Emergence of NMDAR-independent long-term potentiation at hippocampal CA1 synapses following early adolescent exposure to chronic intermittent ethanol: role for sigma-receptors.
Adolescent humans who abuse alcohol are more vulnerable than adults to the development of memory impairments. Memory impairments often involve modifications in the ability of hippocampal neurons to establish long-term potentiation (LTP) of excitatory neurotransmission; however, few studies have examined how chronic ethanol exposure during adolescence affects LTP mechanisms in hippocampus. We investigated changes in LTP mechanisms in hippocamal slices from rats exposed to intoxicating concentrations of chronic intermittent ethanol (CIE) vapors in their period of early-adolescent (i.e., prepubescent) or late-adolescent (i.e., postpubescent) development. LTP was evaluated at excitatory CA1 synapses in hippocampal slices at 24 h after the cessation of air (control) or CIE vapor treatments. CA1 synapses in control slices showed steady LTP following induction by high-frequency stimulation, which was fully dependent on NMDAR function. By contrast, slices from early-adolescent CIE exposed animals showed a compound form of LTP consisting of an NMDAR-dependent component and a slow-developing component independent of NMDARs. These components summated to yield LTP of robust magnitude above LTP levels in age-matched control slices. Bath-application of the sigma-receptor antagonist BD1047 and the neuroactive steroid pregnenolone sulfate, but not acute ethanol application, blocked NMDAR-independent LTP, while leaving NMDAR-dependent LTP intact. Analysis of presynaptic function during NMDAR-independent LTP induction demonstrated increased presynaptic function via a sigma-receptor-dependent mechanism in slices from early-adolescent CIE-exposed animals. By contrast, CIE exposure after puberty onset in late-adolescent animals produced decrements in LTP levels. The identification of a role for sigma-receptors and neuroactive steroids in the development of NMDAR-independent LTP suggests an important pathway by which hippocampal synaptic plasticity, and perhaps memory, may be uniquely altered by chronic ethanol exposure during the prepubescent phase of adolescent development.
Sabeti
Jilla
J
Department of Molecular and Integrative Neurosciences (MIND), The Scripps Research Institute, La Jolla, California 92037, USA. sabetij@scripps.edu
Gruol
Donna L
DL
D000367:Age Factors; D000437:Alcoholism / Q000473:pathology / Q000503:physiopathology; D000818:Animals; D002492:Central Nervous System Depressants / Q000633:toxicity*; D003712:Dendrites / Q000187:drug effects / Q000502:physiology; D004594:Electrophysiology; D000431:Ethanol / Q000633:toxicity*; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D017774:Long-Term Potentiation / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D011284:Pregnenolone / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D017480:Receptors, sigma / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D002492:Central Nervous System Depressants; D016194:Receptors, N-Methyl-D-Aspartate; D017480:Receptors, sigma; C018370:pregnenolone sulfate; D000431:Ethanol; D011284:Pregnenolone