"Four times larger" sounds like quite an exaggeration!
A few references are listed below but it looks like a particular nucleus in
the rat amygdala (posteromedial cortical nucleus) is sexually dimorphic
(larger in males) and that the aromatization of testosterone to estradiol
during sexual differentiation is responsible for the size difference.
Current circulating levels of testosterone also maintain the size difference
in adult rats (since castration of adult rats causes it to shrink to female
size and treatment of adult females causes it to enlarge to male size). But
the total volume of the entire amygdala is not different in male and female
monkeys. Couldn't find any imaging info on human volumes.
References below.
Sherry Ferguson, Ph.D
Research Psychologist
National Center for Toxicological Research/FDA
3900 NCTR Road
Jefferson, AR 72079
AU - Vinader-Caerols C
AU - Collado P
AU - Segovia S
AU - Guillamon A
IN - Area de Psicobiologia, Facultad de Psicologia, Universitat de
Valencia, Valencia, Spain.
TI - Estradiol masculinizes the posteromedial cortical nucleus of
the amygdala in the rat.
SO - Brain Research Bulletin 2000 Oct;53(3):269-73
AB - It has been demonstrated that the posteromedial cortical
amygdaloid nucleus (PMCo), is sexually dimorphic. It is shown
(Experiment 1) that male orchidectomy on the day of birth (D1)
decreases the volume and number of neurons of the PMCo, while a
single injection of propionate testosterone to the female on D1
masculinizes the PMCo in this gender. Since male gonadectomy on D1
(Experiment 2) is counteracted by a single injection of estradiol
benzoate in males it has been suggested that the masculinization of
the PMCo is due to the aromatization of testosterone to estradiol in
this structure. These findings support the hypothesis that the
development of sex differences in structures that belong to the
vomeronasal system are due to the aromatization of testosterone to
estradiol shortly after birth.
AU - Stefanova N
AU - Ovtscharoff W
IN - Department of Anatomy and Histology, Medical University Sofia,
1 G. Sofiisky St., 1431 Sofia, Bulgaria.
[EMAIL PROTECTED]
TI - Sexual dimorphism of the bed nucleus of the stria terminalis
and the amygdala. [Review] [276 refs]
SO - Advances in Anatomy, Embryology & Cell Biology 2000;158:III-X,
1-78
AB - The present review summarizes the up-to-date knowledge on the
sexual dimorphism of the CNS with special regard to the sexual
differentiation of the bed nucleus of the stria terminalis (BST) and
the amygdala in rat. The authors provide new evidence for the sexual
dimorphism and differentiation of GABAergic,
leucine-enkephalin-containing and parvalbumin-immunoreactive neurons
in the BST and the amygdala of the rat. Together with testing the
gender differences, age-related changes in numbers of the neuronal
subpopulations, mentioned above are followed. The authors' results
provide morphological and immunocytochemical data that may be used
for further studies on sexually dimorphic circuitry and its
functional significance. [References: 276]
AU - Cooke BM
AU - Tabibnia G
AU - Breedlove SM
IN - Department of Psychology, University of California, Berkeley,
CA 94720-1650, USA.
TI - A brain sexual dimorphism controlled by adult circulating
androgens.
SO - Proceedings of the National Academy of Sciences of the United
States of America 1999 Jun 22;96(13):7538-40
AB - Reports of structural differences between the brains of men
and women, heterosexual and homosexual men, and male-to-female
transsexuals and other men have been offered as evidence that the
behavioral differences between these groups are likely caused by
differences in the early development of the brain. However, a
possible confounding variable is the concentration of circulating
hormones seen in these groups in adulthood. Evaluation of this
possibility hinges on the extent to which circulating hormones can
alter the size of mammalian brain regions as revealed by Nissl
stains. We now report a sexual dimorphism in the volume of a brain
nucleus in rats that can be completely accounted for by adult sex
differences in circulating androgen. The posterodorsal nucleus of
the medial amygdala (MePD) has a greater volume in male rats than in
females, but adult castration of males causes the volume to shrink
to female values within four weeks, whereas androgen treatment of
adult females for that period enlarges the MePD to levels equivalent
to normal males. This report demonstrates that adult hormone
manipulations can completely reverse a sexual dimorphism in brain
regional volume in a mammalian species. The sex difference and
androgen responsiveness of MePD volume is reflected in the soma size
of neurons there.
AU - Vinader-Caerols C
AU - Collado P
AU - Segovia S
AU - Guillamon A
IN - Departamento de Psicobiologia, UNED, Madrid, Spain.
TI - Sex differences in the posteromedial cortical nucleus of the
amygdala in the rat.
SO - Neuroreport 1998 Aug 3;9(11):2653-6
AB - It has been hypothesized that the vomeronasal system (VNS), a
complex neural network implicated in the control of reproductive
behaviors, is sexually dimorphic. The posteromedial cortical
amygdaloid nucleus (PMCo) belongs to the group of amygdaloid
structures that receive direct olfactory input from the accessory
olfactory bulb. In the present study we looked for sex differences
in this nucleus in male and female adult rats and we found that the
males had larger volumes and more neurons than the females. These
results support the hypothesis that the VNS is a sexually dimorphic
system.
AU - Franklin MS
AU - Kraemer GW
AU - Shelton SE
AU - Baker E
AU - Kalin NH
AU - Uno H
IN - Wisconsin Regional Primate Research Center, University of
Wisconsin, Madison 53715-1299, USA.
TI - Gender differences in brain volume and size of corpus callosum
and amygdala of rhesus monkey measured from MRI images.
SO - Brain Research 2000 Jan 10;852(2):263-7
AB - While it has been established that the weight of the female
rhesus monkey brain is less than that of the male, the sexual
dimorphism of specific brain structures has not been
well-documented. To further understand potential sex differences, we
measured the whole brain volume and the size of the corpus callosum
(mid-sagittal) and amygdala (largest coronal section) in MRI images
from juvenile to adult male and female rhesus monkeys between 8
months and 7.2 years of age. The mean volume of the male brain was
89.2 +/- 1.9 (S.E.M.) compared to the female brain volume of 70.8
+/- 0.72 cm3. The average area of the corpus callosum increased from
8 months to 4.5 years; 0.56 to 0.93 cm2 in males and 0.45 to 0.66
cm2 in females. However, the average area of splenium is
significantly greater in females (0.280 cm2), than males (0.184
cm2). The average area of the amygdala did not change with age; it
was 1.07 +/- 0.037 (S.E.M.) in males and 1.08 +/- 0.022 cm2 in
females. This data suggests that the whole brain volume and the size
of the entire corpus callosum of young adult female rhesus monkeys
are approximately 20% smaller than those of young adult males.
Interestingly, the area of the splenial portion of the corpus
callosum is larger in female monkeys. The size of the amygdala
showed no sex difference.
> -----Original Message-----
> From: Jeff Ricker [SMTP:[EMAIL PROTECTED]]
> Sent: Tuesday, November 27, 2001 6:49 AM
> To: Teaching in the Psychological Sciences
> Subject: Amygdala's role in aggressive behavior
>
> Yesterday, a therapist I know made the claim that recent research ("in
> the last 3 or 4 years") shows that the amygdala is much larger, on
> average, in males than in females ("about four times larger"). He also
> stated that this size difference has been implicated in gender
> differences in aggressive behavior.
>
> I had never before heard that the amygdala is proportionally larger in
> males compared to females; nor had I heard that the amygdala is thought
> to be important for differences in aggressive behavior (or that it is
> involved in aggressive behavior, at all).
>
> Is there someone out there who is knowledgeable about such things and
> who can enlighten me?
>
> Thanks,
>
> Jeff
>
> --
> Jeffry P. Ricker, Ph.D. Office Phone: (480) 423-6213
> 9000 E. Chaparral Rd. FAX Number: (480) 423-6298
> Psychology Department [EMAIL PROTECTED]
> Scottsdale Community College
> Scottsdale, AZ 85256-2626
>
> "Every man is a damn fool for at least five minutes
> every day; wisdom consists in not exceeding the limit."
> Elbert Hubbard
>
> Listowner: Psychologists Educating Students to Think Skeptically (PESTS)
>
> http://www.sc.maricopa.edu/sbscience/pests/index.html
>
>
>
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