Medial Prefrontal Cortex Serotonin Input Regulates Cognitive Flexibility in Mice.

The medial prefrontal cortex (mPFC) regulates cognitive flexibility and emotional behavior. Neurons that release serotonin project to the mPFC, and serotonergic drugs influence emotion and cognition. Yet, the specific roles of endogenous serotonin release in the mPFC on neurophysiology and behavior are unknown. We show that axonal serotonin release in the mPFC directly inhibits the major mPFC output neurons. In serotonergic neurons projecting from the dorsal raphe to the mPFC, we find endogenous activity signatures pre-reward retrieval and at reward retrieval during a cognitive flexibility task. In vivo optogenetic activation of this pathway during pre-reward retrieval selectively improved extradimensional rule shift performance while inhibition impaired it, demonstrating sufficiency and necessity for mPFC serotonin release in cognitive flexibility. Locomotor activity and anxiety-like behavior were not affected by either optogenetic manipulation. Collectively, our data reveal a powerful and specific modulatory role of endogenous serotonin release from dorsal raphe-to-mPFC projecting neurons in cognitive flexibility.

Congenital Partial Absence of Pericardium in an Elderly Patient.

Patients with a complete absence of pericardium require no intervention as they are mostly asymptomatic. Due to the risk of herniation, patients with partial absence of pericardium tend to present with symptoms and may benefit from treatment. We report a case of an elderly patient who presented for severe colitis and was incidentally found to have a partial absence of the pericardium on the right side of the heart.