Biochemical and Biophysical Research Communications
Aspects of excitatory/inhibitory synapses in multiple brain regions are correlated with levels of brain-derived neurotrophic factor/neurotrophin-3
Introduction
Synaptic development is the making of synapses between neurons and is critical for the formation of neural circuits. Improper synaptic development is thought to cause synapse pathology, which is linked to a risk of neurodevelopmental disorders such as autism [1,2] and schizophrenia [3,4]. However, the mechanisms of synaptic development in different brain regions are not fully understood.
Neurotrophins constitute a family of secreted growth factors that regulate neuronal proliferation, development, survival and death, neuritogenesis and pruning, synaptic strength and plasticity [5,6]. Brain-derived neurotrophic factor (BDNF) is a neurotrophin that is predominantly expressed in the brain and is involved in the proliferation, differentiation, maturation and survival of various types of neuron [[6], [7], [8], [9], [10]]. Neurotrophin-3 (NT-3) is also a neurotrophin family member that is expressed in several organs including brain [11], and regulates proliferation, differentiation and survival of neurons [[12], [13], [14]]. BDNF and NT-3 are highly associated with synaptic development and plasticity in several brain regions [[15], [16], [17], [18], [19], [20], [21], [22], [23]]. Therefore, expression and secretion of BDNF and NT-3 are thought to be key factors in regulating neural wiring and functioning during development.
Calcium-dependent activator protein for secretion 2 (CADPS2) is associated with exocytosis of large dense-core vesicles [[24], [25], [26], [27]] and is known to enhance BDNF/NT-3 secretion in hippocampal and cerebellar neurons [[28], [29], [30], [31], [32]]. BDNF/NT-3 and CADPS2 are co-localized in some but not all neuron types in mouse cerebral cortex, hippocampus, cerebellum [30,33] and striatum [[34], [35], [36]]. Thus we predicted that changes in the levels and secretion of BDNF/NT-3 in Cadps2 knock-out (KO) mice would influence synaptic development in various brain regions. Indeed, in Cadps2 mutant mice, synaptic connections and function are affected in the cerebellum [29,30,37] and hippocampus [28], and these alterations might be associated with autistic-like behavior [32,33,38,39].
In the present study, we determined BDNF/NT-3 levels and analyzed excitatory/inhibitory synapses in six different brain regions (cerebellum, hypothalamus, striatum, hippocampus, parietal cortex and prefrontal cortex) in wild-type (WT) and Cadps2 KO mice.
Section snippets
Animals
All experimental protocols were evaluated and approved by the Regulation for Animal Research at RIKEN and Tokyo University of Science, which follows the National Institutes of Health guide for the care and use of Laboratory animals (NIH Publications No. 8023, revised 1978). The generation of Cadps2 KO mice was described previously [33]. Male mice were housed in home cages, with at most four per cage, and maintained under a 12:12-h light–dark cycle, with ad libitum access to water and food. All
Levels of BDNF and NT-3 are altered in multiple brain regions of Cadps2 KO mice
Neurotrophins are expressed at different levels in multiple brain regions and during different developmental stages. Therefore, we investigated changes in age- and region-dependent levels of brain BDNF and NT-3 proteins. We dissected six different brain regions (cerebellum, hypothalamus, striatum, hippocampus, parietal cortex and prefrontal cortex) from WT and Cadps2 KO mice at postnatal weeks 1, 3 and 8, and measured the content of BDNF and NT-3 protein in each brain region by two-site enzyme
Discussion
In the present study, Cadps2 KO mice showed (1) a decrease of BDNF levels in 3–8 week-old hippocampus, but an increase in 1 week-old hypothalamus, (2) a decrease of NT-3 levels in 8 week-old cerebellum and 3 week-old hippocampus, but an increase in 8 week-old parietal cortex, (3) excitatory synaptic vesicles in a presynapse were increased in cerebellum and parietal cortex synapses, but decreased in hippocampus synapses, (4) inhibitory synaptic vesicles were decreased in hippocampus and parietal
Conflicts of interest
The authors declare no conflicts of interest.
Acknowledgement
This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas (Comprehensive Brain Science Network), MEXT KAKENHI (21790219) and JSPS KAKENHI (17H03563), the Takeda Science Foundation, and the Kawano Masanori Memorial Public Interest Incorporated Foundation for Promotion of Pediatrics. We thank Jeremy Allen, PhD, from Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript.
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