At what age is the developing cerebral cortex of the rat comparable to that of the full-term newborn human baby?

By means of a comparative study of experimental data from the literature we estimated at what age the rat cerebral cortex corresponds to that of the full-term newborn human infant with regard to the degree of maturation. As a result of this study we suggest that the 12-13-day-old rat pup fulfills this criterion. This finding should be of use to scientists who use the rat for studying certain processes assumed to occur in the human cerebral cortex around full-term birth.

A sex difference in the human brain and its relation to transsexuality

Transsexuals have the strong feeling, often from childhood onwards, of having been born the wrong sex. The possible psychogenic or biological aetiology of transsexuality has been the subject of debate for many years. Here we show that the volume of the central subdivision of the bed nucleus of the stria terminals (BSTc), a brain area that is essential for sexual behaviour, is larger in men than in women. A female-sized BSTc was found in male-to-female transsexuals. The size of the BSTc was not influenced by sex hormones in adulthood and was independent of sexual orientation. Our study is the first to show a female brain structure in genetically male transsexuals and supports the hypothesis that gender identity develops as a result of an interaction between the developing brain and sex hormones.

Increased number of vasopressin- and oxytocin-expressing neurons in the paraventricular nucleus of the hypothalamus in depression

BACKGROUND

Cerebrospinal fluid levels of arginine vasopressin (AVP) and oxytocin (OXT) have been found to change in mood disorders. In the present study, the numbers of AVP-immunoreactive (IR) and OXT-IR neurons were determined in the paraventricular nucleus (PVN) of the human hypothalamus.

METHODS

Postmortem brain tissue was fixed in formalin, embedded in paraffin, and stained for AVP and OXT using immunocytochemical techniques. The number of IR neurons in the PVN was estimated by morphometry in eight depressed patients ranging in age from 21 to 85 years and eight age-matched controls ranging in age from 23 to 88 years.

RESULTS

The numbers of AVP-IR and OXT-IR neurons in the PVN of patients with mood disorder were increased by 56% and 23%, respectively. No differences were found in AVP-IR or OXT-IR cell numbers between three patients with major depression and three patients with bipolar depression. The numbers of AVP-IR and OXT-IR neurons in two patients with depression not otherwise specified were within the same range as in the six other patients with a mood disorder.

CONCLUSIONS

The AVP and OXT neurons were activated in the PVN in patients with major depression or bipolar disorder. This activation may be associated with activation of the hypothalamic-pituitary-adrenal axis in these patients, since both AVP and OXT are known to potentiate the effects of corticotropin-releasing hormone. Because of their central effects, activation of AVP and OXT neurons may also be related to symptoms of major depression or bipolar disorder.

An enlarged suprachiasmatic nucleus in homosexual men

Morphometric analysis of the human hypothalamus revealed that the volume of the suprachiasmatic nucleus (SCN) in homosexual men is 1.7 times as large as that of a reference group of male subjects and contains 2.1 times as many cells. In another hypothalamic nucleus which is located in the immediate vicinity of the SCN, the sexually dimorphic nucleus (SDN), no such differences in either volume or cell number were found. The SDN data indicate the selectivity of the enlarged SCN in homosexual men, but do not support the hypothesis that homosexual men have a 'female hypothalamus'.

Living by the clock: the circadian pacemaker in older people

The suprachiasmatic nucleus (SCN) of the hypothalamus is considered to be a critical component of a neural oscillator system implicated in the timing of a wide variety of biological processes. The circadian cycles established by this biological clock occur throughout nature and have a period of approximately 24 h. With advancing age, however, these daily fluctuations deteriorate, leading to disrupted cycles with a reduced amplitude. In humans, age-related changes have been described for hormonal rhythms, body core temperature, sleep-wakefulness and several other behavioral cycles. It appears that the disruption of circadian rhythms and the increased incidence of disturbed sleep during aging are paralleled by age-related alterations in the neural and temporal organization of the SCN and a decreased photic input to the clock. The many lines of evidence of age-related decrements in circadian time-keeping and the observed neuronal degeneration of the SCN in senescence strongly suggest that the circadian pacemaker in the human brain becomes progressively disturbed during aging.

Early neuropathological Alzheimer's changes in aged individuals are accompanied by decreased cerebrospinal fluid melatonin levels

Neuropathology is the most reliable criterion for diagnosing Alzheimer's disease (AD). A well-established system for staging the spread of neuropathological changes in AD is available. The clinical use of a biomarker that reflects the neuropathological change occurring in brain tissue has not yet been established. Melatonin is a product that plays not only a major role in the regulation of the circadian rhythms but may also exert neuroprotective effects in AD. Melatonin levels were determined in ventricular postmortem cerebrospinal fluid (CSF) of 121 subjects. Braak staging and a modified Braak staging for cortex (MBSC) were used to evaluate the severity of AD neuropathology. The present study revealed that not only the Braak stages of AD, but also the MBSC were negatively correlated with CSF melatonin levels. By using MBSC, we now demonstrate for the first time that CSF melatonin levels were significantly decreased in the aged individuals with early neuropathological changes in the temporal cortex, where the AD process starts. Those individuals that did not have any neurofibrillary tangle (NFT) or neuritic plaque (NP) in the temporal cortex, had much higher melatonin levels (287 +/- 68 and 280 +/- 64 pg/mL, respectively) than those individuals that had a few NFTs and NPs (82 +/- 4 and 39 +/- 8 pg/mL, respectively) in the temporal cortex. These results suggest that the decrease in CSF melatonin levels may be an early event in the development of AD possibly occurring even before the clinical symptoms.

VIP neurons in the human SCN in relation to sex, age, and Alzheimer's disease

The brains of 46 control subjects and 21 Alzheimer's disease (AD) patients were studied to determine whether there are age-related or AD-related changes in the vasoactive intestinal polypeptide (VIP) neuron population of the human suprachiasmatic nucleus (SCN). The number of VIP expressing neurons in the SCN of females, ranging in age from 10-91 years, did not change during normal aging. In males, however, the number of VIP neurons in the SCN was highest in the young subjects (10-40 years of age), after which, a dramatic decrease occurred in middle-aged subjects. This resulted in an age-dependent sex difference in the VIP cell population of the SCN: young males had twice as many VIP expressing SCN neurons as young females, whereas in the middle-aged groups, the females had twice as many VIP SCN neurons as the males. A significant decrease in the number of VIP expressing neurons in the SCN was found in female presenile AD patients, i.e., those younger than 65 years.

Male-to-female transsexuals have female neuron numbers in a limbic nucleus

Transsexuals experience themselves as being of the opposite sex, despite having the biological characteristics of one sex. A crucial question resulting from a previous brain study in male-to-female transsexuals was whether the reported difference according to gender identity in the central part of the bed nucleus of the stria terminalis (BSTc) was based on a neuronal difference in the BSTc itself or just a reflection of a difference in vasoactive intestinal polypeptide innervation from the amygdala, which was used as a marker. Therefore, we determined in 42 subjects the number of somatostatin-expressing neurons in the BSTc in relation to sex, sexual orientation, gender identity, and past or present hormonal status. Regardless of sexual orientation, men had almost twice as many somatostatin neurons as women (P < 0.006). The number of neurons in the BSTc of male-to-female transsexuals was similar to that of the females (P = 0.83). In contrast, the neuron number of a female-to-male transsexual was found to be in the male range. Hormone treatment or sex hormone level variations in adulthood did not seem to have influenced BSTc neuron numbers. The present findings of somatostatin neuronal sex differences in the BSTc and its sex reversal in the transsexual brain clearly support the paradigm that in transsexuals sexual differentiation of the brain and genitals may go into opposite directions and point to a neurobiological basis of gender identity disorder.

Alterations in circadian rhythmicity of the vasopressin-producing neurons of the human suprachiasmatic nucleus (SCN) with aging

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus is implicated in the temporal organization of circadian rhythms in a variety of physiological, endocrine and behavioral processes. There is a great deal of evidence indicating that aging is characterized by a progressive deterioration of circadian timekeeping. The present study was aimed at investigating whether there are age-related changes in circadian rhythmicity of the vasopressin (VP)-producing neurons in the human SCN. To that end brains obtained at autopsy of 39 subjects, ranging in age from 6 to 91 years, were studied. Subjects were divided into two age groups, viz. 'young subjects' (up to 50 years) and 'elderly subjects' (over 50 years). It is shown that the number of VP-immunoreactive neurons in the human SCN exhibits a marked diurnal oscillation in young, but not in elderly, people. Whereas in young subjects low VP-immunoreactive neuron numbers were found during the night period (22:00-06:00 h) and peak values during the early morning (06:00-10:00 h), the SCN of elderly people showed a reduced amplitude and a tendency for a reversed diurnal pattern with high instead of low values during the night. The findings suggest that the VP synthesis of the human SCN exhibits a circadian rhythm that is disrupted later in life.

Energy metabolism, brain size and longevity in mammals

The mathematical relations between basal energy metabolism, brain size, and life span in mammals have been investigated. The evolutionary level of brain development, or encephalization (c), is a function both of brain weight (E) and of body weight (P) according to (formula; see text) Brain weight was found to be a linear function of the product of encephalization and basal metabolic rate. The oxygen consumption of the brain (Mbrain) is proportional to both encephalization and body weight according to (formula; see text) The ratio of metabolic rate in the cerebral cortex to that in the brain as a whole depends solely upon the degree of encephalization and is independent of the size of the animal. The maximum potential life span of a mammal was found to be proportional to the product of its degree of encephalization and the reciprocal of its metabolic rate per unit weight. Life span may be regarded as the algebraic sum of two components: (1) a deduced somatic component (Lb) inversely related to the basal metabolic rate per unit weight, and (2) an encephalization component (Le) related directly to the evolutionary increase of relative brain size.

Size and shape of the cerebral cortex in mammals. I. The cortical surface

The evolution of the brain in mammals has been accompanied by a progressive enlargement of the cerebral cortex. Allometric analysis of the volume, surface and convolutedness of this cortex shows that among mammals two major groups can be distinguished: (1) species with lissencephalic brains, where surface-volume relationships are determined by linear geometric laws, and (2) species with gyrencephalic brains, where strict geometric similarity no longer applies. Different mathematical models are required to describe the brain morphology in these groups. It has been shown, moreover, that among species with convoluted brains, marine mammals (Cetacea) form a subgroup in that the cerebrocortical surface in these animals is more folded than in terrestrial mammals of similar brain size. Thus it appears that the use of a single allometric relation in studying the effect of size increase on the geometry of the brain - irrespective of convolutedness or ecological strategy - as has been done in previous studies, is unjustified and obscures the differences in the structural organization of mammalian brains. Finally, a dimensionless index of cortical folding is proposed, which indicates that the degree of cortical folding depends not only on the volume of the brain or cortex but on cortical thickness as well.

Morphometry of size/volume variables and comparison of their bivariate relations in the nervous system under different conditions

Comparison of the different approximation equations and procedures to estimate the volume of a brain region with an irregular shape contained in parallel sections indicates that the 'basic volume estimator' using systematic section is very efficient and sufficiently accurate. Important in estimating the volume is the correction for shrinkage and the accuracy of the section thickness determination. Methods to estimate thickness of section are outlined, and the method of differential focusing is discussed. In the Appendix, the corrections are described for overestimation of the volume by overprojection of the cross-sectional area and underestimation by underprojection when the size of cross-sectional area changes non-negligibly within sections. Statistical techniques to compare bivariate linear relations of different groups are reviewed. Emphasis is laid on Model II regression techniques that are used when the two variables considered are both subject to biological variation and measurement error. A new Model II procedure is proposed to compare the coincidence of the slopes of bivariate distributions and to test whether or not an experimental bivariate sample deviates significantly from a control sample when only the control group shows a significant bivariate linear relationship.

Evolution of the human brain: when bigger is better

Comparative studies of the brain in mammals suggest that there are general architectural principles governing its growth and evolutionary development. We are beginning to understand the geometric, biophysical and energy constraints that have governed the evolution and functional organization of the brain and its underlying neuronal network. The object of this review is to present current perspectives on primate brain evolution, especially in humans, and to examine some hypothetical organizing principles that underlie the brain's complex organization. Some of the design principles and operational modes that underlie the information processing capacity of the cerebral cortex in primates will be explored. It is shown that the development of the cortex coordinates folding with connectivity in a way that produces smaller and faster brains, then otherwise would have been possible. In view of the central importance placed on brain evolution in explaining the success of our own species, one may wonder whether there are physical limits that constrain its processing power and evolutionary potential. It will be argued that at a brain size of about 3500 cm(3), corresponding to a brain volume two to three times that of modern man, the brain seems to reach its maximum processing capacity. The larger the brain grows beyond this critical size, the less efficient it will become, thus limiting any improvement in cognitive power.

Vasopressin and the output of the hypothalamic biological clock

The physiological effects of vasopressin as a peripheral hormone were first reported more than 100 years ago. However, it was not until the first immunocytochemical studies were carried out in the early 1970s, using vasopressin antibodies, and the discovery of an extensive distribution of vasopressin-containing fibres outside the hypothalamus, that a neurotransmitter role for vasopressin could be hypothesised. These studies revealed four additional vasopressin systems next to the classical magnocellular vasopressin system in the paraventricular and supraoptic nuclei: a sexually dimorphic system originating from the bed nucleus of the stria terminalis and the medial amygdala, an autonomic and endocrine system originating from the medial part of the paraventricular nucleus, and the circadian system originating from the hypothalamic suprachiasmatic nuclei (SCN). At about the same time as the discovery of the neurotransmitter function of vasopressin, it also became clear that the SCN contain the main component of the mammalian biological clock system (i.e. the endogenous pacemaker). This review will concentrate on the significance of the vasopressin neurones in the SCN for the functional output of the biological clock that is contained within it. The vasopressin-containing subpopulation is a characteristic feature of the SCN in many species, including humans. The activity of the vasopressin neurones in the SCN shows a pronounced daily variation in its activity that has also been demonstrated in human post-mortem brains. Animal experiments show an important role for SCN-derived vasopressin in the control of neuroendocrine day/night rhythms such as that of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes. The remarkable correlation between a diminished presence of vasopressin in the SCN and a deterioration of sleep-wake rhythms during ageing and depression make it likely that, also in humans, the vasopressin neurones contribute considerably to the rhythmic output of the SCN.

Sexual differentiation of the human hypothalamus: ontogeny of the sexually dimorphic nucleus of the preoptic area

Sexual differentiation of the hypothalamus of the human brain is generally believed to take place around midpregnancy and thought to be related to the development of sexual orientation and gender identity. The present life span study on the human sexually dimorphic nucleus (SDN) of more than a hundred subjects revealed, however, that at the age of 2-4 years the SDN cell number reaches a peak value, and that only after this age sexual differentiation becomes manifest. Furthermore, the SDN cell number in homosexual men was not different from that of the male reference group, but significantly larger than the cell number in age-matched women.

Alterations in arginine vasopressin neurons in the suprachiasmatic nucleus in depression

BACKGROUND

Circadian rhythm disturbances are frequently found in depressed subjects. Although it has been presumed that these disturbances may reflect a disorder of the circadian pacemaker, this has never been established. The suprachiasmatic nucleus (SCN) is the pacemaker of the circadian timing system in mammals, and arginine vasopressin (AVP) is one of its major neuropeptides. As peptide content is often taken as a measure for activity, we hypothesized that a decreased number of AVP-immunoreactive (AVP-IR) neurons and amount of AVP-messenger RNA (mRNA) would be present in the SCN of depressed subjects.

METHODS

Brains of 11 subjects suffering from major depression (8 cases) and bipolar disorder (3 cases), and of 11 controls, matched for sex, age, and clock time at death, were collected. The number of AVP-IR neurons in the SCN was determined by means of a digitizer (CalComp Inc, Reading, England). The amount of AVP-mRNA expression in the SCN was quantified with the Interaktive Bild Analyse System image analysis system (Kontron, Munich, Germany).

RESULTS

In depressed subjects, the number of AVP-IR neurons in the SCN was more than one and a half times higher than in controls, while the total masked area of silver grains, as an estimate of the amount of AVP-mRNA, was about one half that of controls.

CONCLUSIONS

Contrary to our hypothesis, an increase in the number of AVP-IR neurons in the SCN in depression was found, together with an expected decrease in AVP-mRNA. These findings suggest that, in depressed patients, both the synthesis and release of AVP in the SCN is reduced, resulting in an impaired functional ability. A disbalance between AVP production and transport needs further investigation in future studies.

Alterations in the hypothalamic paraventricular nucleus and its oxytocin neurons (putative satiety cells) in Prader-Willi syndrome: a study of five cases

Animal experiments have shown that the parvocellular oxytocin (OXT) neurons of the hypothalamic paraventricular nucleus (PVN) inhibit food intake. In the present study, the PVN and its OXT neurons have been investigated in an extreme human eating disorder, i.e. the Prader-Willi syndrome (PWS). PWS patients are characterized by gross obesity, insatiable hunger, hypotonia, hypogonadism, and mental retardation. The PVN of 5 PWS patients (2 males and 3 females), varying in age between 22-64 yr, and 27 controls (14 males and 13 females) without any primary neurological or psychiatric diseases was morphometrically investigated after conventional staining with thionine and immunocytochemical staining for OXT and vasopressin (AVP). The thionine-stained volume of the PVN was 28% smaller in PWS patients (P = 0.028), and the total cell number was 38% lower (P = 0.009). The immunoreactivity for OXT and AVP was decreased in PWS patients, although the variability within the groups was high. A strong and highly significant decrease (42%; P = 0.016) was found in the number of OXT-expressing neurons of the PWS patients. The volume of the PVN-containing OXT-expressing neurons decreased by 54% (P = 0.028) in PWS. The number of AVP-expressing neurons in the PVN did not change significantly. The OXT neurons of the PVN seem to be good candidates for playing a physiological role in ingestive behavior as "satiety neurons" in the human hypothalamus.

Decreased vasopressin gene expression in the biological clock of Alzheimer disease patients with and without depression

Circadian rhythm disturbances are frequently present in Alzheimer disease (AD). In the present study, we investigated the expression of vasopressin (AVP) mRNA in the human suprachiasmatic nucleus (SCN). The in situ hybridization procedure on formalin-fixed paraffin-embedded material was improved to such a degree that we could, for the first time, visualize AVP mRNA expressing neurons in the human SCN and carry out quantitative measurements. The total amount of AVP mRNA expressed as masked silver grains in the SCN was 3 times lower in AD patients (n = 14; 2,135 +/- 597 microm2) than in age- and time-of-death-matched controls (n = 11; 6,667 +/- 1466 microm2) (p = 0.003). No significant difference was found in the amount of AVP mRNA between AD patients with depression (n = 7) and without depression (n = 7) (2,985 +/-1103 microm2 and 1,285 +/- 298 microm2, respectively; p = 0.38). In addition, the human SCN AVP mRNA expressing neurons showed a marked day-night difference in controls under 80 years of age. The amount of AVP mRNA was more than 3 times higher during the daytime (9,028 +/- 1709 microm2, n = 7) than at night (2,536 +/- 740 microm2, n = 4; p = 0.02), whereas no clear diurnal rhythm of AVP mRNA in the SCN was observed in AD patients. There was no relationship between the amount of AVP mRNA in the SCN and age at onset of dementia, duration of AD and the neuropathological changes in the cerebral cortex. These findings suggest that the neurobiological basis of the circadian rhythm disturbances that are responsible for behavioral rhythm disorders is located in the SCN. It also explains the beneficial effects of light therapy on nightly restlessness in AD patients.

Increased cortisol levels in aging and Alzheimer's disease in postmortem cerebrospinal fluid

The hypothalamo-pituitary-adrenal (HPA) axis is activated during aging and even more so in dementia. Increased levels of corticosteroids may be neurotoxic. Therefore we have investigated cortisol levels in cerebrospinal fluid (CSF) of Alzheimer patients and controls. Ventricular postmortem CSF was collected from clinically and neuropathologically well-defined Alzheimer patients (n = 26) and control subjects (n = 21). In the group of Alzheimer patients the mean CSF total cortisol level was 83% higher than that in the controls. In presenile Alzheimer patients (< 65 years of age; n = 13) the CSF-cortisol level was 5 times higher than that of presenile controls (n = 7). In contrast, senile Alzheimer patients (n = 13) and controls of over 65 years of age (n = 14) did not show a significant difference in CSF-cortisol levels. The presence or absence of a difference in the cortisol-CSF levels in, respectively, presenile or senile Alzheimer patients as compared to controls was due to the 3.5-fold rise of CSF-cortisol in control subjects over 65 years of age as compared with controls under 65 years of age. The CSF-cortisol levels in presenile and senile Alzheimer patients were similar. No significant correlation was observed in the Alzheimer patients between age of onset of the dementia and CSF cortisol levels or duration of Alzheimer's disease and CSF cortisol levels. The finding that in senile Alzheimer patients cortisol levels were similar to those of unaffected age-matched controls does not seem to support the cortisol neurotoxicity hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)

The supraoptic and paraventricular nuclei of the human hypothalamus in relation to sex, age and Alzheimer's disease

Volume and total cell number were determined in the supraoptic (SON) and paraventricular (PVN) nuclei of 14 male and 16 female subjects ranging in age from 10 to 93 years. In addition, 4 male and 6 female subjects suffering from Alzheimer's disease (AD) and ranging in age from 46 to 97 years were studied. Subjects were divided into two age groups, viz., "young" for subjects up to 60 years, and "old" for subjects older than 60. No sex differences in volume and in total cell number were observed in the SON and PVN in either age group. In addition, no significant correlation was found between total cell number in the SON and PVN and brain weight. No significant differences in volume and total cell number were found in either the SON or PVN between young and old control subjects or between AD cases and controls, indicating that these nuclei are spared from degenerative changes in senescence and AD. Determination of neuron numbers in the SON supported this view. In contrast, volume and total cell counts in the suprachiasmatic decreased in senescence and were dramatically reduced in AD. The present results indicate the occurrence of differential patterns of cell loss within the human hypothalamus with aging and in AD, which are proposed to be related to functional differences between the hypothalamic nuclei.

Diurnal rhythm of free estradiol during the menstrual cycle

OBJECTIVE

To investigate the diurnal rhythm of estrogens in normally cyclic women during reproductive life.

DESIGN

Multiple saliva sampling in normally cyclic healthy women during reproductive life at different phases of their menstrual cycles was carried out.

METHODS

Salivary estradiol was measured by radioimmunoassay in samples collected every 2 h for 24 h from 15 normally cyclic healthy women during reproductive life during the menstrual phase, the late follicular/peri-ovulation phase, the early to mid luteal phase and the late luteal phase, respectively, of their menstrual cycles. The levels of salivary estradiol were analyzed by means of periodic regression.

RESULTS

A daily biological rhythm of free estradiol was found after quantification with a nonlinear periodic regression model. The observed diurnal free estradiol rhythm consists of two major components: an asymmetrically peaked diurnal cycle and ultradian harmonics in the range of 6 to 12 h. The diurnal and ultradian rhythms were remarkably consistent throughout the menstrual cycle in terms of mesor (24 h mean level), peak width and amplitude. There was a tendency for the 24-h rhythm acrophases to converge in the early morning, while the acrophase of the menstrual phase occurred significantly later than in the late follicular/peri-ovulation phase.

CONCLUSIONS

The diurnal rhythm of estradiol has a similar complex temporal organization for different menstrual phases. The menstrual cycle mainly modulates the acrophase of the diurnal rhythm.

Size and shape of the cerebral cortex in mammals. II. The cortical volume

The geometry of the brain and cerebral cortex in mammals has been studied from an evolutionary perspective and is described in mathematical terms. The volume of the cerebral cortex, in contrast to the cortical surface area, scales to brain volume in a similar way, irrespective of the degree of cortical folding. Among mammals, Cetacea form a subgroup, in that their volumetric data fit an isometric model better than an allometric model. An index of corticalization is presented which contains information about both the mass of interconnective nerve fibers and the degree of intracortical processing. It is shown, furthermore, that a semilogarithmic equation appropriately describes the relationship between mean cortical thickness and brain volume. Finally, allometric equations between brain volume and cortical parameters, which can be used for predictive purposes, are presented.

Functional neuroanatomy and neuropathology of the human hypothalamus

The human hypothalamus is involved in a wide range of functions in the developing, adult and aging subject and is responsible for a large number of symptoms of neuroendocrine, neurological and psychiatric diseases. In the present review some prominent hypothalamic nuclei are discussed in relation to normal development, sexual differentiation, aging and a number of neuropathological conditions. The suprachiasmatic nucleus, the clock of the brain, shows seasonal and circadian variations in its vasopressin neurons. During normal aging, but even more so in Alzheimer's disease, the number of these neurons decreases. In homosexual men this nucleus is larger than in heterosexual men. The difference between the sexually dimorphic nuclei of men and women arises between the ages of 2-4 to puberty. In adult men this nucleus is twice as large as in adult women. In the process of aging, a sex-dependent decrease in cell number occurs. The vasopressin and oxytocin cells of the supraoptic and paraventricular nucleus are present in adult numbers as early as mid-gestation. Lower oxytocin neuron numbers are found in Prader-Willi syndrome, AIDS and Parkinson's disease. Familial hypothalamic diabetes insipidus is based upon a point mutation in the vasopressin-neurophysin-glycopeptide gene. Parvicellular corticotropin-releasing hormone-containing neurons in the paraventricular nucleus increase in number and are activated during the course of aging. In post-menopausal women, the infundibular or arcuate nucleus contains hypertrophic neurons containing oestrogen receptors. These neurons may be involved in the initiation of menopausal flushes. The nucleus tuberalis lateralis may be involved in feeding behaviour and metabolism. In Huntington's disease the majority of its neurons is lost; in Alzheimer's disease it shows very strong cytoskeletal alterations. Tuberomammillary nucleus neurons contain, e.g., histamine or galanine, and project to the cortex. Strong cytoskeletal changes, as well as plaques and tangles are found in this nucleus in Alzheimer's disease. The various hypothalamic nuclei are probably involved in many functions and symptoms of which only a minority has been revealed.

Encephalization in mammals in relation to the size of the cerebral cortex

A new index of encephalization has been proposed based on a reanalysis of the brain-body weight relationship in mammals. The new index, c, is related to the volume of the whole brain as well as to the surface and volume of the cerebral cortex. From an evolutionary point of view the index-cortex relationship is particularly interesting, since the structure of the brain which contributes most to its evolutionary progression is the cerebral cortex. A theory of corticalization has been developed in which the surface of the cerebral cortex is analyzed into two components, Sb, determined by the size of the animal, and Se, associated with an increase in the information-processing capacity. An analogue division has been performed for the cortical volume. Furthermore, an inquiry has been made into the brain structure which can serve as an estimator of body weight. The medulla oblongata appears to be such a structure.