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. 2005 Feb 9;102(8):3064–3069. doi: 10.1073/pnas.0404712102

Fig. 4.

Fig. 4.

Circumstantial evidence for axonal delivery of NT4 in corticotectal cocultures. (A) NPY expression remained low in activity-deprived VC cultures (VC deprived). Even resumption of activity failed to increase the NPY expression (20 DIV under 10 mM Mg2+ and subsequently 10 DIV recovery in 2 mM Mg2+; VC recovery). (B) The cortical explant of corticotectal cocultures displays low numbers of NPY neurons after 15-DIV activity deprivation and transfection with EGFP from 20 to 25 DIV. (C) After NT4 transfection of the tectal explant, NPY neuron numbers increased in the cortical explant. (D) After BDNF transfection of the tectal explant, NPY neuron numbers increased in the cortical explant, and BDNF was more effective than NT4 (see A). (E) DiI injection into the tectal explant of a corticotectal coculture activity-deprived for 20 DIV. Despite the absence of activity, layer V pyramidal cells with apical dendrites reaching layer I were retrogradely labeled, suggesting that their morphological differentiation was not impaired (19). White lines, borders of the cortical explant; black line, border of the tectal explant. Roman numerals mark cortical layers. White matter is oriented downward. (F and G) The cortical expression of NT4 and BDNF mRNA was analyzed by RT-PCR. (F) The NT4 mRNA expression was not altered after tectal transfection with BDNF or NT4 plasmids. Transfection with EGFP plasmids in 25-DIV spontaneously active cultures and in recovery cultures (15 DIV deprived, then 10 DIV active; level was set to 1 for normalization) were used as controls, and the initial activity deprivation did not alter cortical NT4 expression. (G) The same was observed for cortical BDNF mRNA expression in the control conditions, and cortical BDNF mRNA was not changed after tectal NT4 transfection. However, cortical BDNF mRNA expression increased after tectal BDNF transfection. EGFP, transfection with EGFP plasmid alone; BDNF, transfection with EGFP+BDNF plasmid; NT4, transfection with EGFP+NT4 plasmid. (Scale bars: 300 μm.) **, P < 0.01; ***, P < 0.001.