Transient effects of nerve injury on estimates of sensory neuron number in juvenile bullfrog

Abstract

The effect of lumbar spinal nerve (SN) transection on estimates of neuron number was investigated in the dorsal root ganglia (DRGs) of juvenile bullfrogs (Rana catesbeiana). SN8 and SN10 were transected on one side, and SN9 was left intact. Two weeks after nerve injury, estimates of neuron number in DRG8 and DRG10 on both the operated and unoperated sides were more than twice the estimates obtained from control animals. Neuron number in the uninjured DRG9 was also elevated relative to that of control animals. Eight weeks after axotomy, differences in neuron number were less apparent. The mean cross‐sectional area of DRG neurons was reduced 2 weeks after nerve injury in all DRGs. The decrease in mean area was the result of the addition of neurons to the smallest size classes. These data are discussed in the context of previous results showing that neurons are added as juvenile frogs grow to adult size (St. Wecker and Farel [1994] J. Comp. Neurol. 342:430–438). This addition results from the maturation of a population of incompletely differentiated neurons (Meeker and Farel [1997] J. Comp. Neurol. 389:569–576). The present results suggest that axotomy precipitates differentiation of these incompletely differentiated neurons, perhaps as a compensatory response to nerve injury. J. Comp. Neurol. 410:171–177, 1999. © 1999 Wiley‐Liss, Inc.

Generation of New Neurons in Dorsal Root Ganglia in Adult Rats after Peripheral Nerve Crush Injury

“…The first evidence for the existence of neurogenesis and, hence, the presence of neural progenitors in DRG was based on counting methods [ 2 , 3 , 8 , 43 ]. Although the findings were encouraging, the wide range of results obtained from different groups, due to different methods used to quantify neurons [ 13 ], never clarified whether plasticity actually occurs in vivo [ 8 , 17 ].…”

Neurogenesis in the lamprey central nervous system following spinal cord transection

“…Unlike the case in lamprey, ependymal cells in the mouse spinal cord do not appear to generate neurons after injury, as judged from NeuN staining (Barnab e-Heider et al, 2010). However, injury-induced neurogenesis has been seen in other CNS areas: the rat hippocampus (Dash et al, 2001;Farel and Boyer, 1999;Kernie et al, 2001;Snyder et al, 2001;Yagita et al, 2001), the olfactory epithelium (Barber, 1982), and the neocortex (Magavi and Macklis, 2001). Neurogenesis also occurs in the injured brains of lizards (Font et al, 1997(Font et al, , 2001Ramirez-Castillejo et al, 2002) and among fish retinal cone photoreceptors (Cameron and Easter, 1995).…”

Stereological and Allometric Studies on Neurons and Axo-Dendritic Synapses in Superior Cervical Ganglia

“…On the other hand, the increase in neuron number is not always attributable to neurogenesis, but may also be the outcome of late maturation or incomplete differentiation of nerve cells (Ciaronia et al, 2000;Farel, 2003;Miolan and Niel, 1996). In juvenile bullfrogs, dorsal root ganglion (DRG)-a sensory ganglion-houses a population of immature, incompletely differentiated neurons that can be induced to differentiate into a mature form in response to injury (Farel and Boyer, 1999). Indeed, new DRG neurons derive mostly from differentiation rather than from Simple histogram (bar chart) showing the total number of superior cervical ganglion (SCG) neurons across a catalogue of different mammalian species: rats, guinea pigs, preás, pacas, cutias, sheep, capybaras, and horses.…”