Cortical diffusible factors increase MAP-2 immunoreactive neuronal population in thalamic cultures

Area of Science:

• Neuroscience
• Developmental Biology
• Cell Biology

Background:

• Previous studies show embryonic day (E) 16 frontal cortex grafts attract axons from ventrolateral/ventromedial (VL/VM) thalamic nuclei in postnatal rats.
• This suggests potential maturation-promoting signals from the cortex to VL/VM thalamic cells.

Purpose of the Study:

• To investigate the maturation-promoting activity of cortical tissue on VL/VM thalamic cells in vitro.
• To determine if embryonic and early postnatal cortex influences thalamic neuron differentiation and neurite outgrowth.

Main Methods:

• Primary cultures of postnatal day (P) 0-P1 rat VL/VM thalamic cells were established.
• Thalamic cells were co-cultured with E16 or P5 frontal/occipital cortex explants on microporous membranes for 7 days.
• Cell populations, neuronal differentiation (MAP-2 staining), and neurite morphology were analyzed.

Main Results:

• E16 cortex co-culture significantly increased the percentage of MAP-2 positive neurons, indicating enhanced neuronal differentiation.
• E16 cortex also increased the mean number of neurites per neuron without affecting neuritic length.
• P5 cortex showed a lesser increase in neuronal differentiation and promoted neurite elongation but not number.

Conclusions:

• Diffusible molecules from embryonic and early postnatal cortex promote in vitro maturation of VL/VM thalamic neurons.
• These findings extend the known survival-promoting effects of cortical tissue to include maturation-promoting activities.
• The cortex releases factors that influence thalamic neuron development, independent of areal specificity at the embryonic stage.