L-N-iminoethyl-lysine after experimental brain trauma attenuates cellular proliferation and astrocyte differentiation

BACKGROUND: The effects, and thereby possible benefit, of inhibiting nitric oxide synthases (NOS) after brain injury are not fully understood. Nitric oxide (NO) has both neuroprotective and damaging features, and its effect on the cellular proliferation and differentiation that occurs in response to traumatic brain injury (TBI) is largely unknown. This study was undertaken to investigate the effects of the selective inducible NOS-inhibitor, L-N-iminoethyl-lysine (L-NIL), on proliferating cell populations in rat brain areas with self-renewing capacity.

METHODS: A brain contusion was produced using a weight-drop model in rats. Animals received treatment with L-NIL or saline, and were killed after 6 days. Brain sections were stained with a cell marker of proliferation, Ki67, to detect dividing cells in the hippocampus, perilesional zone and the subventricular zone (SVZ).

RESULTS: A significant decrease of proliferating cells was seen in the SVZ bilaterally in L-NIL-treated animals compared to controls. Hippocampal proliferation showed a tendency to decrease in L-NIL-treated animals that did not reach statistical significance. Perilesional proliferation was equal in the treatment group and controls. The percentage of proliferating GFAP expressing cells was, however, lower in L-NIL-treated animals. The proliferating cell populations were predominantly immunoreactive for GFAP, while a smaller population was immunoreactive for Nestin. The inhibition of inducible NOS with L-NIL attenuated the level of cellular proliferation and influenced the differentiation of astrocytes at 6 days after experimental brain contusion.

CONCLUSIONS: Our results confirmed that reactive glial cells dominated the proliferating cell population after TBI and suggested that NO-regulated mechanisms are relevant for post-traumatic cellular proliferation and differentiation, since NO inhibition decreased the number of proliferating cells in the SVZ and the proportion of proliferating cells expressing GFAP, a marker of glial proliferation.