Gestational nicotine exposure regulates expression of AMPA and NMDA receptors and their signaling apparatus in developing and adult rat hippocampus

Abstract

Untimely activation of nicotinic acetylcholine receptor (nAChR) by nicotine results in short- and long-term consequences on learning and behavior. In this study, the aim was to determine how prenatal nicotine exposure affects components of glutamatergic signaling in the hippocampus during postnatal development. We investigated regulation of both nAChRs and glutamate receptors for α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and N-methyl-D-aspartate (NMDA), from postnatal day (P) 1 to P63 after a temporally restricted exposure to saline or nicotine for 14 days in utero. We analyzed postsynaptic density components associated with AMPAR and NMDAR signaling: Calcium/calmodulin-dependent protein kinase II α (CaMKIIα), Calmodulin (CaM), and postsynaptic density-95 (PSD95), as well as presynaptically localized synaptosomal-associated protein 25 (SNAP25). At P1, there was significantly heightened expression of AMPAR subunit GluR1 but not GluR2, and of NMDAR subunits NR1, NR2a and NR2d but not NR2b. NR2c was not detectable. At P1, the postsynaptic proteins CaMKIIα, CaM, and PSD95 were also significantly upregulated, together with presynaptic SNAP25. This enhanced expression of glutamate receptors and signaling proteins was concomitant with elevated levels of [3H] Epibatidine (EB) binding in prenatal nicotine-exposed hippocampus, indicating that α4β2 nAChR may influence glutamatergic function in the hippocampus at P1. By P14, neither [3H]EB binding nor the expression levels of subunits GluR1, GluR2, NR1, NR2a, NR2b, NR2c, or NR2d seemed changed with prenatal nicotine. However, CaMKIIα was significantly upregulated with nicotine treatment while CaM showed downregulation at P14. The effects of nicotine persisted in young adult brains at P63. They exhibited significantly downregulated GluR2, NR1, and NR2c expression levels in hippocampal homogenates and a considerably muted overall distribution of [3H]AMPA binding in areas CA1, CA2, CA3, and the dentate gyrus. Our results suggest that prenatal nicotine exposure can regulate the glutamatergic signaling system throughout postnatal development by enhancing or inhibiting availability of AMPAR and NMDAR or their signaling components. The persistent depression, in adults, of the requisite NR1 subunit for NMDAR assembly, and of GluR2, important for assembly, trafficking, and biophysical properties of AMPAR, indicates that nicotine may alter ionotropic glutamate receptor stoichiometry and functional properties in adults after prenatally restricted exposure.

Developmental Nicotine Exposure Alters AMPA Neurotransmission in the Hypoglossal Motor Nucleus and Pre-Bötzinger Complex of Neonatal Rats

“…Although we show that DNE decreases GluR2/3 subunit expression in the XIIMN and pre-BötC, which suggests a decrease in AMPAR expression, Wang et al (2011) showed that DNE increases hippocampal GluR1 expression. Thus, we cannot exclude the possibility that DNE modifies GluR subunit expression in a differential manner that does not alter total receptor numbers on the postsynaptic membrane.…”

Perinatal nicotine treatment induces transient increases in NACHO protein levels in the rat frontal cortex

“…To study the effect of perinatal nicotine administration, nicotine was administered to pregnant rats through a mini-osmotic infusion pump (Model #2006, Alzet, Cupertino, CA) surgically implanted between the scapulae at gestational day 7, as previously described (Wang et al, 2011; Wang and Gondré-Lewis, 2013). Nicotine hydrogen tartrate (Sigma-Aldrich, St Louis, MO) was prepared fresh on the day of pump implantation and delivered to dams at a rate of 4 mg/kg/day (free base weight) from pregnancy until pups reached PND21.…”

Effects of sex and chronic neonatal nicotine treatment on Na2+/K+/Cl− co-transporter 1, K+/Cl− co-transporter 2, brain-derived neurotrophic factor, NMDA receptor subunit 2A and NMDA receptor subunit 2B mRNA expression in the postnatal rat hippocampus

“…Thus, in neonates, nicotine-stimulated glutamate and GABA release could result in increased excitatory activity, raising intracellular Ca 2+ concentrations with subsequent effects on NMDAR subunit expression. This idea is supported by reports that prenatal exposure to nicotine transiently increases immunoreactivity for NR2A but not NR2B in one day old rat pups (Wang et al, 2011), and that postnatal nicotine exposure increases cortical mRNA expression of NR2A (Hsieh et al, 2002). Therefore, we examined whether CNN treatment altered mRNA expression levels of NR2A and NR2B in the postnatal hippocampus at P5 and P8.…”

“…Postnatal nicotine exposure has previously been found to enhance NMDAR-mediated excitatory postsynaptic potentials and modulate synaptic development in the auditory cortex (Aramakis et al, 2000), and alter expression of NR2A and 2B mRNA in the auditory cortex and medial geniculate nucleus (Hsieh et al, 2002). Within the hippocampus, gestational nicotine increases NR1, 2A, and 2D protein levels (Wang et al, 2011). …”