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. Author manuscript; available in PMC: 2011 Feb 11.
Published in final edited form as: Neuron. 2010 Feb 11;65(3):385–398. doi: 10.1016/j.neuron.2010.01.024

Figure 2. Critical period maturation of glutamate receptor signaling at thalamocortical synapses is altered in FMRP knockout mice.

Figure 2

(Ai) Cartoon representation of para-coronal thalamocortical slice depicting placement of the recording electrode in the layer IV barrels and the extracellular stimulating electrode in the ventrobasal thalamus (VB) (H: hippocampus; IC: internal capsule; C: caudate). (Aii) Bright field image of the thalamocortical slice and (Aiii) image of the barrels in layer IV. Calibration: 250μm (Aiv) Higher magnification image of a spiny stellate neuron in layer IV (SS: spiny stellate; IN: interneuron. Calibration: 25μm (Bi) Time course of development in NMDA/AMPA ratio at thalamocortical synapses in wildtype mice (Fmr1+/y). Relatively high NMDA/AMPA ratio is observed at P4 when synaptic contribution of NMDA receptors is large. Over the course of the first week NMDA/AMPA ratio declines in wildtype mice and then stabilizes at the close of the critical period (depicted by shaded area). (Bii) Representative EPSC recordings from wildtype Fmr1+/y mice at P4 and P7. AMPA receptor mediated EPSCs were measured as the peak current at −70mV and the NMDA component was measured by depolarizing the cell to +40mV and measuring the mean current over a 2.5ms window, 60ms after the onset of the outward current. At this time point the contribution of the outward AMPA component is negligible and the measured current is mediated solely by NMDA receptors (Marie et al., 2005). Calibration: 20pA, 100ms (Ci) Time course of development of NA ratio in Fmr1−/y mice. NA ratio at P4 is significantly lower than in Fmr1+/y mice (0.5 ± 0.1, n = 13, p = 0.0003). Over the critical period NMDA/AMPA ratio increases to maximal level at P7 (1.5 ± 0.2, n = 18, p = 0.0007) and then reverts to similar levels as wildtype recordings beyond this developmental timepoint. (Cii) Representative EPSC recordings from Fmr1−/y mice at P4 and P7 recorded from spiny stellate neurons voltage clamped at −70mV and +40mV. Calibration: 10pA, 100ms.