No abstract

Schedule-induced polydipsia (SIP) is an animal model of compulsive drinking that selects for individual differences and varies across rat strains. The aim of this study was to investigate excessive habit formation by analyzing the SIP licking microstructure among rat strains, and to compare the brain areas activated by SIP in different populations. Wistar, Long Evans and Roman High- and Low-Avoidance rat strains were compared using a cluster analysis of 2 main variables, that is, frequency of licking (percentage of interpellet intervals with drinking episodes) and intensity of licking (mean number of licks per interpellet interval), and were found to exhibit high intensity and frequent licking (compulsive drinkers, CD), low intensity but frequent licking (habitual drinkers, HD), and low intensity and low-frequency licking (low drinkers, LD). The Wistar strain showed a higher frequency and intensity of licking, and had the largest group of CD rats when compared with the other strains. Regarding the acquisition of SIP, CD rats showed a higher intensity of licking when compared with the HD and LD rats. Moreover, c-Fos quantification revealed that rats in the CD group showed hyperactivity in the lateral orbitofrontal cortex and basolateral amygdala when compared with the LD group. Analyzing the SIP microstructure could be a valuable tool for understanding the role of excessive habit formation in the development of compulsive drinking and its underpinning neurobiological mechanisms.

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Compulsive behavior is observed in several neuropsychiatric disorders such as obsessive-compulsive disorder (OCD), anxiety, depression, phobia, and schizophrenia. Thus, compulsivity has been proposed as a transdiagnostic symptom with a highly variable pharmacological treatment. Recent evidence shows that glutamate pharmacotherapy may be of benefit in impaired inhibitory control. The purpose of the present study was: first, to test the comorbidity between compulsivity and other neuropsychiatric symptoms on different preclinical behavioral models; second, to assess the therapeutic potential of different glutamate modulators in a preclinical model of compulsivity. Long Evans rats were selected as either high (HD) or low (LD) drinkers corresponding with their water intake in schedule-induced polydipsia (SIP). We assessed compulsivity in LD and HD rats by marble burying test (MBT), depression by forced swimming test (FST), anxiety by elevated plus maze (EPM) and fear behavior by fear conditioning (FC) test. After that, we measured the effects of acute administration (i.p.) of glutamatergic drugs: N-Acetylcysteine (NAC; 25, 50, 100 and 200 mg/kg), memantine (3.1 and 6.2 mg/kg) and lamotrigine (15 and 30 mg/kg) on compulsive drinking on SIP. The results obtained showed a relation between high compulsive drinking on SIP and a higher number of marbles partially buried in MBT, as well as a higher percentage of freezing on the retrieval day of FC test. We did not detect any significant differences between LD and HD rats in FST, nor in EPM. The psychopharmacological study of glutamatergic drugs revealed that memantine and lamotrigine, at all doses tested, decreased compulsive water consumption in HD rats compared to LD rats on SIP. NAC did not produce any significant effect on SIP. These results indicate that the symptom clusters of different forms of compulsivity and phobia might be found in the compulsive phenotype of HD rats selected by SIP. The effects of memantine and lamotrigine in HD rats point towards a dysregulation in the glutamatergic signaling as a possible underlying mechanism in the vulnerability to compulsive behavior on SIP. Further studies on SIP, could help to elucidate the therapeutic role of glutamatergic drugs as a pharmacological strategy on compulsive spectrum disorders.

These data provide new evidence that low doses of scopolamine and intermediate doses of methamphetamine might therapeutically reduce compulsive behaviors and suggest that there is not a direct participation of the endocannabinoid system in compulsive behavior on SIP. The research in the underlying neurochemical mechanisms of these psychoactive drugs might provide an additional insight on new therapeutic targets in compulsive neuropsychiatric disorders.