{'fraction_non_alphanumeric': 0.01889644746787604, 'fraction_numerical': 0.007936507936507936, 'mean_word_length': 5.58457711442786, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Experience‐independent development of dendritic organization in the avian nucleus laminaris

The third‐order auditory neurons of the avian nucleus laminaris (NL) have distinct dorsal and ventral dendritic tufts that receive their predominant synaptic input from, respectively, the ipsilateral and contralateral cochlear nucleus. Beginning about embryonic day (E) 14 in the chick and continuing for some weeks after hatching, NL neurons undergo a complex series of morphological transformations that result in the formation of a steep anteromedial‐to‐posterolateral gradient of increasing total dendritic length across the nucleus. This gradient perfectly parallels the tonotopic axis of NL. It has been proposed that acoustically evoked activity in the auditory pathway contributes importantly to formation of the gradient of dendritic length in NL and to several other features of dendritic development. The present experiment tested this hypothesis by surgically removing both otocysts (embryonic precursors of the inner ear) and studying the developing NL in the absence of peripheral input. The results of a quantitative study of Golgi‐impregnated material show that at E17 both the steepness and predictability of the spatial gradient of dendritic length in operated animals are indistinguishable from normal. Similarly, the correlation of dorsal and ventral dendritic lengths on individual cells in operated animals is not significantly different from normal. The absolute length of both dendritic fields is reduced below normal, although only dorsal dendrites show a statistically reliable (14%) decrease. This is a significantly smaller effect than the 44% length reduction seen previously in animals with unilateral otocyst removal (T.N. Parks: J. Comp. Neurol. 202:47–57, '81); symmetrical afferent input appears more important to the regulation of NL dendritic length than the absolute level of this input. The only other significant effect of otocyst removal is to retard or prevent the alignment of the gradients of dorsal and ventral dendritic length that occurs normally between E15 and E17; the immature dorsal gradient has a much less prominent lateral‐to‐medial component than the ventral gradient at the same age. Thus, whereas the absolute size of NL dendrites depends upon a normal inner ear, most of the highly specialized dendritic organization of NL can develop normally in the complete absence of peripheral influences. The results suggest that each brainstem auditory nucleus is organized along an intrinsically determined axis that specifies how incoming auditory afferent axons will be organized into tonotopic arrays.