Acute and chronic ethanol exacerbates formalin pain in neonatal rats.

We have previously reported that withdrawal from acute ethanol (EtOH) exposure lowers mechanical thresholds in post-natal day 7 (P7) and post-natal day 21 (P21) rats. The present study tested the hypothesis that daily administration of 4 g/kg 15% EtOH for 5 days in rats during the human developmental equivalent of the third trimester, but not at a later time in development, would alter mechanical thresholds and formalin-induced pain behaviors. A transient decrease in mechanical thresholds (allodynia) was observed in P7 rats upon withdrawal from repeated EtOH between P3 and P7. When challenged with intraplantar formalin on P11, rats exposed to acute or chronic EtOH had enhanced phase II pain behaviors. In contrast to chronic EtOH administration to rats between P3 and P7, prolonged mechanical allodynia was observed in P21 rats upon withdrawal from chronic EtOH between P17 and P21. Formalin responses were unchanged in P25 rats exposed to acute or chronic EtOH. The affects of EtOH on somatosensory processing are dependent upon the age at which exposure occurs.