Elicitation and modification of the rabbit's nictitating membrane reflex following prenatal exposure to cocaine

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The nictitating membrane (NM) reflex was assessed in adult Dutch-belted rabbits exposed to cocaine in utero. The intensity threshold for eliciting the reflex was increased in cocaine progeny and the amplitude of the reflex was decreased at the lower stimulus intensities. However, cocaine and saline progeny showed equivalent rates of habituation of the NM reflex when tested with a suprathreshold eliciting stimulus. Reliable modification of the NM reflex was obtained when the reflex-eliciting stimulus was preceded by an auditory stimulus at intervals of 100–800 ms. Cocaine and saline progeny exhibited an increase in the peak amplitude of the reflex, a shortening of the latency of the reflex, and a shortening of the latency to achieve peak amplitude of the reflex as a function of increases in the interstimulus interval. Furthermore, cocaine progeny showed significantly longer response latencies than saline progeny across all interstimulus intervals, although neither the peak amplitude nor the latency to achieve peak amplitude was affected. Thus, prenatal exposure to cocaine affected elicitation of the defensive NM reflex to an aversive stimulus but did not affect the sensorimotor integration necessary for modification of the reflex by antecedent stimulation.