Septal influences on operant responding in the rat

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Neuroanatomy

Background:

• Septal lesions impact various behaviors, but the specific pathways responsible are not fully understood.
• The septum has critical afferent and efferent connections with the hippocampus (via the fornix) and hypothalamus/brainstem (via the medial forebrain bundle).

Purpose of the Study:

• To investigate the roles of the fornix and medial forebrain bundle in mediating the behavioral effects of septal lesions.
• To determine which specific pathway transection replicates behavioral deficits observed after septal lesions.

Main Methods:

• Surgical transection of the fornix and medial forebrain bundle using an encephalotome near the septal area.
• Assessment of behavioral responding in temporally defined paradigms involving response suppression, including differential reinforcement of low rates, discriminated Sidman avoidance, and fixed interval schedules.

Main Results:

• Forntix transection, with minimal direct damage to septal or hippocampal cells, replicated the effects of large septal lesions on behavioral suppression.
• Transection of the medial forebrain bundle fibers did not alter behavior in any of the tested paradigms.
• Previous studies showed medial forebrain bundle transection reproduces other components of the septal lesion syndrome.

Conclusions:

• The fornix pathway is critical for mediating the behavioral suppression deficits observed after septal lesions.
• The medial forebrain bundle's role in the septal lesion syndrome may be related to other behavioral components not assessed in this study.
• These findings help elucidate the specific neuroanatomical substrates underlying septal control of behavior.