Interplay between thyroxin, BDNF and GABA in injured neurons.

Accumulating experimental evidence suggests that groups of neurons in the CNS might react to pathological insults by activating developmental-like programs for survival, regeneration and re-establishment of lost connections. For instance, in cell and animal models it was shown that after trauma mature central neurons become dependent on brain-derived neurotrophic factor (BDNF) trophic support for survival. This event is preceded by a shift of postsynaptic GABAA receptor-mediated responses from hyperpolarization to developmental-like depolarization. These profound functional changes in GABAA receptor-mediated transmission and the requirement of injured neurons for BDNF trophic support are interdependent. Thyroid hormones (THs) play a crucial role in the development of the nervous system, having significant effects on dendritic branching, synaptogenesis and axonal growth to name a few. In the adult nervous system TH thyroxin has been shown to have a neuroprotective effect and to promote regeneration in experimental trauma models. Interestingly, after trauma there is a qualitative change in the regulatory effect of thyroxin on BDNF expression as well as on GABAergic transmission. In this review we provide an overview of the post-traumatic changes in these signaling systems and discuss the potential significance of their interactions for the development of novel therapeutic strategies.