target- which has reflecting points, called "glints", located at slightly different distances and reflects echoes containing overlapping components with slightly different delays--is perceived in terms of its range profile. The separation of the glints along the range dimension is encoded by the shape of the echo spectrum created by interference between overlapping echo components. However, Eptesicus transforms the echo spectrum back into an estimate of the original delay separation of echo components. The bat thus converts spectral cues into elements of an image expressed in terms of range. The absolute range of the nearest glint is encoded by the arrival time of the earliest echo component, and the spectrally encoded range separation of additional glints is referred to this time-encoded reference range for the image as a whole. Each individual glint is represented by a cross-correlation function for its own echo component, the nearest of which is computed directly from arrival-time measurements while further ones are computed by transformation of the echo spectrum. The bat then sums the cross-correlation functions for multiple glints to form the entire image of the complex target. Range and shape are two distinct features of targets that are separately encoded by the bat's auditory system, but the bat perceives unitary images that require fusion of these features to create a synthetic psychological dimension of range. The bat's use of cross-correlation-like images reveals neural computations that achieve fusion of stimulus features and offers an example of high-level operations involved in the formation of perceptual "wholes".

Animals↗

PubMed1975