Comparative Neuroanatomy at single-neuron resolution

Project summary Although single neurons occasionally project to a single downstream target, it is more often the case that their axons collateralize and project to multiple distinct anatomical areas. This feature of neuroanatomy has been appreciated for over 100 years and is theorized to be critical to coordinating brain-wide states. Despite this, collateral projections have largely been overlooked in contemporary neuroscience. This is because mapping collateral projections has practically been beyond the reach of empirical investigation, especially in non-human primates where single neurons can project over wide areas. To surmount these issues, our goal here is the comprehensive development of a sequencing-based approach that will allow us to reveal the patterns of connections of single neurons in non-human primates using Multiplexed Analysis of Projections by Sequencing (MAPseq). This approach allows the full collateral projections of potentially thousands of individual neurons to be mapped in a single animal. The first step towards our goal is to validate a sequencing-based connectomic approach in macaque monkeys that has previously been developed and validated in mice (Aim1). Then, once validated we will determine the local and long-range connections of individual neurons in one part of the limbic system in macaques, the amygdala. Our primary focus here is to determine the patterns of collateral projections from amygdala to the frontal cortex (FC) as these have been implicated in the pathophysiology of many psychiatric disorders. With the method for discerning the multiple projection targets of single neurons in the macaque brain in hand we will then compare the patterns that we see in amygdala to those in mice (Aim 2). We hypothesize that through the expansion and differentiation of FC in non-human primates, single amygdala neurons in non-human primates will be many more collateral projections compared to mice. In summary, when successful, our approach has the potential to fully discern the projection profiles of single neurons in non-human primates. This will enable novel insights into the neuroanatomical networks present in non-human primates, provide a powerful new tool for investigating comparative anatomy and aid interpretation of functional studies that target the amygdala in both non-human primates and mice.