Suckling in litters with different sizes, and early and late swimming exercise differentially modulates anxiety-like behavior, memory and electrocorticogram potentiation after spreading depression in rats

Abstract

Objective: Analyze the hypothesis that swimming exercise, in rats suckled under distinct litter sizes, alters behavioral parameters suggestive of anxiety and recognition memory, and the electrocorticogram potentiation that occurs after the excitability-related phenomenon that is known as cortical spreading depression (CSD).

Methods: Male Wistar rats were suckled in litters with six or 12 pups (L₆ and L₁₂ groups). Animals swam at postnatal days (P) 8–23, or P60–P75 (early-exercised or late-exercised groups, respectively), or remained no-exercised. Behavioral tests (open field – OF and object recognition – OR) were conducted between P77 and P80. Between P90 and P120, ECoG was recorded for 2 hours. After this ‘baseline’ recording, CSD was elicited every 30 minutes over the course of 2 hours.

Results: Early swimming enhanced the number of entries and the percentage of time in the OF-center (P < 0.05). In animals that swam later, this effect occurred in the L6 group only. Compared to the corresponding sedentary groups, OR-test showed a better memory in the L6 early exercised rats, and a worse memory in all other groups (P < 0.05). In comparison to baseline values, ECoG amplitudes after CSD increased 14–43% for all groups (P < 0.05). In the L₆ condition, early swimming and late swimming, respectively, reduced and enhanced the magnitude of the post-CSD ECoG potentiation in comparison with the corresponding L₆ no-exercised groups (P < 0.05).

Discussion: Our data suggest a differential effect of early- and late-exercise on the behavioral and electrophysiological parameters, suggesting an interaction between the age of exercise and the nutritional status during lactation.

Keywords:

• Swimming exercise
• Nutritional deficiency
• Brain development
• Electroencephalogram
• Cortical spreading depression
• Rat
• Brain excitability
• Litter size

Acknowledgments

The authors thank the financial support from CAPES (AUXPE – CIMAR 1990/2014 and BEX 2036/15-0), CNPq (No. 445101/2014-8), MCT/FINEP/CT-INFRA – PROINFRA – 01/2008. R.C.A. Guedes is Research Fellow from CNPq (No. 303636/2014-9).

Disclaimer statements

Contributors None.

Funding The authors thank the financial support from CAPES (AUXPE – CIMAR 1990/2014 and BEX 2036/15-0), CNPq (No. 445101/2014-8), MCT/FINEP/CT-INFRA – PROINFRA – 01/2008. R. C. A. Guedes is Research Fellow from CNPq (No 303636/2014-9).

Conflicts of interest None.

Ethics approval All experimental procedures were approved by the Ethics Committee for Animal Experiments of our university – CEUA/UFPE (approval protocol number 23076.017295/2012-17), in August 2012, which complies with the Principles of Laboratory Animal Care (National Institutes of Health, Bethesda, USA).

ORCID

Rubem Carlos Araújo Guedes http://orcid.org/0000-0002-2396-4019