The structure and density of dendritic spines is a crucial determinant of neuronal input-output transformation. Several types of dendritic spines exist which are named in accordance to their morphology (thin, mushroom, stubby, branched).The gain, loss, and morphological remodeling of dendritic spines is associated with learning and memory abilities and could therefore explain impairments in cognitive functions through magnetic fields as partially found in previous studies (e. g. Sienkiewicz et al., Cui et al.).
Rats were divided into four groups (n=5 per group): 1.) exposure for 14 days, 2.) sham exposure for 14 days, 3.) exposure for 28 days and 4.) sham exposure for 28 days. Afterwards, the rats were killed and the brain was removed.
In the dendrites of stellate neurons and the basal dendrites of exposed rats (14 and 28 days), a significantly reduced dendritic spine density was found in comparison to the control group. These alterations were due to the loss of the thin and branched dendritic spines. For the stellate neurons, the exposure led to a slight but significant increase in the density of stubby dendritic spines after 28 days, while it did not affect the density of mushroom dendritic spines at the same time. In the basal dendrites of pyramidal cells from exposed rats, a significant decrease in the mushroom spine density was observed after 28 days compared to control group, while the stubby spine density was significantly reduced after 14 days, but partially restored after 28 days. In the apical dendrites of pyramidal cells, the exposure induced a significant reduction in the spine density after 28 days compared to the control group.
The authors conclude that the exposure to extremely low frequency magnetic fields changed the density and morphology of dendritic spines of dendrites in the brain of rats and that these alterations could lead to an impairment in cognitive functions.