Nanomolar concentrations of nicotine and cotinine alter the development of cultured hippocampal neurons via non-acetylcholine receptor-mediated mechanisms.

We investigated the effects of nicotine and its metabolic byproduct cotinine on survival, differentiation and intracellular Ca2+ levels of cultured E18 rat hippocampal neurons. We used a range of concentrations from 1 nM to 10 microM, most of which are within the likely range of human fetal exposure from maternal smoking. Nicotine did not influence neuron survival or neurite production. However, at all concentrations tested, nicotine significantly increased branching of both axons and dendrites, an effect which was not reversed by co-culturing with alpha-bungarotoxin, which blocks the nicotinic acetylcholine receptors that predominate in hippocampal cultures (Alkondon and Albuquerque, 1993; Barrantes et al., 1995b). Cotinine at 100 nM and 1 microM significantly reduced neuron survival and neurite production of surviving neurons, but did not significantly alter axon or dendrite branching. These membrane-permeable compounds may work synergistically in the developing embryo to impair the survival and differentiation of hippocampal neurons via intracellular mechanisms.