Effects of different types of neonatal pain on somatosensory and cognitive development in male juvenile rats

Abstract

AbstractBackgroundPremature infants are inevitably exposed to painful events, including repetitive procedures, inflammation, or mixed stimulation that may induce long‐term behavioral outcomes. Here, we set up three neonatal painful models to investigate their long‐term effect on somatosensation and cognition.MethodsThree types of neonatal pain models in rat were set up. Rat pups were randomly assigned to four groups. The needling pain (NP) group received repetitive needle pricks on the paws from the day of birth (PD0) to postnatal day 7 (PD7) to mimic the diagnostic and therapeutic procedures. The inflammatory pain (IP) group received the injection of carrageenan into the left hindpaw at PD3 to induce IP in peripheral tissues. The mixed pain group received a combination of the NP and IP (NIP). The control (CON) group was untreated. We performed behavioral and biochemical testing of juvenile rats (PD21–PD26).ResultsThe NIP group showed a longer hypersensitivity than the NP group, when given a secondary inflammatory stimulation. NP led to insensitivity to anxiety‐causing stimuli and impairment of fear memory both aggravated by NIP. NP reduced the expression of synapse‐related molecules (GluN1/PSD95/GFAP) in the medial prefrontal cortex, and NIP exacerbated this decrease. The corticosterone secretion in the NIP group increased after the behavioral task, compared with those in other three groups.ConclusionA combination of NP with inflammation occurring in the neonatal period might aggravate the adverse effects of each on somatosensory and cognitive development of rats, the mechanism of which might be associated with the increase of corticosterone secretion and the dysregulation of synaptic molecules.