Depression is a reactional state characterised by reduced receptivity to stimuli and spontaneous and irreversible inhibition. It may occur from the outset or arise out of untreated anxiety problems.
Acute depression is reactional and characterised by excessive sleep, poor appetite and displacement activities.
Chronic depression is characterised by disordered feeding, sleep problems, changes in cleaning and grooming habits, and displacement activities.
Reactional depression in the adult occurs several days after a severe emotional shock. The pet is lethargic, anorexic and no longer grooms itself even though frenzied licking follows any physical contact. Displacement activities are present, and excoriations can develop in the cervical region. This depression can, because of the associated anorexia, be fatal.
Chronic depression in the adult' can develop from acute depression but also from untreated anxiety. It can also result from prolonged administration of synthetic progestagens. The cat appears chronically withdrawn with bouts of agitation, spraying, calling and licking (despite altered grooming habits).
Involutive depression is associated with ageing of the brain and occurs in animals aged 10 years or over. It often has an organic cause like a brain tumour. Loss of grooming and cleaning habits, and sleep problems (with calling and aimless night-time walks) are suggestive signs. Displacement activities can be seen.