Rapid changes in ultrastructure during deafferentation‐induced dendritic atrophy

Abstract

This study describes qualitative and quantitative changes in dendritic ultrastructure during the rapid atrophy of nucleus laminaris (NL) dendrites following deafferentation. The dendrites of n. laminaris neurons in the chick auditory system are segregated into dorsal and ventral dendritic tufts, which receive spatially separated innervation from the ipsilateral and contralateral nucleus magnocellularis, respectively. We have previously shown that removing the input to the ventral side of NL results in the rapid atrophy of the ventral dendrites, whereas the nondeafferented dorsal dendrites of the same cells do not change in length. The ultrastructure of NL was examined in normal animals and after deafferentation. Changes in dendritic ultrastructure were not qualitatively apparent 4 hours after deafferentation. Between 12 and 48 hours the cytoplasm of the ventral dendrites became progressively more lucent, and a gap formed in the transition between the soma and ventral dendritic cytoplasm. Many of the dendrite tips, however, appeared normal even 2 days after deafferentation. Degeneration of dendrite plasma membrane was not visible until 2 days after deafferentation. On the other hand, quantitative measurements revealed a 30% decrease in microtubule density in the initial portion of the ventral dendrite by 4 hours, and a 50-60% decrease from 12 to 48 hours after deafferentation. Neurofilament density in the initial ventral dendrites decreased 50% by 12 hours, and 70% by 2 days after deafferentation. Many of the terminals of the severed afferents remained attached to the atrophying dendrite until 2 days after surgery, when they were in advanced stages of degeneration. Glia apparently were not involved in dendrite loss. The implications of these results on the role of cytoskeleton in the production and maintenance of dendritic shape are discussed.

Rapid regulation of microtubule-associated protein 2 in dendrites of nucleus laminaris of the chick following deprivation of afferent activity

“…In support of this idea, changes in MAP2 immunoreactivity appear to be associated with changes in microtubules in deafferented dendrites. A quantitative analysis reported a 30-60% decrease in microtubules density in the initial portion of the ventral dendritic between 4-48 hours following XDCT transection (Deitch and Rubel, 1989). This time course is comparable to the changes in MAP2 immunoreactivity reported by the current study (see Fig.…”

“…We did not perform statistical analyses on the data from animals with XDCT transection because the n's were too small. These experiments were included only to determine if the changes in MAP2 antibody reacted dendrites following this manipulation are similar to our previous data using a variety of other techniques for measuring dendritic change (Benes et al, 1977;Dietch and Rubel, 1984;1989;Sorensen and Rubel, 2006). Clearly the results are similar.…”

“…After cochlea removal the cochlear ganglion cells and NM neurons begin to die about 18-24 hours after the surgery and by 24 hours about 30% NM neurons have degenerated (Rubel et al, 1990). After XDCT transection, the afferent terminals from NM on the ventral NL dendrites do not show any atrophic changes for at least the first 4 hours, and then they begin to degenerate (Deitch and Rubel, 1989). Fourteen animals received unilateral cochlea removal, 3 survived 1h, 2 survived 3h, 5 survived 6h, 2 survived 14h, and 2 survived Changes in the pattern and intensity of MAP2 immunostaining following either manipulation were positively correlated with post-surgery survival time and varied with the location within the nucleus.…”

Rapid seasonal-like regression of the adult avian song control system

“…In patients afflicted with schizophrenia, neuropil degeneration is correlated with an increase in neuronal density and decrease in somatic area (54)(55)(56) and is regulated by apoptotic mechanisms (57). Neuropil degeneration can occur quickly; dendrites of dentate gyrus neurons show signs of degeneration within hours of status epilepticus (58), and deafferentation leads to rapid atrophy of dendritic arbors within hours (59)(60)(61)(62). In hibernating ground squirrels, the dendritic structure and somatic area of neurons in multiple brain areas rapidly regress in response to temperature-induced torpor on the order of hours to days, but there is no evidence that torpor of this form is driven by changes in circulating hormone levels (63).…”

Modeling coincidence detection in nucleus laminaris

“…The soma is modeled as a truncated ellipsoid of length and diameter 15 μm (Smith and Rubel 1979;Smith 1981;Parks et al 1983;Deitch and Rubel 1989b). Dendritic diameter is 4 μm, and dendritic length is a function of position along the tonotopic axis (Rubel and Parks 1975;Smith and Rubel 1979), (1) which is simply a linear function of logarithmic frequency whose smallest length (20 μm) occurs at and above ~ 2500 Hz, and whose longest length (400 μm) occurs at and below 3 00 Hz.…”