Standard rat chow

Adult (~70 days of age) male Sprague Dawley rats (ARC, Western Australia) were utilised in this study. Rats were pair-housed in standard Makrolon wire-top cages (38x23.5x16cm), kept on a constant 12h light/dark cycle (light phase 0600h-1800h), and provided with standard rat chow (Specialty Feeds, Glen Forrest, Western Australia, Australia) and water ad libitum. Rats were acclimatized to these living conditions for a minimum period of one week prior to any behavioural testing. Both the homeroom and behavioural testing room were located in the same animal facility (Room Temp. 24°C, 40–60% Humidity). All testing was conducted during the light phase and at the same time of day across the sensitisation paradigm. Two separate cohorts of rats were used for the behavioural testing and plasma corticosterone analysis. All procedures were performed with the approval from the University of Queensland Animal Ethics Committee, and followed the Australian code for the care and use of animals for scientific purposes (NHMRC, 8^th Ed, 2013).

All dams were allowed to give birth naturally and all pups were born on day 21–22 of gestation. Within 24 h of birth, all litters were culled to 8 pups, with 4 males and 4 females where possible in order to standardise litter size for suckling. Pups were then cross-fostered to another dam that gave birth within the same 24 h period from either the same or different dietary treatment group. This resulted in 4 groups of offspring: litters from a Control dam cross-fostered onto another Control dam (Control-Control, C-C, n = 8), litters from a Control dam cross-fostered onto a CAF dam (Control-CAF, C-CAF, n = 6), litters from a CAF dam cross-fostered onto a Control dam (CAF-Control, CAF-C, n = 6) and litters from a CAF dam cross-fostered onto another CAF dam (CAF-CAF, n = 6) (Fig. 1).Fig. 1

Diagram of experimental design

Pups remained with their foster mothers until weaning (3 weeks of age). After weaning, the pups were housed with their same-sex littermates (3–4 pups/cage) and were fed with standard rat chow (Specialty Feeds, Glen Forrest, Western Australia, Australia) until 6 weeks of age. Pups were weighed every second day until weaning and once per week thereafter until the end of the experiment.