Psychopharmacology
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Drugs of abuse can affect the functioning of the hypothalamic-pituitary-adrenal (HPA) axis. Acute administration of drugs that serve as reinforcers have been observed to stimulate the rat HPA axis, leading to the suggestion that these stimulatory effects may contribute to the development of drug-maintained behaviors. ⋯ There appears to be little commonality between different classes of abused drugs and their effects on the HPA axis, which calls into question the necessity for HPA axis stimulation in the reinforcement of drug-maintained behavior.
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Administration of an opiate antagonist following acute morphine exposure elevates the startle response in rodents, a phenomenon that may reflect the anxiogenic effects of withdrawal. Previous acute dependence studies have demonstrated escalated withdrawal severity following multiple withdrawal episodes. ⋯ These data demonstrate that repeated withdrawals from acute morphine exacerbate the severity of potentiated startle and hyperalgesia. These paradigms may be useful in examining the neural plasticity underlying the development of opiate dependence.