Diazepam modulates lateral hypothalamic self-stimulation but not stimulation-escape in rats

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Neuropharmacology

Background:

• Electrical stimulation of the lateral hypothalamus (LH) can elicit feeding and self-stimulation in rats.
• The effects of drugs like diazepam (DZ) on these behaviors are not fully understood.
• Distinguishing between reward and aversion systems in the brain is crucial for understanding motivated behaviors.

Purpose of the Study:

• To investigate the neural substrates of reward and aversion in the rat hypothalamus.
• To determine the effects of diazepam (DZ) on stimulation-bound feeding (SBF) and self-stimulation (SS) versus stimulation-escape (SE).
• To differentiate between a diazepam-sensitive reward system and a drug-resistant aversion system.

Main Methods:

• Rats with chronically implanted LH electrodes were tested for SBF and bar-pressing rates for SS and SE.
• Animals were tested with and without systemic diazepam (DZ) administration.
• Histological analysis of electrode placements was performed to correlate behavior with brain regions.

Main Results:

• Pure-reward rats (exhibiting SBF) had electrode tips in the medial forebrain bundle (MFB) and zona inserta near the ventromedial nucleus of the hypothalamus (VMH).
• Reward-escape rats (not exhibiting SBF) had more anterior electrode placements in the MFB.
• Diazepam increased SS rates and decreased SBF thresholds in both groups, while SE rates remained unchanged.

Conclusions:

• The results support the existence of distinct neural substrates for reward and aversion in the LH.
• A diazepam-sensitive reward system is present in both reward and reward-escape rats.
• A drug-resistant aversion system, more strongly engaged in reward-escape rats, operates independently of the reward system.