Academic Service Office for the Medical Science Area, University of Tsukuba, Tsukuba 305-8577, Japan.
Division of Biomedical Science, Institute of Medicine, University of Tsukuba, Tsukuba 305-8577, Japan.
eNeuro. 2024 Aug 28;11(8). doi: 10.1523/ENEURO.0481-23.2024. Print 2024 Aug.
Hunger and thirst drive animals' consumption behavior and regulate their decision-making concerning rewards. We previously assessed the thirst states of monkeys by measuring blood osmolality under controlled water access and examined how these thirst states influenced their risk-taking behavior in decisions involving fluid rewards. However, hunger assessment in monkeys remains poorly performed. Moreover, the lack of precise measures for hunger states leads to another issue regarding how hunger and thirst states interact with each other in each individual. Thus, when controlling food access to motivate performance, it remains unclear how these two physiological needs are satisfied in captive monkeys. Here, we measured blood ghrelin and osmolality levels to respectively assess hunger and thirst in four captive macaques. Using an enzyme-linked immunosorbent assay, we identified that the levels of blood ghrelin, a widely measured hunger-related peptide hormone in humans, were high after 20 h of no food access (with water). This reflects a typical controlled food access condition. One hour after consuming a regular dry meal, the blood ghrelin levels in three out of four monkeys decreased to within their baseline range. Additionally, blood osmolality measured from the same blood sample, the standard hematological index of hydration status, increased after consuming the regular dry meal with no water access. Thus, ghrelin and osmolality may reflect the physiological states of individual monkeys regarding hunger and thirst, suggesting that these indices can be used as tools for monitoring hunger and thirst levels that mediate an animal's decision to consume rewards.
饥饿和口渴驱使动物进行消费行为，并调节它们对奖励的决策。我们之前通过在控制水摄入的情况下测量血液渗透压来评估猴子的口渴状态，并研究了这些口渴状态如何影响它们在涉及液体奖励的决策中承担风险的行为。然而，猴子的饥饿评估仍然做得很差。此外，由于缺乏对饥饿状态的精确测量，导致另一个问题，即个体的饥饿和口渴状态如何相互作用。因此，当控制食物摄入以激励表现时，仍然不清楚这两种生理需求如何在圈养猴子中得到满足。在这里，我们测量了血液胃饥饿素和渗透压水平，分别评估了四只圈养猕猴的饥饿和口渴状态。使用酶联免疫吸附测定法，我们发现血液胃饥饿素水平（一种在人类中广泛测量的与饥饿相关的肽激素）在 20 小时没有食物摄入（只有水）后升高。这反映了一种典型的控制食物摄入的情况。在吃完一顿常规的干饭后的 1 小时，四只猴子中有三只的血液胃饥饿素水平降至基线范围内。此外，从同一样本测量的血液渗透压（水合状态的标准血液学指标）在没有水摄入的情况下进食常规干饭后升高。因此，胃饥饿素和渗透压可能反映了个体猴子的饥饿和口渴生理状态，表明这些指标可以用作监测饥饿和口渴水平的工具，从而调节动物对奖励的消费决策。
