200 - Primary cilia loss renders pyramidal neurons susceptible to perinatal ketamine-induced dendritic degeneration and learning deficits

Poster Number: 200
Publication Number: 200.142

Nemanja Saric, Children's National Health System, Washington, DC, United States; Li Wang, Children's National Health System, DC, DC, United States; Kazue Hashimoto-Torii, Nationwide Children's Hospital, Washington, DC, United States; Nobuyuki Ishibashi, Children's National Health System, Washington, DC, United States

Background: Recent clinical studies have demonstrated a strong link between anesthetic exposure and neurodevelopmental outcomes in children with CHD. Protein-damaging de novo gene mutations have been demonstrated to be strong predictors of neurodevelopmental anomalies in congenital heart disease (CHD), and at least 50% of these genes have been found to be associated with primary cilia structure and/or function. 

Objective: Therefore, studying the combined effect of anesthesia and primary cilia gene mutations may shed light on the neurodevelopmental abnormalities observed in CHD children.

Design/Methods: Using Emx1cre; Ift88 f/f, in which primary cilia are lost specifically in cortical excitatory neurons, we administered either PBS or Ketamine at postnatal day 7 (P7). We examined markers of cytoskeletal degeneration at P8 in the medial prefrontal cortex as well as behavioral testing at P30 using water T-maze to assess their spatial memory performance and cognitive flexibility. Separate cohorts were also tested for gross and fine motor deficits using the accelerated rotarod and pellet reach task, respectively. To assess pyramidal neuron morphology, we used two other inducible Cre/lox mice to specifically label layer II (Nes-Cre/ERT2) and layer V (ER81-Cre/ERT2) neurons. To examine if the observed learning-related deficits were related to altered dendritic spine dynamics we then performed two-photon imaging on Ift88 cHET+Ket and cKO+Ket Thy1-GFPM animals and compared spine density and turnover in the motor cortex.

Results: During the reversal learning paradigm, the Ift88 knockout mice that were exposed to ketamine (cKO+Ket) showed a strongly reduced ability to learn compared to other groups, indicative of a cognitive flexibility deficit. This same group demonstrated significant motor deficits, with a reduced rate of motor learning in both gross and fine motor tasks. We found significant enhancement in immunoreactivity of cytoskeletal degeneration markers in the cKO+Ket mice compared to the other three groups (cHET+PBS, cHET+Ket, and cKO+PBS). The effects of ketamine on dendritic morphology were also specific to this group.

Conclusion(s): Our findings indicate that primary cilia deficiency, due to a common genetic predisposition with CHD, exacerbates the toxicity of neonatal anesthesia, suggesting a novel therapeutic treatment strategy for the prevention of neurobehavioral abnormalities in this population.