The development of compulsive coping behaviour is associated with a downregulation of Arc in a Locus Coeruleus neuronal ensemble

Abstract

Some compulsive disorders have been considered to stem from the loss of control over coping strategies, such as displacement. However, the cellular mechanisms involved in the acquisition of coping behaviours and their subsequent compulsive manifestation in vulnerable individuals have not been elucidated. Considering the role of the locus coeruleus (LC) noradrenaline-dependent system in stress and related excessive behaviours, we hypothesised that neuroplastic changes in the LC may be associated with the acquisition of an adjunctive polydipsic water drinking, a prototypical displacement behaviour, and the ensuing development of compulsion in vulnerable individuals. Thus, male Sprague Dawley rats were characterised for their tendency, or not, to develop compulsive polydipsic drinking in a schedule-induced polydipsia (SIP) procedure before their fresh brains were harvested. A new quantification tool for RNAscope assays revealed that the development of compulsive adjunctive behaviour was associated with a low mRNA copy number of the plasticity marker Arc in the LC which appeared to be driven by specific adaptations in an ensemble of tyrosine hydroxylase (TH)+, zif268− neurons. This ensemble was specifically engaged by the expression of compulsive adjunctive behaviour, not by stress, because its functional recruitment was not observed in individuals that no longer had access to the water bottle before sacrifice, while it consistently correlated with the levels of polydipsic water drinking only when it had become compulsive. Together these findings suggest that downregulation of Arc mRNA levels in a population of a TH+/zif268− LC neurons represents a signature of the tendency to develop compulsive coping behaviours.

The development of compulsive coping behavior depends on dorsolateral striatum dopamine-dependent mechanisms

“…These results together replicate both previous evidence of individual differences in the tendency to lose control over stress reducing polydipsic water drinking [ 52 , 77 , 78 ] and our original demonstration of individual differences in the reliance on alcohol to cope with stress, the latter being a gateway for the development of excessive and compulsive alcohol drinking [ 52 ].…”

“…At the population level, individuals in the present study developed an adaptive coping response under a SIP procedure [ 75 ], expressed as non-regulatory adjunctive polydipsic drinking behavior. While exposure to intermittent food delivery in food restricted individuals activates the hypothalamic-pituitary-adrenal (HPA) axis [ 13 ] and increases anxiety [ 31 ], the development of polydipsic water drinking, which was shown here to remain stable over up to 42 days, has long been shown to reduce the activity of the HPA axis [ 52 , 77 , 78 ].…”

“…However, within 2 weeks some individuals progressively lost control over the polydipsic drinking response and developed hyperdipsia, a compulsive coping strategy [ 74 , 75 , 80 – 82 ]. In these HD rats, no changes in anxiety levels were seen following SIPw, revealing that in these individuals, even though it has become compulsive, coping behavior remains acutely anxiolytic [ 77 ] and mitigates the otherwise anxiety-inducing effects of the procedure [ 31 ]. This observation lends additional support to the construct validity of hyperdipsia as a model of compulsive behavior, since in compulsive disorders compulsions remain acutely anxiolytic in the context of an overall stress surfeit [ 83 ].…”

Pan‐striatal reduction in the expression of the astrocytic dopamine transporter precedes the development of dorsolateral striatum dopamine‐dependent incentive heroin seeking habits

“…Our in‐house MATLAB‐based pipeline was used to quantitatively detect clusters of RNA molecules (i.e. ‘puncta’) around the nuclei of identified cells (see Velazquez‐Sanchez et al, 2023 for a detailed description of the technical and theoretical elements of our analysis pipeline). The software package is available online (https://gitlab.com/lemur01/rnascopeanalysis).…”

“…RNAscope TM was performed according to the manufacturer's instructions for fresh frozen tissue using the RNAscope TM Multiplex Fluorescent Reagent Kit (Advanced Cell Diagnostics) as previously described (Velazquez-Sanchez et al, 2023). Brain sections were first fixed in chilled 10% NBF for 30 min on ice, rinsed three times in PBS and dehydrated in increasing concentrations of ethanol (50%, 70%, 100% and 100%).…”