Men Are From Mars, Women Are From Venus: Stress, Pets, and Oxytocin

VOL. V NO. I JANUARY/FEBRUARY 2003 86 The theme of the book from which this title is borrowed, and which I confess I have not read, is that men and women are different in the ways in which they respond to stress and manage their lives. The region of the brain that regulates the stress response is the amygdala, which is located deep in the heart of the brain stem.1 It is one part of the network of brain nuclei known as the limbic system, the most ancient part of the brain. In mammals such as the rat it comprises the bulk of the cerebrum, but in man it is overlaid by the cerebral cortex. In Freudian terms, the limbic system represents the id, and the cortex the ego and superego. Stimulation of the amygdala produces the emotion of fear, and activates a cascade of changes. The most important connections relevant to the cardiovascular system are with the hypothalamus: activation of the lateral nucleus stimulates the sympathetic nervous system to produce acute increases in heart rate and blood pressure; and stimulation of the paraventricular nucleus leads to release of the corticotrophin-releasing factor, adrenocorticotropic hormone, and cortisol. A third link to the locus ceruleus activates adrenergic and cholinergic neurons, which leads to behavioral arousal. The whole package represents the fight and flight response first described by Walter Cannon in 1932.2 Although this response is the one that has received the greatest attention, it is only part of the picture. A whole host of hormones that have cardiovascular effects have been reported to be released during exposure to stress.3 Activation of the sympathetic nervous system releases norepinephrine, epinephrine, and dopamine, and also neuropeptide Y.4 Since stimulation of the sympathetic nerves also triggers renin release from the kidneys, the renin-angiotensin system is also activated. Other hormones that have been shown to be released during exposure to stress include endorphins,5 endothelin, and the posterior pituitary hormones oxytocin and vasopressin.6 The basic biochemistry of the stress response is the same in both sexes, so far as is known. But there are subtle differences in the ways in which stress is perceived. An example of how the two sexes respond differently during stress is provided by a recent experimental study conducted by Stroud et al.7 Healthy male and female undergraduates were exposed to two different stressors, and their response measured as the increase of salivary cortisol (which reflects blood levels quite well). One was called an “achievement challenge,” in which subjects were asked to perform difficult arithmetic tasks, and the other was a “social isolation” task, in which subjects interacted socially with trained confederates who treated them in a negative and hostile way. The men showed an increase of cortisol during the achievement challenge task, but not to the social interaction task, while exactly the opposite pattern of response was seen in the women. Interestingly, these different responses did not appear to be due to differences in the cognitive perception of the stress, since both men and women said that they found the stressors equally stressful. While the male response to threat is to adopt aggressive behavior—the “fight” of the fight and flight, the archetypal female response may be directed more to affiliation, as shown by the bigger stress response in women when subjected to social isolation. It has recently been proposed by two psychologists, Drs. Shelley Taylor and Laura Cousino Klein,8 that there is a fundamentally different stress response in women, which they have called “tend Men Are From Mars, Women Are From Venus: Stress, Pets, and Oxytocin