Improved timed-mating, non-invasive method using fewer unproven female rats with pregnancy validation via early body mass increases.

For studies requiring accurate conception-timing, reliable, efficient methods of detecting oestrus reduce time and costs, whilst improving welfare. Standard methods use vaginal cytology to stage cycle, and breeders are paired-up using approximately five proven females with proven males to achieve at least one conception on a specific day. We describe an alternative, fast, consistent, non-invasive method of timed-mating using detection of lordosis behaviour in Wistar and Lister-Hooded rats that used unproven females with high success rates. Rats under reverse lighting had body masses recorded pre-mating, day (d) 3-4, d8, d10 and d18 of pregnancy. Using only the presence of the oestrus dance to time-mate females for 24 hours, 89% of Wistar and 88% of Lister-Hooded rats successfully conceived. We did not observe behavioural oestrus in Sprague-Dawleys without males being present. Significant body mass increases following mating distinguished pregnant from non-pregnant rats, as early as d4 of pregnancy (10% ± 1.0 increase cf. 3% ± 1.2). The pattern of increases throughout gestation was similar for all pregnant rats until late pregnancy, when there were smaller increases for primi- and multiparous rats (32% ± 2.5; 25% ± 2.4), whereas nulliparous rats had highest gains (38% ± 1.5). This method demonstrated a distinct refinement of the previous timed-mating common practice used, as disturbance of females was minimised. Only the number required of nulli-, primi- or multiparous rats were mated, and body mass increases validated pregnancy status. This new breeding management method is now established practice for two strains of rat and has resulted in a reduction in animal use.

Chronic amphetamine enhances visual input to and suppresses visual output from the superior colliculus in withdrawal.

Heightened distractibility is a core symptom of Attention Deficit Hyperactivity Disorder (ADHD). Effective treatment is normally with chronic orally administered psychostimulants including amphetamine. Treatment prevents worsening of symptoms but the site of therapeutic processes, and their nature, is unknown. Mounting evidence suggests that the superior colliculus (SC) is a key substrate in distractibility and a therapeutic target, so we assessed whether therapeutically-relevant changes are induced in this structure by chronic oral amphetamine. We hypothesized that amphetamine would alter visual responses and morphological measures. Six-week old healthy male rats were treated with oral amphetamine (2, 5 or 10 mg/kg) or a vehicle for one month after which local field potential and multiunit recordings were made from the superficial layers of the SC in response to whole-field light flashes in withdrawal. Rapid Golgi staining was also used to assess dendritic spines, and synaptophysin staining was used to assess synaptic integrity. Chronic amphetamine increased local field potential responses at higher doses, and increased synaptophysin expression, suggesting enhanced visual input involving presynaptic remodelling. No comparable increases in multiunit activity were found suggesting amphetamine suppresses collicular output activity, counterbalancing the increased input. We also report, for the first time, five different dendritic spine types in the superficial layers and show these to be unaffected by amphetamine, indicating that suppression does not involve gross postsynaptic structural alterations. In conclusion, we suggest that amphetamine produces changes at the collicular level that potentially stabilise the structure and may prevent the worsening of symptoms in disorders like ADHD.

Repeated intermittent oral amphetamine administration results in locomotor tolerance not sensitization.

BACKGROUND: The phenomenon of locomotor sensitization to injected amphetamine is well-characterised. The increased locomotor activity found acutely is enhanced with repeated intermittent treatment. This effect arises due to hypersensitization of the dopaminergic system and is linked to drug addiction. A clinical population exposed to chronic repeated intermittent amphetamine treatment, such as is found for attention deficit hyperactivity disorder (ADHD), may be expected to be more at risk of addiction following this treatment. However, evidence suggests the opposite may be true. This suggests the route of administration may determine the direction of effects. AIMS AND METHODS: We aimed to establish how an oral amphetamine treatment regimen, similar to that used in ADHD, impacts on locomotor activity, specifically whether tolerance or sensitization would arise. Healthy hooded Lister rats were given amphetamine (2 mg/kg, 5 mg/kg and 10 mg/kg) or a vehicle solution once daily for 4 weeks with a 5 day on, 2 day off schedule. Locomotor activity was measured on the first day of treatment to establish the acute effects and on the final day of treatment to examine the chronic effects. RESULTS: As expected, acute doses of amphetamine increased locomotor activity, although this only reached statistical significance for the 5 mg/kg and 10 mg/kg doses. By contrast, after chronic treatment, animals administered these doses showed reduced activity indicating drug tolerance rather than sensitization had occurred. CONCLUSION: We suggest that the route of administration used in ADHD, which results in more stable and longer duration drug levels in the blood, results in tolerance rather than sensitization and that this effect could explain the reduced likelihood of substance addiction in those treated with psychostimulants for ADHD.

Chronic amphetamine treatment affects collicular-dependent behaviour.

Distractibility can be defined as an attention deficit where orientation toward irrelevant targets cannot be inhibited. There is now mounting evidence that the superior colliculus is a key neural correlate of distractibility, with increased collicular-activity resulting in heightened distractibility. Heightened distractibility is reduced by amphetamine, which acutely suppresses collicular responsiveness. However, when amphetamine is used to treat distractibility, it is given chronically, yet no data exist on whether chronic amphetamine treatment affects the colliculus. Here, the effect of chronic amphetamine treatment was assessed in healthy hooded lister rats on two collicular dependent behaviours following a twenty-eight day treatment period: i) orienting to visual stimuli, and ii) height-dependent modulation of air-righting. We found no significant impact of amphetamine treatment on visual orienting despite showing dose-dependent decreases in orienting to repeated stimuli. However, we did find that treatment with amphetamine significantly reduced the ability to modulate righting according to the height the animal is dropped from - a function known to be dependent on the colliculus. We suggest that the results are in line with previous research showing acute amphetamine suppresses collicular activity and we speculate that the psychostimulant may increase receptive field size, altering time-to-impact calculations carried out by the colliculus during air-righting.