Abstract
Recent clinical and pre-clinical research suggests that affective biases may play an important role in the development and perpetuation of mood disorders. Studies in animals have also revealed that similar neuropsychological processes can be measured in non-human species using behavioural assays designed to measure biases in learning and memory or decision-making. Given the proposed links between hormones and mood, we used the affective bias test to investigate the effects of different hormone treatments in both male and female rats. Animals were pre-treated with acute doses of hormone or vehicle control prior to learning each of two independent substrate-reward associations. During a subsequent choice test, positive or negative biases were observed by animal’s preference towards or away from the substrate learnt during drug treatment respectively. In both sexes, oestradiol and the oestrogen-like compound bisphenol A induced positive biases, whilst blockade of oestrogen hormones with formestane induced a negative bias. Progesterone induced a negative bias in both sexes, but testosterone only induced a negative bias in males. Blocking testosterone with flutamide induced a positive bias in both sexes at the higher dose (10 mg/kg). The oxytocin analogue, carbetocin induced positive biases in both sexes but the vasopressin analogue, desmopressin, induced a positive bias in male rats only. These results provide evidence that modulating levels of hormones using exogenous treatments can induce affective biases in rats. They also suggest that hormone-induced affective biases influence cognitive and emotional behaviour and could have longer-term effects in some mood disorders.
Highlights
Recent findings suggest that affective biases, may play an important role in the cause and treatment of depression (Harmer et al, 2017; Robinson, 2018)
Acute treatment with the male gonadal hormone, testosterone induced a negative bias in males only (0.0–10.0 mg/kg, RM ANOVA F2,10 = 19.80, p = 0.0001, Fig. 1B) for both 1.0 mg/kg and 10.0 mg/kg doses of testosterone
Our studies have shown that acute hormone treatments can induce affective biases in male and female rats
Summary
Recent findings suggest that affective biases (the process whereby cognitive functions such as learning and memory and decision-making are modified by emotional state), may play an important role in the cause and treatment of depression (Harmer et al, 2017; Robinson, 2018). Antidepressant treatments have been shown to positively bias emotional processing in both healthy volunteers and patients which importantly, can occur after acute or short-term treatment and before subjective changes in mood become apparent (Mogg et al, 2006; Roiser et al, 2012) Building on these empirical observations and underlying neuropsychological hypotheses, tasks have been developed for non-human species which may facilitate quantification of similar affective biases (Mendl et al, 2009; Hales et al, 2014; Robinson, 2018)
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