Fluoxetine Potentiates Oral Methylphenidate-Induced Gene Regulation in the Rat Striatum

Vilazodone, a Selective Serotonin Reuptake Inhibitor with Diminished Impact on Methylphenidate-Induced Gene Regulation in the Striatum: Role of 5-HT1A Receptor

Selective serotonin reuptake inhibitors (SSRIs), including fluoxetine, are frequently combined with medical psychostimulants such as methylphenidate (Ritalin), for example, in the treatment of attention-deficit hyperactivity disorder/depression comorbidity. Co-exposure to these medications also occurs with misuse of methylphenidate as a recreational drug by patients on SSRIs. Methylphenidate, a dopamine reuptake blocker, produces moderate addiction-related gene regulation. Findings show that SSRIs such as fluoxetine given in conjunction with methylphenidate potentiate methylphenidate-induced gene regulation in the striatum in rats, consistent with a facilitatory action of serotonin on addiction-related processes. These SSRIs may thus increase methylphenidate's addiction liability. Here, we investigated the effects of a novel SSRI, vilazodone, on methylphenidate-induced gene regulation. Vilazodone differs from prototypical SSRIs in that, in addition to blocking serotonin reuptake, it acts as a partial agonist at the 5-HT1A serotonin receptor subtype. Studies showed that stimulation of the 5-HT1A receptor tempers serotonin input to the striatum. We compared the effects of acute treatment with vilazodone (10-20 mg/kg) with those of fluoxetine (5 mg/kg) on striatal gene regulation (zif268, substance P, enkephalin) induced by methylphenidate (5 mg/kg), by in situ hybridization histochemistry combined with autoradiography. We also assessed the impact of blocking 5-HT1A receptors by the selective antagonist WAY-100635 (0.5 mg/kg) on these responses. Behavioral effects of these drug treatments were examined in parallel in an open-field test. Our results show that, in contrast to fluoxetine, vilazodone did not potentiate gene regulation induced by methylphenidate in the striatum, while vilazodone enhanced methylphenidate-induced locomotor activity. However, blocking 5-HT1A receptors by WAY-100635 unmasked a potentiating effect of vilazodone on methylphenidate-induced gene regulation, thus confirming an inhibitory role for 5-HT1A receptors. Our findings suggest that vilazodone may serve as an adjunct SSRI with diminished addiction facilitating properties and identify the 5-HT1A receptor as a potential therapeutic target to treat addiction.

Effect of cesarean section on the risk of autism spectrum disorders/attention deficit hyperactivity disorder in offspring: a meta-analysis

PURPOSE

This study was conducted to investigate the relationship between cesarean section (CS) offspring and autism spectrum disorders (ASD)/attention deficit hyperactivity disorder (ADHD).

METHODS

Searching of the databases (PubMed, Web of Science, Embase, and Cochrane Library) for studies on the relationship between mode of delivery and ASD/ADHD until August 2022. The primary outcome was the incidence of ASD/ADHD in the offspring.

RESULTS

This meta-analysis included 35 studies (12 cohort studies and 23 case-control studies). Statistical results showed a higher risk of ASD (odds ratio (OR) = 1.25, P < 0.001) and ADHD (OR = 1.11, P < 0.001) in CS offspring compared to the VD group. Partial subgroup analysis showed no difference in ASD risk between CS and VD offspring in sibling-matched groups (OR = 0.98, P = 0.625). The risk of ASD was higher in females (OR = 1.66, P = 0.003) than in males (OR = 1.17, P = 0.004) in the CS offspring compared with the VD group. There was no difference in the risk of ASD between CS under regional anesthesia group and VD group (OR = 1.07, P = 0.173). However, the risk of ASD was higher in the CS offspring under general anesthesia than in the VD offspring (OR = 1.62, P < 0.001). CS offspring developed autism (OR = 1.38, P = 0.011) and pervasive developmental disorder-not otherwise specified (OR = 1.46, P = 0.004) had a higher risk than VD offspring, but there was no difference in Asperger syndrome (OR = 1.19, P = 0.115). Offspring born via CS had a higher incidence of ADHD in different subgroup analyses (sibling-matched, type of CS, and study design).

CONCLUSIONS

In this meta-analysis, CS was a risk factor for ASD/ADHD in offspring compared with VD.

Fluoxetine potentiates methylphenidate-induced behavioral responses: Enhanced locomotion or stereotypies and facilitated acquisition of cocaine self-administration

The medical psychostimulant methylphenidate (MP) is used to treat attention-deficit hyperactivity disorder and recreationally as a "cognitive enhancer". MP is a dopamine reuptake inhibitor, but does not affect serotonin. Serotonin contributes to addiction-related gene regulation and behavior. Previously, we showed that enhancing serotonin action by adding a selective serotonin reuptake inhibitor, fluoxetine (FLX), to MP potentiates MP-induced gene regulation in striatum and nucleus accumbens, mimicking cocaine effects. Here, we investigated the behavioral consequences of MP+FLX treatment. Young adult male rats received MP (5 mg/kg, i.p.) or MP+FLX (5 mg/kg each) daily for 6-8 days. Behavioral effects were assessed in an open-field test during the repeated treatment. Two weeks later the motor response to a cocaine challenge (25 mg/kg) and the rate of acquisition of cocaine self-administration behavior were determined. Our results demonstrate that FLX potentiates effects of MP on open-field behavior. However, we found differential behavioral responses to MP+FLX treatment, as approximately half of the rats developed high rates of focal stereotypies (termed "MP+FLX/high reactivity" group), whereas the other half did not, and only showed increased locomotion ("MP+FLX/low reactivity" group). Two weeks later, cocaine-induced locomotion and stereotypies were positively correlated with MP+FLX-induced behavior seen at the end of the repeated MP+FLX treatment. Moreover, the MP+FLX/high reactivity group, but not the low reactivity group, showed facilitated acquisition of cocaine self-administration. These results demonstrate that repeated MP+FLX treatment can facilitate subsequent cocaine taking behavior in a subpopulation of rats. These findings suggest that MP+FLX exposure in some individuals may increase the risk for psychostimulant use later in life.

Chronic oral methylphenidate plus fluoxetine treatment in adolescent rats increases cocaine self-administration

Background

Depression and attention deficit hyperactivity disorder are known to be comorbid. Treatment of these commonly coexisting diseases typically involves the combined prescription of methylphenidate (MP), a psychostimulant, and fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI). MP and cocaine have similar mechanisms of action and this study examined the effects of chronic treatment of MP combined with FLX on cocaine consumption in rats.

Methods

Four groups of rats received access to drinking solutions of water (control), MP (30/60 mg/kg/day), FLX (20 mg/kg/day), or the combination of MP (30/60 mg/kg/day) plus FLX (20 mg/kg/day), during 8 h per day for one month. Following these drug treatments, rats were allowed to self-administer cocaine for 14 days.

Results

Our results showed that, during the first week of cocaine self-administration, the MP-treated rats had significantly greater numbers of active lever presses (plus 127%) and increased consumption of cocaine compared to the control rats. In contrast, during week two of cocaine self-administration, the rats treated with the MP + FLX combination showed significantly more lever presses (plus 198%) and significantly greater cocaine consumption (plus 84%) compared to the water controls.

Conclusion

Chronic oral treatment during adolescence with the combination of MP plus FLX resulted in increased cocaine use after 2 weeks of cocaine self-administration in rats. These novel findings suggest that the combined exposure to these two drugs chronically, during adolescence, may produce increased vulnerability towards cocaine abuse during young adulthood.

Combined methylphenidate and fluoxetine treatment in adolescent rats significantly impairs weight gain with minimal effects on skeletal development

Methylphenidate (MP) is frequently prescribed to treat Attention-Deficit/Hyperactivity Disorder (ADHD); however, many patients with ADHD experience depression and anxiety. As such, concomitant administration of selective serotonin reuptake inhibitors such as fluoxetine (FLX) is common. Our laboratory and others have shown that MP impairs skeletal development in preclinical and clinical settings, and FLX has also been linked to skeletal deficits. Unfortunately, little is known about the effects of combined MP and FLX treatment on skeletal development. The objective of this study was to investigate the effects of MP and FLX on bone morphology and biomechanical properties in adolescent rats. Four-week-old male Sprague-Dawley rats were randomly divided into the following 4 groups: Water, MP, FLX, and MP + FLX. As body weights in the MP, FLX, and MP + FLX groups were all lower than Water, the data were compared directly and after adjusting to body weight via linear regression. The direct comparison revealed that MP + FLX rats had significantly shorter (~12 %) and narrower femora and tibiae (~10 %) compared to most other groups, along with shorter (26-35 %), disorganized tibial growth plates. MicroCT analyses of the trabecular compartment of the proximal tibia identified reductions of 47 % for TV, 86 % for BV, 74 % for BV/TV, 68 % for Tb.N, 25 % in Tb.Th, and 74 % in vBMD concomitant with increases of 44 % for Tb.Sp for MP + FLX compared to Water. Similar analyses of femoral midshaft cortical bone identified reductions of 29 % for Ct.V, 30 % for Ps.V, 30 % for Ec. V, and 51 % for pMOI, as well as increases of 17 % for Ct.Th and 2 % for TMD for MP + FLX compared to Water. Biomechanically, MP + FLX femora were weaker, as indicated by a reduction in ultimate force (14 %) in MP + FLX compared to Water. The microstructural and biomechanical effects of MP + FLX were eliminated after adjustment for body weight, though the detrimental effects on growth plate morphology remained. We conclude that while the adverse microstructural and biomechanical effects of MP + FLX seen via direct comparison are predominantly attributable to reductions in body weight rather than direct effects on bone, MP and FLX, particularly in combination show detrimental effects on growth plate structure and chondrocyte morphology. These findings warrant further research into the effect of these drugs on weight gain, skeletal development and growth plate morphology, as well as consideration by physicians treating children and adolescents with ADHD.

Combined Chronic Oral Methylphenidate and Fluoxetine Treatment During Adolescence: Effects on Behavior

BACKGROUND

Attention Deficit Hyperactivity Disorder (ADHD) can be comorbid with depression, often leading to the prescription of both methylphenidate (MP) and selective serotonin reuptake inhibitor (SSRI) antidepressants, such as fluoxetine (FLX). Moreover, these drugs are often misused as cognitive enhancers. This study examined the effects of chronic oral co-administration of MP and FLX on depressive- and anxiety-like behaviors.

METHODS

Adolescent rats received daily either water (control), MP, FLX, or the combination of MP plus FLX in their drinking water over the course of 4 weeks.

RESULTS

Data analysis shows a decrease in food consumption and body weight for rats exposed to FLX or the combination of MP and FLX. Sucrose consumption was significantly greater in FLX or MP+FLX groups compared to controls. FLX-treated rats showed no effect in the elevated plus maze (EPM; open arm time) and forced swim test (FST; latency to immobility). However, rats treated with the combination (MP+FLX) showed significant anxiolytic-like and anti-depressive-like behaviors (as measured by EPM and FST), as well as significant increases in overall activity (distance traveled in open field test). Finally, the combined MP+FLX treatment induced a decrease in anxiety and depressive- like behaviors significantly greater than the response from either of these drugs alone.

CONCLUSION

These behavioral results characterize the long-term effects of these drugs (orally administered) that are widely co-administered and co-misused and provide important insight into the potential neurobiological and neurochemical effects. Future research will determine the potential risks of the long-term use of MP and FLX together.

Dopamine, Immunity, and Disease

The neurotransmitter dopamine is a key factor in central nervous system (CNS) function, regulating many processes including reward, movement, and cognition. Dopamine also regulates critical functions in peripheral organs, such as blood pressure, renal activity, and intestinal motility. Beyond these functions, a growing body of evidence indicates that dopamine is an important immunoregulatory factor. Most types of immune cells express dopamine receptors and other dopaminergic proteins, and many immune cells take up, produce, store, and/or release dopamine, suggesting that dopaminergic immunomodulation is important for immune function. Targeting these pathways could be a promising avenue for the treatment of inflammation and disease, but despite increasing research in this area, data on the specific effects of dopamine on many immune cells and disease processes remain inconsistent and poorly understood. Therefore, this review integrates the current knowledge of the role of dopamine in immune cell function and inflammatory signaling across systems. We also discuss the current understanding of dopaminergic regulation of immune signaling in the CNS and peripheral tissues, highlighting the role of dopaminergic immunomodulation in diseases such as Parkinson's disease, several neuropsychiatric conditions, neurologic human immunodeficiency virus, inflammatory bowel disease, rheumatoid arthritis, and others. Careful consideration is given to the influence of experimental design on results, and we note a number of areas in need of further research. Overall, this review integrates our knowledge of dopaminergic immunology at the cellular, tissue, and disease level and prompts the development of therapeutics and strategies targeted toward ameliorating disease through dopaminergic regulation of immunity. SIGNIFICANCE STATEMENT: Canonically, dopamine is recognized as a neurotransmitter involved in the regulation of movement, cognition, and reward. However, dopamine also acts as an immune modulator in the central nervous system and periphery. This review comprehensively assesses the current knowledge of dopaminergic immunomodulation and the role of dopamine in disease pathogenesis at the cellular and tissue level. This will provide broad access to this information across fields, identify areas in need of further investigation, and drive the development of dopaminergic therapeutic strategies.