Connexin43 (Cx43) is highly expressed in astrocytes (AS), and its expression is reduced in the prefrontal cortex of depressive patients. It showed that some antidepressants increase the expression of neurotrophic factors like a brain-derived neurotrophic factor (BDNF) mediated by lysophosphatidic acid (LPA) receptors. The current study examined whether decrease in Cx43 expression affect their expression. Primary cultured AS were prepared from the cerebral cortex of neonatal Wistar rats. The expression of Cx43 was downregulated with RNA interference. The expression of mRNA and protein were measured by real-time PCR and western blotting, respectively. Knockdown of Cx43 increased the amitriptyline (AMI)-induced BDNF expression in cultured AS. This enhancement was significantly suppressed by blockade of LPA1/3 receptors, Src tyrosine kinase, or extracellular signal-regulated kinase (ERK). The current study revealed that reduced Cx43 expression potentiates the AMI-induced BDNF expression in cortical AS. In addition, LPA1/3-mediated Src-ERK signaling might be essential in the potentiation of AMI-induced BDNF expression in Cx43-downregulated AS. These results indicate the downregulation of Cx43 observed in the depressive patients might contribute to therapeutic effect of antidepressants.