Changes in neuronal transmission in the rat hippocampus during behavior

Area of Science:

• Neuroscience
• Behavioral Neuroscience

Background:

• The hippocampus plays a crucial role in memory and navigation.
• Theta activity in the hippocampus is associated with various behavioral states.

Purpose of the Study:

• To investigate how different behaviors (running, drinking, pressing) affect hippocampal CA1 and dentate gyrus activity.
• To explore the influence of the medial septum on hippocampal synaptic efficacy.

Main Methods:

• Implanted stimulating and recording microelectrodes in rat brains.
• Trained rats in a straight alley task involving bar pressing, running, and drinking for water reward.
• Recorded evoked potentials (field EPSP, population spike) and theta activity in the CA1 region and dentate gyrus.

Main Results:

• Commissural stimulation evoked field EPSP and population spikes in CA1, but not dentate.
• CA1 population spike amplitude was highest during running and lowest during drinking.
• Dentate gyrus field potentials showed an inverse pattern, maximal during drinking.
• Perforant path stimulation evoked cell discharges in the dentate gyrus, maximal during drinking.
• Behavior-dependent changes correlated with theta activity frequency and power.
• Stimulation during the negative-going phase of the dentate theta cycle yielded greater granule cell responses.

Conclusions:

• Behavioral states significantly modulate hippocampal CA1 and dentate gyrus excitability.
• The medial septum exerts a powerful influence on the efficacy of hippocampal afferent pathways.
• Theta rhythm phase-dependent stimulation affects neuronal responses in the dentate gyrus.