Comparison of the number of vasopressin-producing hypothalamic neurons in rats and humans

Hypothalamus enlargement in mood disorders

OBJECTIVE

The purpose of this study was to determine, in vivo, whether the hypothalamus volume is reduced in patients with mood disorders.

METHODS

The cross-sectional study included 20 unmedicated (MDDu) and 20 medicated patients with major depressive disorder, 21 patients with bipolar disorder, and 23 controls. Twenty of the controls were matched to the MDDu. Seven Tesla, T1-weighted magnetic resonance images were acquired and processed using methods specifically developed for high-precision volumetry of the hypothalamus.

RESULTS

An overall group difference was observed for the left hypothalamus volume corrected for intracranial volume. Planned contrasts identified that the left hypothalamus was approximately 5% larger in each patient group compared with the control group. A paired t-test with the 20 matched pairs of MDDu and controls and without correction for covariates confirmed the larger left hypothalamus volume in MDDu.

CONCLUSIONS

Contrary to our expectations, the hypothalamus volume was increased in patients with uni- and bipolar affective disorders. The effect was left-sided and independent of medication status or statistical correction for covariates. Supported by emerging evidence that the stress response may be related to structural and functional asymmetry in the brain, our finding suggests a crucial role of the hypothalamus in mood disorders.

Eating and hypothalamus changes in behavioral-variant frontotemporal dementia

OBJECTIVE

Behavioral-variant frontotemporal dementia (bvFTD) is a progressive neurodegenerative brain disorder, clinically characterized by changes in cognition, personality, and behavior. Marked disturbances in eating behavior, such as overeating and preference for sweet foods, are also commonly reported. The hypothalamus plays a critical role in feeding regulation, yet the relation between pathology in this region and eating behavior in FTD is unknown. This study aimed to address this issue using 2 complementary approaches.

METHODS

First, 18 early stage bvFTD patients and 16 healthy controls underwent high-resolution structural magnetic resonance imaging and assessment of eating behavior. Hypothalamic volumes were traced manually on coronal images. Second, postmortem analyses of 12 bvFTD cases and 6 matched controls were performed. Fixed hypothalamic tissue sections were stained for a cell marker and for peptides regulating feeding behaviors using immunohistochemistry. Stereological estimates of the hypothalamic volume and the number of neurons and glia were performed.

RESULTS

Significant atrophy of the hypothalamus in bvFTD was present in both analyses. Patients with high feeding disturbance exhibited significant atrophy of the posterior hypothalamus. Neuronal loss, which was observed only in bvFTD cases with Tar DNA protein-43 deposition, was also predominant posteriorly. In contrast, orexin (hypocretin), neuropeptide Y, cocaine- and amphetamine-regulating transcript, and vasopressin-containing neurons that regulate appetite were spared in posterior nuclei known to participate in feeding regulation.

INTERPRETATION

Degeneration and consequent dysregulation within the hypothalamus relates to significant feeding disturbance in bvFTD. These findings provide a basis for the development of therapeutic models.

Comparison of the spatial distribution of seven types of neuroendocrine neurons in the rat paraventricular nucleus: toward a global 3D model

The paraventricular nucleus of the hypothalamus (PVH) coordinates neuroendocrine, autonomic, and behavioral responses to help maintain energy and body water balance. The rat paraventricular nucleus has three major divisions: descending with axonal projections to somatomotor-behavioral and autonomic circuitry, magnocellular neuroendocrine with projections directly to the posterior pituitary, and parvicellular neuroendocrine with projections to the median eminence for controlling anterior pituitary hormone secretion. The present work was undertaken to provide high-resolution mapping of spatial relationships among the two magnocellular neuroendocrine and five parvicellular neuroendocrine neuron types throughout the nucleus. Double immunohistochemical labeling for two neuron types combined with retrograde labeling to identify neuroendocrine neurons positively was used in individual sections spaced 45 mum apart, along with a grid transfer method for reducing plane of section artifacts when comparing staining pattern data between animals. The results indicate that whereas each neuroendocrine neuron phenotype displays a unique distribution pattern, there is extensive partial overlap in a complex pattern between small "hot spots" with a relatively high density of a particular neuron type and few if any other phenotypes. In addition, the distribution of non-neuroendocrine neurons staining with each of the markers (but not retrogradely labeled) was mapped and compared with each other and with the neuroendocrine neuron populations. This spatial organization raises important questions about the differential functional regulation of individual-and perhaps sets of-neuroendocrine motor neuron populations in the PVH by synaptic mechanisms and by less traditional mechanisms like dendritic neurotransmitter release and gap junctions within and between neuron types.

Alcohol tolerance in large-conductance, calcium-activated potassium channels of CNS terminals is intrinsic and includes two components: decreased ethanol potentiation and decreased channel density

Tolerance is an important element of drug addiction and provides a model for understanding neuronal plasticity. The hypothalamic-neurohypophysial system (HNS) is an established preparation in which to study the actions of alcohol. Acute application of alcohol to the rat neurohypophysis potentiates large-conductance calcium-sensitive potassium channels (BK), contributing to inhibition of hormone secretion. A cultured HNS explant from adult rat was used to explore the molecular mechanisms of BK tolerance after prolonged alcohol exposure. Ethanol tolerance was intrinsic to the HNS and consisted of: (1) decreased BK potentiation by ethanol, complete within 12 min of exposure, and (2) decreased current density, which was not complete until 24 hr after exposure, indicating that the two components of tolerance represent distinct processes. Single-channel properties were not affected by chronic exposure, suggesting that decreased current density resulted from downregulation of functional channels in the membrane. Indeed, we observed decreased immunolabeling against the BK alpha-subunit on the surface of tolerant terminals. Analysis using confocal microscopy revealed a reduction of BK channel clustering, likely associated with the internalization of the channel.

Selective neuron loss in the paraventricular nucleus of hypothalamus in patients suffering from major depression and bipolar disorder

The structural basis for depressive disorders remains unknown. Studies using neuroimaging and postmortem brain tissue indicate that anatomic substrates may contribute to major depression disorder (MDD) and bipolar disorder (BD). The present study used design-based stereology to assess neuron loss in 2 well-defined hypothalamic structures, the paraventricular nucleus (PVN) and supraoptic nucleus (SON), in clinically well-studied cases with severe depression. The left or right diencephalon was blocked from 26 brains removed at autopsy from age-matched controls (5 male/3 female) and patients with MDD (6 male/5 female) and BD (5 male/2 female). Serial sections were cut at an instrument setting of 60 microm through the entire PVN and SON from left hypothalamus and 8 to 10 sections per brain were systematic-random sampled and stained with cresyl violet. A trained operator blind to clinical diagnosis used computerized stereology to estimate total neuron numbers in PVN and SON. The results revealed a selective, robust reduction of approximately 50% in total neuron number in the PVN for major depression and bipolar cases compared with age-matched controls, with no differences in neuron numbers in the SON. This selective neuronal loss in the PVN appears to identify an important neurobiologic substrate for the behavioral manifestations of depression.

The human hypothalamo-neurohypophysial system in health and disease

The present paper reviews the changes observed in the human supraoptic (SON) and paraventricular (PVN) nuclei, and their projections to the neurohypophysis, median eminence and to other brain areas in health and disease.

Dissociated central and peripheral release of vasopressin, but not oxytocin, in response to repeated swim stress: new insights into the secretory capacities of peptidergic neurons

To investigate the effects of an ethologically-relevant stressor on central and peripheral release of arginine vasopressin and oxytocin, we forced adult male Wistar rats to swim for 10 min and simultaneously measured the release of the two peptides (i) within the hypothalamic supraoptic and paraventricular nuclei (by means of the microdialysis technique) and (ii) into the blood (by chronically-implanted jugular venous catheters). Forced swimming caused a significant rise in the release of arginine vasopressin and oxytocin within both the supraoptic nuclei (four-fold and three-fold, respectively) and the paraventricular nuclei (three-fold and four- to five-fold, respectively). Release patterns measured before, during and after repeated stress exposure on three consecutive days indicated that, at the level of the hypothalamus, the two neuropeptides are critically involved in the rats' stress response in a peptide-, locus- and stress-specific manner. Particularly, despite a general reduction of the recovery of the microdialysis probes over the time, the release of arginine vasopressin within the paraventricular nuclei and of oxytocin within the supraoptic nuclei tended to increase upon repeated stress exposure. Measurement of plasma peptide concentrations revealed that the central release of oxytocin was accompanied by a secretion of this peptide into the systemic circulation. In contrast, arginine vasopressin, assayed in the same plasma samples, failed to respond to the stressor. The latter finding is consistent with a dissociated release of the neuropeptide from different parts of a single neuron (soma/dendrites vs axon terminals). It provides evidence that under physiological conditions plasma hormone levels do not necessarily reflect the secretory activity of central components of the respective neuropeptidergic system.

Loss of vasopressin-immunoreactive neurons in alcoholics is dose-related and time-dependent

The chronic consumption of alcohol significantly reduces the number of vasopressin-producing neurons in the rat supraoptic nucleus [Maderia et al. (1993) Neourscience 56, 657-672] suggesting this region is particularly vulnerable to alcohol neurotoxicity. As hypothalamic vasopressin producing neurons are necessary for fluid homeostasis, it is important to assess if similar changes occur in humans. We analysed arginine vasopressin-immunoreactive neurons in the magnocellular hypothalamic nuclei of ten chronic alcoholic men (consuming > 80 g of ethanol per day) and four age- and sex-matched controls (consuming < 10g of ethanol per day). Brains were collected at autopsy and fixed in formalin. Serial 50 mu m-thick-sections of the hypothalamus were stained and assessed. The volume of the paraventricular and supraoptic nuclei and number of neurons were estimated using Cavalieri's principle and the optical dissector technique. The volume of these nuclei significantly correlated with the number of neurons and the number of vasopressin-immunoreactive neurons, and these measures significantly correlated with the maximum daily intake of alcohol. There was a loss of neurons at consumption levels greater than 100 g of ethanol per day, principally affecting the supraoptic nucleus although neuron loss also occurred in the paraventricular nucleus in cases with long histories of alcohol consumption. These results indicate that chronic alcohol consumption is toxic to hypothalamic vasopressin-producing neurons in a concentration- and time-dependent manner. As these magnocellular neurons are osmo-receptive, neuronal loss may result in fluid imbalances.