Cats have given so much for human health and scientific progress!

In the field of life science and medical research, animal experiments are a must for many studies. People are accustomed to using "white mice" to refer to experimental animals used in scientific research, but experimental animals are not only mice, but also nematodes, zebrafish, fruit flies, naked mole rats, rabbits, dogs, monkeys, and -

Our dear cats.

Yes, this cute little animal, which has a large number of "cat cult" followers, has another identity: a certified experimental animal. They even contributed to scientists winning the Nobel Prize.

1912: Cats Undergo Kidney Transplants

The relationship between cats and the Nobel Prize can be traced back to 1912.

That year, French doctor Alexis Carrel was awarded the Nobel Prize in Physiology or Medicine for his work on three-point anastomosis and organ transplantation . Carrel was later criticized for his political beliefs, but due to his outstanding achievements when he was young, he was still called the "Father of Organ Transplantation", and this title was also mentioned for his series of organ transplantation experiments on various animals.

Perhaps the most popular story about Carrel is that he successfully transplanted two kidneys from a dog into another dog that had already had a kidney transplant. In fact, he also successfully transplanted two kidneys into a cat, and in 1908 he performed the first successful single kidney transplant in a cat, proving that a single kidney transplant could maintain normal life activities .

A cat that had undergone a kidney transplant. This is what it looked like 21 days after the surgery. It was looking at a piece of meat. Reference [1]

Looking through Carrel's papers published between 1906 and 1908, we can see a lot of records about kidney transplants in cats:

Experiment 9. October 14, 1907

Prepared host: Gray female cat, living in the laboratory for several months; young and in good health.

On October 1, the urine was examined - yellow, clear, density 1.039, urea 5.9 g/ml, no albumin. The abdomen and viscera were opened as usual. The intestines were protected by a sterile Japanese silk towel coated with vaseline. The kidneys were dissected and removed: the ovarian vein, the inferior and superior renal veins and the two aortic collaterals were ligated.

…

On October 15, the cat looked a little sick, drank water, and walked around in its cage. From 4 pm yesterday to now, there was only 25 ml of urine, dark yellow, with a little blood and albumin, density 1.051.

On October 16, the cat improved, drank milk and ate a little meat, and the urine volume was 16 ml.

On October 17, I was in good condition. I drank milk and ate meat.

October 18th, same as above

On October 21, the cat had fully recovered and was a normal cat just like before the operation.

…

November 7 The cat was a little depressed and paced back and forth in its cage.

On the morning of November 14 the cat seemed fine, but in the evening it looked ill, making noises from its nose and refusing to eat.

November 18 The cat is very weak

Died at 1:00 PM on November 19th.

Thanks to Carrel's proof that " after removing both kidneys, a life can be saved by transplanting only one kidney ", people realized that donors only need to donate half of their kidneys to save lives, which also laid the groundwork for later living kidney transplants.

In the following decades, with the development of technology, in 1954, doctors John P. Merrill and David Hume of Harvard University in the United States successfully performed the first living organ transplant in human history, donating one kidney of an identical twin brother to his older brother who suffered from uremia. In this way, the older brother's life was extended by eight more years, and the younger brother who lost one kidney also lived safely to the age of 79.

For people at that time, uremia was a terminal illness like a tumor, and the five-year survival rate was not high. The success of living kidney transplantation undoubtedly brought hope of survival to patients.

1932: Cat's Classroom

Around the same time that Carrel’s cats were receiving organ transplants, neurophysiologist Charles S. Sherrington was using cats to explore neural reflexes and proprioception, research that won him the Nobel Prize in Physiology or Medicine in 1932.

While teaching at Oxford University, Sherrington was always surrounded by cats. He taught a mammal-related course, and there were usually five or six cats in the classroom as teaching tools. His laboratory was called " cat class " by students because of the experimental cats everywhere.

In 1898, Sherrington discovered that if the brainstem was cut transversely between the superior and inferior colliculi of a cat's midbrain, the cat would become rigid, with its head and tail raised, spine stiff, and limbs straight. This phenomenon is called decerebrate rigidity, and is caused by excessive tension in the extensor muscles (also known as anti-gravity muscles, which can straighten the limbs or other parts of the body when they contract). Based on this, Sherrington discovered the stretch reflex , which is a reflex that occurs when muscles are overly tense.

a. Cat in a decerebrate state; b. Stimulation of the left front paw of a cat in a decerebrate state; c. Stimulation of the left hind paw of a cat in a decerebrate state | Reference [3]

How cats stand and walk also attracted Sherrington's interest. In 1910, Sherrington described a phenomenon: even if the brain was removed, cats could still stand and make regular alternating walking movements. Therefore, he believed that the animals' standing and regular walking were caused by the sensory stimulation generated by the lower limbs touching the ground. The "standing reflex" or "stepping reflex" triggered by the sensory stimulation did not require the participation of the brain, but directly passed through the spinal cord, which made people understand the movement a step further .

A cat standing with its brain removed | References [4]

In 1917, Sherrington turned his attention to the cat's auricle and its reflexes . He carefully defined and studied the various reflexes of the cat's ear, including the retraction reflex, folding reflex, covering reflex, itch reflex and head shaking reflex, and proved that these reflexes do not require the involvement of the brain. In the paper, he wrote:

"The cat's pinnae are sensitive and flexible, producing a number of reflexes. One of these I have mentioned briefly in previous studies, and I know of no other attention paid to them, although they have undoubtedly been encountered by other observers."

Hand-drawn cat ears from Sherrington’s paper | References [5]

He also found that cats can respond to dog barking, cat meowing, and bird singing by wagging their tails or raising their hair without the need for brain involvement. These studies on various reflexes such as cat ears and tail wagging have made people realize that there are more types of neural reflexes than imagined.

1981: The real cat with an eyepatch

If a mascot had to be chosen for the 1981 Nobel Prize ceremony, a cat would have been the most appropriate, because the Nobel Prize in Physiology or Medicine that year was awarded to two teams of scientists, both of whom chose to use cats for their experiments: Roger W. Sperry, who discovered the functional specialization of the cerebral hemispheres, and David H. Hubel and Torsten N. Wiesel, who figured out information processing in the visual system.

In Sperry's time, people had discovered through anatomy that the left and right brains were connected by a bundle of fibers. This bundle of fibers was flat in shape and about 10 cm long, and was named the " corpus callosum ." But at that time, people only knew that the "corpus callosum" structurally connected the left and right brains, and did not know its specific functional role. So Sperry wanted to try to cut off the corpus callosum to find out whether it could transmit information between the two hemispheres of the brain.

He chose visual signals as the information that the brain needed to receive, so that he could easily achieve signal input to one hemisphere of the brain by covering one eye.

In a study published in 1953, Sperry placed blindfolds on cats with cut corpus callosum and taught them to discern squares and circles. He first had the cats cover their left eye and learn to discern different shapes with their right eye, then switched gears and covered their right eye and had the cats learn to discern the exact same shapes with their left eye.

The results showed that when the information transmission between the brains is normal, the second learning is a reinforcement of the first learning content, so the learning rate will be much faster than the first learning. However, for the kittens whose corpus callosum was cut, the knowledge learned with the right eye was still completely unfamiliar when the left eye learned it the second time, which shows that after the corpus callosum was cut, the two hemispheres of the brain could not transmit information .

A cat with one eye covered needs to use its other eye to distinguish several different sets of shapes. Reference [6]

After confirming that the corpus callosum is the bridge for information exchange between the two hemispheres of the brain, Sperry keenly realized that patients whose corpus callosum was cut off for the treatment of epilepsy would undoubtedly be the best experimental subjects for studying the left and right functions of the brain. As a result, Sperry became a leading figure in the field of cognitive neuroscience and played an indispensable role in the development of brain science.

Huber and Wiesel were also keen on studying cats' eyes. This is because cats have shorter snouts, which are more similar to the flat facial structure of humans. It is also easier to design blocked fields of vision when doing vision-related experiments. In addition, cats' eye sockets are larger than the size of their skulls, and their visual systems are more complete, making them easier to study.

In their 25-year collaboration, Huber and Wiesel have advanced the exploration of the neural mechanisms of vision . They developed a method to measure the activity of individual cells in the visual cortex, then showed cats light bands of different directions and wavelengths, and used microelectrodes to measure the potential changes of visual neurons to identify different types of visual neurons. The results showed that some cells in the cat's primary visual cortex are very sensitive to the direction of light, while other cells are sensitive to the wavelength of light.

Cat looking at light strips in experiment | References [7]

In addition, they also studied the effects of monocular visual deprivation on the visual cortex during the visual development period by suturing the eyelids of kittens, and found that visual encoding is formed after birth and requires a necessary factor, which is "visual stimulation". During the golden period of visual development, if the eyes are closed for a few days, the visual cortex will undergo permanent functional changes. Therefore, they proposed the concept of the " critical period " of visual nerve development.

On this basis, more studies have proven that not only vision needs stimulation from external information in the early stages of development, but also hearing, language acquisition, and motor function. At the same time, the concept of the critical period of neurodevelopment has opened a new door for understanding and treating cataracts and strabismus in children. If we can seize the critical period of visual development to perform surgical treatment and correct vision for children, many children can avoid lifelong low vision or blindness.

In fact, there are many stories about cats in scientific research (not just research that won the Nobel Prize). Some of the research is closely related to human health, such as physiological research on the pancreas and liver, the discovery of acetylcholine, the development of antidepressant drugs, etc. Cats are present in all of them.

Let's say: Thank you cats.

Image: Giphy.com

References

[1] Carrel, A., Transplantation in Mass of the Kidneys. J Exp Med, 1908. 10(1): p. 98-140.

[2]Ebeling, AH and A. Carrel, Remote Results of Complete Homotransplantation of the Cornea. J Exp Med, 1921. 34(5): p. 435-40.

[3]Sherrington, CS, Decerebrate Rigidity, and Reflex Coordination of Movements. J Physiol, 1898. 22(4): p. 319-32.

[4]Sherrington, CS, Flexion-reflex of the limb, crossed extension-reflex, and reflex stepping and standing. J Physiol, 1910. 40(1-2): p. 28-121.

[5]Sherrington, CS, Reflexes elicitable in the cat from pinna vibrissae and jaws. J Physiol, 1917. 51(6): p. 404-31.

[6]Myers, RE, Interocular transfer of pattern discrimination in cats following section of crossed optic fibers. J Comp Physiol Psychol, 1955. 48(6): p. 470-3.

[7]Hubel, DH, Single unit activity in lateral geniculate body and optic tract of unrestrained cats. J Physiol, 1960. 150: p. 91-104.

Author: A Hardy

Editor: Maiya Yang

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