Submitted on October 20, 2006
Accepted on December 5, 2006
Strain-specific nicotinic modulation of glutamatergic transmission in the CA1 field of the rat hippocampus: August Copenhagen Irish versus Sprague-Dawley
Manickavasagom Alkondon1, Edna F. R. Pereira1, Michelle C. Potter2, Frederick C. Kauffman3, Robert Schwarcz4, and Edson X Albuquerque1*
1 Dept. Pharmacol. Exp. Ther., University of Maryland School of Medicine, Baltimore, Maryland, United States
2 Maryland Psych. Res. Ctr., University of Maryland School of Medicine, Baltimore, Maryland, United States
3 Dept. Pharmacol. Toxicol., Rutgers University, Piscataway, New Jersey, United States
4 Dept. Pharmacol. Exp. Ther., University of Maryland School of Medicine, Baltimore, Maryland, United States; Maryland Psych. Res. Ctr., University of Maryland School of Medicine, Baltimore, Maryland, United States
* To whom correspondence should be addressed. E-mail: ealbuque{at}umaryland.edu.
Pre-pulse inhibition (PPI), a measure of sensorimotor gating impaired in patients with schizophrenia, is more sensitive to disruption by apomorphine in prepubertal August Copenhagen Irish (ACI) than Sprague-Dawley (SD) rats. In brain regions including the hippocampus, PPI is modulated by 
7* nicotinic receptors (nAChRs) and kynurenic acid (KYNA), a kynurenine metabolite that blocks 7 nAChRs. Here, KYNA levels and nAChR activities were measured in the hippocampi of 10-23-day-old ACI and SD rats of both sexes. Hippocampal KYNA levels were not different between ACI and SD rats. In hippocampal slices from both rat strains, choline (10 mM) evoked 7* nAChR-mediated type IA currents in CA1 stratum radiatum (SR) interneurons. In the presence of 7 nAChR antagonists, acetylcholine (ACh, 1 mM) evoked 4
2* nAChR-mediated type II currents. ACh also triggered excitatory postsynaptic currents (EPSCs) that resulted from 34* nAChR activation in glutamatergic neurons/axons synapsing onto the interneurons. The magnitude of the nicotinic responses did not differ significantly between male and female rats. Only the magnitude of 34* nAChR responses and the frequency of spontaneous EPSCs recorded from CA1 SR interneurons differed between the rat strains, being significantly larger in ACI than SD rats. These results indicate that the 34* nAChR activity in glutamatergic neurons/axons and the number of glutamatergic terminals synapsing onto CA1 SR interneurons are larger in prepubertal ACI than SD rats. The differential sensitivity of these rats to PPI disruption by apomorphine may result from strain-specific levels of glutamatergic activity and its strain-specific modulation by 34* nAChRs in the hippocampus.
