Recent quotes:

Opioids produce analgesia via immune cells: Researchers from the Charité find new signaling pathway -- ScienceDaily

"We were able to show that opioid agonists activate opioid receptors on immune cells, which triggered the release of endogenous painkillers (opioid peptides) and produced analgesia in a mouse model of neuropathic pain," explains Prof. Machelska. She adds, "This led us to conclude that opioids can exert enhanced analgesia when they act directly in painful tissue -- providing that this tissue is inflamed and contain immune cells."

Pain tolerance predicts human social network size : Scientific Reports

Animal awareness of others' needs

As long ago as 1959, Russell Church of Brown University set up a test which allowed laboratory rats in half of a cage to get food by pressing a lever. The lever also delivered an electric shock to rats in the other half of the cage. When the first group realised that, they stopped pressing the lever, depriving themselves of food. In a similar test on rhesus monkeys reported in the American Journal of Psychiatry in 1964, one monkey stopped giving the signal for food for 12 days after witnessing another receive a shock. There are other examples of animals preferring some sort of feeling over food.