Jp. Golden et al., DEVELOPMENT OF TERMINALS AND SYNAPSES IN LAMINAE-I AND LAMINAE-II OF THE RAT MEDULLARY DORSAL HORN AFTER INFRAORBITAL NERVE TRANSECTION AT BIRTH, Journal of comparative neurology, 383(3), 1997, pp. 339-348
Infraorbital nerve damage at birth kills neurons and alters anatomical
, physiological, and biochemical properties of surviving cells in all
portions of the trigeminal brainstem complex, with the exception of la
minae I and II of the medullary dorsal horn. The resiliency of laminae
I and II may be due to rapid terminal sprouting and reactive synaptog
enesis in this region. To test this hypothesis, quantitative electron
microscopy revealed the types and numbers of terminals, synapses, and
degenerating and growth cone-like profiles in the left laminae I and I
I at 1, 4, 17, and 90 days after left infraorbital nerve section. Cont
rol data were derived from normal newborns and from the right laminae
I and II and the left infraorbital nerve of every experimental animal.
Deafferented laminae I and II contained a median of 11.7, 8.2, 21.8,
and 38.2 synapses/100 mu m(3) on days 1, 4, 17, and 90, respectively.
At corresponding ages, there were 17.1, 19.4, 36.2, and 32 terminals;
14.4, 4.2, 5.1, and 0.3 degenerating profiles; and 4.6, 2.2, 0.1, and
0 growth cone-like profiles/100 mu m(2). Significant differences from
the control right side are: 1) The percentage area occupied by termina
ls is less on days 1 and 17; 2) terminal density does not increase fro
m day 0 to day 4 as it does on the control side; 3) the density of deg
enerating profiles is higher on day 17; 4) growth cones are less dense
on days 4 and 17; and 5) synapse density is lower on days 1 and 4. Ax
on number in the infraorbital nerve was highly predictive of terminal
and synapse densities in deafferented laminae I and II at all ages. Th
us, in laminae I and II, 1) the time course and nature of development
are altered by deafferentation at birth; 2) reorganization of terminal
s and synapses occurs within a day of the lesion; 3) by day 90, there
are no remaining lesion effects; and 4) the status of the injured nerv
e predicts central terminal and synapse densities. These are signs of
injury-induced transganglionic degeneration and sprouting. The source
of the latter is unknown, although areal fraction data suggest that ''
replacement'' terminals may not be of primary afferent origin. (C) 199
7 Wiley-Liss, Inc.