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Biomedical subjects

R J Andrew

Publications and source records attributed to R J Andrew.

12 recordsLinked to original sources
PubMed1979

Distractibility changes during the oestrous cycle of the rat.

Experiments described which were designed to test the hypothesis that the ease with which rats will shift attention between stimuli varies with the oestrous cycle. It was predicted from the results of earlier work that at oestrus, animals will shift attention less readily than at dioestrus, provided that attention is already focussed on a specific stimulus. Data from two-stimulus tests, and runway tests confirmed this prediction. It is suggested that the nature of the underlying changes may be similar to those induced in young chicks by exogenous testosterone, and may involve changes in hippocampal function.

Animals↗
PubMed1976

A copulatory system in the hypothalamus and tegmentum of the domestic chick.

A tract in the chick is described that runs from the posterior nucleus paraventricularis magnocellularis (PVM) through the lateral hypothalamus to a small area of the anterior tegmentum, which is adjacent to the ventral tegmental area. Bilateral lesions of the posterior PVM or of the PVM tract or of its tegmental destination abolish the facilitation of copulation in male chicks by testosterone. The effect is specific in that the facilitation of attack is either unaffected or only slightly depressed by such lesions, while being itself specifically depressed by other hypothalamic lesions. No other hypothalamic tracts were found that were necessary for the facilitation of copulation. An equivalent copulatory system probably exists in the mammal, with a more diffuse distribution in the preoptic area but with similar connections back to the tegmentum.

Aggression↗
PubMed1975

Effects of testosterone on the behaviour of the domestic chick. I. Effects present in males but not in females.

In male chicks, specific facilitation of male copulatory movements occurs at a lower dosage of testosterone oenanthate than does facilitation of approach to the test object, or of attack. The latter effects can be dissociated in other ways from the first; they may depend upon a single central change in visual responsiveness or persistence. Females show none of these changes, although they are capable of the behaviour patterns involved, and do show other behavioural effects of testosterone. On day 3 normal males copulate and attack more, and flee less than do females.

Age Factors↗
PubMed1975

Effects of testosterone on the behaviour of the domestic chick. II. Effects present in both sexes.

In female chicks, testosterone increases both binocular fixation of the thrusting hand and avoidance of direct gaze. The hand is thus treated as though it had become more conspicuous. Males show signs of such changes, which are obscured by a progressive locking of attention on the hand, along with which develop head shaking and pecking. These latter three effects, together with later full attacks, may be a consequence of increased persistence in males due to testosterone. In both sexes testosterone facilitates waltzing and three characteristic calls, probably by specific effects. Latencies and dosage dependency are similar in both sexes. Ten changes in behaviour due to testosterone can be explained by as few as five basic effects, both general and specific.

Aggression↗
PubMed1975

Effects of testosterone on the calling of the domestic chick in a strange environment.

Testosterone affects calling in a strange environment in two independent ways. In both sexes, short calls increase in number at the expense of peeps early in the test (when they would in any case be numerous) probably as a result of an increased tendency to repeat the call which has just been given. In males only, peeps are reduced in number during established calling, as a result of the interpolation of brief periods of silence. There is no accompanying depression of escape, but the visual scanning usual during peeps is reduced. The replacement of peeps by silence and immobility may be a consequence of an increase in persistence of attention to particular stimuli.

Animals↗
PubMed1975

Midbrain structures controlling vocalization in the domestic chick.

Bilateral lesions confined to the anterior intercollicular area (ICo) produce muting in domestic chicks. Calling is lost both in open field test, and to novel stimuli which evoke pecking. Lesions of the medial edge of the ICo also mute, perhaps by cutting connections with the central mesencephatic grey. Partial destruction of the ICo allows full intensity calling but with greatly increased latency. If an area ventral to the ICo is also destroyed, one type of calling reappears: it is still not readily evoked by particular stimuli which are effective in normal chicks but it often occurs during locomotion. Crowing survives ICo lesions and presumably depends on a different route to lower centres. Totally deaf birds show quite normal calling, so that hearing deficits are probably not involved in the muting. Finally, mammalian homologues of the ICo and its connections are identified.

Animals↗
PubMed1975

The effects of muting lesions on emotional behaviour and behaviour normally associated with calling.

Bilateral intercollicular lesions in the chick abolish or depress not only calling, but also those phases of behaviour when calling would have been occurring. These include: long bouts of excited feeding immediately after food is made available; examining and pecking moving targets and novel objects; persistent scanning, and inhibition of other behaviour in a novel environment. Deaf birds behave precisely like controls, so that possible auditory deficits are not involved. During calling phases significant visual stimuli are treated as if they were starting or conspicuous. Conversely, continuous examination of a stimulus causes calling to diminish or disappear even though response continues; a brief period when the stimulus is not seen causes calling to begin again when it is once more perceived. In addition to the increased effectiveness of relevant visual stimuli, motor facilitation is usual in calling phases, as is inhibition of irrelevant responses. Emotional behaviour in man and other mammals is compared to calling phases in the chick.

Animals↗
PubMed1975

Changes in visual responsiveness following intercollicular lesions and their effects on avoidance and attack.

In the normal chick, conspicuous visual stimuli induce targetting and pecking together, with vocalization. All three are abolished by lesion of the intercollicular area (ICo) or of connections passing through its medial margin. After such lesions, chicks also cease to treat significant visual stimuli as if they were startling and exciting, and may delay response as a result. However, they are still able to recognise, orient accurately to, and respond appropriately to, a variety of complex visual stimuli (e.g. food grains, copulation object). In addition, they are little affected by strange surroundings. Lesion evidence suggests the mammalian subcollicular area to have similar functions to the ICo and to be homologous with it. A route (present in bird), which is well-known in mammals for its association with threat, defense and escape evoked by strange and frightening objects (amygdala-diencephalic periventricular system-central mesencephalic grey, A-DPS-CMG) is stimuli via the 2 ICo (subcollicular area). Two different mechanisms may be involved caudal to the ICo. One consists of tectal afferents which might modulate the evocation of targetting, pecking and other responses via the tectum. The other is the predorsal system of tectal efferents which may mediate such responses. Classical syndromes of tameness and unresponsiveness produced by various interruptions of the A-DPS-CMG route may depend on interruption of connections to these midbrain mechanisms. Attack is depressed by ICo lesions as one aspect of reduced responsiveness to conspicuous and startling visual stimuli. Avoidance, which is apparently mediated by a separate system, much as in Anura, is facilitated.

Animals↗