Michael Noonan, PhD

Professor of Animal Behavior



Sex Differences in Anterior Commissure Size in the Rat

Noonan, M., Smith, M.A., Kelleher, K. and Sanfilippo, M.A. Sex differences in anterior commissure size in the rat. Brain Research Bulletin, 1998, 45, 101-104.

Earlier studies have shown that the corpus callosum of rats tends to be larger in males than in females. We report here that the anterior commissure of rats is also larger in males than in females. The sizes of the two commissures were positively correlated in both sexes, but significantly more so in females than in males. The anterior commissure size difference in rats reported here is opposite in direction from that reported elsewhere for humans, and we speculate that this may derive from differences in the relative proportions of the constituent fibers which make up the anterior commissure in the two species.

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Preference of Laboratory Rats for Potentially Enriching Stimulus Objects

Chmiel, D. & Noonan, M. Preference of laboratory rats for potentially enriching stimulus objects. Laboratory Animals, 1996, 30, 97-101.

In an effort to identify suitable stimulus objects which could be placed into standard laboratory cages in order to provide rats with a degree of environmental enrichment, the preference of rats to spend time near 15 diverse objects was measured in a free-choice paradigm. Rats showed no preference for objects such as pipes and partitions which we had reasoned might satisfy a wall-hugging tendency. They also showed no preference for objects which we had reasoned to be potentially interesting as manipulanda. The rats did show reliable preferences for spending time with some, but not all, chewable objects. A block of wood predrilled with holes was the most attractive, and we cautiously recommend that researchers consider providing laboratory rats with such an object to allow them the opportunity to exercise a fundamental, species-typical behaviour— chewing.

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Septal Lesions Impair Rats' Morris Test Performance, but Facilitate Left-right Response Differentiation

Noonan, M., Penque, M. & Axelrod, S. Septal lesions impair rats' Morris-test performance but facilitate left-right response differentiation. Physiology & Behavior, 1996, 60, 895-900.

Lesions in the septum impaired performance on the Morris test. a task in which the rat locates a hidden escape platform by use of fixed landmarks, but facilitated a water maze-based left— right response differentiation, a task in which the rat finds a hidden escape ramp by means of its internal sense of direction. These results are interpreted as supporting an allocentric/egocentric dichotomy with respect to navigation, and support the notion that rats approach spatial problems with a hierarchy of potential solutions in which allocentric solutions take precedence over egocentric ones. The septal lesions are inferred to disrupt the allocentric mapping system.

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Improved Acquisition of Left-right Response Differentiation in the Rat Following Section of Corpus Callosum

Noonan, M. & Axelrod, S. Improved acquisition of left-right response differentiation in the rat following section of corpus callosum. Behavioural Brain Research, 1991, 46, 135-142.

Split-brained rats learned a left—right response differentiation in a water maze significantly faster than rats with sham surgery. It is unlikely that this superiority resulted from improvement in performance variables since callosotomized rats did not differ significantly from sham operates in speed of acquisition of a brightness discrimination in the same apparatus. Additionally, callosotomy likewise had no effect on the acquisition of a water-maze task requiring consistent unilateral responses. The superiority of the callosotomized animals in forming the left—right response differentiation supports a hypothesis implicating the forebrain commissures in left—right confusion.

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Partial Callosotomy and Left-Right Response Differentiation in the Rat: Separate Anterior and Posterior Facilitatory Effects

Noonan, M. & Axelrod, S. Partial callosotomy and left-right response differentiation in the rat: Separate anterior and posterior facilitatory effects. Behavioral Neuroscience, 1992, 106, 433-436.

Earlier research demonstrated that complete section of the corpus callosum in the rat reduced the number of trials required to acquire a left—right response differentiation (LRRD). This study was designed to investigate whether the facilitatory effect on LRRD could be produced by section of an anatomical subdivision of the callosum. Rats with sections of the anterior or posterior corpus callosum mastered the LRRD task faster than sham subjects, but more slowly than rats with total callosal section; section of the middle portion of the callosum had no such effect. The partial facilitatory effects of anterior and posterior callosotomy appear to be independent, and suggest that the callosal intermixing of lateral information, which contributes to left—right confusion, occurs at both the sensory and motor levels of processing

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Failure of Induced Asymmetries to Improve Left-Right Response Differentiation in the Rat

Noonan, M. & Axelrod, S. Failure of induced asymmetries to improve left-right response differentiation in the rat. Journal of General Psychology, 1990, 117, 197-202.

Rats (and humans) appear to be able to distinguish between left and right by referring to an intrinsic asymmetry as a navigational aid; this suggests that experimentally induced asymmetries might also facilitate such a distinction. We assessed the effects of asymmetries produced by unilateral shaving, unilateral vibrissotomy, and asymmetrical cortical lesions on acquisition of a left—right response differentiation. None of the treatments improved performance relative to appropriate control treatments; the rats were evidently unable to use these induced asymmetries to form the lateral differentiation. The results are related to evidence provided in an earlier report (Noonan & Axelrod. 1989) that even some reliable intrinsic asymmetries cannot function as navigational aids.

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Behavioral Bias and Left-Right Response Differentiation in the Rat

Noonan, M. & Axelrod, S. Behavioral bias and left-right response differentiation in the rat. Behavioral and Neural Biology, 1989, 52, 406-410.

To examine the proposition that lateral asymmetry facilitates left—right re sponse differentiation in rats, we examined the relationships between the strengths of several behavioral biases and the scores on a learning task requiring left—right response differentiation. No support was found for a simple model positing a monotomc relationship between any behavioral bias and the learning scores. However, performance showed a U-shaped relationship to one behavioral bias. This finding conforms to a curvilinear model in whieh rats at either extreme of asymmetry are disadvantaged, at low degrees of asymmetry by a lack of navigational reference, and at high degrees by resultant strong position habits; moderately asymmetrical rats have neither disadvantage and are best able to use the asymmetry as a reference in processing left—right information.

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Effects of Medial Preoptic Lesions on Placentophagia and on the Onset of Maternal Behavior in the Rat

Noonan, M. & Kristal, M. B. The effects of medial preoptic lesions on placentophagia and on the onset of maternal behavior in the rat. Physiology & Behavior, 1979, 22, 1197-1202.

Lesions of the medial preoptic area (MPO) were produced through permanently indwelling electrodes 24 hours prior to parturition in pregnant rats, or 24 hours prior to donor-placenta presentation in virgin rats determined in a pretest to be placentophages. The lesions had no disruptive effect on placentophagia in the virgin females. However, MPO lesions did delay the onset of placentophagia, pup-retrieval, and nest-building in some parturient rats. In others, lesions produced an impairment (in latency and quality) only of nest-building. None showed any impairment of pup-licking, or in the clear tendency to leave excreted waste away from the gathered pups. These results suggest the possibility of at least semi-independent mechanisms for the various components of maternal behavior.

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Nonparturitional Exposure to Donor Placenta and Placentophagia After Lateral Hypothalamic Lesions in Rats

Noonan, M. & Kristal, M. B. Nonparturitional exposure to donor placenta and placentophagia after lateral hypothalamic lesions in rats. Bulletin of the Psychonomic Society Bull. Psychon. Soc. 12, 140–142 (1978).

Previous research has shown that parturitionally experienced rats with lateral hypothalamic (LH) lesions that rendered them otherwise aphagic, still ate placenta when it was delivered (pregnant subjects) or presented (nonpregnant subjects). Subsequent studies have shown that some virgin rats are spontaneously attracted to donor placenta, whereas the others clearly avoid it. The present study was designed to demonstrate that the sparing of placentophagia after LH lesions observed in the earlier study was not due merely to the previous ingestion of placenta, per se, or to inadvertent selection for spontaneous placentophages. Virgin placentophages were allowed to consume donor placenta; some were then bred. Prior to parturition or after an equivalent time interval, LH lesions were produced through indwelling electrodes. The next day, not only were the animals with properly placed lesions aphagic to a cookie/milk mash, but none ate delivered or presented placenta.

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Learning in Escape/Avoidance Tasks in Female Rats Does Not Vary With Reproductive Condition

Kristal, M. B., Axelrod, S., & Noonan, M. Learning in escape/avoidance tasks in female rats does not vary with reproductive condition. Physiology & Behavior, 1978, 21, 251-256.

To determine whether the development of novel stimulus-response associations by the mother during the periparturient period is attributable to a general facilitation of learning produced by the hormonal milieu during that period, learning ability under various reproductive conditions was assessed in two tasks unrelated to the periparturitional situation. The two tasks, selected because they equalized the various groups for motivation and performance variables, were acquisition of a water-maze escape (including two reversals), and acquisition and retention of an unsignalled shuttlebox shock avoidance. The groups tested in the water maze were a midpregnant group, an immediately prepartum group, and an immediately postpartum group. In the shuttlebox, the same conditions (different rats) were compared, together with a nonpregnant estrus condition, and a nonpregnant diestrus condition. The results of both experiments indiciate that although learning occurred, the characteristics of acquisition and retention were not influenced by reproductive condition.

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