Figure 4.

Calcium-Permeable AMPARs Mediate Glutamatergic Responses at Septo-habenular Inputs

(A and B) Immunohistochemical data demonstrated the presence of both GluA1 and GluA2 AMPAR subunits in the MHb (A). Nevertheless, electrically evoked AMPAR responses showed a large rectification index (B, right bar graph; the theoretical index [R.I.] for perfectly linear IV curves is shown by the dotted line, and values from each cell are depicted by points), suggesting the absence of GluA2 from postsynaptic densities under our recording conditions. Average EPSCs recorded at +50 mV (top) and −60mV (bottom) are illustrated for a typical cell on the left.

(C) Application of NASPM, a blocker of calcium-permeable AMPA conductances, rapidly and potently inhibited EPSCs.

(D) Two-photon calcium imaging experiments demonstrated that AMPAR activation triggers calcium elevations in MHb cell dendrites, which were blocked by NASPM. Quantification is depicted in the right bar graph. The time courses of the NASPM effect on calcium transients and EPSC amplitudes were similar (data not shown). Calcium increases were observed in several ROIs along dendrites (control, black; following NASPM, blue). However, rise times and amplitudes were largely heterogeneous, suggesting intracellular calcium diffusion from precise entry spots, probably identifying synaptic sites.

Pooled data are represented as mean ± SEM.