Effects of Ghrelin Administration on Dopamine and Effort

University Hospital Tuebingen

Status and phase: Completed; Phase 2; Phase 1

Conditions: Major Depressive Disorder

Treatments: Other: Placebo; Drug: Ghrelin

Study type: Interventional

Funder types: Other

Identifiers

NCT05318924

DFG KR 4555/7-1

Details and patient eligibility

About

Ghrelin is a stomach-derived hormone and the only known circulating peptide that stimulates appetite. Animal studies have conclusively shown that ghrelin increases dopaminergic neurotransmission and, thereby, enhances effort. However, similar evidence on the putative role of ghrelin in humans is still lacking. Here, the investigators propose to conduct a [11C]-raclopride PET/MR study after intravenous administration of ghrelin vs. saline in healthy individuals. First, during an intake visit, the investigators will assess fasting blood levels of hormones involved in appetitive behavior such as ghrelin, leptin, and insulin. In addition, the investigators will conduct a set of tasks that have been associated with dopamine function (i.e., effort and reinforcement learning). Second, the investigators will assess the effects of intravenous administration of ghrelin on dopamine signaling using a double-blind randomized cross-over design. To this end, participants will be infused with ghrelin (vs. saline) while we determine dopamine release (via PET imaging) and assess cerebral blood flow and functional connectivity at rest (via concurrent MR imaging). Furthermore, the investigators will conduct an instrumental motivation task (IMT) where participants have to exert physical effort to obtain rewards. Based on preclinical studies and indirect evidence from human studies, the investigators hypothesize that ghrelin will increase dopamine release in the striatum and that this will, in turn, lead to an increase in the willingness to work for rewards. Moreover, the investigators expect that ghrelin-induced dopamine release will be associated with an elevated tracking of reward utility in the mesolimbic circuit during the IMT, which is known to be associated with response vigor. Collectively, the proposed project would provide a unique resource to test an important link between the gut and the brain in the regulation of appetitive behavior. If ghrelin were to enhance effort expenditure for rewards via dopamine signaling in humans, then restoring sensitivity to ghrelin might be the more promising therapeutic approach compared to antagonizing the ghrelin receptor.

Enrollment: 26 patients

Sex: All

Ages: 20 to 50 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Healthy control participants: never fulfilled the criteria of any mood or anxiety disorder (except specific phobia)
• Patients with major depressive disorder: diagnosis according to DSM-5 within 12 months before enrollment and presence of at least mild symptoms at enrollment (BDI II >= 14)

Exclusion criteria

• lifetime history of a brain injury, schizophrenia, bipolar disorder, and a severe substance use disorder according to DSM-5
• obsessive-compulsive disorder, trauma- and stressor-related disorder, somatic symptom disorder, and eating disorder within a 12-month interval before the test day.
• Neuroimaging Study involving ghrelin infusion: contraindication for PET/MR (e.g., metal implants or prostheses, pregnancy, claustrophobia)

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: Triple Blind

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26 participants in 3 patient groups, including a placebo group

Ghrelin infusion

Experimental group

Description:

To achieve approximately stable elevated ghrelin levels during the infusion procedure, the investigators will use a loading dose of 1 mcg/kg as well as an infusion rate of 0.051 mcg/kg/min in line with recent studies (Farokhnia, Grodin, Lee et al., 2017) and general recommendations (Garin, Burns, Kaul et al., 2013).

Treatment:

Drug: Ghrelin

Placebo infusion

Placebo Comparator group

Description:

Saline

Treatment:

Other: Placebo

Patients with MDD

No Intervention group

Description:

Patients with major depressive disorder will be enrolled for comparison to healthy participants on the reward task battery, but not randomized to the ghrelin vs. saline infusion.