The Neuroscience of Pain In Pets

If you have ever come across some lectures with neuroscientists or psychologists on pain, you will likely hear the story of a man who fell on a nail.  He understandably was in agony and had to be given strong painkillers on the way to the hospital.  But, when arriving at the hospital, it was discovered that the nail had in fact gone through the gaps in his toes and not penetrated his foot at all.

What on earth was going on here?

You can’t say his pain wasn’t real, because to him it was sheer agony.  But it was his perception of what had occurred which fuelled his response and need for strong painkillers.

The brain had constructed a response based on cues from the environment; the pain signal was therefore appropriate to stop the man in his tracks and prevent the likelihood he would fall on another nail.

Except the brain got it a little wrong.

This example is great for showing us that pain is subjective and a perception; but we already knew this didn’t we? What may be painful for one person, may not even result in a wince from another.

This is also true for our dogs.  We joke that certain breeds are a little sensitive, and then we find other breeds completely stoic when suffering a chronic issue.

If pain is crucial to our survival, quite literally, but it can be subjective, what on earth is it?

Let’s take a look at the neuroscience of pain.

The Neuroscience of Pain

Pain is a sensation and as such is processed in the brain.

It is a necessary function that warns the body of potential or actual injury.

It occurs when nociceptor fibres detect painful stimulus on the skin or in an internal organ (peripheral nervous system).  The detection signal is picked up by receptors in the spinal cord and brainstem and transmitted to various areas of the brain as sensory information.

The facilitators of this are known as neurotransmitters and as we know these are in essence, chemical messengers.  Some transmitters are excitatory, meaning they facilitate the transmission of the message, and some are inhibitory, meaning they impede transmission.  Both types of messengers are important in the modulation of pain.  For example, excitatory neurotransmitters acting without an inhibitory system results in pain.

Several neurotransmitters are involved, but glutamate and substance P (SP) are the main ones involved in pain.

Glutamate is usually involved in the rapid neurotransmission of acute pain, such as with mechanical stimuli or temperature stimuli producing quick, sharp pain.

SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. SP transmits pain by secretion from nerves and inflammatory cells, and acts by binding to certain receptors on the spinal cord.

SP is typically seen in chronic pain cases due to its slow excitatory connection.

The success in treating pain with opiates, such as morphine, that block nociceptive transmission of pain within the spinal cord is perceived to be, in part, due to a decrease in the release of SP.

Recent data has indicated a role for dopamine in pain too.

Dopamine is already known to play important roles in thinking, memory, movement, and reward. However, researchers have shown that dopaminergic neurotransmission plays a central role in modulating pain perception and analgesia within certain parts of the brain including the insula, thalamus, basal ganglia, anterior cingulate cortex and periaqueductal grey.  It is thought that low levels of dopamine could contribute to the perception of painful symptoms.

Amino Acids and Pain Management

The body’s three primary pain modulators appear to be the neurotransmitters endorphin, serotonin, and GABA (gamma amino butyric acid).

Each of these pain fighters is produced from very specific nutrients called amino acids.  Amino acids are required for the production and maintenance of almost every function and tissue in the body.

Amino acids are found in abundance in protein rich foods, but you can also find them in supplement form.
DLPA (DL-phenylalanine) is a natural amino acid that has been used to treat chronic pain. DLPA inhibits several enzymes that are responsible for the destruction of endorphins. Endorphins are pain-killing hormones and by inhibiting their destruction, pain relief is prolonged. It can also potentiate opiate analgesia and prolong the effects of acupuncture.
Tryptophan (Trp) is an indispensable amino acid for domestic canines.  Tryptophan, and ultimately the serotonergic system, has been shown to influence behaviours related to anxiety, stress, fear, and aggression which may play a role chronic pain, and its perception.

Acute Vs Chronic Pain

Acute pain, which serves as a warning signal of injury or illness, normally comes on quickly and lasts for a short time.

If not treated properly, acute pain can develop into chronic pain in which the pain persists even after the initial injury or illness is healed.

When this happens, considerable changes occur in both the peripheral and central nervous systems (CNS) as well as in the psychological profiles of sufferers.

Some recent studies have found that information about the transition from acute pain to chronic pain could be documented by changes in brain structure and function.

In general, where acute pain largely activates brain regions involved in nociceptive information processing, chronic pain is consistently and substantially encoded by brain regions related to emotional and motivational states of sufferers. This suggests that we should also consider how stressed or anxious our pets may be alongside their pain experiences.

What is particularly interesting about this concept is that our pets can’t talk, so it can be particularly difficult to establish their emotional and motivational states.

This is even more worrying when we consider veterinarian and public opinion of pain sensitivity in certain breeds of dogs.

A study carried out in 2020 wanted to establish whether there is a breed difference in pain sensitivity in dogs. But, as pain is a perception and there are significant limitations in subjectivity scales, the researchers thought asking veterinarians and the general public would be an interesting discussion.

This is what they found.

  • Breeds associated with breed specific legislation were thought to have a lower pain sensitivity
  • 90% of respondents thought there would be a breed difference in pain sensitivity
  • Huskies, Chihuahuas, Pomeranians, Dachshunds, and German Shepherds were all thought to have a lower sensitivity to pain
  • Vets thought golden retrievers had a relatively high pain sensitivity, whereas the general public thought they had a low sensitivity
  • The general public through Labrador retrievers had a high pain sensitivity, whereas vets thought they had a low pain sensitivity.

Findings Here

What’s interesting is the disparity in this study, the difference between breeds but also between the opinions of the general public and veterinarians.

We must consider how the emotional or motivational state of our pet may influence their perception of pain, along with any preconceived ideas we may have about their ability to tolerate pain.

As we have established, pain is a perception and the only one who is feeling that sensation, at whatever sensitivity, is the dog.  Until dogs can speak, we have no idea how they are perceiving it.

We just have to watch for signs.

Possible Signs of Pain:

  • Constant licking
  • Panting
  • Pacing
  • Nibbling at certain areas of the body
  • Persistent itching in a concentrated area
  • Anxious or depressed behaviour
  • Aggressive/grumpy behaviour
  • Inappropriate toileting behaviour
  • Lethargy
  • Unusual vocalisation/yelping
  • Limping
  • Abnormal gait/walking behaviour
  • Stiffness
  • Skin dysfunction
  • Gut dysfunction

If you would like to learn more about pain, check out our blog below:

Dogs in Pain – What It Is and How To Look For It

If you would like any support with your pet’s pain management plan, then please check out our services to see how we can help.

Thanks for reading,

MPN Team

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