Postnatal development of GAP-43 immunoreactivity in the auditory brainstem of the rat

Abstract

Extensive data link the growth associated protein GAP-43 to axonal elongation and synapse formation during development and in plastic responses of nervous tissue. We have studied the changing levels of GAP-43 expression in the auditory brainstem nuclei of the developing rat by applying immunocytochemical techniques. By the first postnatal day (P1), GAP-43 was expressed at high concentrations in all subdivisions of the cochlear nuclear complex and the superior olivary complex. At this stage, neuropil structures recognized by the antibody did not show any varicosities on cellular processes in all these regions. By P8, the texture of the stain has turned markedly more granular, a pattern likely to reflect the formation of presynaptic endings. A predominantly granular distribution of GAP-43 has developed by P12. At that time, the staining intensity is markedly reduced compared to the levels of the newborn. By P16, the auditory brainstem nuclei have lost most of their GAP-43 immunoreactivity, but a distinct level of staining persisted into adulthood in all of them. This staining was restricted to boutons, which are thought to be presynaptic terminals. We conclude that a moderate but apparently relevant potential for plasticity is retained in these auditory structures. Should the patterns of neural signals, mediated by the inner ear, change during adulthood, the central structures appear to be able to respond with the formation of altered synaptic connectivity.

Transient Expression of Acetylcholinesterase in the Posterior Ventral Cochlear Nucleus of Rat Brain

“…On the basis of GAP-43 labeling, Horvath et al (1997) concluded that synapses in the cochlear nucleus are formed by about P8. The electron microscopic data in the present study support the conclusion that synapses are morphologically mature by P8.…”

GAP-43 in synaptic plasticity: molecular perspectives

“…59 In the auditory brainstem, high levels of GAP-43 protein are evident in all subdivisions of the cochlear nuclear complex and the superior olivary complex at PND0. 60 Between PND8 and PND12, the GAP-43 staining pattern in these regions became punctate, indicating the formation of presynaptic endings. By PND16, the auditory brainstem nuclei appear mostly devoid of GAP-43 immunoreactivity, with the exception of staining localized to presynaptic terminals.…”

“…By PND16, the auditory brainstem nuclei appear mostly devoid of GAP-43 immunoreactivity, with the exception of staining localized to presynaptic terminals. 60 In the cat visual cortex, phosphorylation of GAP-43 increased approximately 10-fold from PND1 to weeks 3-13 (the critical period of synaptic plasticity) then decreased to 2.5-fold of PND1 by week 51. 61 Protein quantification of GAP-43 in the cortex and hippocampus was elevated at PND14 and PND21 during an active period of synaptogenesis.…”

Nicotinic cholinergic intercellular communication: Implications for the developing auditory system

“…Peak expression before mature synapse formation (P0-P5) suggests either a non-synaptic role for 7 nAChRs or the early presence of synapses. Synapses at these early ages are not expected, because GAP-43, a marker of growth cones, is still heavily expressed (Horvath et al, 1997). In the nuclei of the lateral lemniscus and the lateral periolivary nucleus, peak expression (P15-20) coincides with a transitional maturation period after the onset of hearing.…”

“…There are no available data indicating when synapses are Wrst formed in the VCN, but it is probable that synapses are not present in the VCN at birth. DiVuse GAP-43 labeling before P8 in the rat suggests that growth cones are still predominant (Horvath et al, 1997).…”