Interestingly, before birth GABA functions as an excitatory neurotransmitter for certain neurons in the developing brain, meaning that activation of its receptor results in an increased probability of the post-synaptic neuron conducting an action potential. Presuming that the GABA receptor gene product is the same before and after birth, a possible explanation for this change is:

Explanation:

Γ-Aminobutyric acid (GABA) is a non-protein amino acid that is widely present in microorganisms, plants and animals. It is the main inhibitory neurotransmitter in the central nervous system (CNS) of mammals.

It plays the leading role in reducing neuronal excitability throughout the nervous system. In humans, GABA is directly responsible for the regulation of muscle tone.

Although, in chemical terms, it is an amino acid, in the scientific and medical communities they rarely refer to GABA as such because the term "amino acid" by convention refers to the α amino acids and GABA is not. It is also not considered as part of any protein.

In spastic diplegia in humans from an early age, GABA absorption is negatively affected by the nerves damaged by the lesion in the upper motor neurons characteristic of the condition which leads to the development of muscular hypertonia signaled by those nerves that are incapable of absorbing GABA.