The Response to Postnatal Stress: Amino Acids Transporters and PKC Activity

Abstract

It is well known that animals exposed to stressful stimuli during their early life develop different neurological disorders when they become adults. In this study, we evaluated the effect of acute cold stress on gamma-aminobutyric acid (GABA) and L-Serine (L-Ser) transporters in vitro, using the uptake of [(3)H]-GABA and [(3)H]L-Ser by synaptosomes-enriched fractions isolated from rat cerebral cortex during postnatal development. GABA and L-Ser uptake studies in vitro will be used in this investigation as a colateral evidence of changes in the expression of transporters of GABA and L-Ser. We observed that the maximum velocity (V (max)) in L-Ser and GABA uptake after stress session increased in all stages studied. In contrast, K (m) values of L-Ser uptake enhancent in almost age calculated, excluding at PD21 after cold stress during development, at the same time as K (m) (uptake affinity) values of GABA increased in just about age considered but not at PD5 compared with the control group. Finally we investigated the mechanism by which cells regulate the substrate affinity of L-Ser and GABA transporters. We demonstrated a significantly increase in total PKC activity to PD5 from PD21. Pretreatment with PKC inhibitor: staurosporine (SP) led to a restoration of control uptake in several postnatal-days suggesting a relationship between amino acids system and PKC activation. These findings suggest that a single exposure to postnatal cold stress at different periods after birth modifies both GABA and L-Ser transporters and the related increase in total PKC activity could be intracellular events that participate in neuronal plasticity by early life stress, which could be relevant to function of transporters in the adult rat brain.

Consequences of Postnatal Stress: Maternal Separation in Rats Induces Long-Lasting Changes on Glutamate Transporters

“…Rat pups subjected to MS were separated from their mother at postnatal day (PD) (PD1 is the day after birth) PD5, PD7 and PD13 and were placed in separation cages for 1 h [32,33]. Litters were of 10-11 pups.…”

“…To evaluate the effect of AMS plus cold stress rat pups were separated from their mother and exposed to cold (4ºC) during 1 h [33]. Neonates were placed together in a small cage.…”

“…The pellet (P2=crude synaptosomal fraction) was suspended with a glass-PTFE homogenizer in fresh Krebs buffer and again centrifuged at 20,000 g for 20 min. This procedure was repeated three times; the resulting pellet was re-suspended and was used in uptake experiments within 5 hrs of preparation [33,36]. Time course experiments were performed to demonstrate that Glu uptake is linear until 5 min (data not shown).…”

“…Determination of Na + -dependent high-affinity Glu uptake was performed as described by Odeon et al [33]. Uptake experiments were carried out using fresh synaptosome enriched fractions at a concentration of 20 mg of the original tissue (wet weight) per 1 ml of incubation medium.…”

“…Such changes in cell-surface expression can up and down-regulate membrane proteins within minutes and much faster than would be possible by protein synthesis [19,33,45].…”