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The role of 5-HT1A and 5-HT1B receptors in MDMA self-administration

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posted on 2021-11-15, 18:03 authored by Aronsen, Dane

Rationale: 3,4-methylenedioxymethamphetamine (MDMA) is a less efficacious reinforcer than other drugs of abuse. However, following repeated self-administration, responding increases for some animals and efficacy becomes comparable to other drugs of abuse. MDMA-stimulated serotonin (5-HT) release was negatively associated with acquisition of MDMA self-administration, and a neurotoxic 5-HT lesion reduced the latency to acquire self-administration. These findings suggest that MDMA-produced 5-HT release is an important component of self-administration. The receptor mechanisms are not, however, well understood, although it has often been suggested that the mechanism involves 5-HT-mediated inhibition of dopamine. Both 5-HT1A and 5-HT1B receptors are well localised to regulate dopamine release, and both have been implicated in modulating the reinforcing effects of many drugs of abuse.   Objectives: The first objective was to establish specific behavioural assays to reflect 5-HT1A and 5-HT1B receptor activation. Then, using the established behavioural assays, the aim was to determine the role of 5-HT1A and 5-HT1B receptors in the acquisition of MDMA self-administration. The impact of substantial MDMA self-administration on 5-HT1A and 5-HT1B receptors was also assessed.  Methods: Firstly, dose-effect relationships for the hyperactive response to the 5-HT1A receptor agonist, 8-OH-DPAT (0 – 3.0 mg/kg) and the hyperactive and adipsic response to the 5-HT1B/1A receptor agonist, RU 24969 (0 – 3.0 mg/kg) were determined. Selectivity of these responses was determined by co-administration of the 5-HT1A receptor antagonist, WAY 100635, or the 5-HT1B/1D receptor antagonist, GR 127935. Secondly, a pretreatment regimen of the RU 24969 (2 × 3.0 mg/kg/day, 3 days), which had been suggested to down-regulate 5-HT1B/1A receptors, was administered prior to self-administration testing. The effect of this manipulation on both the acquisition of MDMA self-administration, and the behavioural responses to 5-HT1A and 5-HT1B receptor activation, was measured. A further study measured behavioural responses to 5-HT1A or 5-HT1B receptor agonists prior to self-administration, to determine whether the variability in these responses would predict the variability in the latency to acquisition of MDMA self-administration. Lastly, the effect of substantial MDMA self-administration (350 mg/kg) on dose-response curves for the behavioural effects of 5-HT1A or 5-HT1B receptor activation was assessed.   Results: The hyperactive response to the 5-HT1B/1A receptor agonist, RU 24969, was blocked by the 5-HT1A receptor antagonist, WAY 100635, but not the 5-HT1B receptor antagonist, GR127935. Similarly, the hyperactive response to the 5-HT1A receptor agonist, 8-OH-DPAT, was dose-dependently blocked by WAY 100635. GR 127935, but not WAY 100635, blocked the adipsic response to RU 24969. Repeated administration of RU 24969 produced rightward shifts in the dose-response curves for 8-OH-DPAT-produced hyperactivity and RU 24969-produced adipsia, and also greatly facilitated the acquisition of MDMA self-administration. However, there was no correlation between latency to acquire MDMA self-administration and the hyperactive response to 8-OH-DPAT or the adipsic response to RU 24969, and MDMA self-administration failed to alter these behavioural response to activation of 5-HT1A or 5-HT1B receptors.   Conclusions: The hyperactive response to 8-OH-DPAT and the adipsic response to RU 24969 reflect activation of 5-HT1A and 5-HT1B receptors, respectively. The variability in acquisition of MDMA self-administration was reduced by a treatment that also down-regulated 5-HT1A and 5-HT1B receptors, however there was no further indication that these receptors play a critical role in the self-administration of MDMA. Instead, it seems likely that other 5-HT receptors have a greater impact on MDMA self-administration.

History

Copyright Date

2016-01-01

Date of Award

2016-01-01

Publisher

Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline

Cognitive and Behavioural Neuroscience

Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level

Doctoral

Degree Name

Doctor of Philosophy

ANZSRC Type Of Activity code

1 PURE BASIC RESEARCH

Victoria University of Wellington Item Type

Awarded Doctoral Thesis

Language

en_NZ

Victoria University of Wellington School

School of Psychology

Advisors

Schenk, Susan; Ellenbroek, Bart