The main goals of the study are to assess uptake and distribution of Lu AF90103 in the brain when given at tracer levels (microdose) in healthy young men.

Inclusion Criteria:

• The participant has a body mass index (BMI) ≥18.5 and ≤30.0 kilograms (kg)/square meter (m^2) at the Screening Visit.
• The participant is, in the opinion of the investigator, generally healthy based on medical history; a physical examination; vital signs; an electrocardiogram (ECG); and the results of the clinical chemistry, hematology, urinalysis, serology, and other laboratory tests.

Exclusion Criteria:

• The participant has taken disallowed medication <1 week prior to the first dose of study drug or <5 half-lives prior to the Screening Visit for any medication taken.
• The participant has or has had any clinically significant immunological, cardiovascular, respiratory, metabolic, renal, hepatic, gastrointestinal, endocrinological, hematological, dermatological, venereal, neurological, or psychiatric disease or other major disorder.
• The participant has had surgery or trauma with significant blood loss <3 months prior to the first dose of study drug.
• The participant is exposed to significant levels of ionizing radiation at work. Note: Other inclusion and exclusion criteria may apply.