Refinements to rodent head fixation and fluid/food control for neuroscience.

The use of head fixation in mice is increasingly common in research, its use having initially been restricted to the field of sensory neuroscience. Head restraint has often been combined with fluid control, rather than food restriction, to motivate behaviour, but this too is now in use for both restrained and non-restrained animals. Despite this, there is little guidance on how best to employ these techniques to optimise both scientific outcomes and animal welfare. This article summarises current practices and provides recommendations to improve animal wellbeing and data quality, based on a survey of the community, literature reviews, and the expert opinion and practical experience of an international working group convened by the UK's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs). Topics covered include head fixation surgery and post-operative care, habituation to restraint, and the use of fluid/food control to motivate performance. We also discuss some recent developments that may offer alternative ways to collect data from large numbers of behavioural trials without the need for restraint. The aim is to provide support for researchers at all levels, animal care staff, and ethics committees to refine procedures and practices in line with the refinement principle of the 3Rs.

Phosphodiesterase 10A inhibitor, MP-10 (PF-2545920), produces greater induction of c-Fos in dopamine D2 neurons than in D1 neurons in the neostriatum.

Studies described here tested the hypothesis that phosphodiesterase 10A inhibition by a selective antagonist, MP-10, activates the dopamine D2 receptor expressing medium spiny neurons to a greater extent than the D1 receptor expressing neurons. We used regional pattern of c-Fos induction in the neostriatal subregions of rodents and direct assessment of D1-positive and -negative neurons in the DRd1a-tdTomato mice for the purpose. MP-10 (1, 3, 10 or 30 mg/kg, PO) dose-dependently increased c-Fos immunopositive nuclei in all regions of neostriatum. However, the effect was statistically greater in the dorsolateral striatum, a region known to be activated preferentially by the D2 antagonism, than the D1-activated dorsomedial striatum. The D2 antagonist, haloperidol (0.3, 1, or 3 mg/kg, PO) produced an identical, regional pattern of c-Fos induction favoring the dorsolateral striatum of the rat. In contrast, the D1 agonist, SKF82958 (0.5, 1, or 2 mg/kg, PO), induced greater expression of c-Fos in the dorsomedial striatum. The C57Bl/6 mouse also showed regionally preferential c-Fos activation by haloperidol (2 mg/kg, IP) and SKF82858 (3 mg/kg, IP). In the Drd1a-tdTomato mice, MP-10 (3 or 10 mg/kg, IP) increased c-Fos immunoreactivity in both types of neurons, the induction was greater in the D1-negative neurons. Taken together, both the regional pattern of c-Fos induction in the striatal sub-regions and the greater induction of c-Fos in the D1-negative neurons indicate that PDE10A inhibition produces a small but significantly greater activation of the D2-containing striatopallidal pathway.

Corticosterone urinalysis and nicotinic receptor modulation in rats.

A routine method of measuring circulating corticosterone (CORT) levels in rats involves sampling of plasma from cannulated animals. However, being somewhat invasive, this method can potentially be confounded by its inherently stressful nature. This study investigated the feasibility of measuring corticosterone using a non-invasive sampling method from voided urine of male rats. Reliability was assessed pharmacologically with nicotinic compounds previously demonstrated to modulate plasma glucocorticoid levels. Nicotine (0.1-1mg/kg sc) dose-dependently increased corticosterone levels in rat urine at 30-70 min following administration. The short-lived nature of this elevation was confirmed as CORT levels measured 6 and 24h later were shown to have returned to basal levels. Both basal and nicotine-induced (0.5mg/kg sc) elevations in urinary CORT were consistent between groups of animals with weights ranging from 200 to 400 g. The magnitude of urinary CORT elevation induced by nicotine (0.5mg/kg sc) was found to be similar to that induced by a forced swim stressor in male Lister ) antagonist mecamylamine (0.05-0.5mg/kg sc) dose-dependently reversed the effects of nicotine (0.5mg/kg sc) on urinary CORT. Finally, the alpha(4)beta(2)-subunit preferring agonist TC-2559 induced a dose-dependent increase in CORT, whereas alpha(7)- and beta(4)-subunit preferring ligands had no effect, suggestive of the potential for differential involvement of nicotinic receptor subtypes in the mediation of this response. In conclusion, urinary corticosterone sampling in rats represents a robust assay sensitive to experimental manipulations of both pharmacological and behavioural relevances.