Three-part study investigating the safety and tolerability of AZD2423 multiple doses in 98 healthy volunteers: Part 1 80 young and elderly subjects in a parallel, double blind, randomised study. Part 2 - 6 subjects in an open, non-randomised study. Part 3 - 12 subjects in a three-way cross over, open label, partially randomised study.

Part 1 has 2 Arms, AZD2423 or Placebo, Multiple dosing during 10-14 days . Part 2 has 1 Arm AZD2423 Multiple dosing and Part 3 has 3 Arms AZD2423 single dosing or AZD2423 single dosing with food or AZD2423 single dosing, Fasting Condition

Inclusion Criteria:

• Provision of signed and dated, written informed consent prior to any study specific procedures
• Healthy male and non-fertile female subjects aged ≥20 to ≤55 years inclusive and healthy male and female subjects aged ≥65 to ≤80 years inclusive with suitable veins for cannulation or repeated venepuncture.
• Have a body mass index (BMI) between ≥18 and ≤30 kg/m2, as calculated by the investigator, and weigh at least 50 kg and no more than 100 kg.
• Clinically normal physical findings including supine blood pressure, pulse rate, ECG, and laboratory assessments in relation to age, as judged by the investigator. In addition, normal ophthalmoscopy is required for the CSF panel subjects (Part 2).

Exclusion Criteria:

• History of any clinically significant disease or disorder which, in the opinion of the investigator, may either put the subject at risk because of participation in the study,or influence the results or the subject's ability to participate in the study
• History or presence of gastrointestinal, hepatic or renal disease or any other condition known to interfere with absorption, distribution, metabolism or excretion of drugs.
• Any clinically significant illness/infection or medical/surgical procedure or trauma, as judged by the Principal Investigator, within 3 months of the first administration of investigational product.