Table 1.

Methods for estimation of NPCs migration in the brain.

Method	Description of the method	Advantages	Limitations
Estimation of neuroblasts migration patterns in fixed brain slices.	In fixed brain slices signs of neuroblasts migration are observed: distribution of cells from the supposed place of origin to the supposed destination; orientation of chains of cells and cell processes in the direction toward the destination.	It is a non-invasive and simple research method that facilitates the estimation of cell migration in the brain at the time of animal euthanasia.	This approach facilitates the estimation of the direction of migration only of the cells migrating at the time of animal euthanasia. Furthermore, although the distribution of neuroblasts in the fixed brain slice describes the general direction of migration, it fails to prove the origins and direction of migration of each cell.
Local administration of antimitotic agents.	The Ara-C antimitotic agent is administered into a particular brain region to suppress neurogenesis in it.	The method facilitates the reduction or exclusion of any participation of a brain region in replenishment with neurons in another region.	The method is invasive and potentially causes adverse effects. The results of such experiments can be unequivocally interpreted only in the absence of any effects, i.e., when killing proliferating cells in one region doesn’t affect the number of new neurons in the other.
			Moreover, antimitotic drugs can diffuse in brain tissue from the region of injection to the remote brain areas. Thus, spatial specificity of antimitotic effect should be carefully verified.
Surgical separation of brain regions.	Surgical separation prevents migration from one brain region into another.	This method facilitates the exclusion of any participation of a brain region in replenishment with neurons in another region.	The method is invasive, and potentially causes adverse effects.
Local labeling of cells in the brain.	Local administration of stains or genetic vectors carrying the reporter gene. Alternatively, transgenic animals can be administered with special agents that induce expression of a reporter gene in them (tamoxifen or a genetic vector with the recombinase gene can serve as an inductor).	This method helps prove the origin of a particular neuron from a particular brain region. Moreover, the method is suitable for direct observation of cell migration.	The method is invasive, and potentially causes adverse effects.
Direct observation of cell migration in live brain slices.	Preliminary in vivo staining of neuroblasts, obtaining of live brain slices and detection.	The method facilitates a detailed observation of individual cell behavior.	The conditions in the live brain slice cannot be equal to the conditions in the live animal brain: cutting the brain into slices results in damage to many cells, and isolating a slice from the whole brain removes potential influences from other cells in the whole brain. Moreover, brain slices remain viable for quite a short time (usually studies last up to one day), which is not enough to observe the long-term fate of migrated cells.
Direct observation of in vivo cell migration.	Preliminary in vivo staining of neuroblasts and subsequent bioluminescent or MRI detection. Alternatively, two-photon microscopy through a cranial window.	The method facilitates the tracing of long-term cell migration in the live brain.	In general, the method has a low-resolution capacity, as it facilitates the observation of the migration of only large cell groups. However, a recently developed technique of intravital microscopy through a cranial window, in combination with two-photon microscopy, facilitates the tracing of individual cells deep within the brain tissue. Still, cranial window is a highly invasive approach.