The US geriatric population is growing and using more opioids than ever before. The purpose of this study was to determine whether aging influenced the reinforcing efficacy of morphine in male and female rats using a rodent intravenous self-administration paradigm. Male and female aged (20-24 months) and young (2-4 months) Wistar rats were tested at 2 doses of morphine (0.75 mg/kg/infusion and 0.25 mg/kg/infusion). During 10 days of self-administration, aged rats took significantly less morphine than their younger counterparts at the 0.25 mg/kg/infusion dose. Aged males also earned significantly fewer infusions on a progressive ration reinforcement schedule at this dose, suggesting that the reinforcing efficacy of morphine is decreased for this group at this dose. These effects dissipated when a separate group of animals had access to the 0.75 mg/kg/infusion dose for both sexes. Our results indicate that morphine is less reinforcing at lower doses in aged male, but not female rats. This research has potential clinical implications for the chronic treatments involving opioids in aged individuals.

中文翻译：

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衰老降低了对吗啡增强功效的敏感性

美国老年人口正在增长，使用的阿片类药物比以往任何时候都多。本研究的目的是使用啮齿动物静脉内自我给药范例确定衰老是否影响吗啡对雄性和雌性大鼠的强化功效。雄性和雌性年龄（20-24 个月）和年轻（2-4 个月）Wistar 大鼠在 2 个剂量的吗啡（0.75 mg/kg/输注和 0.25 mg/kg/输注）下进行测试。在 10 天的自我给药期间，在 0.25 毫克/千克/输注剂量下，老年大鼠服用的吗啡明显少于年轻大鼠。在此剂量下，老年男性在渐进式定量强化计划中的输注量也显着减少，这表明该剂量组的吗啡强化效果降低。当另一组动物接触到 0 时，这些影响就会消失。75 mg/kg/输注剂量，男女均可。我们的结果表明，在老年雄性大鼠而非雌性大鼠中，吗啡在较低剂量下的增强作用较小。这项研究对老年人涉及阿片类药物的慢性治疗具有潜在的临床意义。