Organization and development of brain stem auditory nuclei of the chicken: Organization of projections from N. magnocellularis to N. laminaris

The tonotopic and topographic organization of the bilateral projection from second‐order auditory neurons of nucleus magnocellularis (NM) to nucleus laminaris (NL) was examined in young chickens. In one group of birds, the NM axons which innervate the contralateral NL were severed by cutting the crossed dorsal cochlear tract at the midline. Heavy terminal degeineration in NL was confined to the neuropil area immediately ventral to the perikaryl lamina. Very little degeneration was seen in the dorsal neuropil region. In a second series of animals, the characteristic frequency (CF) of cells in an area of NM was first determined by microelectrode recording techniques and then a small electrolytic lesion was made through the recording electrode. Following survival periods of 24–48 hours, the distribution of projections from the lesioned area to the ipsilateral and contralateral NL was examined usinig the Fink‐Heimer method.