Research

We combine in vitro and in vivo approaches to gain understanding how extracellular signals act on neurotransmission and we work in the identification of novel pathways regulating synaptic functions.

Through the use of Single Cell Cholinergic Microcultures (SCMs), it is possible to investigate how neighboring cells affect synaptic transmission.  We demonstrated that Schwann cells were capable to modify short-term plasticity of cholinergic synapses (Pérez-González, et al. J. Physiol, 2008). We next investigated the factors responsible for such action and found that Secreted Protein Acidic and Rich in Cysteine (SPARC) is one of the molecules participating in the control of synaptic functions by glia (Albrecht et al. Mol. Cel. Neurosci., 2012).  SPARC is a molecule exclusively produced by glial cells in the nervous system. Our results showed that SPARC arrests cholinergic synapses to an immature phenotype.  One of the evidences supporting this finding came from correlative electrophysiology and electron microscopy experiments.
The action of SPARC is concentration dependent. If the concentration of SPARC is particularly high, synaptic contacts are disassembled and eliminated through a cell-autonomous program (López-Murcia et al., PNAS, 2015). The ability of SPARC to eliminate synapses was demonstrated first in SCMs and was confirmed in neuromuscular junctions in living Xenopus tropicalis tadpoles.

Left, effect of SPARC (red) on short term depression.  Reconstruction of representative presynaptic terminals from recorded neurons illustrates that SPARC decreases the overall number of synaptic vesicles, which likely increases paired pulse depression (see Albrecht et al. Mol. Cel. Neurosci., 2012)

Right, correlative electrophysiology and electron microscopy experiments showed that synapses established in SCMs disassemble in the presence of SPARC in a time and concentration dependent manner.
For details see López-Murcia et al., PNAS, 2015.

The transition from an early synaptic contact to a fully functional synapse is poorly understood, because this is a complex process that lasts days and is affected by multiple factors, as for example those produced by glia. We aim to understand the molecular mechanisms that control the process of synaptic maturation during normal development using Xenopus tropicalis tadpoles. Their transparency, accessibility to electrophysiology and imaging approaches, as well as, a great amenability to genetic modification allows us to address in vivo our in vitro findings.   
Olfactory receptor neurons (ORNs) have their cell bodies located in the olfactory epithelium and send their axons to the olfactory bulb to establish synaptic contacts within glomeruli. The great transparency of Xenopus tropicalis tadpoles allows direct visualization of ORNs.  The easiness to study presynaptic terminal function in ORNs of X. tropicalis tadpoles by combining electron microscopy, electrophysiology and imaging allows us to validate our in vitro findings within a neuronal network (Terni et. al, JCN (2017) and Terni et al., JoVE (2018)).

Image of a tadpole indicating the location of the olfactory system. Subpopulations of ORNs can be labeled in transgenic lines using genetically encoded fluorescent reporters. As a result, glomeruli can be visualized at the level of left and right olfactory bulbs.