Too Little and Too Much: Balanced Hippocampal, But Not Medial Prefrontal, Neural Activity Is Required for Intact...

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Behavioral Neuroscience

Background:

• Impaired GABAergic inhibition (neural disinhibition) in the prefrontal cortex and hippocampus is linked to cognitive deficits.
• The novel object recognition (NOR) task is a standard method for assessing cognitive deficits in rodents.
• The specific roles of prefrontal and hippocampal GABAergic inhibition in NOR performance remain unclear.

Purpose of the Study:

• To investigate the contribution of medial prefrontal cortex (mPFC), dorsal hippocampus (DH), and ventral hippocampus (VH) GABAergic inhibition to NOR task performance.
• To differentiate the effects of neural disinhibition versus functional inhibition on NOR in these brain regions.

Main Methods:

• Male Lister hooded rats were used in a within-subject design.
• Intracerebral microinfusions of the GABA_A receptor antagonist picrotoxin (disinhibition) or agonist muscimol (inhibition) were administered bilaterally to mPFC, DH, and VH.
• NOR task performance was assessed after a 1-minute retention delay, comparing regional saline, picrotoxin, and muscimol infusions.

Main Results:

• Neither mPFC neural disinhibition nor functional inhibition impacted NOR performance.
• Neural disinhibition in both DH and VH significantly impaired NOR, primarily by reducing novel object exploration time.
• DH functional inhibition impaired NOR, while VH functional inhibition showed non-specific behavioral effects at higher doses.

Conclusions:

• Hippocampal, but not prefrontal, GABAergic inhibition is essential for NOR at a 1-minute retention delay.
• Optimal NOR performance requires balanced neural activity in the DH; both hypo- and hyper-activity impair memory.
• The NOR task is a valuable tool for studying hippocampal GABAergic dysfunction in rodent models.