Effects of Tectal Grafts on Sound Localization Deficits Induced by Inferior Colliculus Lesions in Hooded Rats

• Published in: Experimental neurology 1997-05, Vol.145 (1), p.16-23
• Main Authors: Zrull, Mark C., Coleman, James R.
• Format: Article
• Language: English
• Subjects: Animals; Behavior, Animal - physiology; Biological and medical sciences; Brain Stem - physiology; Brain Stem - surgery; Brain Tissue Transplantation; Cell Count; Denervation; Female; Fetal Tissue Transplantation; Inferior Colliculi - cytology; Inferior Colliculi - surgery; Inferior Colliculi - transplantation; Male; Medical sciences; Neurosurgery; Pregnancy; Rats; Rats, Inbred Strains; Skull, brain, vascular surgery; Sound Localization - physiology; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1006/exnr.1997.6439

The goals of this research were to examine the role of the inferior colliculus (IC) in mediating sound localization behavior and the ability of tectal grafts to restore function after IC ablation in the Long-Evans rat. Previous work has suggested that the IC is a major center for processing of information used in localizing sound sources in space. Adult rats were trained on a lick suppression paradigm to discriminate the location of the second pulse in a noise burst pair presented in the horizontal interaural plane. Following baseline testing, rats received bilateral IC lesions, bilateral lesions followed in 1 week by bilateral tectal grafts, or were sham operated. Sound localization ability was then tested 15 to 30 days and 40 to 50 days following surgical procedures. Performance across experimental groups was statistically the same during baseline testing. During the first operative test period lesion-only and grafted animals showed deficits in sound localization ability relative to controls. By the second postoperative test period control and grafted animals did not differ statistically in sound localization ability and performance of both groups was superior to that of lesion-only animals. Histology revealed a similar extent of IC damage in lesion-only and lesion-graft animals and revealed the presence of implanted tectal tissue in all grafted animals. There was significant neuron loss in the dorsal nucleus of lateral lemniscus (DNLL) in lesion-only animals relative to grafted rats and sham controls. Behavioral results suggest that the IC of pigmented rat is important for sound localization ability. The sparing of DNLL neurons in grafted animals suggests that the tectal grafts may directly integrate into or aid intrinsic recovery of the host auditory pathway.