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Temporary inactivation of the retrorubral fields decreases the rewarding effect of medial forebrain bundle
1Department of Psychology, University of Wisconsin-Whitewater, 800 W. Main St., Whitewater, WI 53190, USA. waracyzm@mail.uww.edu
Abstract:
Prior studies indicate that lesioning the retrorubral fields (RRF) decreases the rewarding effect of medial forebrain bundle (MFB) stimulation, although these studies did not make the RRF their primary target. This study directly investigates the role of the RRF in MFB self-stimulation using transient lidocaine-induced inactivation of target tissue rather than permanent lesioning. In 18 rats with MFB stimulation electrodes, inactivation of the RRF via 0. 5 and 1.0 microl of 4% lidocaine produced immediate, substantial upward shifts in the frequency required to maintain half-maximal self-stimulation response rates whereas injecting comparable volumes of saline did not. Bilateral inactivation was particularly effective, especially at medium and high stimulation currents, although unilateral inactivation ipsilateral to the stimulation site was also effective. Contralateral inactivation alone did not substantially change the stimulation's reward value, although contralateral inactivation appeared to contribute to the effectiveness of bilateral inactivation. The frequency required to maintain half-maximal responding returned to baseline levels by 15-20 min after lidocaine infusion. In seven rats whose infusion sites were not in the RRF, lidocaine inactivation did not consistently degrade the stimulation's reward value. These results indicate that some neural elements located in the RRF contribute to the rewarding effect of MFB stimulation. Possible roles for these elements in the anatomical substrate for MFB self-stimulation are discussed.
Insights
The retrorubral fields (RRF) are crucial for the rewarding effects of medial forebrain bundle (MFB) stimulation. Transient inactivation of the RRF significantly alters self-stimulation reward, confirming its role in reward pathways.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
- Reward System Research
Background:
- Previous research suggests a role for the retrorubral fields (RRF) in the rewarding effects of medial forebrain bundle (MFB) stimulation.
- However, these studies did not specifically target the RRF, leaving its precise contribution unclear.
Purpose of the Study:
- To directly investigate the role of the RRF in the rewarding effects of MFB self-stimulation.
- To determine if transient inactivation of the RRF alters MFB self-stimulation reward thresholds.
Main Methods:
- Used transient lidocaine-induced inactivation of the RRF in rats with MFB stimulation electrodes.
- Administered varying volumes of lidocaine or saline to assess effects on self-stimulation response rates.
- Compared effects of unilateral and bilateral RRF inactivation, as well as inactivation ipsilateral and contralateral to the stimulation site.
Main Results:
- Lidocaine inactivation of the RRF caused significant upward shifts in the frequency required for half-maximal MFB self-stimulation.
- Bilateral inactivation was most effective, particularly at higher stimulation currents; unilateral inactivation also showed effects.
- Effects were transient, with reward value returning to baseline within 15-20 minutes post-infusion.
Conclusions:
- Neural elements within the RRF are essential for mediating the rewarding effects of MFB stimulation.
- These findings highlight the RRF as a key component of the anatomical substrate underlying reward.
- Transient inactivation provides a valuable method for studying the dynamic role of specific brain regions in reward.