Figure 4. Decreased NMDAR-mediated [Ca²⁺]_i transients in DRG neurons from Cre+ mice.

DRG neurons from Cre+ and Cre− mice were placed in primary culture and loaded with Fura-2. [Ca²⁺]_i increases in small to medium size (<40 μm diameter) neurons were measured in response to short (4 sec) application of 250 μM NMDA and 10 μM glycine in Mg²⁺-deficient Hank’s buffer. As an internal control we also quantified [Ca²⁺]_i responses to subsequent addition of 10 μM capsaicin (CAP). Traces on the left are representative of the responses of two neurons from Cre− mice, one of which responded to capsaicin (top trace), while the other did not (lower trace). The response of neurons from Cre+ mice to NMDA and glycine was similar to that of Cre− mice, except there were significantly fewer neurons that responded to NMDA and the peak [Ca²⁺]_i response of those that did respond was smaller. The bar graph on the right shows the peak [Ca²⁺]_i response of 38 neurons from Cre− and 12 neurons from Cre+ mice (t₄₇ = 3.828, P=0.0004, Welch-corrected t-test). Values in parenthesis inside the bars indicate the portion of neurons that responded with a detectable increase in [Ca²⁺]_i (≥10 nM).There was no significant difference between the 2 groups in the frequency (~50%; 46 of 81 neurons from Cre+ mice, 29 of 63 neurons from Cre− mice) or magnitude (~200 nM) of the response to subsequent application of 10 μM capsaicin.