Early postnatal nociceptive stimulation results in deficits of spatial memory in male rats.
Prematurely-born infants are exposed to multiple invasive procedures while in the intensive care unit. Newborn rats and humans have similar behavioral responses to noxious stimulation. Previous studies have shown that early noxious stimuli may alter dentate gyrus neurogenesis and the behavioral repertoire of adult rats. We evaluated the late effects of noxious stimulation administered during different phases of development on two spatial memory tests; object recognition (OR) and Morris water maze (WM) tests. Noxious stimulation was induced by an intra-plantar injection of complete Freund's adjuvant (CFA) on postnatal (P) day 1 (group P1) or 8 (P8). Control animals were not stimulated. Behavioral tests were conducted on P60 in both male and female animals. In the WM, three domains were evaluated: acquisition, probe trial performance and reversal re-acquisition. The number of Nissl stained cells in the dentate granule cell layer was assessed by stereological counting. The OR test revealed that P1 male rats had poor long-term memory compared to the control and P8 groups. In the WM, no short- or long-term memory differences were detected between early postnatal-stimulated male and female rats and their respective controls. However, the ability to find the hidden platform in a new position was reduced in P1 male rats. The number of dentate granule cells in P8 males was higher than in all other groups. This study demonstrates that noxious stimulation on P1 results in spatial learning deficits in male animals, but does not disrupt the development of the hippocampus-dependent strategies of learning and memory.
Departamento de Fisiologia, Universidade Federal de São Paulo, São Paulo 04023-062, Brazil.
Cristiane
C
Amaral
Departamento de Psicobiologia, Universidade Federal de São Paulo, São Paulo 04023-062, Brazil.
Bruno
B
Antonio
Departamento de Psicobiologia, Universidade Federal de São Paulo, São Paulo 04023-062, Brazil.
Maria Gabriela Menezes
MG
Oliveira
Departamento de Fisiologia, Universidade Federal de São Paulo, São Paulo 04023-062, Brazil; Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, ON M5T 1R8, Canada; Division of Neurosurgery, Toronto Western Hospital, University of Toronto, 399 Bathurst Street, M5T2S8, Canada.
Clement
C
Hamani
Disciplina de Pediatria Neonatal, Departamento de Pediatria, Universidade Federal de São Paulo, São Paulo 04023-062, Brazil.
Ruth
R
Guinsburg
Departamento de Fisiologia, Universidade Federal de São Paulo, São Paulo 04023-062, Brazil. Electronic address: lucovolan@gmail.com.
Luciene
L
Covolan
D000818:Animals; D000831:Animals, Newborn; D002452:Cell Count; D005260:Female; D006624:Hippocampus / Q000166:cytology*; D008297:Male; D055495:Neurogenesis / Q000502:physiology; D009474:Neurons / Q000166:cytology*; D059225:Nociception / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D021641:Recognition, Psychology / Q000502:physiology*; D012737:Sex Factors; D065852:Spatial Memory / Q000502:physiology*
Hippocampus; Newborn; Nociception; Object recognition; Sex difference; Water maze