Role of locus coeruleus and serotonergic drug actions on schedule-induced polydipsia

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

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 Bed Nucleus of the Stria Terminalis, Homeostatic Satiety, and Compulsions: What Can We Learn From Polydipsia?

A compulsive phenotype characterizes several neuropsychiatric illnesses - including but not limited to - schizophrenia and obsessive compulsive disorder. Because of its perceived etiological heterogeneity, it is challenging to disentangle the specific neurophysiology that precipitates compulsive behaving. Using polydipsia (or non-regulatory water drinking), we describe candidate neural substrates of compulsivity. We further postulate that aberrant neuroplasticity within cortically projecting structures [i.e., the bed nucleus of the stria terminalis (BNST)] and circuits that encode homeostatic emotions (thirst, hunger, satiety, etc.) underlie compulsive drinking. By transducing an inaccurate signal that fails to represent true homeostatic state, cortical structures cannot select appropriate and adaptive actions. Additionally, augmented dopamine (DA) reactivity in striatal projections to and from the frontal cortex contribute to aberrant homeostatic signal propagation that ultimately biases cortex-dependent behavioral selection. Responding becomes rigid and corresponds with both erroneous, inflexible encoding in both bottom-up structures and in top-down pathways. How aberrant neuroplasticity in circuits that encode homeostatic emotion result in the genesis and maintenance of compulsive behaviors needs further investigation.

Effects of atomoxetine on attention and impulsivity in the five-choice serial reaction time task in rats with lesions of dorsal noradrenergic ascending bundle

Atomoxetine, a noradrenaline reuptake inhibitor (NRI), which is a non-stimulating medicine that is used for the treatment of patients with attention deficit hyperactivity disorder (ADHD), has been found to be effective in reducing behavioral impulsivity in rodents, but its efficacy in a dorsal noradrenergic ascending bundle (DNAB)-lesioned condition has not been examined. The present study aimed to investigate the effects of DNAB lesions on attention and impulsive control in the five-choice serial reaction time task (5-CSRTT) in rats treated with atomoxetine. The drug-induced changes in noradrenaline efflux in the medial prefrontal cortex were also measured. 5-CSRTT-trained rats were included in one of the following groups: N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4)/Atomoxetine, Sham/Atomoxetine, DSP-4/Saline, or Sham/Saline. Acute atomoxetine (0.3 mg/kg) was administered 14 days after the DSP-4 regime. The behavioral testing included manipulations of the inter-trial interval (ITI), stimulation duration and food satiety. In vivo microdialysis of the noradrenaline efflux in the medial prefrontal cortex and the expression of the noradrenaline transporter (NAT) in the DNAB areas were examined. Atomoxetine reduced impulsivity and perseveration in the long-ITI condition with no effects on any other variables. This phenomenon was not influenced by DSP-4 pre-treatment. The DNAB-lesioned rats had lower noradrenaline efflux in the medial prefrontal cortex. DSP-4 caused no change in NAT expression in the DNAB areas. These findings suggested that noradrenaline reuptake may not be exclusively responsible for the atomoxetine effects in adjusting impulsivity. The role of DNAB should also be considered, particularly in conditions requiring greater behavioral inhibition.

The amphetamine sensitization model of schizophrenia symptoms and its effect on schedule-induced polydipsia in the rat

RATIONALE

Amphetamine enhances dopamine (DA) transmission and induces psychotic states or exacerbates psychosis in at-risk individuals. Amphetamine sensitization of the DA system has been proposed as a rodent model of schizophrenia-like symptoms. In humans, excessive nonphysiologic drinking or primary polydipsia is significantly associated with a diagnosis of schizophrenia. In rodents, nonphysiologic drinking can be induced by intermittent presentation of food in the presence of a drinking spout to a hungry animal; this phenomenon is termed, "schedule-induced polydipsia" (SIP).

OBJECTIVE

This study aims to determine the effects of amphetamine sensitization on SIP.

METHODS

We injected rats with amphetamine (1.5 mg/kg) daily for 5 days. Following 4 weeks of withdrawal, animals were food restricted and exposed to the SIP protocol (noncontingent fixed-time 1-min food schedule) for daily 2-h sessions for 24 days.

RESULTS

Results showed that previously amphetamine-injected animals drank more in the SIP protocol and drank more than controls when the intermittent food presentation schedule was removed.

CONCLUSIONS

These findings suggest that hyperdopaminergia associated with schizophrenia may contribute to the development of polydipsia in this population. Whether animals that develop SIP have DA dysfunction or aberrant activity of other circuits that modulate DA activity has yet to be clearly defined.

Comportamento adjunto: controvérsias e contribuições teóricas

A área de investigação sobre comportamento adjunto, cujas pesquisas tiveram início na década de 60, é extensa e controvertida. O presente trabalho analisa as interpretações mais importantes do fenômeno, e mostra que diversas características apresentadas como próprias do comportamento adjunto também estão presentes em outros comportamentos. Falk interpretou o comportamento adjunto como atividade deslocada, Staddon como comportamento induzido por esquema, Timberlake como parte de um sistema comportamental pré-programado, e Wetherington questionou a existência de uma terceira classe de comportamento. Conclui-se que as tentativas de sistematização têm se mostrado incompletas devido à diversidade de topografias de comportamentos adjuntos e a sua dependência de variáveis tanto do esquema como da espécie e do ambiente.

Schedule-induced polydipsia and the nucleus accumbens: electrochemical measurements of dopamine efflux and effects of excitotoxic lesions in the core

The efflux of dopamine (DA) in the nucleus accumbens (NAcc) core during the acquisition of schedule-induced polydipsia (drinking in response to intermittent food presentation) was measured using rapid scan voltammetry. DA efflux increased throughout the SIP sessions, always reaching a peak after the session had terminated. There was, however, no relationship between the acquisition of the drinking response to intermittent food presentation and DA efflux. When water was absent from the test chamber, DA efflux still increased and reached a peak after food delivery was terminated, dissociating drinking and increased DA efflux. Taken in conjunction with previously presented data, these results suggest that the presence of DA in the NAcc core might be necessary for the development of SIP but that its efflux does not bear a systematic relationship to the acquisition of adjunctive behaviour. In a second experiment the effects of NMDA-induced lesions of the NAcc core on the acquisition and performance of SIP were examined. Lesioned rats did not differ to controls in terms of water intake, mean drinking bout length, latency to panel press for food or to begin drinking. The number of drinking bouts/min was reduced in lesioned rats, but did not reach statistical significance; the number of panel presses/min was significantly reduced in lesioned rats. These data demonstrate that the NAcc core is not necessary for the development of SIP but that elements of performance are affected. This suggests that the development of SIP can be fractionated and that different neural elements control different aspects of its expression. These data are used to support the hypothesis that the NAcc core is involved in focusing behaviour and regulating switching between response options.