Most of the research on depression seems quite human focused. Can cats also get depressed in the same way there's depression for humans?
Human depression has been modeled in a variety of animal models, including cats (Wilner, 1984). Cats show comparable signs of distress when subject to maternal separation, including separation phenomena of protest, followed by despair. Although it is hard to project the DSM-V criteria onto cats, they can show comparable behaviors when subject to anxiety and stress.
- Wilner, Psychoneuropharmacol (1984); 83(1): 1-16
There is a lot of research on depression in animals.
Wikipedia has a good summary of the comparison of depression between animals and humans:
It is difficult to develop an animal model that perfectly reproduces the symptoms of depression in patients. Many animals lack self-consciousness, self-reflection, and consideration; moreover, hallmarks of the disorder such as depressed mood, low self-esteem or suicidality are hardly accessible in non-humans. However, depression, as other mental disorders, consists of endophenotypes that can be reproduced independently and evaluated in animals.
The following endophenotypes have been described:
- Anhedonia: The loss of interest is a core symptom of depression.
- Anhedonia in rodents can be assessed by sucrose preference or by intracranial self-stimulation.
- Behavioral despair: Behavioral despair might be assessed with tests such as the forced-swimming test or the tail suspension test.
- Changes in appetite or weight gain: Depression is often associated with changes in appetite or weight gain, which is easily measured in rodents.
- Neuroanatomy: Depressed subjects display decreased hippocampal volume and rodents exposed to chronic stress or excess glucocorticoids exhibit similar signs of hippocampal loss of neurons and dendritic atrophy.
- Neuroendocrine disturbances: Disturbances of the hypothalamic–pituitary–adrenal axis (HPA) are one of the most consistent symptoms in major depression. The functionality of the HPA can be assessed by dexamethasone suppression test .
- Alterations in sleep architecture: Disturbances in the circadian rhythm and especially in the sleep architecture are often observed in depressed. In rodents, it is accessible via electroencephalography(EEG).
- Anxiety-related behavior: Anxiety is a symptom with high prevalence in depression. Therefore, animal models of depression often display altered anxiety-related behavior.
One of the early popular models of depression based on animal behaviour is learned helplessness theory:
Learned helplessness theory is the view that clinical depression and related mental illnesses may result from a perceived absence of control over the outcome of a situation.
This has been replicated in many animals, including cats. (A nice review of learned helplessness in humans here.)
Modern theories of depression include many other causes besides learning, not all of which are applicable to animals. So ultimately, cats do get depressed, in a way similar in some respects to humans, but in other aspects, not the same.