Neuregulin-1 modulates hippocampal gamma oscillations: implications for schizophrenia

Abstract

Alterations in gamma-frequency oscillations are implicated in psychiatric disorders, and polymorphisms in NRG-1 and ERBB4, genes encoding Neuregulin-1 (NRG-1) and one of its receptors, designated ErbB4, are associated with schizophrenia. Here we show that NRG-1 selectively increases the power of kainate-induced, but not carbachol-induced, gamma oscillations in acute hippocampal slices. NRG-1beta is more effective than NRG-1alpha, a splice variant with lower affinity for ErbB receptors, and neither isoform affects the network activity without prior induction of gamma oscillations. NRG-1beta dramatically increases gamma oscillation power in hippocampal slices from both rats (2062 +/- 496%) and mice (710 +/- 299%). These effects of NRG-1beta are blocked by PD158780, a pan-specific antagonist of ErbB receptors, and are mediated specifically via ErbB4 receptors, because mice harboring a targeted mutation of ErbB4 do not respond to NRG-1. Moreover, we demonstrate that 50% of gamma-amino butyric acidergic parvalbumin (PV)-positive interneurons, which heavily contribute to the generation of gamma oscillations, express ErbB4 receptors. Importantly, both the number of PV-immunoreactive interneurons (-31%) and the power of kainate-induced gamma oscillations (-60%) are reduced in ErbB4 knockout mice. This study provides the first plausible link between NRG-1/ErbB4 signaling and rhythmic network activity that may be altered in persons with schizophrenia.

Figure 1.

Modulation of kainate-induced gamma oscillations by NRG-1 in rat hippocampal slices. (A–C) Representative sample traces (top) and power spectra (bottom) of kainate-induced gamma oscillations in rat slices (black: control; red: NRG-1 treated); note difference in scales. (A) NRG-1β (n = 6; P = 0.015) and (B) NRG-1α (n = 4; P = 0.031) significantly increase the power of kainate-induced gamma oscillations, whereas (C) preincubation with the ErbB inhibitor PD158780 (PD) prior to NRG-1β treatment prevents an increase (n = 6; P = 0.13). (D) Quantification of relative gamma power in response to different NRG-1 and ErbB inhibitor treatments. NRG-1β increases the power of kainate-induced (KA) gamma oscillations more strongly than NRG-1α (β: n = 6, α: n = 4, P = 0.027) or NRG-1β after ErbB inhibitor treatment (KA + PD/NRG-1β, n = 6, P = 0.013). NRG-1β has no effect in control slices without prior application of kainate (contr/NRG-1β, n = 4, P = 0.73).

Figure 2.

NRG-1β increases kainate-induced, but not carbachol-induced, gamma oscillations and its effect is absent in slices from ErbB4^MHC-ErbB4−/− mice. (A–C) Representative sample traces (top) and power spectra (bottom) of gamma oscillations; note difference in scales. (A) Kainate-induced (n = 12; P = 0.004) or (B) carbachol-induced (n = 8; P = 0.2) gamma oscillations in slices from WT mice (black: control; red: NRG-1β treated). (C) Kainate-induced gamma oscillations in slices from ErbB4^MHC-ErbB4−/− mice (black: control; red: NRG-1β treated). (D) Quantification of the effects of NRG-1β on kainate-induced gamma oscillations in hippocampal slices from WT or ErbB4^MHC-ErbB4−/− mice. NRG-1β increases significantly the power of kainate-induced oscillations (n = 12; P = 0.004), whereas NRG-1β (2 nM) has no effect in WT slices without prior application of kainate (n = 10; P = 0.18). Coapplication of 10 μM PD158780 prevents NRG-1β modulation of kainate-induced gamma oscillations (n = 8, P = 0.47), which differs from NRG-1β + kainate-induced oscillations (P = 0.038). The NRG-1β modulation of kainate-induced gamma oscillations in ErbB4^MHC-ErbB4−/− slices is absent (n = 14, P = 0.26) and therefore significantly different from WT littermates (P = 0.018), demonstrating that the effects of NRG-1β require signaling via ErbB4 receptors.

Figure 3.

PV-expressing neurons coexpress ErbB4 in WT hippocampus and are reduced in ErbB4^MHC-ErbB4−/− mice. (A) PV immunohistochemistry, and (B) mounted image of ErbB4 (red) and PV (green) double-immunofluorescence on sections from WT mice. ErbB4-positive somata are distributed throughout all layers, whereas PV-expressing somata are mostly near to pyramidal cells. Scale bar = 600 μm. Insert: Pyramidal cell layer of CA3, showing coexpression of ErbB4 and PV (arrowheads). (C) Almost 50% of PV-immunoreactive (IR) cells coexpress ErbB4 throughout all layers; (D) however, less ErbB4-IR cells coexpress PV, notably in slm. (E) PV-expressing cells are reduced by 31% in ErbB4^MHC-ErbB4−/− mice (WT vs. ErbB4^MHC-ErbB4−/− mice, n = 4 each, 16–20 sections per animal, P = 0.017). (F) Quantitative analysis confirms that most PV-IR somata are near pyramidal cells, either in the so, sp, or lower stratum radiatum (sr), whereas slm is almost devoid of PV-IR cells. WT and ErbB4^MHC-ErbB4−/− mice do not differ in across-layer distribution of PV-positive cells (n = 2 each). (C–F) Total numbers of counted cells are presented on top of the columns.