Kainic acid lesions of the dorsal nucleus of the lateral lemniscus: effects on binaural evoked responses in rat auditory cortex.
The effects of unilateral lesions of the dorsal nucleus of the lateral lemniscus (DNLL) on binaural processing were examined by measuring the amplitude of auditory cortical evoked responses in the albino rat. Lesions were made by pressure injection of small quantities of kainic acid through a micropipette lowered into the lateral lemniscus. Comparisons were made between normal animals and animals with unilateral DNLL damage. In normal animals, the amplitude of evoked potentials recorded from left and right primary auditory cortex varied as a function of the time difference between clicks delivered to the two ears. Maximum responses were obtained from the hemisphere contralateral to the leading click, and response amplitude was progressively reduced as the interaural time difference (ITD) was shifted in favor of the ipsilateral ear over the range from +600 microseconds to -600 microseconds. The functions in the left and right hemisphere were symmetrical mirror images of one another. Destruction of the DNLL had no significant effect on the maximum response amplitude, evoked response threshold, or response latency in either hemisphere. On the other hand, the lesion did have the effect of greatly reducing the slope of the ITD function in the hemisphere contralateral to the lesion. The change in slope was attributed to a reduction in the strength of inhibition produced by stimulation of the ipsilateral ear. No effect was seen on the slope of the function in the ipsilateral hemisphere. Animals with lesions that spared DNLL but destroyed the intermediate and ventral nucleus of the lateral lemniscus had normal binaural response functions. These data show that the DNLL plays an important role in shaping binaural responses in the contralateral auditory pathway.
Glenn
S L
SL
Psychology Department, Carleton University, Ottawa, Ontario, Canada.
Kelly
J B
JB
D000818:Animals; D001303:Auditory Cortex / Q000502:physiology*; D004423:Ear / Q000502:physiology*; D005072:Evoked Potentials, Auditory; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D011149:Pons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D007608:Kainic Acid