Profile of Nucleotide Catabolism and Ectonucleotidase Expression from the Hippocampi of Neonatal Rats After Caffeine Exposure

Nucleotides and nucleosides play an important role in neurodevelopment acting through specific receptors. Ectonucleotidases are the major enzymes involved in controlling the availability of purinergic receptors ligands. ATP is co-released with several neurotransmitters and is the most important source of extracellular adenosine by catabolism exerted by ectonucleotidases. The main ectonucleotidases are named NTPDases (1-8) and 5'-nucleotidase. Adenosine is a powerful modulator of neurotransmitter release. Caffeine blocks adenosine receptor activity as well as adenosine-mediated neuromodulation. Considering the susceptibility of the immature brain to caffeine and the need for correct purinergic signaling during fetal development, we have analyzed the effects of caffeine exposure during gestational and lactational periods on nucleotide degradation and ectonucleotidase expression from the hippocampi of 7-, 14-and 21-days-old rats. Nucleotides hydrolysis was assessed by colorimetric determination of inorganic phosphate released. Ectonucleotidases expression was performed by RT-PCR. ATP and ADP hydrolysis displayed parallel age-dependent decreases in both control and caffeine-treated groups. AMP hydrolysis increased with caffeine treatment in 7-days-old rats (75%); although there was no significant difference in AMP hydrolysis between control (non caffeine-treated) rats and 14- or 21-days caffeine-treated rats. ADP hydrolysis was not affected by caffeine treatment. Caffeine treatment in 7- and 14-days-old rats decreased ATP hydrolysis when compared to the control group (19% and 60% decrease, respectively), but 21-days-treated rats showed an increase in ATP hydrolysis (39%). Expression levels of NTPDase 1 and 5 decreased in hippocampi of caffeine-treated rats. The expression of 5'-nucleotidase was not affected after caffeine exposure. The changes observed in nucleotide hydrolysis and ectonucleotidases expression could promote subtle effects on normal neural development considering the neuromodulatory role of adenosine.