The effects of buspirone on occupancy of dopamine receptors and the rat gambling task

Neurotransmitters crosstalk and regulation in the reward circuit of subjects with behavioral addiction

Behavioral addictive disorders (BADs) have become a significant societal challenge over time. The central feature of BADs is the loss of control over engaging in and continuing behaviors, even when facing negative consequences. The neurobiological underpinnings of BADs primarily involve impairments in the reward circuitry, encompassing the ventral tegmental area, nucleus accumbens in the ventral striatum, and prefrontal cortex. These brain regions form networks that communicate through neurotransmitter signaling, leading to neurobiological changes in individuals with behavioral addictions. While dopamine has long been associated with the reward process, recent research highlights the role of other key neurotransmitters like serotonin, glutamate, and endorphins in BADs' development. These neurotransmitters interact within the reward circuitry, creating potential targets for therapeutic intervention. This improved understanding of neurotransmitter systems provides a foundation for developing targeted treatments and helps clinicians select personalized therapeutic approaches.

New clues for the role of cerebellum in schizophrenia and the associated cognitive impairment

Schizophrenia (SZ) is a complex neuropsychiatric disorder associated with severe cognitive dysfunction. Although research has mainly focused on forebrain abnormalities, emerging results support the involvement of the cerebellum in SZ physiopathology, particularly in Cognitive Impairment Associated with SZ (CIAS). Besides its role in motor learning and control, the cerebellum is implicated in cognition and emotion. Recent research suggests that structural and functional changes in the cerebellum are linked to deficits in various cognitive domains including attention, working memory, and decision-making. Moreover, cerebellar dysfunction is related to altered cerebellar circuit activities and connectivity with brain regions associated with cognitive processing. This review delves into the role of the cerebellum in CIAS. We initially consider the major forebrain alterations in CIAS, addressing impairments in neurotransmitter systems, synaptic plasticity, and connectivity. We then focus on recent findings showing that several mechanisms are also altered in the cerebellum and that cerebellar communication with the forebrain is impaired. This evidence implicates the cerebellum as a key component of circuits underpinning CIAS physiopathology. Further studies addressing cerebellar involvement in SZ and CIAS are warranted and might open new perspectives toward understanding the physiopathology and effective treatment of these disorders.

Individual strategies in the rat gambling task are related to voluntary alcohol intake, but not sexual behavior, and can be modulated by naltrexone

INTRODUCTION

Gambling disorder (GD) is the first non-substance or behavioral addiction to be included in substance-related and addictive disorders in DSM-5. Since GD is a younger phenomenon relative to alcohol and substance use disorders, little is known about potential unique features in GD and to what extent characteristics are shared with alcohol and substance use disorders. The rat gambling task (rGT) is used to study decision-making in rats. This study aimed to identify individual differences in rGT strategies and explore the stability of these strategies over time. Moreover, motor impulsivity, sexual behavior, and voluntary alcohol intake were examined in rats with different rGT strategies. Finally, the response to naltrexone on performance in rats with different rGT strategies was investigated.

METHODS

Male Lister hooded rats (n = 40) underwent repeated testing in the rGT, repeated copulatory behavioral tests, and 7 weeks of voluntary alcohol intake through a modified intermittent two-bottle free-choice paradigm. Finally, rats were treated with naltrexone prior to testing in the rGT.

RESULTS

The results revealed individual choice strategies in the rGT that were stable over time, even after multiple interruptions and other behavioral testing. The rats with a risky choice strategy displayed higher motor impulsivity and voluntary alcohol intake than the other groups. No difference in sexual behavior was found between the different rGT groups. Finally, in all rats irrespectively of rGT strategy, treatment with naltrexone decreased the number of completed trials and premature responses, and increased omissions, which indicates an overall lowered motivation.

DISCUSSION

In conclusion, rats with risky rGT strategies had higher voluntary alcohol intake but not elevated sexual behavior, indicating shared underlying mechanisms between rGT strategies and alcohol intake but not natural rewards in terms of sexual behavior. Finally, naltrexone treatment resulted in an overall lowered motivation in the rGT.

Co-treatment with low doses of buspirone prevents rewarding effects of methylphenidate and upregulates expression of 5-HT1A receptor mRNA in the nucleus accumbens

Accumulating studies consistently show that methylphenidate (MPD), the first line drug for treating Attention-Deficit Hyperactivity Disorder (ADHD), is abused by patients to whom the drug is prescribed. Like other psychostimulants, only low doses of MPD improve cognitive performance while higher doses impair it. Preventing the use of high doses of MPD is important for retaining its therapeutic efficacy. Previously, it has been shown that performance in Morris water maze test is improved in rats treated, orally, with MPD in doses of 2.5 mg/kg; but higher doses (5 mg/kg) impair it. The present study is designed to monitor rewarding effects of 2.5 mg/kg MPD in conditioned place preference (CPP) paradigm and its potential inhibition in buspirone co-treated animals. Our results show that rewarding effects of MPD in CPP paradigm are prevented in rats co-treated with buspirone in doses of 0.1 and 0.3 mg/kg. Animals treated with MPD exhibit a downregulation of 5-HT1A receptor mRNA in the nucleus accumbens which is also prevented in rats co-treated with 0.1 and 0.3 mg/kg but not 1.0 and 2.0 mg/kg buspirone. Administration of buspirone in these doses is not rewarding in CPP test and upregulates 5-HT1A receptor mRNA in the nucleus accumbens. The findings suggest that co-use of low doses of buspirone can prevent rewarding effects of MPD to help retain its therapeutic efficacy.

The Cerebellar Dopaminergic System

In the central nervous system (CNS), dopamine (DA) is involved in motor and cognitive functions. Although the cerebellum is not been considered an elective dopaminergic region, studies attributed to it a critical role in dopamine deficit-related neurological and psychiatric disorders [e.g., Parkinson's disease (PD) and schizophrenia (SCZ)]. Data on the cerebellar dopaminergic neuronal system are still lacking. Nevertheless, biochemical studies detected in the mammalians cerebellum high dopamine levels, while chemical neuroanatomy studies revealed the presence of midbrain dopaminergic afferents to the cerebellum as well as wide distribution of the dopaminergic receptor subtypes (DRD1-DRD5). The present review summarizes the data on the cerebellar dopaminergic system including its involvement in associative and projective circuits. Furthermore, this study also briefly discusses the role of the cerebellar dopaminergic system in some neurologic and psychiatric disorders and suggests its potential involvement as a target in pharmacologic and non-pharmacologic treatments.

Exploring dopaminergic transmission in gambling addiction: A systematic translational review

Dopamine has a crucial and well-documented role in the development and maintenance of Gambling Disorder (GD). This systematic review adopts a translational approach aimed at providing a comprehensive synthesis of current clinical and preclinical knowledge on dopaminergic function in GD at a neurobiological level. To this end, we present and discuss converging dopaminergic alterations and phenotypes. Preclinical and clinical review protocols were registered on the PROSPERO database (CRD42019124404, CRD42019124405). The literature search was conducted in accordance with PRISMA guidelines using three databases (PubMed, Web of Science, Scopus). We identified 67 preclinical studies using pharmacological and non-pharmacological manipulations of the gambling-like phenotype and 33 human studies investigating either genetic polymorphisms or functional brain imaging data. Dopamine transporter and D2, D3, D4 receptor alterations showed strongest translational concordance. Though no postsynaptic dopaminergic alterations were observed, several studies point at dysfunctions in presynaptic dopamine trafficking in GD, suggestive of hyperdopaminergic states. Developing meaningful translational models is essential to working towards the development of an integrated conceptual framework for GD and neurobiologically-based treatment interventions.

Serotonergic treatment normalizes midbrain dopaminergic neuron increase after periaqueductal gray stimulation

Electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) in rats has been shown to elicit panic-like behaviour and can be a useful as an unconditioned stimulus for modelling anticipatory fear and agoraphobia in a contextual fear conditioning paradigm. In this study, we further analysed our previous data on the effects of escitalopram (a selective serotonin reuptake inhibitor, SSRI) and buspirone (a 5-HT1A receptor partial agonist) on dlPAG-induced anticipatory fear behaviour in a rat model using freezing as a measure. We then attempted to unravel some of the interactions with dopamine signalling using tyrosine hydroxylase (TH) immunohistochemistry to probe the effects on dopaminergic neurons. We showed that acute treatment of escitalopram, but not buspirone, was effective in reducing anticipatory freezing behaviour, while chronic administrations of both drugs were effective. We found that the dlPAG stimulation induced increase number of dopaminergic neurons in the ventral tegmental area (VTA) which was reversed in both chronic buspirone and escitalopram groups. We further found a strong positive correlation between the number of dopaminergic neurons and freezing in the VTA and showed positive correlations between dopaminergic neurons in the VTA and substantia nigra pars compacta (SNpc) in escitalopram and buspirone groups, respectively. Overall, we showed that chronic treatment with an SSRI and a 5-HT1A agonist reduced anticipatory freezing behaviour which seems to be associated, through correlative studies, with a reversal of dlPAG stimulation induced increase in number of dopaminergic neurons in the VTA and/or SNpc.

Behavioral effects of buspirone in a mouse model of posttraumatic stress disorder

Buspirone presents a unique profile of action, which involves activation of 5-HT_1A receptors and complex effects on D₂-like dopaminergic receptors. This medication is studied in terms of potential clinical repositioning to conditions that are associated with dopaminergic dysfunctions including schizophrenia and substance use disorder. Buspirone antagonizes D₃ and D₄ receptors, however, depending on the dose it differentially interacts with D₂ receptors. Previously, we reported that some of D₂/D₃ dopaminergic agonists attenuate PTSD-like behavioral symptoms in mice. Here we investigated whether buspirone could also affect PTSD-like symptoms. We used the single prolonged stress (mSPS) protocol to induce PTSD-like behavior in adult male CD-1 mice. Buspirone (0.5, 2, or 10 mg/kg, i.p.) was injected for 15 consecutive days. The subjects were repeatedly examined in a variety of behavioral tests measuring conditioned freezing response, antidepressant-like effects, anxiety, and ultrasonic vocal response to the restraint stress. Mouse SPS resulted in prolonged immobility in the forced swim test and freezing in the fear-conditioning test, and produced symptoms of anxiety. Buspirone dose-dependently decreased the exaggerated freezing response in mice, but only at the dose of 2 mg/kg exhibited the anxiolytic-like effect in the elevated plus maze test. Buspirone reduced the number of ultrasonic calls in mSPS-exposed mice but revealed no antidepressant-like effect in the forced swim test. Present data suggest some positive effects of buspirone in the treatment of selected PTSD-like symptoms and prompt for its further clinical evaluation.

Brain and Cognition for Addiction Medicine: From Prevention to Recovery Neural Substrates for Treatment of Psychostimulant-Induced Cognitive Deficits

Addiction to psychostimulants like cocaine, methamphetamine, and nicotine poses a continuing medical and social challenge both in the United States and all over the world. Despite a desire to quit drug use, return to drug use after a period of abstinence is a common problem among individuals dependent on psychostimulants. Recovery for psychostimulant drug-dependent individuals is particularly challenging because psychostimulant drugs induce significant changes in brain regions associated with cognitive functions leading to cognitive deficits. These cognitive deficits include impairments in learning/memory, poor decision making, and impaired control of behavioral output. Importantly, these drug-induced cognitive deficits often impact adherence to addiction treatment programs and predispose abstinent addicts to drug use relapse. Additionally, these cognitive deficits impact effective social and professional rehabilitation of abstinent addicts. The goal of this paper is to review neural substrates based on animal studies that could be pharmacologically targeted to reverse psychostimulant-induced cognitive deficits such as impulsivity and impairment in learning and memory. Further, the review will discuss neural substrates that could be used to facilitate extinction learning and thus reduce emotional and behavioral responses to drug-associated cues. Moreover, the review will discuss some non-pharmacological approaches that could be used either alone or in combination with pharmacological compounds to treat the above-mentioned cognitive deficits. Psychostimulant addiction treatment, which includes treatment for cognitive deficits, will help promote abstinence and allow for better rehabilitation and integration of abstinent individuals into society.

Dose related effects of buspirone on pain, learning / memory and food intake

The present study concerned extending the therapeutic use of buspirone for treating pain and improving cognition. Effects of single and repeated administration of buspirone were therefore monitored on pain threshold in the hot plate test and on spatial memory in the water maze test in rats. Effects on cumulative food intake were also monitored. The drug was administered intraperitoneally in doses of 0.1, 0.3, 1.0 and 2.0 mg/kg. We found that single and repeated administration of buspirone in doses of 0.1 mg/kg decreased pain threshold in the hot plate test, while doses of 1.0 and 2.0 mg/kg increased it. Effects of single and repeated administration were not different. A dose of 0.3 mg/kg had no effect. Food intake increased following single as well as repeated administration of 0.1 mg/kg buspirone; higher doses had no effect. Low doses (0.1 and 0.3 mg/kg) improved acquisition and retention of memory in the water maze test, while memory extinction was reduced. Higher doses had either no effect (1.0 mg/kg) or impaired (2.0 mg/kg) performance in this test. The results suggest potential therapeutic use of selected doses of buspirone as an analgesic and nootropic drug.

Dopamine and serotonin metabolism associated with morphine reward and its inhibition with buspirone: A study in the rat striatum

Adaptations within the nucleus accumbens (NAc) and caudate nucleus (CN) dopamine neurotransmission are involved in behavioral sensitization and enhanced incentive motivation towards drug paired stimuli which lead to drug addiction. Serotonin (5-hydroxytryptamine; 5-HT) can modulate dopamine neurotransmission to reduce rewarding effects of drugs of abuse. A recent study from our laboratory shows that rewarding effects of morphine are inhibited in rats co-treated with buspirone. To understand the neurochemical mechanism involved in morphine addiction and its inhibition with buspirone, present study determines the effects of buspirone, morphine and their co-administration on the metabolism of serotonin and dopamine in the NAc and CN. We find that rewarding effects of morphine are associated with an enhancement and attenuation of dopamine metabolism, respectively in the CN and NAc. Serotonin metabolism is enhanced in both regions. Co-administration of buspirone not only prevents rewarding effects of morphine, but its effects on the metabolism of dopamine and serotonin in the NAc and CN are also reversed. Results suggest that 5-HT1A receptor dependent modulation of dopamine neurotransmission in the CN and NAc is involved in the modulation of the rewarding effects of morphine in buspirone co-treated animals. The findings documenting an important role of 5-HT1A receptors in drug addiction suggest that synthetic opioid drugs with agonist activity of 5-HT1A receptors may prove non addictive analgesics.

Buspirone Counteracts MK-801-Induced Schizophrenia-Like Phenotypes through Dopamine D3 Receptor Blockade

Background: Several efforts have been made to develop effective antipsychotic drugs. Currently, available antipsychotics are effective on positive symptoms, less on negative symptoms, but not on cognitive impairment, a clinically relevant dimension of schizophrenia. Drug repurposing offers great advantages over the long-lasting, risky and expensive, de novo drug discovery strategy. To our knowledge, the possible antipsychotic properties of buspirone, an azapirone anxiolytic drug marketed in 1986 as serotonin 5-HT_1A receptor (5-HT_1AR) partial agonist, have not been extensively investigated despite its intriguing pharmacodynamic profile, which includes dopamine D₃ (D₃R) and D₄ receptor (D₄R) antagonist activity. Multiple lines of evidence point to D₃R as a valid therapeutic target for the treatment of several neuropsychiatric disorders including schizophrenia. In the present study, we tested the hypothesis that buspirone, behaving as dopamine D₃R antagonist, may have antipsychotic-like activity.

Materials and Methods: Effects of acute administration of buspirone was assessed on a wide-range of schizophrenia-relevant abnormalities induced by a single administration of the non-competitive NMDAR antagonist MK-801, in both wild-type mice (WT) and D₃R-null mutant mice (D₃R^-/-).

Results: Buspirone (3 mg⋅kg^-1, i.p.) was devoid of cataleptogenic activity in itself, but resulted effective in counteracting disruption of prepulse inhibition (PPI), hyperlocomotion and deficit of temporal order recognition memory (TOR) induced by MK-801 (0.1 mg⋅kg^-1, i.p.) in WT mice. Conversely, in D₃R^-/- mice, buspirone was ineffective in preventing MK-801-induced TOR deficit and it was only partially effective in blocking MK-801-stimulated hyperlocomotion.

Conclusion: Taken together, these results indicate, for the first time, that buspirone, might be a potential therapeutic medication for the treatment of schizophrenia. In particular, buspirone, through its D₃R antagonist activity, may be a useful tool for improving the treatment of cognitive deficits in schizophrenia that still represents an unmet need of this disease.