Effects of medial geniculate lesions on sound localization by the rat

Rats with bilateral lesions of the medial geniculate body were tested on a two-choice sound-localization task that required a directional response to a distant sound source. Stimuli included both broadband and filtered noise bursts presented singly or in repetitive trains. Separate tests were conducted with loudspeakers 180 and 60 degrees apart, centered around 0 degree azimuth. With complete bilateral destruction of the medial geniculate, rats could localize both trains and single bursts of noise and were capable of high levels of performance even at small angles of speaker separation. Some evidence of impaired performance was noted with high-frequency noise bursts, but generally the deficits were not severe. Animals with lesions that extended caudally into the brachium of the inferior colliculus and lateral tegmentum were severely impaired in their ability to localize sounds even at large angles of speaker separation. Three of the four animals in this group were incapable of localizing single bursts even with loudspeakers separated by 180 degrees, and the fourth was unable to perform above chance at 60 degrees. The effects of medial geniculate lesions were very similar to those reported previously for rats with lesions of the auditory cortex, but contrasted with reports of severe impairments in sound localization following damage to the auditory cortex in other mammalian species.

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Cytoarchitecture of the medial geniculate body and thalamic projections to the auditory cortex in the rufous horseshoe bat (Rhinolophus rouxi)

Anatomy and Embryology ◽

10.1007/s00429-004-0424-z ◽

2004 ◽

Vol 209 (1) ◽

pp. 59-76 ◽

Cited By ~ 15

Author(s):

Susanne Radtke-Schuller

Keyword(s):

Auditory Cortex ◽

Medial Geniculate Body ◽

Thalamic Projections ◽

Medial Geniculate ◽

Horseshoe Bat

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MESENCEPHALIC AREAS CONTROLLING PULSATILE OXYTOCIN RELEASE IN THE SUCKLED RAT

Journal of Endocrinology ◽

10.1677/joe.0.0910233 ◽

1981 ◽

Vol 91 (2) ◽

pp. 233-244 ◽

Cited By ~ 42

Author(s):

T. S. JUSS ◽

J. B. WAKERLEY

Keyword(s):

Medial Geniculate Body ◽

Milk Ejection ◽

Ventral Tegmentum ◽

Irregular Pattern ◽

Oxytocin Release ◽

Medial Geniculate ◽

Radiofrequency Lesions ◽

Milk Ejection Reflex ◽

Bilateral Lesions ◽

And Control

Experiments were performed on anaesthetized lactating rats to investigate the effects of radiofrequency lesions of the mesencephalon on the milk-ejection reflex. In lesioned and control rats, intramammary pressure recordings were used to estimate oxytocin release (number and relative amplitude of the intermittent milk-ejection responses) during a 3-h suckling test with ten pups. Bilateral lesions (diameter 0·5–1·5 mm) of the lateral tegmentum (near the brachium of the inferior colliculus and medial geniculate body) seriously disrupted the milk-ejection reflex, reducing the number of rats ejecting milk (two out of ten v. all 12 controls, P<0·001) and the amount of oxytocin they released (1·35±0·35 (s.e.m.) v. 15·52±2·19 mu. for controls, P<0·05). Unilateral lesions of the lateral tegmentum also impaired milk ejection and, if the suckling stimulus was restricted only to the contralateral nipples, oxytocin release was virtually abolished. Bilateral lesions placed more medially in the intermediate tegmentum were far less disruptive (eight out of nine rats ejected milk), though the amount of oxytocin released in this group (8·64±1·88 mu.) was still significantly (P<0·05) lower than controls. All rats with lesions of the central grey (nine) or ventral tegmentum (eight) displayed reflex milk ejection, as did those with multiple lesions of the tectum, central grey and ventral tegmentum (seven); in these three groups the amounts of oxytocin released (13·88±2·68, 13·10±1·90 and 11·04±1·95 mu. respectively) did not differ significantly from controls. Damage to the ventral tegmentum produced an irregular pattern of milk ejection characterized by occasional abnormally short (<2 min) milk-ejection intervals, though the overall number of responses in 3 h was less than that of controls (20·83±1·82 v. 14·50±1·30 mu., P<0·05). In conclusion, these results delineate two mesencephalic areas of particular importance in the milk-ejection reflex: (a) the lateral tegmentum, which appears to be concerned with transmission of the suckling stimulus from the contralateral nipples and is indispensable for oxytocin release, and (b) the ventral tegmentum which, although not an essential component of the reflex, may contribute to the timing of the intermittent milk-ejection responses.

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