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Overview: A quick glance at the title might lead you to believe
that this is going to be a very interesting lecture. Well it is interesting,
but not in the way you think! You will see how the role of hormones in
behaviour has been elucidated by removing the endocrine glands, observing
the animals behaviour and then replacing hormones to reverse the effects
of the original intervention. This is a fundamental scientific strategy
(remove - observe - replace - observe) and crops up in many behavioural
experiments. A very important question is: Do the effects of these hormone
manipulations reflect an effect of hormones on the animal's brain, or are
the effects secondary to changes in peripheral tissues? It would be nice
to believe that we were observing central effects - after all we are principally
interested in the brain. But the possibility that the animal's behaviour
is affected by more mundane peripheral effects needs to be experimentally
verified. Studies which address this issue are described.
 Table of Contents
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Learning objectives
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Frank Beach is generally considered to be the founding father of the study of the effects of hormones on behaviour - an area of scientific investigation that is known today as behavioural endocrinology or psychoendocrinology. His first book, Hormones and Behavior (1948), summarizes all that was known at the time and organized the field for all subsequent investigators. Beach devoted his whole life to basic research and justified his endeavors as follows: To what degree should my choice of research work be governed by human needs, by social imperatives, and how am I going to justify spending all of my energies on any research that does not bear directly on pressing human problems.... The solution, or rationalization, that I have finally come up with is that it is a perfectly worthwhile way of spending one's life to do your level best to increase human knowledge, and it is not necessary nor is it always even desirable to be constrained by possible applicability of what you find to immediate problems. This may sound very peculiar to some young people, but it is a value judgment which I myself have made and which I can live with. As you probably realize, Frank Beach is my hero, and I have spent a large part of my research career following up his fascinating work on the role of sensory systems in controlling reproductive behaviors.
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| Points to ponder
Why do you think - at one time - female rats were viewed as passive recipients of male sexual sexual behaviour? What does this tell us about the effect of the influence of researchers' attitudes and values? Can you think of other examples of this effect? |
This list of behavioural measures is by no means exhaustive.
Tests of sexual behaviour are either:
| Point to ponder
How would you measure the effect(s) of hormones on human sexual behaviour? |
| Point to ponder
If you were called as an expert witness in the trial of a pedophiliac, what treatment would you recommend? |
The hypogonadal men kept daily diaries of their sexual behaviour and penile erections. The biggest effects of testosterone injections were reported one week after injection. This corresponds to the time of peak effect on plasma testosterone level. This diagram shows these effects. Notice that the effects are dose-dependent, and that the values do not reach 100% for any of the measures, even at the highest dose of testosterone (400 mg).
Of course one possibility is that not enough testosterone was injected. This is unlikely because studies indicate that plasma testosterone levels as high as 1500 ng/100 ml (the level seen after injection of 400 mg testosterone enanthate) are rare in normal men. In fact the most surprising thing about male testosterone level is its huge range - shown in red in the diagram below. In general there is a tendency for testosterone level to increase during teenage years and the 20s. it usually remains steady in middle life, but after 60 there is a decline to the level seen in young boys. Nevertheless as this diagram shows there are a lot of 90 year old men out there with teenage levels of circulating testosterone! (Vermeulen et al, J. Clin. Endocrinol. Metab.,34, 730-735, 1972).
Global Variation in Male Testosterone and Age by Peter T. Ellison et al at Harvard contains a nice diagram showing the decline in male salivary testosterone level as a function of age.
Supplementary ReadingHEFCE, the funding body for universities and colleges for the UK, has purchased a 3 year license to IDEAL, the Academic Press online journal library. If you are a member of a UK academic institution (i.e. HEFCE funded) you now have full access rights to this online library which enables you to read the full text of articles in Academic Press journals. Note IDEAL uses your computer's IP internet address to allow access. Consequently you may not gain automatic access if you are a HE student using a PC at home.The following articles cover topics raised in the lecture in greater depth:
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| VIAGRA (sildenafil citrate)
The Viagra story is interesting - in the context of this lecture - because it emphasizes the importance of peripheral factors in the control of sexual behaviour. A pill hailed as a "magic bullet" for the way it combats male impotence has created the greatest demand for a drug in the history of the American pharmaceutical industry. Originally developed as a heart medication, it is the first oral pill for impotence and it works for at least 70 per cent of sufferers. There are side effects. For example, about 16 per cent of men in the tests reported headaches. Another potential problem is that the drugs may mask early warning signs of heart disease. The Virginia Urology Center explains Viagra's biochemical mechanism as follows: "To achieve an erection the brain produces a chemical (cyclic GMP) that relaxes specific muscles and allows the blood to flow into the penis. After orgasm, another chemical, (Phosphodiesterase) is produced to remove cyclic GMP, so blood can flow out of the penis. Viagra™ is a Phosphodiesterase Type (5 PDE-5) Inhibitor that, increases the time cyclic GMP is available to achieve or maintain an erection for sexual activities." The underlying mechanisms of male and female impotence may be similar. Female genitals fill with blood during sexual stimulation just as male genitals do, resulting in engorgement of the clitoris and lubrication of the vagina. Therefore female trials of Viagra are under way in Europe and the U.S |
Figure 2. Percentage of Patients Reporting an Improvement in Erections. |
The following description of clinical studies of Viagra appeared on
the Pfizer Viagra site
" The frequency of patients reporting improvement of erections in response to a global question in four of the randomized, double-blind, parallel, placebo controlled fixed dose studies (1797 patients) of 12 to 24 weeks duration is shown in Figure 2. These patients had erectile dysfunction at baseline that was characterized by median categorical scores of 2 (a few times) on principal IIEF questions. Erectile dysfunction was attributed to organic (58%; generally not characterized, but including diabetes and excluding spinal cord injury), psychogenic (17%), or mixed (24%) etiologies. Sixty-three percent, 74%, and 82% of the patients on 25 mg, 50 mg and 100 mg of VIAGRA, respectively, reported an improvement in their erections, compared to 24% on placebo." Further details can be obtained from the Pfizer Viagra site |
The Virginia Urology Center Impotence/Sexual
Dysfunction site has detailed answers to the following questions:
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