Abstracts

Rationale: There are only sparse data on effects of short term early exposure of immature brain to benzodiazepines on behavior and neurogenesis. Present experiment analyzed whether such exposure affects neurogenesis and cognitive abilities later in life. The postnatal administration in rats was chosen because brain development at this stage corresponds approximately to that in human newborns.Methods: Clonazepam (CZP; suspension in saline 1mg/5ml with one drop of Tween 80) was administered from postnatal day (P) 7 until P11 at daily doses 0.5 or 1.0 mg/kg i.p. Starting at P12 till P23 animals were exposed to homing test and latency to the home cage and number of correct responses were recorded. Further, to assess short- and long- term memory the animals were submitted to three-trial passive-avoidance paradigm, at P12, P15, P18, and P23 at three intervals 0, 2 and 24 hours. Habituation within- and between- sessions was assessed in the open field (OF) to investigate learning and memory in adult animals (P70). In four consecutive days rats were exposed to OF always for 10 min and distance moved and time spent in central zone were compared between the 1st and 4th session. Spatial memory was tested in the Morris water maze. Additional groups of animals were used to determine the effects of early CZP exposure on neurogenesis in adulthood. Newborn doublecortin positive (DCX+) neurons were detected with immunohistochemistry and their number in the dentate gyrus was assessed stereologically.Results: P12 and P23 rats with early life exposure to CZP (1.0 mg/kg/day) exhibited extended latency to homing response and decreased number of correct homing responses. No impairment of short- or long-term memory was found in the passive avoidance test, all animals had increased latency to enter the dark compartment at 2 and 24 hours. However animals exposed to CZP showed a shorter latency to enter the dark compartment in the first session. Early CZP exposure did not impair habituation, but CZP animals spent more time in central zone of OF. In the Morris water maze both control and CZP animals were able to learn the task, but animals with high dose of CZP spent more time swimming. Early exposure to CZP in a dose of 1mg/kg/day decreased number of DCX+ neurons by 24.2% (p=0.015). Conclusions: Short term exposure to CZP during early postnatal development affected behavioral responsiveness related to motivation and learning of juvenile rats. In the adulthood, animals exposed to CZP exhibited impaired non-associative learning and acquisition of the MWM task. Cognitive impairment was associated with decline of neurogenesis in the adult brain. Supported by Grant 305/09/0846 and P304/12/G069 of the Grant Agency of the Czech Republic and and Research Project RVO 67985823.