Inattention, hyperactivity, autism, emotional disturbance, social incompetence, epilepsy, and lower intellectual abilities are found in about 50% of preterm-born children. These disorders are attributed to an imbalance between inhibitory GABAergic and excitatory glutamatergic transmission in neuronal circuits. Premature birth and associated complications---hypoxia, hypotension, and sepsis--can affect the generation of GABAergic interneurons and disrupt neuronal circuitry. Therefore, we ask how interneurons develop in the second half of pregnancy, and how prematurity disrupts their generation, density, and distribution. Answering these questions will determine the bases of cognitive and behavioral disorders in preterm-born children. Interneurons releasing GABA constitute the major population of cortical inhibitory neurons and are classified based on the neuropeptides they produce. They are generated into both dorsal subventricular zone (SVZ) and ventral SVZ (ganglionic eminence, GE) in humans and only in GE in rodents. Their formation is regulated by transcription factors including, Nkx2.1, Dlx1/2, Lhx6, and Mash1. Prematurity can impact the development of interneurons. This is because oxygen level regulates neurogenesis and preterm birth deprives the infants of the hypoxic intrauterine environment along with the placental hormones and maternal nutrients. Despite this, the development of interneurons has not been studied in the second half of pregnancy and there is no information on how premature birth affects interneurons. Therefore, we hypothesize that a) interneurons and their precursors undergo distinct developmental changes in their density, proliferation, and distribution with advance in gestational age and that b) prematurity disrupts their generation and distribution. Our approach is to a) use human tissues for studying interneuron development in late pregnancy and b) employ both human samples and a rabbit model to assess the effect of prematurity on GABAergic neurogenesis. Human studies are imperative as the human cortex is unique and more complex than animals.
Aim #1 : Generation of late-born interneurons (20-40 weeks): Evaluate a) the proliferation and density of subtypes of interneurons-GABA+, parvalbumin+, calretinin+, somatostatin+-and their precursors-Nkx2.1+, Dlx1/2+, Mash1+, and b) gene expression of transcription factors regulating GABAergic neurogenesis, Nkx2.1, Dlx1/2, Lhx6, Mash1, in the dorsal SVZ and GE of human fetuses &preterm infants (20-40 weeks).
Aim #2 : Effect of prematurity on GABAergic neurogenesis: A) HUMAN: Compare the density and proliferation of a) subtypes of interneurons, and b) their progenitors (Dlx1/2+, Nkx2.1+, and Mash1+) in the GE and dorsal SVZ between two sets of premature infants- long postnatal survival (24 week gestational age + 2 week old=26 weeks) vs. short postnatal survival (26 wk gestation + <3d old=26 weeks)--of equivalent postmenstrual age (gestational age + postnatal age) B) RABBIT model: To compare preterm (E29, 3 d old) and term (E32,<2 h old) pups of an equivalent postmenstrual age for parameters as in human experiments.
Interneurons are inhibitory neurons that modulate the cognitive processes including executive function, learning, memory, and intelligence. Abnormalities in their density are associated with anxiety disorders, reduced social skills, epilepsy, autism, and other psychiatric disorders. In this proposal, we will determine how these inteneurons develop in the second half of pregnancy and how preterm birth affects the formation of interneurons.