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The Journal of Neuroscience, August 2, 2006, 26(31):8025-8039; doi:10.1523/JNEUROSCI.0842-06.2006

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Neurobiology of Disease
Progression of Cellular Adaptations in Medial Prefrontal and Orbitofrontal Cortex in Response to Repeated Amphetamine

Houman Homayoun and Bita Moghaddam

Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260

Correspondence should be addressed to Bita Maghaddam, Department of Neuroscience, University of Pittsburgh, A210 Langley Hall, Pittsburgh, PA 15260. Email: moghaddam{at}bns.pitt.edu

Recent theories on addiction implicate adaptive changes in prefrontal cortex (PFC) neurons in reinforcing and psychotomimetic properties of psychostimulants, yet little is known about how neuronal responses to these drugs change over time. Here we describe electrophysiological evidence for a progressive and sustained change in the response of PFC neurons to amphetamine during repeated exposure. In spontaneously behaving rats and in rats engaged in an instrumental responding task, we followed the activity of medial PFC (mPFC) and orbitofrontal cortex (OFC) neurons during daily exposure to amphetamine and after a post-withdrawal challenge. Repeated amphetamine increased the number of responsive neurons and the magnitude of responses and modified spontaneous burst patterns. These changes were apparent after a few exposures to amphetamine, were amplified after withdrawal, and were region specific in that repeated amphetamine increasingly produced inhibitory responses in mPFC and excitatory responses in OFC. In behaviorally engaged animals, the gradual enhancement in mPFC inhibition and OFC overactivation correlated with a progressive impairment of instrumental responding. Furthermore, these changes were evident predominately in neurons that displayed phasic responses during task-related events. These rapid-onset and sustained cellular adaptations suggest that even limited exposure to psychostimulants may reduce the influence of mPFC neurons on behavior while at the same time exaggerating information encoded by OFC neurons.

Key words: psychostimulant; cortical plasticity; ensemble unit recording; freely moving rats; psychosis; addiction

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Received Aug. 29, 2005; revised June 6, 2006; accepted June 6, 2006.

Correspondence should be addressed to Bita Maghaddam, Department of Neuroscience, University of Pittsburgh, A210 Langley Hall, Pittsburgh, PA 15260. Email: moghaddam{at}bns.pitt.edu

This article has been cited by other articles:

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