Lateralization of Hippocampal Dentate Spikes and Sharp-Wave Ripples in Urethane Anesthetized Rats Depends on...

Area of Science:

• Neuroscience
• Physiology
• Chronobiology

Background:

• Neural activity and bodily functions exhibit rhythmic interactions.
• Hippocampal sharp-wave ripples (SPW-Rs) and dentate spikes (DSs) are crucial for memory consolidation.
• The synchronization of SPW-Rs and DSs between brain hemispheres is influenced by physiological states.

Purpose of the Study:

• To investigate the relationship between hippocampal oscillations (SPW-Rs and DSs) and physiological rhythms (breathing and cardiac cycles).
• To examine how cholinergic and parasympathetic tone affects the interhemispheric synchrony of SPW-Rs and DSs.
• To understand the impact of urethane anesthesia on these neural and bodily interactions.

Main Methods:

• Recording of dorsal hippocampal local-field potentials, electrocardiogram, and respiration in urethane-anesthetized rats.
• Administration of atropine to reduce cholinergic and parasympathetic tone.
• Analysis of the phase relationships between hippocampal events and physiological cycles, and their bilateral occurrence.

Main Results:

• Hippocampal oscillations showed variable phase-locking to breathing and no clear relation to cardiac cycles.
• Decreased breathing rate, indicative of increased parasympathetic tone, preceded SPW-R bouts.
• SPW-Rs and DSs were predominantly unilateral; slow breathing and atropine decreased SPW-R bilaterality, while atropine and NREM sleep states increased DS bilaterality.

Conclusions:

• Urethane anesthesia appears to desynchronize DSs but not SPW-Rs between hemispheres.
• Reduced cholinergic and/or parasympathetic tone dissociates SPW-Rs and synchronizes DSs.
• Further research is needed to determine the behavioral and memory consolidation implications of these findings.