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. Author manuscript; available in PMC: 2012 Jun 26.
Published in final edited form as: Neuron. 2011 Jun 23;70(6):1128–1142. doi: 10.1016/j.neuron.2011.04.027

Figure 3. Activity-Dependent Elimination of Inactive DG Axons in Two tTA Lines that Express tTA in Different Numbers of DG Neurons.

Figure 3

(A) Developmental expression patterns of tTA in the DG of two tTA lines, DG-S and DG-A. Expression patterns were examined by mating the DG-S and DG-A mouse with the nls-lacZ mouse. LacZ-stained horizontal sections between P15 and P30 are shown. Nuclei of tTA-expressing cells are stained in blue. In DG-S::nls-lacZ mice less than half of dentate neurons in the granule cell layer (GCL) express tTA, while in DG-A::nls-lacZ mice almost all dentate neurons do. Between P15 and P30, the percentage of tTA-expressing cells in the GCL was not changed in either transgenic mouse. ML, molecular layer.

(B) Immunostaining of DG sections from DG-S::nls-lacZ and DG-A::nls-lacZ mice for β-gal (green) and NeuN (red); nuclear DAPI staining is shown in blue. Pictured areas correspond to the boxed areas in (A). β-gal positive cells in the DG of both bitransgenic mice are NeuN positive, indicating that they are mature neurons. Scale bar is 50 μm.

(C) Percentage of β-gal positive neurons in the DG of DG-S::nls-lacZ and DG-A::nls-lacZ mice. Bars are mean ± SEM. Data are from 8 (DG-S) and 4 (DG-A) mice.

(D and E) Evoked fEPSPs were recorded in acute slices from CA3 of DG-A::TeTxLC-tau-lacZ, DG-S::TeTxLC-tau-lacZ, and control mice (P15–P17). (D) Sample traces of fEPSP recordings. (E) Input-output curves. Input-output relationships were measured by varying the stimulus input intensity and measuring the fEPSP slope. 32 slices from DG-A::TeTxLC-tau-lacZ, 22 slices from DG-S::TeTxLC-tau-lacZ, and 52 slices from control mice. Each was from at least 5 mice. Relative to control mice, the fEPSP slope was decreased by ~80% and ~44% in the DG-A::TeTxLC-tau-lacZ and DG-S::TeTxLC-tau-lacZ mice, respectively.

(F and G) Developmental elimination of inactive DG axons. DG-S (F) and DG-A (G) mice were mated with TeTxLC-tau-lacZ mice to inactivate tTA-expressing neurons. Horizontal sections of the hippocampus from P12 to P30 were lacZ-stained. In both bitransgenic mice, inactive axons from the DG neurons still projected to CA3 by P12 (F and G). In DG-S::TeTxLC-tau-lacZ mice, in which a moderate number of DG neurons express TeTxLC, inactive axons were eliminated by P25 (F). In DG-A::TeTxLC-tau-lacZ mice, in which almost all DG neurons are inactivated, inactive axons were also eliminated by P25 (G).

(H) Quantification of the lacZ-staining intensity in the stratum lucidum layer of CA3 from P12 to P25. Data are shown as percentage of corresponding P12 mice. Data are mean ± SEM. The numbers of mice analyzed were: DG-A::TeTxLC-tau-lacZ, P12, 6 mice; P15, 5 mice; P20, 5 mice; P25, 5 mice; DG-S::TeTxLC-tau-lacZ, P12, 5 mice; P15, 5 mice; P20, 5 mice; P25, 5 mice.

(I and J) Maintenance of lacZ-expressing DG axons in DG-A::tau-lacZ (no TeTxLC) mice during development. (I) A horizontal section of the hippocampus from P25 DG-A::tau-lacZ mice was lacZ -stained. Active axons from DG neurons remained in CA3 at P25. (J) Horizontal sections from P15 and P23 DG-A::tau-lacZ mice were immunostained with the anti-β-gal antibody, and the staining intensity in the hilus was quantified. Intensities are normalized against the intensity of P15 mice. Bars are mean ± SEM. Data are from 5 mice.