The effect of a reduced streptozocin dose and social housing on well-being, mechanical hypersensitivity and burrowing behaviour in type 1 diabetes rodents

Background and aimsThe Streptozocin (STZ) induced type 1 rodent model of diabetes is widely used to preclinically evaluate the efficacy of novel analgesics against diabetic polyneuropathy (Islam, 2013). Burrowing is a spontaneously-expressed rodent behaviour that reflects animal well-being (Deacon, 2006; Jirkof, 2014). Burrowing is reduced in mononeuropathic pain states and reversed by clinical analgesics (Andrews, 2012, Lau, 2013, Rutten, 2018) suggesting its usefulness as a measure of pain with improved face validity over evoked measures of hypersensitivity. However, burrowing deficits following a high dose of STZ (75mg/kg) reflects diabetes-associated alteration of the animals’ well-being; and not spontaneous pain, due to a lack of reversal with the clinical analgesic, pregabalin (Rutten, 2018). Previously our group have reported a similar decline in burrowing following a high dose (65mg/kg) of STZ that is resistant to pregabalin, but can be reversed by social pairing, indicating pair housing of diabetic rats can improve their well-being and consequently burrowing behaviour (Fisher 2016). In this study we compared a low and high dose of STZ on the development of type 1 diabetes, burrowing performance, mechanical hypersensitivity and reversal with pregabalin.•MethodsThis work was conducted in accordance with guidelines established by the Animals (Scientific Procedures) Act 1986 / ASPA Amendment Regulations 2012. Male Wistar rats (350-400g, Charles River, UK) were administered a single intraperitoneal injection of 55mg/kg (low dose), 65mg/kg STZ (high dose) or 20mM citrate buffer (pH 4.5, control). Mechanical hypersensitivity was evaluated using Von Frey threshold, burrowing was assessed by displacement of pea shingle after 120 min. Between day 14 and 18 post-STZ pregabalin (30mgkg) was administered orally for 2 days and mechanical hypersensitivity and burrowing were evaluated up to 2 hours post-treatment.•ResultsA low STZ dose (55mgkg) reduced toxicity, body weight loss, polyphagia, polydipsia and the development of burrowing deficits as a measure of wellbeing over a period of 18 days. Both the low and high STZ dose (55 and 65mg/kg, respectively) induced rapid and sustained changes in rats that are seen in diabetic patients, including hyperglycaemia (28.83±1.21mmol/L versus 33.08±0.15mmol/L) and neuropathic pain (mechanical hypersensitivity paw withdrawal threshold (PWT) 6.04±0.84g versus 5.06±0.65g) which were completely reversed by pregabalin (30mg/kg po over 2 days). A >60% change in PWT from baseline was used as the threshold for the development of mechanical hypersensitivity. There was no significant difference in pain responders between both diabetic STZ dose groups (55mgkg: 12 out of 15 responded mean % change 71.5±3.28%; 65mgkg: 14 out of 17 responded with mean % change 78.9±2.2%) sustained for up to 18 days. For up to 10 days (post STZ administration) burrowing performance of low and high dose STZ-diabetic rats significantly increased (compared to control rats) if they burrowed with their respective cage partner (rather than on their own). After two weeks (post STZ administration) burrowing performance progressively declined in both STZ-diabetic groups and was not reversed by pregabalin. •ConclusionsWe conclude a low 55mgkg dose of STZ improves well-being (body weight, polyphagia, polydipsia, burrowing) of diabetic rats with no change in face and predictive validity using the analgesic pregabalin on mechanical hyperalgesia, compared with a higher 65mgkg STZ dose. Progressive Impairments in burrowing over 18 days following both a low and high STZ dose may be directly caused by an increase in spontaneous pain and / or diabetes-associated alteration of animals’ wellbeing. Reversal of burrowing performance of only diabetic STZ rats by social pairing demonstrates diabetic rats are sensitive to short term isolation from their partners (conspecifics), in contrast to control rats. Consideration of the dose of STZ and pair housing during pain testing endpoints (PWT, burrowing) is recommended to maximise the welfare and wellbeing of diabetic rodents and identify the effectiveness of analgesics on burrowing performance at earlier time points in this model.