Medial septal lesions mimic effects of both selective dorsal and ventral hippocampal lesions

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Neuroanatomy

Background:

• The medial septal area (MS) plays a crucial role in hippocampal function.
• Previous studies on MS lesions have yielded varied results, potentially due to different lesioning techniques.
• Understanding the specific contributions of MS projections to dorsal and ventral hippocampus is essential.

Purpose of the Study:

• To investigate the behavioral consequences of electrolytic medial septal (MS) lesions.
• To determine if MS lesions affect dorsal and ventral hippocampus similarly or distinctly.
• To clarify the role of MS deafferentation in observed behavioral changes.

Main Methods:

• Electrolytic lesions were made in the medial septal area (MS) of rodents.
• Acetylcholinesterase staining was used to assess the extent of hippocampal deafferentation.
• A battery of behavioral tests was employed, including the T-maze, successive alleys, social interaction, and a fear conditioning paradigm (post-shock freezing).

Main Results:

• MS lesions impaired spatial working memory, similar to dorsal hippocampal lesions.
• MS lesions reduced anxiety-like behaviors (successive alleys, social interaction, hyponeophagia) and fear responses (post-shock freezing), mirroring ventral hippocampal lesion effects.
• Histological analysis confirmed depletion of acetylcholinesterase in both dorsal and ventral hippocampus following MS lesions.

Conclusions:

• Electrolytic MS lesions induce a unique behavioral profile by simultaneously deafferenting dorsal and ventral hippocampal regions.
• The observed behavioral effects are likely due to the combined impact on both hippocampal subfields.
• These findings challenge the notion that dorsal hippocampal lesion effects are solely due to demyelination of fibers of passage through the septal pole.