A cytoarchitectonic atlas of the mouse hypothalamus

The temporal and spatial pattern of leptin receptor-expressing cells in the developing mouse hypothalamus

The arcuate nucleus is a crucial hypothalamic brain region involved in regulating body weight homeostasis. Neurons within the arcuate nucleus respond to peripheral metabolic signals, such as leptin, and relay these signals via neuronal projections to brain regions both within and outside the hypothalamus, ultimately causing changes in an animal's behaviour and physiology. There is a substantial amount of evidence to indicate that leptin is intimately involved with the postnatal development of arcuate nucleus melanocortin circuitry. Further, it is clear that leptin signalling directly in the arcuate nucleus is required for circuitry development. However, as leptin receptor long isoform (Leprb) mRNA is expressed in multiple nuclei within the developing hypothalamus, including the postsynaptic target regions of arcuate melanocortin projections, this raises the possibility that leptin also signals in these nuclei to promote circuitry development. Here, we used RT-qPCR and RNAscope® to reveal the spatio-temporal pattern of Leprb mRNA in the early postnatal mouse hypothalamus. We found that Leprb mRNA expression increased significantly in the arcuate nucleus, ventromedial nucleus and paraventricular nucleus of the hypothalamus from P8, in concert with the leptin surge. In the dorsomedial nucleus of the hypothalamus, increases in Leprb mRNA were slightly later, increasing significantly from P12. Using duplex RNAscope®, we found Leprb co-expressed with Sim1, Pou3f2, Mc4r and Bdnf in the paraventricular nucleus at P8. Together, these data suggest that leptin may signal in a subset of neurons postsynaptic to arcuate melanocortin neurons, as well as within the arcuate nucleus itself, to promote the formation of arcuate melanocortin circuitry during the early postnatal period.

An anatomically distinct subpopulation of orexin neurons project from the lateral hypothalamus to the olfactory bulb

Olfactory cues play a key role in natural behaviors such as finding food, finding mates, and avoiding predators. In principle, the ability of the olfactory system to carry out these perceptual functions would be facilitated by signaling related to an organism's physiological state. One candidate pathway includes a direct projection from the hypothalamus to the main olfactory bulb, the first stage of olfactory sensory processing. The pathway from the hypothalamus to the main olfactory bulb is thought to include neurons that express the neuropeptide orexin, although the proportion that is orexinergic remains unknown. A current model proposes that the orexin population is heterogeneous, yet it remains unknown whether the proportion that innervates the main olfactory bulb reflects a distinct subpopulation of the orexin population. Herein, we carried out combined retrograde tract tracing with immunohistochemistry for orexin-A in the mouse to define the proportion of hypothalamic input to the main olfactory bulb that is orexinergic and to determine what fraction of the orexin-A population innervates the bulb. The numbers and spatial positions of all retrogradely labeled neurons and all the orexin-A-expressing neurons were quantified in sequential sections through the hypothalamus. Retrogradely labeled neurons were found in the ipsilateral hypothalamus, of which 22% expressed orexin-A. The retrogradely labeled neurons that did and did not express orexin-A could be anatomically distinguished based on their spatial position and cell body area. Remarkably, only 7% of all the orexin-A neurons were retrogradely labeled, suggesting that only a small fraction of the orexin-A population directly innervate the main olfactory bulb. These neurons spatially overlapped with the orexin-A neurons that did not innervate the bulb, although the two cell populations were differentiated based on cell body area. Overall, these results support a model in which olfactory sensory processing is influenced by orexinergic feedback at the first synapse in the olfactory processing pathway.

Adult Neurogenesis in the Mammalian Hypothalamus: Impact of Newly Generated Neurons on Hypothalamic Function

In mammals, adult neurogenesis was first demonstrated in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus of the hippocampal formation. Further research showed that adult neurogenesis persists in other brain structures, such as the cerebral cortex, piriform cortex, striatum, amygdala, and hypothalamus. However, the origin of newly generated cells in these structures is not clear. Accumulating evidence indicates that newly generated neurons in the striatum or amygdala are derived from the SVZ, while in the adult hypothalamus, the proliferation of progenitor cells occurs in the ependymal cells lining the third ventricle, which give rise to new neurons. The heterogeneous cellular organization of the ependymal layer of the hypothalamus leads to different conclusions regarding the type of hypothalamic progenitor cells. In addition, adult hypothalamic neurogenesis occurs at low levels. Based on comparative and functional approaches, we synthesize the knowledge of newly generated cells in the adult hypothalamus. The aim of this review is to provide new insights on adult neurogenesis in the mammalian hypothalamus, with particular attention given to marsupial species. We highlight the number of adult-born neurons in various hypothalamic nuclei, debating whether their low number has an impact on hypothalamic function.

Leveraging genetic diversity in mice to inform individual differences in brain microstructure and memory

In human Alzheimer's disease (AD) patients and AD mouse models, both differential pre-disease brain features and differential disease-associated memory decline are observed, suggesting that certain neurological features may protect against AD-related cognitive decline. The combination of these features is known as brain reserve, and understanding the genetic underpinnings of brain reserve may advance AD treatment in genetically diverse human populations. One potential source of brain reserve is brain microstructure, which is genetically influenced and can be measured with diffusion MRI (dMRI). To investigate variation of dMRI metrics in pre-disease-onset, genetically diverse AD mouse models, we utilized a population of genetically distinct AD mice produced by crossing the 5XFAD transgenic mouse model of AD to 3 inbred strains (C57BL/6J, DBA/2J, FVB/NJ) and two wild-derived strains (CAST/EiJ, WSB/EiJ). At 3 months of age, these mice underwent diffusion magnetic resonance imaging (dMRI) to probe neural microanatomy in 83 regions of interest (ROIs). At 5 months of age, these mice underwent contextual fear conditioning (CFC). Strain had a significant effect on dMRI measures in most ROIs tested, while far fewer effects of sex, sex*strain interactions, or strain*sex*5XFAD genotype interactions were observed. A main effect of 5XFAD genotype was observed in only 1 ROI, suggesting that the 5XFAD transgene does not strongly disrupt neural development or microstructure of mice in early adulthood. Strain also explained the most variance in mouse baseline motor activity and long-term fear memory. Additionally, significant effects of sex and strain*sex interaction were observed on baseline motor activity, and significant strain*sex and sex*5XFAD genotype interactions were observed on long-term memory. We are the first to study the genetic influences of brain microanatomy in genetically diverse AD mice. Thus, we demonstrated that strain is the primary factor influencing brain microstructure in young adult AD mice and that neural development and early adult microstructure are not strongly altered by the 5XFAD transgene. We also demonstrated that strain, sex, and 5XFAD genotype interact to influence memory in genetically diverse adult mice. Our results support the usefulness of the 5XFAD mouse model and convey strong relationships between natural genetic variation, brain microstructure, and memory.

GABAergic and Glutamatergic Phenotypes of Neurons Expressing Calcium-Binding Proteins in the Preoptic Area of the Guinea Pig

The mammalian preoptic area (POA) has large populations of calbindin (CB), calretinin (CR) and parvalbumin (PV) neurons, but phenotypes of these cells are unknown. Therefore, the question is whether neurons expressing CB, CR, and/or PV are GABAergic or glutamatergic. Double-immunofluorescence staining followed by epifluorescence and confocal microscopy was used to determine the coexpression patterns of CB, CR and PV expressing neurons with vesicular GABA transporters (VGAT) as specific markers of GABAergic neurons and vesicular glutamate transporters (VGLUT 2) as specific markers of glutamatergic neurons. The guinea pig was adopted as, like humans, it has a reproductive cycle with a true luteal phase and a long gestation period. The results demonstrated that in the guinea pig POA of both sexes, ~80% of CB+ and ~90% of CR+ neurons coexpress VGAT; however, one-fifth of CB+ neurons and one-third of CR+ cells coexpress VGLUT. About two-thirds of PV+ neurons express VGAT, and similar proportion of them coexpress VGLUT. Thus, many CB+, CR+ and PV+ neurons may be exclusively GABAergic (VGAT-expressing cells) or glutamatergic (VGLUT-expressing cells); however, at least a small fraction of CR+ cells and at least one-third of PV+ cells are likely neurons with a dual GABA/glutamate phenotype that may coexpress both transporters.

The absence of retinal input disrupts the development of cholinergic brainstem projections in the mouse dorsal lateral geniculate nucleus

Background

The dorsal lateral geniculate nucleus (dLGN) of the mouse has become a model system for understanding thalamic circuit assembly. While the development of retinal projections to dLGN has been a topic of extensive inquiry, how and when nonretinal projections innervate this nucleus remains largely unexplored. In this study, we examined the development of a major nonretinal projection to dLGN, the ascending input arising from cholinergic neurons of the brainstem. To visualize these projections, we used a transgenic mouse line that expresses red fluorescent protein exclusively in cholinergic neurons. To assess whether retinal input regulates the timing and pattern of cholinergic innervation of dLGN, we utilized the math5-null (math5^−/−) mouse, which lacks retinofugal projections due to a failure of retinal ganglion cell differentiation.

Results

Cholinergic brainstem innervation of dLGN began at the end of the first postnatal week, increased steadily with age, and reached an adult-like pattern by the end of the first postnatal month. The absence of retinal input led to a disruption in the trajectory, rate, and pattern of cholinergic innervation of dLGN. Anatomical tracing experiments reveal these disruptions were linked to cholinergic projections from parabigeminal nucleus, which normally traverse and reach dLGN through the optic tract.

Conclusions

The late postnatal arrival of cholinergic projections to dLGN and their regulation by retinal signaling provides additional support for the existence of a conserved developmental plan whereby retinal input regulates the timing and sequencing of nonretinal projections to dLGN.

Neurotransmitters and neuropeptides in gonadal steroid receptor-expressing cells in medial preoptic area subregions of the male mouse

Testosterone is involved in male sexual, parental and aggressive behaviors through the androgen receptor (AR) and estrogen receptor (ER) α expressed in the brain. Although several studies have demonstrated that ERα and AR in the medial preoptic area (MPOA) are required for exhibiting sexual and aggressive behaviors of male mice, the molecular characteristics of ERα- and AR-expressing cells in the mouse MPOA are largely unknown. Here, we performed in situ hybridization for neurotransmitters and neuropeptides, combined with immunohistochemistry for ERα and AR to quantitate and characterize gonadal steroid receptor-expressing cells in the MPOA subregions of male mice. Prodynorphin, preproenkephalin (Penk), cocaine- and amphetamine-related transcript, neurotensin, galanin, tachykinin (Tac)1, Tac2 and thyrotropin releasing hormone (Trh) have distinct expression patterns in the MPOA subregions. Gad67-expressing cells were the most dominant neuronal subtype among the ERα- and AR-expressing cells throughout the MPOA. The percentage of ERα- and AR-immunoreactivities varied depending on the neuronal subtype. A substantial proportion of the neurotensin-, galanin-, Tac2- and Penk-expressing cells in the MPOA were positive for ERα and AR, whereas the vast majority of the Trh-expressing cells were negative. These results suggest that testosterone exerts differential effects depending on both the neuronal subtypes and MPOA subregions.

Distinct preoptic-BST nuclei dissociate paternal and infanticidal behavior in mice

Paternal behavior is not innate but arises through social experience. After mating and becoming fathers, male mice change their behavior toward pups from infanticide to paternal care. However, the precise brain areas and circuit mechanisms connecting these social behaviors are largely unknown. Here we demonstrated that the c-Fos expression pattern in the four nuclei of the preoptic-bed nuclei of stria terminalis (BST) region could robustly discriminate five kinds of previous social behavior of male mice (parenting, infanticide, mating, inter-male aggression, solitary control). Specifically, neuronal activation in the central part of the medial preoptic area (cMPOA) and rhomboid nucleus of the BST (BSTrh) retroactively detected paternal and infanticidal motivation with more than 95% accuracy. Moreover, cMPOA lesions switched behavior in fathers from paternal to infanticidal, while BSTrh lesions inhibited infanticide in virgin males. The projections from cMPOA to BSTrh were largely GABAergic. Optogenetic or pharmacogenetic activation of cMPOA attenuated infanticide in virgin males. Taken together, this study identifies the preoptic-BST nuclei underlying social motivations in male mice and reveals unexpected complexity in the circuit connecting these nuclei.

Articulated whole-body atlases for small animal image analysis: construction and applications

PURPOSE

Using three publicly available small-animal atlases (Sprague-Dawley rat, MOBY, and Digimouse), we built three articulated atlases and present several applications in the scope of molecular imaging.

PROCEDURES

Major bones/bone groups were manually segmented for each atlas skeleton. Then, a kinematic model for each atlas was built: each joint position was identified and the corresponding degrees of freedom were specified.

RESULTS

The articulated atlases enable automated registration into a common coordinate frame of multimodal small-animal imaging data. This eliminates the postural variability (e.g., of the head, back, and front limbs) that occurs in different time steps and due to modality differences and nonstandardized acquisition protocols.

CONCLUSIONS

The articulated atlas proves to be a useful tool for multimodality image combination, follow-up studies, and image processing in the scope of molecular imaging. The proposed models were made publicly available.

Cyto- and chemoarchitecture of the hypothalamic paraventricular nucleus in the C57BL/6J male mouse: a study of immunostaining and multiple fluorescent tract tracing

The paraventricular nucleus of the hypothalamus (PVH) plays a critical role in the regulation of autonomic, neuroendocrine, and behavioral activities. This understanding has come from extensive characterization of the PVH in rats, and for this mammalian species we now have a robust model of basic PVH neuroanatomy and function. However, in mice, whose use as a model research animal has burgeoned with the increasing sophistication of tools for genetic manipulation, a comparable level of PVH characterization has not been achieved. To address this, we employed a variety of fluorescent tract tracing and immunostaining techniques in several different combinations to determine the neuronal connections and cyto- and chemoarchitecture of the PVH in the commonly used C57BL/6J male mouse. Our findings reveal a distinct organization in the mouse PVH that is substantially different from the PVH of male rats. The differences are particularly evident with respect to the spatial relations of two principal neuroendocrine divisions (magnocellular and parvicellular) and three descending preautonomic populations in the PVH. We discuss these data in relation to what is known about PVH function and provide the work as a resource for further studies of the neuronal architecture and function of the mouse PVH.

Neuromolecular basis of parental behavior in laboratory mice and rats: with special emphasis on technical issues of using mouse genetics

To support the well-being of the parent-infant relationship, the neuromolecular mechanisms of parental behaviors should be clarified. From neuroanatomical analyses in laboratory rats, the medial preoptic area (MPOA) has been shown to be of critical importance in parental retrieving behavior. More recently, various gene-targeted mouse strains have been found to be defective in different aspects of parental behaviors, contributing to the identification of molecules and signaling pathways required for the behavior. Therefore, the neuromolecular basis of "mother love" is now a fully approachable research field in modern molecular neuroscience. In this review, we will provide a summary of the required brain areas and gene for parental behavior in laboratory mice (Mus musculus) and rats (Rattus norvegicus). Basic protocols and technical considerations on studying the mechanism of parental behavior using genetically-engineered mouse strains will also be presented.

Leptin-sensitive neurons in mouse preoptic area express alpha 1A- and alpha 2A-adrenergic receptor isoforms

Leptin binding to its functional receptor stimulates the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signalling pathway, finally resulting in nuclear translocation of the phosphorylated STAT3 (P-STAT3). Systemic treatment with leptin (3mg/kg; intraperitoneal injection) induced the appearance of P-STAT3-immunoreactive cells in adult mouse preoptic area (POA). Here we show that the vast majority of leptin-responsive cells were located in medial POA (mPOA), followed by the median preoptic nucleus. Rare, scattered and weakly stained cells were found in ventromedial preoptic nucleus and lateral preoptic area. Co-localization studies disclosed that mPOA leptin-responsive cells were neurons, and that a large proportion expressed the alpha(1A)- and/or alpha(2A)-adrenergic receptor (AR) isoforms. Although understanding the functional relevance of leptin-responsive POA neurons requires further investigation, the finding that they bear alpha-ARs suggests that they may be targeted by the ascending noradrenergic system, which densely innervates the mPOA, and thus be involved in thermoregulation, arousal and/or the sleep-wake cycle.

Synaptic Regulation of Proopiomelanocortin Neurons Can Occur Distal to the Arcuate Nucleus

Energy homeostasis is controlled to a large extent by various signals that are integrated in the hypothalamus. It is generally considered that neurons in each of the hypothalamic nuclei are regulated by afferent projections that terminate within the cell body region of the nucleus. However, here it is shown that hypothalamic proopiomelanocortin (POMC) neurons receive synaptic inputs onto distal dendrites that reside outside of the cell body region in the arcuate nucleus. Previous studies using whole cell recordings from identified neurons in brain slices have shown that cannabinoids reduce GABA release from inhibitory synapses onto the POMC cells. Here it was found that endocannabinoids inhibited GABAergic inhibitory postsynaptic currents in POMC neurons only in intact sagittal brain slices, but not coronal, horizontal, or sagittal slices that were truncated rostrally at the level of the optic chiasm. Thus endocannabinoids inhibited presynaptic GABA release only at an anatomically distinct subset of POMC–neuron dendrites that extends rostrally beyond the arcuate nucleus into preoptic hypothalamic regions. There are two key results. First, the activity of POMC neurons can be regulated by afferent input at sites much farther from the soma than previously recognized. Second, endocannabinoids can act to inhibit inputs only at selective dendrites. POMC neurons play a critical role in the maintenance of body weight. Therefore these data suggest that energy balance may be regulated, in part, by modulation of POMC neuron activity at sites outside of the arcuate nucleus.

Digimouse: a 3D whole body mouse atlas from CT and cryosection data

We have constructed a three-dimensional (3D) whole body mouse atlas from coregistered x-ray CT and cryosection data of a normal nude male mouse. High quality PET, x-ray CT and cryosection images were acquired post mortem from a single mouse placed in a stereotactic frame with fiducial markers visible in all three modalities. The image data were coregistered to a common coordinate system using the fiducials and resampled to an isotropic 0.1 mm voxel size. Using interactive editing tools we segmented and labelled whole brain, cerebrum, cerebellum, olfactory bulbs, striatum, medulla, masseter muscles, eyes, lachrymal glands, heart, lungs, liver, stomach, spleen, pancreas, adrenal glands, kidneys, testes, bladder, skeleton and skin surface. The final atlas consists of the 3D volume, in which the voxels are labelled to define the anatomical structures listed above, with coregistered PET, x-ray CT and cryosection images. To illustrate use of the atlas we include simulations of 3D bioluminescence and PET image reconstruction. Optical scatter and absorption values are assigned to each organ to simulate realistic photon transport within the animal for bioluminescence imaging. Similarly, 511 keV photon attenuation values are assigned to each structure in the atlas to simulate realistic photon attenuation in PET. The Digimouse atlas and data are available at http://neuroimage.usc.edu/Digimouse.html.

Distribution of androgen-binding protein in the rat hypothalamo-neurohypophyseal system, co-localization with oxytocin

Androgen-binding protein (ABP) is known to be expressed in the male and female rat hypothalamus. In the present study, we observed immunocytochemically ABP in neurons of the magnocellular hypothalamic nuclei, in the preoptic region and in the lateral hypothalamus. Dense fiber networks with varicosities, containing ABP immunofluorescence, were visible throughout the hypothalamus, the median eminence and in the posterior pituitary lobe. Double immunostaining revealed a partial coexistence of ABP-and oxytocin immunoreactivity in a portion of the magnocellular perikarya. ABP was isolated by affinity chromatography from hypothalamus homogenates. Western blots resulted in immunoreactive (IR) bands with an approximate molecular weight of 35 and 50 kDa. Mass spectrometry of these preparations confirmed the presence of ABP, which was almost identical to ABP isolated from rat testis. It is likely that ABP, expressed in magnocellular oxytocinergic neurons, is subject to axonal transport and release in the hypothalamo-neurohypophyseal system.

Influence of sex and estrus cycle on the sexual dimorphisms of the hypothalamic ventromedial nucleus: stereological evaluation and Golgi study

Neurons in the ventromedial nucleus of the hypothalamus (VMN) display structural and biochemical sex differences in response to estrogen. Despite this fact, reports on sex differences in the morphology of the VMN are restricted to its volume and synaptic patterning. The aim of this study was to characterize the neuroanatomical sexual dimorphisms in the VMN and to investigate whether endogenous changes in ovarian steroid secretion influence such dimorphisms. The VMN of adult male rats and intact, aged-matched female rats killed on proestrus and diestrus day 1 was examined by using stereological methods applied to conventionally stained sections and Golgi-impregnated material. The VMN contained 55,000 neurons in rats of both sexes, but its volume was, on average, 1.25 times larger in males than in females. The volume was greater in proestrus than in diestrus rats due to parallel changes in the neuronal somatic size. Unlike the dorsomedial division, neurons in the ventrolateral division had longer dendritic trees in proestrus than in diestrus females and males. The spine density was consistently higher in females than in males in both VMN divisions. In addition, in the ventrolateral part the magnitude of the sex differences varied across the estrus cycle, and reached the greatest value when females were in proestrus. The volume of the neuropil was significantly larger in males than in females, and was not affected by the estrus phase. Our results reveal that the magnitude of the neuroanatomical sex differences in the VMN vary across the estrus cycle due to the trophic influence of estrogen upon its neurons. They also show that the fundamental sex difference in the structure of the VMN is accounted for by the neuropil components.

Arcuate nucleus of the hypothalamus: effects of age and sex

The arcuate nucleus of the hypothalamus (ARN) is involved in a variety of functions known to be sexually dimorphic and altered by aging. Although the effects of sex and age on the synaptic organization and neurochemistry of the ARN have been extensively analyzed, data regarding sex-related differences and age-induced effects on the total number of neurons and volume of the ARN in adult and aged male and female rats are controversial. To address this issue, we have quantitatively analyzed the ARN of male and female Wistar rats aged 6 and 24 months. The optical fractionator, the optical rotator, and the Principle of Cavalieri were used as the estimators of the total number of neurons, mean nuclear volume of ARN neurons, and volume of the ARN, respectively. In addition, a Golgi study was carried out to analyze the dendritic trees of its neurons. We found that in young adult rats, the volume of the ARN is 0.9 mm3 in males and 0.7 mm3 in females, whereas the total number of neurons is 100 x 10(3) in males and 86 x 10(3) in females. ARN neurons of males and females have identical mean nuclear volumes, which we estimated to be 300 microm3. No significant effects of age were found in these parameters, both in males and in females. In adult rats, no sex-related differences were detected in the number of dendritic segments and in the total dendritic length, but the dendritic branching density and the spine density were greater in females than in males. In aged rats there was a significant reduction in the number of dendritic segments, in the total dendritic length, and in the branching and spine densities that, although evident in both sexes, was more marked in females. Our results show that the total number of neurons and the volume of the ARN are sexually dimorphic in adult and aged rats and that neither of these parameters is altered by aging. Conversely, aging induces regressive changes in the dendritic arborizations of ARN neurons of males and females and abolishes the sexual dimorphic pattern of their organization.

Noradrenergic innervation of the hypothalamus of rhesus monkeys: distribution of dopamine-beta-hydroxylase immunoreactive fibers and quantitative analysis of varicosities in the paraventricular nucleus

The distribution of noradrenergic processes within the hypothalamus of rhesus monkeys (Macaca mulatta) was examined by immunohistochemistry with an antibody against dopamine-beta-hydroxylase. The results revealed that the pattern of dopamine-beta-hydroxylase immunoreactivity varied systematically throughout the rhesus monkey hypothalamus. Extremely high densities of dopamine-beta-hydroxylase-immunoreactive processes were observed in the paraventricular and supraoptic nuclei, while relatively lower levels were found in the arcuate and dorsomedial nuclei and in the medial preoptic, perifornical, and suprachiasmatic areas. Moderate levels of dopamine-beta-hydroxylase immunoreactivity were found throughout the lateral hypothalamic area and in the internal lamina of the median eminence. Very few immunoreactive processes were found in the ventromedial nucleus or in the mammillary complex. Other midline diencephalic structures were found to have high densities of dopamine-beta-hydroxylase immunoreactivity, including the paraventricular nucleus of the thalamus and a discrete subregion of nucleus reuniens, the magnocellular subfascicular nucleus. A moderate density of dopamine-beta-hydroxylase immunoreactive processes were found in the rhomboid nucleus and zona incerta whereas little dopamine-beta-hydroxylase immunoreactivity was found in the fields of Forel, nucleus reuniens, or subthalamic nucleus. The differential distribution of dopamine-beta-hydroxylase-immunoreactive processes may reflect a potential role of norepinephrine as a regulator of a variety of functions associated with the nuclei that are most heavily innervated, e.g., neuroendocrine release from the paraventricular and supraoptic nuclei, and gonadotropin release from the medial preoptic area and mediobasal hypothalamus. Additionally, quantitative analysis of dopamine-beta-hydroxylase-immunoreactive varicosities was performed on a laser scanning microscope in both magnocellular and parvicellular regions of the paraventricular nucleus of the hypothalamus. The methodology employed in this study allowed for the high resolution of immunoreactive profiles through the volume of tissue being analyzed, and was more accurate than conventional light microscopy in terms of varicosity quantification. Quantitatively, a significant difference in the density of dopamine-beta-hydroxylase-immunoreactive varicosities was found between magnocellular and parvicellular regions, suggesting that parvicellular neurons received a denser noradrenergic input. These differential patterns may reflect an important functional role for norepinephrine in the regulation of anterior pituitary secretion through the hypothalamic-pituitary-adrenal stress axis.

Changes of NGF level in mouse hypothalamus following intermale aggressive behaviour: biological and immunohistochemical evidence

Nerve growth factor (NGF) immunoreactivity was detected in the hypothalamus of adult male mice. NGF-immunoreactive cell bodies were examined through consecutive brain sections, and it was found that most of the NGF-positive cells were located in the dorsomedial and mediolateral portions of the hypothalamus. Tissue culture bioassays showed that hypothalamic extract elicits neurite outgrowth from both chick sensory ganglia and rat superior cervical ganglia neurons, and that these effects are inhibited by addition of NGF antibodies. Our results also showed that intermale aggressive behaviour induced by 6-8 weeks of social isolation induces an NGF increase in the hypothalamic area, which is not abolished by sialoadenectomy, suggesting that the increased brain NGF is locally synthesized, and does not come from salivary sources. Likewise, the level of NGF in the hypothalamus of adrenalectomized fighting mice increased, although to a much lesser extent, when compared to hypothalamic levels of sham-operated fighting mice. The present results and a recent report showing that aggressive behaviour causes an increase of mRNANGF in hypothalamic areas are discussed in relation to a possible functional role of NGF in these brain structures.

Estradiol-concentrating cells in the brains of hypogonadal female mice and in their intraventricular preoptic area implants

Estradiol-concentrating cells were evaluated in the brains of hypogonadal female mice and in their intraventricular preoptic area brain grafts using autoradiography for [3H]estradiol. Normal distribution of estradiol-concentrating cells was observed in the brains of the hypogonadal mice with dense collections of these cells in the lateral septum; the medial preoptic area; the medial anterior hypothalamus; the ventromedial, arcuate, and periventricular nuclei of the hypothalamus; and the medial and cortical nuclei of the amygdala. In addition, estradiol-concentrating cells were present in all the transplants, with the estimated number of such cells in the transplants ranging from 390 to 2600. There was no correlation between numbers of estradiol-concentrating cells within the transplants and degree of reproductive recovery in the hypogonadal mice. Gonadotropin-releasing hormone (GnRH) immunocytochemistry of alternate sections revealed GnRH-immunoreactive material within the grafts and immunoreactive fibers exiting the grafts and entering the hosts' median eminence. No specific relationship between GnRH cells and estradiol-concentrating cells was evident within the grafts, nor was there any indication of identity of estrogen-concentrating cells with GnRH cells.

Quantitative autoradiographic maps of local cerebral glucose metabolism in awake rats: I. Septal region and anterior hypothalamus

Quantitative 14C-2-deoxyglucose autoradiography was used to determine the local cerebral glucose metabolic rate (lCMRG) of nuclei in the septal region and anterior hypothalamus of awake, unanesthetized rats. The lCMRG of the medial and lateral septal areas, preoptic areas, medial preoptic nuclei, suprachiasmatic nuclei, supraoptic nuclei, anterior hypothalamic nuclei, and paraventricular nuclei were measured. The lCMRG of each nucleus was mapped at successive rostral-caudal levels to determine significant internuclear and intranuclear variations. These data provide a detailed neuroanatomic map of cerebral energy metabolism of the septal and anterior hypothalamic regions in animals under standardized conditions.

The cytoarchitecture, histochemistry and projections of the tuberomammillary nucleus in the rat

The normal morphology, efferent projections and possible neurotransmitter content of neurons in the tuberomammillary nucleus (caudal magnocellular nuclei of Bleier et al.) [Bleier, Cohn and Siggelkow (1979) In Anatomy of the Hypothalamus, Vol. 1, pp. 137-220] have been examined in the adult male rat. In Nissl-stained sections, the nucleus can be divided into a dorsomedial, ventral and diffuse part, each of which consists of large, darkly stained neurons cradling the mammillary body. The ventral part is by far the largest and consists of some 2500 neurons on each side of the brain. Immunohistochemical studies indicate that a majority of the large neurons in all three parts of the nucleus stain with antisera against glutamate decarboxylase and [Met]enkephalyl-Arg6-Phe7 heptapeptide and that a smaller subset of these neurons (about 10%) also stain with an antiserum against substance P. Single injections of retrogradely transported fluorescent tracers were made into 18 different sites in 86 animals and the results indicate that all three parts of the tuberomammillary nucleus on one side of the brain send fibers to or through various parts of the neocortex, hippocampal formation, amygdala, basal ganglia, thalamus, superior colliculus and cerebellum on both sides of the brain and that the projection neurons are not organized in a highly topographic way. Injections of two different fluorescent tracers in the same animal indicate that individual neurons in the nucleus may give rise to both ascending and descending projections, as well as projections to widely divergent parts of the forebrain. Together with previous results, this evidence suggests that the tuberomammillary nucleus has widespread projections to the numerous brain structure located in the forebrain and in the caudal medulla (it may not project to the spinal cord), and that its axons may release a mixture of neuroactive substances including gamma-amino butyrate and several peptides. Although its functional significance remains to be investigated, morphological evidence suggests that the tuberomammillary nucleus may constitute one of a series of neurotransmitter-specific cell groups in the brainstem and basal forebrain with diffuse efferent projections that may be involved in the modulation of attention or behavioral state, rather than the processing of specific sensory or motor information.

Further studies of the secretory process in hypothalamo-neurohypophysial neurons: an analysis using immunocytochemistry, wheat germ agglutinin-peroxidase, and native peroxidase

The axonal endoplasmic reticulum (ER) and synaptic-like (micro)vesicles within axon terminals of the neurohypophysis and their contribution to the secretory process in hypothalamo-neurohypophysial neurons have been investigated cytochemically in normal mice and in mice given 2% salt water to drink for stimulation of hormone synthesis in and release from these neurons. Cytochemical techniques included the peroxidase-antiperoxidase (PAP) immunocytochemical method for localization of neurophysin, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) as a tracer for the anterograde axonal transport of membrane from within the perikaryon, and blood-borne native horseradish peroxidase (HRP) as a tracer for internalized axon terminal membrane. The primary antiserum employed was directed against neurophysins I and II, the carrier proteins for the peptide hormones oxytocin and vasopressin, respectively. PAP reaction product was observed over neurosecretory granules but never over the endoplasmic reticulum, microvesicles or other organelles in axons and terminals of the neurohypophysis. WGA-HRP was delivered extracellularly to cell bodies of paraventricular neurons by cerebral ventriculocisternal perfusion. Internalized perikaryal surface membrane tagged with WGA-HRP was recycled through the innermost Golgi saccule (GERL) from which neurosecretory granules were formed. The anterograde axonal transport of membrane-bound WGA-HRP was manifested within the neurosecretory granules; WGA-HRP did not label the axonal reticulum or terminal microvesicles in the neurohypophysis. Blood-borne native HRP endocytosed into neurohypophysial terminals was associated with a plethora of microvesicles measuring 40-70 nm in diameter and vacuoles similar in size to the 100-300-nm-wide neurosecretory granules. The microvesicles contributed to the formation of numerous vacuoles. The internalization of axon terminal membrane as microvesicles incorporating HRP was quantitatively greater than vacuoles in both salt-stressed and control mice. The results suggest that in the hypothalamo-neurohypophysial system of the mouse the axonal ER and terminal microvesicles are not involved in the transport, storage, and exocytosis of neurosecretory material and perhaps other molecules processed through the innermost Golgi saccule. Nevertheless, a prominent population of the microvesicles within axon terminals of the neurohypophysis does participate in the secretory process. These vesicles are involved directly in the internalization of the terminal surface membrane subsequent to release of secretory granule content.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of catecholamine neurons in the hypothalamus and preoptic region of mouse

The distribution and morphology of cells containing tyrosine hydroxylase (TH) were mapped by using the immunoperoxidase technique in the hypothalamus and preoptic area in two strains of mouse, CBA/J and BALB/cJ. On the basis of rostral-caudal contiguities between cell aggregates, hypothalamic preoptic neurons were subdivided into three arbitrary groups: (1) dorsal, (2) intermediate, and (3) ventral. New or more prominent collections of TH cells were observed, and in some regions, cells were more complexly organized than originally described. In the dorsal group, a rostral collection of small ovoid cells, previously not described, were located in the anterior preoptic nucleus (APN) of Loo ('31) and extended rostrally and ventrally into the preoptic periventricular gray. The next constituent occupied the paraventricular nucleus (PVN), and was composed of two classes of cells: (1) a small ovoid cell within anterior and medial parvocellular PVN in contiguity rostrally with a similar cell in APN and (2) a larger, angular cell within and adjacent to the lateral PVN in contiguity caudally with cells in the zona incerta (ZI). Further caudally, a larger and more pleomorphic collection of TH neurons was localized in the medial ZI, particularly at midtuberal levels. These cells were not scattered, as previously reported, but were differentiated into two clear-cut densities, a larger medial island and a more elongated lateral island. Cells of ZI, both large and small, extended caudally into the dorsal hypothalamic and subparafascicular nuclei and periventricular gray. In contrast to previous descriptions, no cells were seen in the nucleus reuniens. In the intermediate group, the most rostral constituent occupied the preoptic periventricular gray, extended as far as the lamina terminalis, and merged dorsocaudally with cells in APN. While the variably shaped cells of the hypothalamic periventricular gray (PVG) were still present in the retrochiasmatic region, a striking absence of these cells was noted at midtuberal levels between the dorsomedial and arcuate hypothalamic nuclei. At this level, a new group of small-round TH cells, resembling those of the arcuate nucleus, was identified in the dorsomedial hypothalamic nucleus (DMN). At caudal tuberal levels, similar neurons were found in the posterior hypothalamic nucleus (PH). These neurons overflowed medially into the PVG and caudoventrally into the arcuate nucleus. In the ventral group, the most rostral constituent, composed of both small and ovoid cells in the retrochiasmatic area, appeared to represent the rostral commissural portion of the arcuate nucleus (Arc).(ABSTRACT TRUNCATED AT 400 WORDS)

Tritiated 2-deoxy-D-glucose: a high-resolution marker for autoradiographic localization of brain metabolism

The technique for autoradiographic localization of 2-deoxy-D-glucose (2DG) uptake has become a useful method for observing alterations of functional brain activity resulting from experimental manipulation. Autoradiographic resolution is improved using tritiated ([3H]) rather than carbon-14 ([14C)]2DG, due to the lower energy and shorter path of tritium emissions. In addition, lower 2DG uptake by white matter relative to gray matter is exaggerated in the [3H]2DG autoradiographs due to the greater absorption of tritium emissions by lipids. Using [3H]2DG, it is possible to observe differential metabolic labeling in various individual nuclei or portions of nuclei that is unresolvable using [14C]2DG in the awake, normal animal. Heterogeneous patterns of 2DG uptake seen only with [3H]2DG are found in the nucleus accumbens, the anterior portion of the basolateral nucleus of the amygdala, specific nuclei of the inferior olivary complex, various hypothalamic regions, and a region straddling the border of the medial and lateral habenular nuclei. The lamination of differential 2DG uptake in the hippocampus is better localized using [3H]2DG. Autoradiographic resolution of labeled 2DG is further improved when the brain is perfused prior to frozen sectioning, due perhaps to selective fixation and retention of intracellular labeled 2-deoxy-glycogen. A series of [3H]2DG autoradiographs are presented together with views of the Nissl-stained sections that produced the autoradiographs.

Ventromedial nucleus of the hypothalamus: convergent excitatory and inhibitory responses to fimbria and stria terminalis stimulation

Field and extracellular unitary potentials were recorded in the ventromedial nucleus of the hypothalamus (VMH) of urethane-anesthetized rabbits after stimulation of the fimbria and stria terminalis. Stimulation of the lateral portion of the fimbria, which carries fibers from the ventral subiculum of the hippocampal formation, evoked a two-component response. An early excitatory response, with an average latency of 10 msec, predominated along the lateral margins of the VMH. A later inhibitory potential with an average latency of 15 msec was seen predominantly within the central portions of the VMH. Stimulation of the dorsal component of the stria terminalis produced two similar response patterns: an early excitatory response with an average latency of 16 msec, followed by an inhibitory potential with an average latency of 25 msec. The topographical distribution of these two components of the response was nearly identical to that produced by lateral fimbria stimulation. In contrast, stimulation of the ventral component of the stria terminalis evoked a simple excitatory response with an average latency of 10 msec which was maximal within the core of the VMH. Extracellular unitary recordings showed that the early negativity associated with stimulation of each of these three pathways reflects a monosynaptic excitation of VMH cells and that there was convergence of the three excitatory inputs at the single cell level.

A direct projection from the hypothalamus to the area postrema in the rat, as demonstrated by the HRP and autoradiographic methods

A direct hypothalamic afferent to the area postrema was found in the rat. After an injection of tritiated amino acids into the hypothalamus, labeled fibers and terminals were observed in the entire part of the area postrema, with dense patches of silver grains present in places. Cells of origin of this novel projection were identified with the retrograde horseradish peroxidase (HRP) method in the dorsal hypothalamic area at the most rostral level of the dorsomedial hypothalamic nucleus.

The descending afferent connections of the paraventricular nucleus of the hypothalamus (PVN)

The distribution of afferents to the paraventricular nucleus of the hypothalamus (PVN) was studied following iontophoresis of horseradish peroxidase (HRP) into the nucleus. This report describes the descending connections to this structure. The PVN receives a substantial input from limbic system structures, especially from the lateral septal nucleus and the ventral portion of the subicular cortex. A small number of labeled cells were found in the amygdala, primarily the medial nucleus. Of the circumventricular organs, the subfornical organ and OVLT both project to the PVN, the former very strongly. In both the preoptic area and hypothalamus, medial cell groups have more input than do the lateral areas. Labeled cells were found in the medial and hypothalamus, medial cell groups have more input than do the lateral areas. Labeled cells were found in the medial and lateral preoptic areas, suprachiasmatic nucleus, ventromedial nucleus, arcuate nucleus, retrochiasmatic and lateral hypothalamic areas. Of particular interest is the finding that the PVN receives input from the contralateral PVN and ipsilateral SON. Of the other diencephalic structures only the zone incerta showed a consistent number of labeled cells. The results are discussed in relationship to the possible neural structures that might mediate the response of the PVN neurons to adrenalectomy.

Efferents from the medial anterior hypothalamic area in the guinea pig

Medial anterior hypothalamic connections were studied with H3-proline and autoradiography. Most of the axons projected to other hypothalamic nuclei. The major pathways were found ventral medial to the fornix and in the periventricular tract. Substantial projections were apparent in the ventromedial and dorsomedial nuclei with less label in the arcuate nucleus. The dorsal premammillary nuclei were labeled bilaterally, particularly with more caudal injections of anterior hypothalamus. Efferents were evident in the posterior hypothalamus and continued into the central gray of the midbrain. Labeled fibers reached the ventral tegmental area and in the reticular formation were traced only through pons. Rostral projections were to the medial and lateral preoptic areas and ventral lateral septum. The bed nucleus of stria terminals was labeled a very few fibers reached the medial amygdaloid nucleus. The periventricular nucleus of thalamus was labeled.

The distribution of spinal projection neurons in the hypothalamus of the rat, studied with the HRP method

The distribution and number of hypothalamospinal tract (HST) neurons were studied following injections of horseradish peroxidase (HRP) at various levels of the rat spinal cord. The hypothalamus was divided into four areas and one nucleus, that is, the dorsal (DHA), posterior (PHA), medial (MHA) and lateral (LHA) hypothalamic areas and the paraventricular nucleus (PVN). The total numbers of HST neurons labeled with HRP varied according to the injection levels: 6,160 (C2 injections), 3,808 (T8), 1,961 (L1), 919 (L7) and 13 (S4). With C2 injections LHA contained 3,464 neurons, which accounted for 56% of the full number of HST neurons; similarly, PVN, 1,114 (18%); MHA, 865 (14%); DHA and PHA, 817 (12%). With L7 injections, LHA contained 444 labeled neurons, which accounted for 48% of the total; PVN, 327 (36%); MHA, 71 (8%); DHA with PHA, 77 (8%). As for the rostrocaudal distribution of labeled neurons, there was only a slight difference between the C2 and L6 injections in LHA, but no difference was noticed in PVN, DHA nor PHA. The present findings suggest that 70% of HST neurons may project to the cervical and thoracic cords. Although the number of labeled HST neurons decreased as the injection sites were placed caudally, no clearcut topographical arrangement was recognized in terms of the spinal projection levels.

Efferents of the medial preoptic area in the guinea pig: an autoradiographic study

Medial preoptic axons were traced into the diagonal band of Broca and septum, particularly lateral septum. Other labeled fibers could be followed dorsally from medial preoptic area injections adjacent to the stria medullaris, and in the periventricular fiber system and the stria terminalis and its bed nucleus. The anterior and medial amygdaloid nuclei were labeled by fibers via the stria terminalis and other arching over the optic tract and through the substantia innominata. The lateral habenula was labeled. Labeled periventricular fibers reached the periventricular nucleus of the thalamus. Descending efferents were traced principally below the fornix and in the adjacent lateral hypothalamus to label the anterior hypothalamus, the tuberal nuclei, and median eminence. Axons of the medial preoptic area joined the medial part of the medial forebrain bundle and distributed to the reticular formation and the central gray of the midbrain and pons. A small amount of contralateral connections were described.

Neurogenesis in the basal forebrain of the Chinese hamster (Cricetulus griseus). I. Time of neuron origin

The time of neuron origin has been determined in the basal ganglia and related basal forebrain structures of the Chinese hamster with the aid of 3H-thymidine autoradiography. Large-celled structures like the globus pallidus, nucleus of the horizontal limb of the diagonal band of Broca as well as large cells in the rostral part of the substantia innominata, in the caudate-putamen-complex and in the olfactory tubercle arise early (E12--E16), whereas medium-sized and small cells in the basal forebrain have a persistent origin over a much longer period. Neuron formation in the basal forebrain persists decrementally until P4. A clear caudorostral spatiotemporal gradient as well as a distinct 'outside-in' gradient have been observed in the caudate-putamen-complex. Medium-sized neurons in the neostriatum and in the nucleus accumbens, generated simultaneously, are usually arranged in scattered clusters. The present data on time of neuron origin strongly support other evidence which points to the conclusion that the nucleus accumbens can be considered as a ventromedial extension of the caudate-putamen-complex.

Development of the diencephalon in the rat. II. Correlation of the embryonic development of the hypothalamus with the time of origin of its neurons

The development of the nuclei of the hypothalamus was examined in normal and X-irradiated embryos from day 13 (E13) to the day before birth (E22). The diencephalic neuroepithelium was subdivided into three lobes (dorsal, medial, and ventral) and two lobules (superior and inferior). The hypothalamus is derived from the ventral lobe and the inferior lobule. The ventral neuroepithelial lobe generates the neurons of most of the early arising hypothalamic structures, including those of the lateral tier nuclei associated with the medial forebrain bundle, and the heterogeneous intermediate tier nuclei. A specialized neuroepithelial region lining the diamond shaped ventricle produces the early neurohypophysial magnocellular neurons; the neurons of the paraventricular nucleus remain at this site, whereas the neurons of the supraoptic nucleus could be traced migrating laterally. The neurons of the late arising hypophysiotropic area of the posterior hypothalamus are derived from components of the inferior neuroepithelial lobule: the dorsomedial and ventromedial nuclei apparently from a shared matrix in the main portion of the inferior lobule; the tuberomammillary-arcuate complex from its posteroventral recess. The triple-decked and sequentially produced components of the mammillary system may arise from separate neuroepithelial sites. The autoradiographic results of the previous study (Altman and Bayer, '78a) showed that the structural and functional heterogeneity of the mature hypothalamus is paralleled by cytogenetic heterochronicity; the present embryonic observations indicate that many of the distinguishable components of the hypothalamus arise from a mosaic of heterogeneous neuroepithelial sites.

Development of the diencephalon in the rat. I. Autoradiographic study of the time of origin and settling patterns of neurons of the hypothalamus

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day 13 (E13 + 14) until the day before birth (E21 + 22). This double labelling procedure was combined with an injection schedule of a single day delay between groups (E13 + 14; E14 + 15; E15 + 16 . .). The two injections assured the comprehensive labelling of practically all neurons of a given structure prior to the onset of their differentiation (comprehensive labelling), whereas the progressive daily delay in injections made it possible to estimate the proportion of neurons formed in various regions of the hypothalamus on a single day. Hypothalamic areas or nuclei were assigned into four classes on the basis of their cytogenetic isochronicity. Structures composed of the earliest arising (class 1) neurons constitute a lateral tier that includes the lateral preoptic and lateral hypothalamic areas, and the lateral mammillary nucleus. Structures composed of early arising (class 2) neurons form a heterogeneous collection of nuclear systems, including the paraventricular, internuclear and supraoptic magnocellular neurons, and several intermediate tier nuclei of the anterior and posterior hypothalamus. The late arising (class 3) and latest arising (class 4) nuclei constitute a periventricular system anteriorly and a more extensive region posteriorly. The latter two nuclear systems may constitute the hypophysiotropic area of the hypothalamus. The nuclei of the mammillary system, which are produced sequentially, are distinguished from other hypothalamic structures by their more rapid generation time. Internuclear labelling gradients were used to infer the neuroepithelial site of origin and settling pattern of neurons. Common sites of origin were indicated for the following structures: the magnocellular neurohypophysial neurons; the neurons of the dorsomedial and ventromedial nuclei; and the neurons of the tubermammillary and arcuate nuclei. The sites of origin of these groups of nuclei were related to specialized ventricular linings in the mature hypothalamus.