Dr. Sengelaub et al., DENERVATION-INDUCED SPROUTING OF INTACT PERIPHERAL AFFERENTS INTO THECUNEATE NUCLEUS OF ADULT RATS, Brain research, 769(2), 1997, pp. 256-262
In adult monkeys with dorsal rhizotomies extending from the second cer
vical (C-2) to the fifth thoracic (T-5) vertebrae, cortex deprived of
its normal inputs regained responsiveness to inputs conveyed by intact
peripheral afferents from the face [T.P. Pens, P.E. Garraghty, A.K. O
mmaya, J.H. Kaas, E. Taub, M. Mishkin, Massive reorganization of the p
rimary somatosensory cortex after peripheral sensory deafferentation,
Science 252 (1991) 1857-1860]. It has been suggested that the extent o
f this massive topographic reorganization may be due to the establishm
ent of novel connections between intact afferents and neurons denervat
ed after dorsal rhizotomy [P.E. Garraghty, D.P. Hanes, S.L. Florence,
J.H. Kaas, Pattern of peripheral deafferentation predicts reorganizati
onal limits in adult primate somatosensory cortex, Somatosens. Motor R
es. 11 (1994) 109-117]. Using adult rats with comparably extensive dor
sal rhizotomies, we employed anatomical tracing techniques to address
this possibility. Subcutaneous hindpaw injections of horseradish perox
idase conjugated to either wheat germ agglutinin or cholera toxin subu
nit B revealed aberrant expansions of gracile projections into the cun
eate and, in one case, external cuneate nucleus within three months of
the deafferentation. It seems plausible that such modest sprouting of
ascending projections at the level of the brainstem may form function
al connections which, through divergence, ultimately drive a larger po
pulation of neurons in cortex. This new growth may well account for bo
th the substantial cortical reorganization observed in the 'Silver Spr
ing monkeys' [T.P. Pens, P.E. Garraghty, A.K. Ommaya, J.H. Kaas, E. Ta
ub, M. Mishkin, Massive reorganization of the primary somatosensory co
rtex after peripheral sensory deafferentation, Science 252 (1991) 1857
-1860] and the 'referred sensation' phenomena (see J.P. Donoghue, Plas
ticity of adult sensorimotor representations, Curr. Opin. Neurobiol.,
5 (1995) 749-754 for review) reported to follow proximal Limb amputati
ons in humans. (C) 1997 Elsevier Science B.V.