Accordingly, in addition to assessing HC3 binding and Ch AT activity, we determined the HC3/Ch AT ratio as an index of presynaptic activity relative to the number of cholinergic nerve terminals (Abreu-Villaça et al., 2004; Slotkin et al., 1994, 2007a).We also contrasted the specific effects on ACh synaptic development with assessments of systemic toxicity (maternal weight gain, litter characteristics, postnatal body and brain region weights), and determinations of whether prenatal nicotine treatment enhanced the subsequent ability of chlorpyrifos to inhibit cholinesterase.In particular, we showed how drug therapies commonly used in preterm labor enhance the subsequent vulnerability of the developing brain to chlorpyrifos, a commonly-used organophosphate pesticide (Aldridge et al., 2005; Levin et al., 2014; Meyer et al., 2005; Rhodes et al., 2004; Slotkin et al., 2013, 2014a).
By itself nicotine elicited overall upregulation of the ACh markers, albeit with selective differences by sex, region and age.
Our study thus encompassed four treatment groups: control, nicotine alone, chlorpyrifos alone, and nicotine followed by chlorpyrifos.
We assessed the impact on brain regions comprising the major ACh projections and their corresponding cell bodies, focusing on well-established markers of ACh synaptic function: the concentration of α4β2 n ACh Rs, binding of hemicholinium-3 (HC3) to the presynaptic high-affinity choline transporter, and activity of choline acetyltransferase (Ch AT).
Accordingly, in the present work, we examined the impact of fetal nicotine exposure on the subsequent effects of postnatal chlorpyrifos directed toward the development of ACh systems in the rat brain.
Nicotine was given throughout gestation via implanted osmotic minipump, at a dose (3 mg/kg/day) that produces nicotine plasma levels similar to those in moderate smokers (Lichtensteiger et al., 1988; Murrin et al., 1987; Trauth et al., 2000); we specifically chose a lower dose than in our previous work simulating heavy smoking (Slotkin, 2004, 2008), so as to produce submaximal changes in order to leave room for additional effects of chlorpyrifos.
The convergence of nicotine and chlorpyrifos on ACh pathways makes this a likely combination for enhanced vulnerability.