Loss of erbB signaling in oligodendrocytes alters myelin and dopaminergic function, a potential mechanism for neuropsychiatric disorders

Abstract

Several psychiatric disorders are associated with white matter defects, suggesting that oligodendrocyte (OL) abnormalities underlie some aspects of these diseases. Neuregulin 1 (NRG1) and its receptor, erbB4, are genetically linked with susceptibility to schizophrenia and bipolar disorder. In vitro studies suggest that NRG1-erbB signaling is important for OL development. To test whether erbB signaling contributes to psychiatric disorders by regulating the structure or function of OLs, we analyzed transgenic mice in which erbB signaling is blocked in OLs in vivo. Here we show that loss of erbB signaling leads to changes in OL number and morphology, reduced myelin thickness, and slower conduction velocity in CNS axons. Furthermore, these transgenic mice have increased levels of dopamine receptors and transporters and behavioral alterations consistent with neuropsychiatric disorders. These results indicate that defects in white matter can cause alterations in dopaminergic function and behavior relevant to neuropsychiatric disorders.

Fig. 1.

Transgene expression is specific to OL lineage cells. (a) Western blot analysis of spinal cord lysates shows that the time course of DN-erbB4 expression closely resembles that of myelination. Actin was used as a loading control. (b) Immunostaining for DN-erbB4 protein in coronal sections of adult corpus callosum shows expression only in white matter of Tg mice. (c) Immunostaining of cingulate cortex in adult Tg mice for DN-erbB4 (green) and PLP (red) shows overlap. Blue shows DAPI-stained nuclei. (d) Immunoprecipitation of erbB2 from corpus callosum followed by phosphotyrosine Western blot shows that erbB2 phosphorylation is reduced in the white matter of adult Tgs. (Scale bars: 100 μm in b and 20 μm in c.)

Fig. 2.

OL structure and number are altered in the absence of erbB signaling. (a) Representative EM of myelinated axons in the corpus callosum. (Insets) Higher magnification of myelin in WT and Tg animals. (b) Quantification of the g-ratio in WT (open bars) and Tg (filled bars) optic nerve (OPN) and corpus callosum (CC). Tg mice have thinner myelin sheaths than WTs (P = 0.031). (c) Representative images of PLP in situ hybridization in corpus callosum sections. (d) Quantification of PLP⁺ cells in corpus callosum shows a higher density of OLs in Tg mice (P = 0.007). (e) The density of PDGFαR⁺ OL progenitors is not altered in Tg mice (P = 0.36). (f) Three-dimensional reconstructions of representative WT and Tg frontal cortex OLs. For quantification of OL morphology see Table 1. Error bars represent SEM. (Scale bars: 80 nm in a, 26 nm in Insets, 50 μm in c, and 20 μm in f.)

Fig. 3.

Behavioral alterations in Tg mice. (a) Locomotor activity in the open field as a function of time in WT (open squares) and Tg (black diamonds) mice. Tg animals habituate to a greater extent (F_1,4 = 6.28; P < 0.0001). (b) Tg mice spend less time in the center of the open-field chamber (P = 0.0004). (c) Tg mice spend less time on the open arms of an elevated plus maze (P = 0.033). (d) Tg mice take longer to investigate an intruder after repeated exposure in a social investigation test (F_1,3 = 3.68; P = 0.02). (e) Tg mice attempt to mount intruder mice less frequently than WTs (F_1,3 = 2.73; P = 0.05). (f) Tg mice sensitize more robustly to amphetamine than WT mice (F_4,176 = 7.54; P < 0.001). Error bars represent SEM.

Fig. 4.

Dopaminergic neurotransmission is altered in Tg mice. (a) Autoradiography of D1-like and D2-like receptors and DAT binding on brain sections. For quantification see SI Table 2. (Scale bar: 4 mm.) (b) c-fos induction in the striatum in response to amphetamine is significantly higher in Tg mice (P = 0.04). (c) c-fos induction in the striatum in response to DHX is significantly higher in Tg mice (P = 0.01). (d) Representative traces of evoked dopamine release in nucleus accumbens in response to a 1-mA current pulse to the medial forebrain bundle. (e) Amplitude of evoked dopamine release is enhanced in Tg compared with WT mice (n = 10; 0.1 mA, P = 0.044; 1 mA, P = 0.007). Error bars represent SEM.