Different chronic cocaine administration protocols induce changes on dentate gyrus plasticity and hippocampal dependent behavior

• Published in: Synapse (New York, N.Y.) Vol. 64; no. 10; pp. 742 - 753
• Main Authors: Perez, M.F., Gabach, L.A., Almiron, R.S., Carlini, V.P., De Barioglio, S.R., Ramirez, O.A.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-10-2010
• Subjects: Analysis of Variance; Anesthetics, Local - adverse effects; Animals; Behavior, Animal - drug effects; Biophysics; Chi-Square Distribution; Cocaine; Cocaine - adverse effects; Dentate gyrus; Dentate Gyrus - drug effects; Dose-Response Relationship, Drug; Drug abuse; Drug addiction; Drug Administration Schedule; Electric Stimulation - methods; Excitatory Postsynaptic Potentials - drug effects; Excitatory Postsynaptic Potentials - physiology; Hippocampus; In Vitro Techniques; Learning; Long-term potentiation; Long-Term Potentiation - drug effects; Long-Term Potentiation - physiology; Male; Memory; Motor Activity - drug effects; Motor Activity - physiology; Patch-Clamp Techniques; Plasticity (hippocampal); Plasticity (synaptic); Psychomotor Performance - drug effects; Psychomotor Performance - physiology; Rats; Rats, Wistar; sensitization; Statistics as Topic; Synapses; synaptic plasticity; Withdrawal
• ISSN: 0887-4476; 1098-2396; 1098-2396
• DOI: 10.1002/syn.20788

Hippocampus is a limbic structure that participates in learning and memory formation. Specifically the dentate gyrus has been described as a hippocampal subregion with high rates of plasticity and it is targeted by different psychoactive drugs modulating synaptic plasticity. Repeated cocaine administration induces sensitization to the locomotor effects and it is believed that sensitization involves the same mechanisms of drug seeking and relapse. Although, the mechanisms underlying sensitization is not fully understood. In this work we investigated the impact of repeated intraperitoneal administration of cocaine (15 or 20 mg/kg/day along 5 or 15 days respectively; and 15 mg/kg/day along 5 day followed by a challenge dose after three days of withdrawal) on the dentate gyrus synaptic plasticity, differentiating between sensitized and nonsensitized rats. Furthermore, we correlated changes on the hippocampal synaptic plasticity to memory retention. Our results revealed that the prevalence of cocaine sensitization (around 50%) was identical in all protocols used. The results found in the threshold to generate LTP were similar for all protocols used, being the threshold values cocaine‐treated groups (sensitized and nonsensitized) significantly reduced compared to controls, observing the highest reduction in the sensitized group. Moreover, we observed a facilitated retention of recent memory formation only in sensitized animals the nonsensitized subjects remained at the control levels. In conclusion, sensitization to cocaine generates a high efficiency of hippocampal synaptic plasticity that may underlie the aberrant engagement of learning processes occurred during drug addiction. Synapse 64:742–753, 2010. © 2010 Wiley‐Liss, Inc.