Prefrontal cortex modulates firing pattern in the nucleus reuniens of the midline thalamus via distinct corticothalamic pathways. (24th September 2018)

• Record Type: Journal Article
• Authors: Zimmerman, Eric C.; Grace, Anthony A.
• Is Part Of: European journal of neuroscience. Volume 48:Number 10(2018)
• Page Start: 3255
• Page End: 3272
• Publication Date: 2018-09-24
• Subjects: corticothalamic circuits -- limbic thalamus -- thalamic bursting -- thalamic reticular nucleus; Nervous system -- Periodicals; 612.8
• DOI: 10.1111/ejn.14111
• Languages: English
• ISSNs: 0953-816X

Abstract

Abstract: The thalamus has long been recognized for its role in relaying sensory information from the periphery, a function accomplished by its "first‐order" nuclei. However, a second category of thalamic nuclei, termed "higher‐order" nuclei, have been shown instead to mediate communication between cortical areas. The nucleus reuniens of the midline thalamus (RE) is a higher‐order nucleus known to act as a conduit of reciprocal communication between the medial prefrontal cortex (mPFC) and hippocampus. While anatomical and behavioural studies of RE are numerous, circuit‐based electrophysiological studies, particularly those examining the impact of cortical input and the thalamic reticular nucleus (TRN) on RE neuron firing, are sparse. To characterize RE neuron firing properties and dissect the circuit dynamics of the infralimbic subdivision of the mPFC (ilPFC), the TRN and RE, we used in vivo, extracellular, single‐unit recordings in male Sprague Dawley rats and manipulated neural activity using targeted pharmacological manipulations, electrical stimulation and a projection‐specific implementation of designer receptors exclusively activated by designer drugs (DREADDs). We show that ilPFC inhibition reduces multiple burst firing parameters in RE, whereas ilPFC stimulation drives burst firing and dampens tonic firing. In addition, TRN inhibition reduces the number of spontaneously active neurons in RE. Finally, inhibition of ilPFC terminals in RE selectively enhances a subset of burst firing parameters. These findings demonstrate that ilPFC input, both via direct projections and via the TRN, can modulate RE neuron firing pattern in nuanced and complex ways. They also highlight the ilPFC‐TRN‐RE circuit as a likely critical component of prefrontal–hippocampal interactions. Abstract : The nucleus reuniens (RE) is a higher‐order thalamic nucleus that receives input from infralimbic prefrontal cortex (ilPFC) and the thalamic reticular nucleus (TRN) and projects to hippocampus. How these inputs modulate RE firing is not well characterized. We show that manipulation of the ilPFC and/or TRN predominantly modulates burst firing parameters in RE suggesting that ilPFC, both via direct projections and via the TRN, can modulate RE neuron firing pattern in nuanced and complex ways.