The Role Of ErbB4 In Regulating The Development And Function Of GABAergic Circuits In Mice Forebrain

ErbB4 (epidermal growth factor receptor 4, EGFR 4, ErbB4) is the receptor of neurogrowth factor, neuregulin 1 and a susceptibility gene for schizophrenia. NRG1/ErbB4 signals have been hypothesized to function in a number of cortical developmental processes, such as synaptic formation, axon guidance and myelination. Several recent studies showed that the expression of ErbB4 is mainly restricted to GABAergic interneurons, specifically, to parvalbumin (PV) fast-spiking (FS) interneurons. In mouse PFC, the 40%-50% of GABAergic interneuron are PV positive, and PV interneuron can be further divided into two main types by their axon/dendrites morphology:basket cell and chandelier cell. And the basket cell represents 85% of PV positive interneurons in the mouse medial PFC (mPFC), the remaining 15% is chandelier cell. The dysfunction of GABAergic circuits mediated by PV is closely involved in many neuropsychiatric diseases. But how does ErbB4 work in GABAergic circuits mediated by PV (especially basket cells) is currently unknown.Meanwhile, the expression of ErbB4 is not only in cortex, but also in other forebrain areas, like striatum and hypothalamus. And striatum is an important.brain area related to learning and memory, motor activity and reward. Dysfunction of GABAergic circuits in striatum may leads to diseases like Parkinson’s disease, Huntington disease and autism. Until now, little is known about the roles of ErbB4 signals during the development of GABAergic circuitry in mice forebrain. In order to answer these questions, we performed our investigation as follows.We used forebrain GABAergic intemeuron specific promoter Dlx5/6-cre to knockout ErbB4 in mice. Combined with biochemistry, electrophysiology and immunostaining methods to understand the role of ErbB4 in regulating the development of GABAergic circuits mediated by PV basket cells in mice PFC. We found the migration of interneurons and the lamina distribution of PV interneuron in PFC had no obvious change after knockout ErbB4. Second, the inhibitory synaptic formation on PV interneurons was not altered, but activity-dependent GABA transmission was decreased in ErbB4 mutant mice. Furthermore, the number of excitatory synapses in early development on PV interneuron didn’t changed significantly, but the number of exciatory synapses in the maturation period was significantly decreased in ErbB4 knockout mice. These results demonstrate that lack of ErbB4 may affect the excitatory input on PV interneurons, at the same time, the activity of PV interneuron was also decreased. And in this case, the inhibition ability of PV interneuron was decreased and finally results in hyperactivity of cortical pyramidal neurons. The disruption of the balance of excitation and inhibition in GABAergic circuits may lead to several neuropsychiatric diseases.Use the same mouse line, we found the expression of ErbB4 was also observed in striatum. But there is few studies work on the mechanism underlies the development of inhibitory circuitry between medium spiny neurons (MSN). We used a reporter line Ai9-tdTomato crossed with Dlx5/6-cre and identify the expression of ErbB4 on MSNs. Then we applied biochemistry and immunostaining technologies to investigate the results of GABAergic synapses after knockout ErbB4 in. striatum. We found the expression of GABAAR alphal (al) subunit was significantly increased in striatum of mutant mice, but expression of a2 and β2 subunits of GABAAR were sustained. Together with the receptor increase, the expression of GAD67 was also increased. Then we used whole-cell recording found the frequency and amplitude of mininautre inhibitory postsynaptic current on MSNs was significantly increased in knockout mice. At last, we subjected these mice to behavior tests and found the mutant mice have hyperactivity in open field test, impaired learning and memory in conditional fear memory test and abnormality in social novelty recognition.In one word, our results suggest that ErbB4 knockout in mice forebrain not only affect the final maturation of excitatory synapses on PV basket interneurons and activity-dependent GABA transmission of PV basket interneurons in mPFC, but also regulate the development and function of inhibitory circuits in striatum. Furthermore, lack ErbB4 results in impaired behavior performance. These results indicate that ErbB4 has different regulation pattern in different brain regions. Our findings can provide a new understanding of mechanisms underlying the regulation of ErbB4 in GABAergic circuits and indicate a new perspective for understanding the pathology of neuropsychiatric diseases.