The neocortex contains a multitude of cell types that are segregated into layers and functionally distinct areas. To investigate the diversity of cell types across the mouse neocortex, here we analysed 23,822 cells from two areas at distant poles of the mouse neocortex: the primary visual cortex and the anterior lateral motor cortex. We define 133 transcriptomic cell types by deep, single-cell RNA sequencing. Nearly all types of GABA (γ-aminobutyric acid)-containing neurons are shared across both areas, whereas most types of glutamatergic neurons were found in one of the two areas. By combining single-cell RNA sequencing and retrograde labelling, we match transcriptomic types of glutamatergic neurons to their long-range projection specificity. Our study establishes a combined transcriptomic and projectional taxonomy of cortical cell types from functionally distinct areas of the adult mouse cortex.

The hypothalamic neuropeptide oxytocin (OT), which controls childbirth and lactation, receives increasing attention for its effects on social behaviors, but how it reaches central brain regions is still unclear. Here we gained by recombinant viruses selective genetic access to hypothalamic OT neurons to study their connectivity and control their activity by optogenetic means. We found axons of hypothalamic OT neurons in the majority of forebrain regions, including the central amygdala (CeA), a structure critically involved in OT-mediated fear suppression. In vitro, exposure to blue light of channelrhodopsin-2-expressing OT axons activated a local GABAergic circuit that inhibited neurons in the output region of the CeA. Remarkably, in vivo, local blue-light-induced endogenous OT release robustly decreased freezing responses in fear-conditioned rats. Our results thus show widespread central projections of hypothalamic OT neurons and demonstrate that OT release from local axonal endings can specifically control region-associated behaviors.

18Neocortex contains a multitude of cell types segregated into layers and functionally distinct regions. To 19investigate the diversity of cell types across the mouse neocortex, we analyzed 12,714 cells from the 20 primary visual cortex (VISp), and 9,035 cells from the anterior lateral motor cortex (ALM) by deep single-21cell RNA-sequencing (scRNA-seq), identifying 116 transcriptomic cell types. These two regions represent 22 distant poles of the neocortex and perform distinct functions. We define 50 inhibitory transcriptomic cell 23 types, all of which are shared across both cortical regions. In contrast, 49 of 52 excitatory transcriptomic 24 types were found in either VISp or ALM, with only three present in both. By combining single cell RNA-25 seq and retrograde labeling, we demonstrate correspondence between excitatory transcriptomic types and 26 their region-specific long-range target specificity. This study establishes a combined transcriptomic and 27projectional taxonomy of cortical cell types from functionally distinct regions of the mouse cortex. 28 29 1