Past events

The introduction of two-photon microscopy for in vivo imaging has opened the door to chronic monitoring of individual neurons in the adult brain and the study of structural plasticity mechanisms at a very fine scale. Perhaps the biggest contribution of this modern anatomical method has been the discovery that even across the stable excitatory dendritic scaffold there is significant capacity for synaptic remodeling, and that synaptic structural rearrangements are a key mechanism mediating neural circuit adaptation and behavioral plasticity in the adult. To monitor the extent and nature of excitatory and inhibitory synapse dynamics on individual L2/3 pyramidal neurons in mouse visual cortex in vivo, we labeled these neurons with a fluorescent cell fill as well as the fluorescently tagged synaptic scaffolding molecules, Teal-Gephyrin to label inhibitory synapses, and mCherry-PSD-95 to label excitatory synapses. We simultaneously tracked the daily dynamics of both synapse types using spectrally resolved two-photon microscopy. We found that aside from the lower magnitude of excitatory synaptic changes in the adult, as compared to inhibitory ones, excitatory synapse dynamics appear to follow a different logic than inhibitory dynamics. While excitatory dynamics seem to follow a sampling strategy to search for and create connections with new presynaptic partners, inhibitory synapse dynamics likely serve to locally modulate gain at specific cellular locales.

Animal ability to effectively locate and navigate towards food sources is central for survival. Here, using C. elegans nematodes, we revealed a previously unknown mechanism underlying efficient navigation in chemical gradients. This mechanism relies on the orchestrated dynamics of two types of chemosensory neurons: one coding gradients via stochastic pulsatile dynamics, and the second coding the gradients deterministically in a graded manner. The pulsatile dynamics obeys a novel principle where the activity adapts to the magnitude of the gradient derivative, allowing animals to take trajectories better oriented towards the target. The robust response of the second neuron to negative derivatives promotes immediate turns, thus alleviating costs of erroneous turns possibly incurred by the first neuron. This mechanism empowers an efficient navigation strategy which outperforms the classical biased-random walk strategy. Importantly, this mechanism is generalizable and other sensory modalities may use similar principles for efficient gradient-based navigation.

The hypothalamo-neurohypophyseal system (HNS) is an evolutionarily conserved neuroendocrine interface through which the brain regulates body homeostasis by means of releasing neuro-hormones (i.e. oxytocin and vasopressin) from the hypothalamus to the blood circulation. The basic components of the HNS are the hypothalamic axonal projections, endothelial blood vessels and astroglial-like cells, termed pituicytes. These three tissue types converge and interact at the ventral forebrain to establish an efficient neuro-vascular interface, which allows the release of neurohormones from the brain to the periphery. In contrast to BBB-containing CNS vessels, neurohypophyseal capillaries are permeable, which enables bypassing the BBB to transfer HNS hormones and blood-borne substances between brain and circulation. I will present our recent molecular and functional analysis that revealed a new role for pituicytes, in establishing a permeable neuro-vascular conduit that bypasses the BBB.