Hippocampal and thalamic afferents form distinct synaptic microcircuits in the mouse infralimbic frontal cortex

• Published in: Cell reports (Cambridge) 2021-10, Vol.37 (3), p.109837-109837, Article 109837
• Main Authors: Graham, Kourtney, Spruston, Nelson, Bloss, Erik B.
• Format: Article
• Language: English
• Subjects: Animals; Behavior, Animal; circuit; frontal cortex; Frontal Lobe - cytology; Frontal Lobe - metabolism; Frontal Lobe - physiology; hippocampus; Hippocampus - cytology; Hippocampus - metabolism; Hippocampus - physiology; interneuron; Interneurons - metabolism; Interneurons - physiology; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Nerve Growth Factors - genetics; Nerve Growth Factors - metabolism; Neural Inhibition; Neural Pathways - cytology; Neural Pathways - metabolism; Neural Pathways - physiology; Neuroanatomical Tract-Tracing Techniques; Parvalbumins - genetics; Parvalbumins - metabolism; projection neuron; rabies tracing; Somatostatin - genetics; Somatostatin - metabolism; synapse; Synapses - metabolism; Synapses - physiology; thalamus; Thalamus - cytology; Thalamus - metabolism; Thalamus - physiology; Vasoactive Intestinal Peptide - genetics; Vasoactive Intestinal Peptide - metabolism
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2021.109837

The selection of goal-directed behaviors is supported by neural circuits located within the frontal cortex. Frontal cortical afferents arise from multiple brain areas, yet the cell-type-specific targeting of these inputs is unclear. Here, we use monosynaptic retrograde rabies mapping to examine the distribution of afferent neurons targeting distinct classes of local inhibitory interneurons and excitatory projection neurons in mouse infralimbic frontal cortex. Interneurons expressing parvalbumin, somatostatin, or vasoactive intestinal peptide receive a large proportion of inputs from the hippocampus, while interneurons expressing neuron-derived neurotrophic factor receive a large proportion of inputs from thalamic regions. A similar dichotomy is present among the four different excitatory projection neurons. These results show a prominent bias among long-range hippocampal and thalamic afferent systems in their targeting to specific sets of frontal cortical neurons. Moreover, they suggest the presence of two distinct local microcircuits that control how different inputs govern frontal cortical information processing. [Display omitted] •Neurons in the infralimbic (IL) cortex mediate flexible forms of behavior•IL neurons receive input from multiple brain regions•Rabies mapping identifies inputs to inhibitory and excitatory neurons•Hippocampal and thalamic afferents differentially target specific IL neurons Patterns of synaptic connectivity govern the functional properties of neural circuits. Graham et al. map the afferent neurons targeting eight specific cell classes in mouse infralimbic cortex. Inputs from the hippocampus and thalamus are differentially targeted to specific neurons, suggesting two distinct synaptic microcircuits control circuit transformations.