Lesions and inactivation implicate dorsolateral hindbrain in MFB self-stimulation

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Neurobiology

Background:

• The medial forebrain bundle (MFB) is crucial for reward processing.
• The precise neural circuits mediating MFB reward are not fully understood.
• The motor nucleus of the trigeminal nerve (Mo5) and adjacent structures are implicated in reward pathways.

Purpose of the Study:

• To investigate the role of the motor nucleus of the trigeminal nerve (Mo5) and surrounding areas in the rewarding effects of medial forebrain bundle (MFB) stimulation.
• To determine if lesions or inactivation of the Mo5 region alter the reward value of MFB stimulation.

Main Methods:

• Two experiments were conducted using rats.
• Experiment 1: Serial bilateral lesions of the Mo5 and surrounding areas, followed by assessment of MFB stimulation reward using the rate-frequency curve shift paradigm.
• Experiment 2: Uni- and bilateral injections of lidocaine to temporarily inactivate the target area, assessing MFB stimulation reward.

Main Results:

• Lesions affecting the motor nucleus of the trigeminal nerve (Mo5) did not consistently alter MFB stimulation reward.
• Lesions and lidocaine inactivation near the descending fibers of the superior cerebellar peduncle (scp) significantly increased the reward value of MFB stimulation.
• Inactivation in the ventral cerebellum also increased MFB stimulation reward, particularly when contralateral to the MFB stimulation site.

Conclusions:

• The area around the lateral pole of the superior cerebellar peduncle (scp), potentially involving cerebellar pathways, plays a significant role in medial forebrain bundle (MFB) stimulation reward.
• The motor nucleus of the trigeminal nerve (Mo5) itself may not be critical for MFB reward.
• These findings elucidate specific neural substrates involved in reward processing mediated by the MFB.