The role of GLU K5-containing kainate receptors in entorhinal cortex gamma frequency oscillations

Abstract

Using in vitro brain slices of hippocampus and cortex, neuronal oscillations in the frequency range of 30-80 Hz (gamma frequency oscillations) can be induced by a number of pharmacological manipulations. The most routinely used is the bath application of the broad-spectrum glutamate receptor agonist, kainic acid. In the hippocampus, work using transgenic kainate receptor knockout mice have revealed information about the specific subunit composition of the kainate receptor implicated in the generation and maintenance of the gamma frequency oscillation. However, there is a paucity of such detail regarding gamma frequency oscillation in the cortex. Using specific pharmacological agonists and antagonists for the kainate receptor, we have set out to examine the contribution of kainate receptor subtypes to gamma frequency oscillation in the entorhinal cortex. The findings presented demonstrate that in contrast to the hippocampus, kainate receptors containing the GLU(K5) subunit are critically important for the generation and maintenance of gamma frequency oscillation in the entorhinal cortex. Future work will concentrate on determining the exact nature of the cellular expression of kainate receptors in the entorhinal cortex.

Figure 1

Gamma frequency oscillations can be induced in layer III of the MEC by application of kainate. (a) Extracellular field recordings showing 1 second epochs of activity (i) in control setting, (ii) following application of 400 nM kainate, and (iii) following application of 10 μM NBQX in the presence of 400 nM kainate. Scale bar represents 200 milliseconds and 100 μV.

Figure 2

Antagonizing GLU_K5-containing KARs with UBP302 inhibits kainate-driven gamma frequency oscillations in the MEC. (a) Extracellular field recordings showing 1 second epochs of activity (i) in the presence of 400 nM kainate, (ii) following 10 μM UBP302 application, and (iii) during a washout period into 400 nM kainate. (b) Pooled power spectra (n = 9) produced from 60 second epochs of extracellular field recorded data, showing a control recording (black), a recording in the presence of 400 nM kainate (blue), application of 10 μM UBP302 (green), and washout back into 400 nM kainate (red). Scale bar represents 200 milliseconds and 100 μV.

Figure 3

Preincubation of slices in UBP302 inhibits the ability of the MEC network to produce kainate-driven gamma frequency oscillations. (a) Extracellular field recordings showing 1 second epochs of activity (i) following preincubation with 10 μM UBP302, (ii) following application of 400 nM kainate onto preincubated slices, and (iii) during a washout period into 400 nM kainate. (b) Pooled power spectra (n = 11) produced from 60 second epochs of extracellular field recorded data, showing a control recording (black), a recording following 10 μM UBP302 preincubation (blue), 400 nM kainate application following preincubation (green), and washout into 400 nM kainate (red). Scale bar represents 200 milliseconds and 100 μV.

Figure 4

Activation of GLU_K5-containing KARs can induce gamma frequency oscillations in the MEC. (a) Extracellular field recordings showing 1 second epochs of activity in a control setting (i) following application of 1 μM, (ii) 2 μM (iii), and 5 μM ATPA (iv). (b) Pooled line graphs (n = 10) demonstrating the effects of varying ATPA concentration on (i) frequency, (ii) area power, and (iii) peak amplitude of gamma oscillations in the MEC. Scale bar represents 200 milliseconds and 100 μV.

Figure 5

ATPA-generated gamma frequency oscillations in the MEC are reduced by application of the GLU_K5 selective antagonist, UBP302. (a) Extracellular field recordings showing 1 second epochs of activity (i) in the presence of 5 μM ATPA and (ii) following application of 10 μM UBP302. (b) Pooled power spectra (n = 4) produced from 60 second epochs of extracellular field recorded data, showing a control recording (black), recording in the presence of 5 μM ATPA (blue), and application of 10 μM UBP302 (green). Scale bar represents 200 milliseconds and 100 μV.

Figure 6

Blocking homomeric GLU_K5-containing KARs significantly reduces kainate-driven gamma frequency oscillations in the MEC. (a) Extracellular field recordings showing 1 second epochs of activity (i) in the presence of 400 nM kainate and (ii) following application of 10 μM NS3763. (b) Pooled power spectra (n = 8) produced from 60 second epochs of extracellular field recorded data, showing a control recording (black), recording in the presence of 400 nM kainate (blue), application of 10 μM NS3763 (green), and a washout back into 400 nM kainate (red). Scale bar represents 200 milliseconds and 100 μV.

Figure 7

Blocking homomeric GLU_K5-containing KARs effectively reduces power and amplitude of ATPA-generated gamma frequency oscillations in the MEC (a) Extracellular field recordings showing 1 second epochs of activity (i) in the presence of 5 μM ATPA and (ii) following application of 15 μM NS3763. (b) Pooled power spectra (n = 4) produced from 60 second epochs of extracellular field recorded data, showing a control recording (black), recording in the presence of 5 μM ATPA (blue), and application of 15 μM NS3763 (green). Scale bar represents 200 milliseconds and 100 μV.

Figure 8

Carbachol-induced gamma frequency oscillations are not dependent on GLU_K5-containing KARs. (a) Extracellular field recordings showing 1 second epochs of activity (i) in the presence of 20 μM carbachol, (ii) following 10 μM UBP302 application, and (iii) during a washout period into 20 μM carbcahol. (b) Pooled power spectra (n = 6) produced from 60 second epochs of extracellular field recorded data, showing a control recording (black), recording in the presence of 20 μM carbachol (blue), application of 10 μM UBP302 (green), and washout back into 20 μM carbachol (red). Scale bar represents 200 milliseconds and 100 μV.