Concomitant behavioral and PFC neuronal activity recorded following dose-response protocol of MPD in adult male rats
Sidish S Venkataraman1, Catherine Claussen1, Michael Joseph1
1University of Texas McGovern Medical School at Houston, Department of Neurobiology and Anatomy, 6431 Fannin Street, Houston, TX 77030, United States.
Abstract:
The use of methylphenidate (MPD), a commonly prescribed drug to treat attention-deficit hyperactivity disorder (ADHD), has steadily increased over the past 25 years. This trend has been accompanied by more MPD abuse by ordinary individuals for its cognitive enhancing effects. Therefore, understanding the effects of MPD on the prefrontal cortex (PFC), a brain area involved in higher cortical processing such as executive function, language, planning, and attention regulation, is of particular importance. The goal of this study is to investigate the effects of acute and chronic dose-response characteristics following MPD exposure on both the PFC neuronal population and behavioral activity in freely behaving animals implanted previously with permanent electrodes within the PFC. Four groups of animals were used: saline (control), 0.6, 2.5, and 10.0mg/kg MPD. It was observed that the same dose of either 0.6, 2.5, or 10.0mg/kg repetitive (chronic) MPD exposure elicited behavioral sensitization in some animals and behavioral tolerance in others, and that the majority of PFC units recorded from animals expressing behavioral sensitization to chronic MPD exposure responded to MPD by increasing their neuronal firing rate, whereas the majority of PFC neurons recorded from animals expressing behavioral tolerance in response to chronic MPD responded by decreasing their neuronal firing rate. This data suggests that in animals that display behavioral sensitization, chronic MPD exposure causes an increase in the number of post-synaptic D1 dopamine receptors leading to an increase in behavioral and neuronal firing rate, while in animals that display behavioral tolerance, chronic MPD exposure causes an increase in the number of post-synaptic D2 dopamine receptors leading to a decrease in behavioral and neuronal firing rate. This dichotomy needs to be further investigated.
Insights
Methylphenidate (MPD) affects the prefrontal cortex (PFC) differently with chronic use, causing either increased or decreased neuronal activity. This response is linked to changes in dopamine receptors, suggesting distinct pathways for behavioral sensitization and tolerance.
Area of Science:
- Neuroscience
- Pharmacology
Background:
- Methylphenidate (MPD) use for ADHD and its abuse for cognitive enhancement have increased.
- The prefrontal cortex (PFC) is crucial for executive functions, making MPD's effects on it important.
- Understanding MPD's impact on PFC neuronal and behavioral activity is vital.
Purpose of the Study:
- To investigate acute and chronic dose-response effects of MPD on PFC neuronal and behavioral activity.
- To analyze MPD's impact on freely behaving animals with implanted PFC electrodes.
Main Methods:
- Four animal groups received saline (control), 0.6, 2.5, or 10.0mg/kg MPD.
- Chronic MPD exposure was administered.
- PFC neuronal activity and behavioral responses were recorded.
Main Results:
- Chronic MPD induced either behavioral sensitization or tolerance in animals.
- Animals with sensitization showed increased PFC neuronal firing rates.
- Animals with tolerance showed decreased PFC neuronal firing rates.
Conclusions:
- Chronic MPD exposure leads to distinct PFC responses, increasing D1 dopamine receptors in sensitization and D2 receptors in tolerance.
- This suggests different neurobiological mechanisms underlie MPD-induced behavioral sensitization and tolerance.
- Further investigation into this dichotomy is warranted.
