Logo Microglia and serotonin axons Dorsal raphe nucleus

The Brain Serotonin Matrix, Microglia, and Blood Platelets

A summary is being prepared.

The Stochastic Process of the Brain Serotonergic Matrix

Serotonergic fibers
Images: (1) A simulated fiber driven by a 3D-stochastic process. (2) A simulated development of 150 fibers that perform a simple random walk. The fibers are not restricted to any layer, which differ only in the length of the step. (3) Serotonergic fibers in the mouse insular cortex. Scale bar = 100 µm.

Virtually all neural processes in the mammalian brain are embedded in a matrix of meandering fibers that release serotonin, a signaling molecule that dates back to the earliest multicellular life forms. The density of this "serotonergic" matrix varies across brain regions, and its perturbations can profoundly affect perception, emotional states, and transitions between wakefulness and sleep. In humans, altered densities of serotonin-releasing fibers have been associated with Autism Spectrum Disorder, prolonged exposure to MDMA ("Ecstasy"), and other conditons.

It is currently assumed that brain regions use an unknown mechanism to actively build and maintain specific serotonergic fiber densities. We have introduced an alternative and more parsimonious hypothesis which states that region-specific densities arise as a mathematical consequence of the stochastic behavior of individual fibers, with no global supervision (Janusonis (2017) Serotonin in space: Understanding single fibers. ACS Chemical Neuroscience 8: 893-896).

In the project, we investigate the 3D-stochastic process that drives single serotonergic fibers. This collaborative effort brings together experimental neurobiology, computer image analysis, and stochastic mathematics.

The project is supported by the California NanoSystems Institute

The Architectures of Early Vertebrate Brains

Elasmobranch brain Elasmobranch brain
Images: (1) A section through a shark cerebellum. (2) Iba1-positive ependymoglia in the swellshark forebrain.

Many sharks have large brains that in their relative size overlap with mammalian brains. The shark brains conform to the general vertebrate plan, but they also show a remarkable variability in how brain divisions are built anatomically and used functionally. This spectrum of possibilities reveals which mammalian brain features are highly idiosyncratic and represent only one of many other possibilities. It also shows what future brains may become, by evolution or human design.

We study the brain cytoarchitectures of a number of shark species, in both the Galeomorphii and Squalomorphii superorders. Some of the extant clades date back to the Triassic (pre-Jurassic) period. We have recently demonstrated that swellsharks express Iba1 (a mammalian microglia-specific protein) in radial ependymoglia, a major element of the shark brain scaffolding (Janusonis (2018) Some galeomorph sharks express a mammalian microglia-specific protein in radial ependymoglia of the telencephalon. Brain, Behavior and Evolution, in press).

This program is rapidly expanding (in species diversity and analysis depth), and we are interested in new collaborations.