Hyperbilirubinemia remains one of the most frequent clinical diagnoses in the 
neonatal period. This condition may lead to the deposition of unconjugated 
bilirubin (UCB) in the central nervous system, causing nerve cell damage by 
molecular and cellular mechanisms that are still being clarified. To date, all 
the studies regarding bilirubin-induced neurological dysfunction were performed 
in monotypic nerve cell cultures. The use of co-cultures, where 
astrocyte-containing culture inserts are placed on the top of neuron cultures, 
provides the means to directly evaluate the cross-talk between these two 
different cell types. Therefore, this study was designed to evaluate whether 
protective or detrimental effects are produced by astrocytes over UCB-induced 
neurodegeneration. Our experimental model used an indirect co-culture system 
where neuron-to-astrocyte signaling was established concomitantly with the 24 h 
exposure to UCB. In this model astrocytes abrogated the well-known UCB-induced 
neurotoxic effects by preventing the loss of cell viability, dysfunction and 
death by apoptosis, as well as the impairment of neuritic outgrowth. To this 
protection it may have accounted the induced expression of the multidrug 
resistance-associated protein 1 and the 3.5-fold increase in the values of 
S100B, when communication between both cells was established independently of 
UCB presence. In addition, the presence of astrocytes in the neuronal 
environment preserved the UCB-induced increase in glutamate levels, but raised 
the basal concentrations of nitric oxide and TNF-α although no UCB effects were 
noticed. Our data suggest that bidirectional signalling during astrocyte-neuron 
recognition exerts pro-survival effects, stimulates neuritogenesis and sustains 
neuronal homeostasis, thus protecting cells from the immediate UCB injury. These 
findings may help explain why irreversible brain damage usually develops only 
after the first day of post-natal life.