Biology session

Fractalkine is a signal molecule that plays a role in the immune system and in the central nervous system (CNS) in cell migration and cell-cell communication. CX3CR1 (fractalkine receptor) is important for sustaining normal activity of microglia in the brain, and of the monocytes, dendritic and NK cells, in the periphery.

In our experiments transgenic mice (C57Bl6 background), in wich a certain part of the CX3CR1 gene was replaced by a green fluorescent protein (GFP) were used. Heterozygote CX3CR1(+/−) animals express normal fractalkine receptor, whereas homozygote CX3CR1(−/−) mice do not not have functional receptor, while cells expressing the fractalkine receptor appear in green in both genotypes. Previous results indicated that CX3CR1(−/−) mice are resistant in ischemic brain damage. The aim of our present experiments was to investigate effects of insulin-induced hypoglycemia and to test glucose tolerance and behavior in mice with deficient fractalkine signaling. We observed that after overnight starvation CX3CR1(−/−) animals have lost less body weight and their blood glucose levels were higher than in fasted C57Bl6 control animals. Intraperitoneal injection of insulin resulted in a further drop of blood glucose in both mouse strains, however, the degree of decline was smaller in fractalkine receptor- deficient animals. Using c-Fos based functional anatomical mapping strategy we have identified neuronal activation patterns in the brain of control, fasted and fasted plus insulin-injected animals. c-fos is an immediate-early gene that is expressed rapidly and transiently within the challenged neurons. On the frontal sections from perfusion fixed mouse brain we have revealed c-Fos protein by means of indirect immuncytochemistry and c-Fos positive profiles were counted in the paraventricular nucleus of the hypothalamus (PVN). In this region, we found more c-Fos positive neurons in homozygous CX3CR1(−/−) fed control and fasted males than in control and in starving wild-type (C57Bl6) mice. Fasted plus insulin-injected animals from both mouse strain we observed more c-Fos positive neurons, than in control and fasted mice, but we did not detect difference in fractalkine-receptor deficient and wild-type animals.

We compared behaviour of heterozygota CX3CR1(+/−) males with C57Bl6 males in two standard anxiety tests: open field and elevated plus maze (EPM). In open field test in the periphery and in the centre of field spent time% respectively in EPM test in open arm and in closed arm of the maze indicate the degree of anxiety. We did not find significant difference in the two mouse strain (p-value < 0.05).

Our results shows that the fractalkine-fractalkine receptor system participate in regulate of central and peripherial mechanism.