Adarsh K. Gulati

The influence of cultured Schwann cells on regeneration through acellular basal lamina grafts

Acellular basal lamina grafts have been shown to be less immunogenic in comparison to cellular grafts, but possess a limited potential for supporting axonal regeneration through them. The present study describes the effect of cultured Schwann cells on enhancing regeneration through acellular grafts. 2 cm long acellular grafts, and in vitro Schwann cell populated acellular grafts were used to repair a surgically created gap in the host peroneal nerve. The transplants were analyzed at 1, 2, 4 and 8 weeks to determine their ability to support axonal regeneration. Host axonal regeneration through Schwann cell cocultured acellular grafts occurred rapidly and was significantly better as compared to non-cultured acellular grafts. The results demonstrate a beneficial effect of Schwann cell culture pretreatment on regeneration through acellular grafts and an improved recovery of the target muscle. The procedure of first preparing acellular grafts with subsequent coculture with Schwann cells offers a novel approach for the repair of injured nervous tissue.

Nerve growth factor promotes CNS cholinergic axonal regeneration into acellular peripheral nerve grafts

Peripheral nerve grafts promote vigorous regeneration of adult mammalian CNS axons. Elimination of nerve-associated cells by freeze-thawing abolishes this promoting quality, possibly by creating inhibitory cellular debris and/or destroying the production of stimulatory factors by living Schwann or other cells. Here, debris-free acellular peripheral nerve segments placed between the disconnected septum and the hippocampal formation acquired almost no cholinergic axons after 1 month. However, such acellular nerve grafts treated before implantation with purified beta-nerve growth factor (NGF) contained nearly as many longitudinally oriented cholinergic axons as did fresh cellular nerve grafts. These results suggest that (i) NGF is required for the regeneration of adult CNS cholinergic axons into nerve grafts and (ii) an important function of living cells within peripheral nerve may be the production of neuronotrophic factors such as NGF.

The effect of X-irradiation on skeletal muscle regeneration in the adult rat

Muscle regeneration was induced by transplanting the extensor digitorum longus (EDL) muscle in adult rats to examine the effect of X-irradiation on muscle regeneration. The EDL muscles were removed, irradiated with X-rays to administer 650 R, 2,000 R or 10,000 R, and transplanted into the original animal and location. Muscles from non-irradiated control group and each irradiated group were analyzed morphologically at 4, 7, 14 and 30 days post-transplantation. The regeneration pattern in the non-irradiated and 650-R irradiated muscles was similar. A majority of myofibers underwent degeneration followed by regeneration from the precursor myosatellite cells. The myosatellite cells proliferated, differentiated into myoblasts and then fused to form myotubes and myofibers. Muscles exposed to 2,000 R underwent initial degeneration and myosatellite cell activation, however, considerably fewer myotubes regenerated in these muscles. In muscles exposed to 10,000 R, again myofiber degeneration and myosatellite cell activation was evident, but these cells remained undifferentiated and did not fuse to form myotubes. These results show a dose-dependent inhibition in muscle regeneration due to irradiation.

Peripheral nerve regeneration through short- and long-term degenerated nerve transplants

The present study was designed to compare regenerative potential of normal and degenerated nerve grafts. Peripheral nerves in rats were induced to undergo in situ degeneration for a period of 6 weeks, 3, 6 and 12 months. During early phase of denervation the myelin and axons degenerated and were absorbed. With prolonged denervation (i.e. 12 months), such nerves were reduced in size and exhibited extensive fibrosis. A 2 cm long segment of the degenerated nerve was transplanted in an surgically created gap in the host peroneal nerve to evaluate their regeneration supporting ability. Regeneration of host axons occurred rapidly through nerves degenerated for a period up to 3 months. The extent of regeneration was compromised in 6-month degenerated nerve group, and was significantly reduced in the 12-month degenerated nerve grafts. These results show that with extended degeneration interval, the regeneration supporting ability of nerves is compromised. It is concluded that nerve repair should not be excessively delayed in order to compromise recovery.

Chronic spinal cord transection does not affect peripheral nerve regeneration.

Spinal cord transection is known to cause progressive changes in motor neurons and hind limb muscles. In the present study, regeneration of the peroneal nerve was examined in rats 25 weeks after a T9 spinal cord transection. Successful regeneration and innervation of the target muscle was observed after crush injury to the nerve in the spinal cord transected animals. It is concluded that the ability of peripheral nerve to regenerate remains preserved after spinal cord injury.