RESUMO
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.
Assuntos
Lobo Frontal/fisiologia , Hipocampo/fisiologia , Interneurônios/fisiologia , Sinapses/fisiologia , Tálamo/fisiologia , Animais , Comportamento Animal , Lobo Frontal/citologia , Lobo Frontal/metabolismo , Hipocampo/citologia , Hipocampo/metabolismo , Interneurônios/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fatores de Crescimento Neural/genética , Fatores de Crescimento Neural/metabolismo , Inibição Neural , Vias Neurais/citologia , Vias Neurais/metabolismo , Vias Neurais/fisiologia , Técnicas de Rastreamento Neuroanatômico , Parvalbuminas/genética , Parvalbuminas/metabolismo , Somatostatina/genética , Somatostatina/metabolismo , Sinapses/metabolismo , Tálamo/citologia , Tálamo/metabolismo , Peptídeo Intestinal Vasoativo/genética , Peptídeo Intestinal Vasoativo/metabolismoRESUMO
CA1 pyramidal neurons are a major output of the hippocampus and encode features of experience that constitute episodic memories. Feature-selective firing of these neurons results from the dendritic integration of inputs from multiple brain regions. While it is known that synchronous activation of spatially clustered inputs can contribute to firing through the generation of dendritic spikes, there is no established mechanism for spatiotemporal synaptic clustering. Here we show that single presynaptic axons form multiple, spatially clustered inputs onto the distal, but not proximal, dendrites of CA1 pyramidal neurons. These compound connections exhibit ultrastructural features indicative of strong synapses and occur much more commonly in entorhinal than in thalamic afferents. Computational simulations revealed that compound connections depolarize dendrites in a biophysically efficient manner, owing to their inherent spatiotemporal clustering. Our results suggest that distinct afferent projections use different connectivity motifs that differentially contribute to dendritic integration.