Lateral mammillary body neurons in mouse brain are disproportionately vulnerable in Alzheimer's disease

The neural circuits governing the induction and progression of neurodegeneration and memory impairment in Alzheimer's disease (AD) are incompletely understood. The mammillary body (MB), a subcortical node of the medial limbic circuit, is one of the first brain regions to exhibit amyloid deposition in the 5xFAD mouse model of AD. Amyloid burden in the MB correlates with pathological diagnosis of AD in human postmortem brain tissue. Whether and how MB neuronal circuitry contributes to neurodegeneration and memory deficits in AD are unknown. Using 5xFAD mice and postmortem MB samples from individuals with varying degrees of AD pathology, we identified two neuronal cell types in the MB harboring distinct electrophysiological properties and long-range projections: lateral neurons and medial neurons. lateral MB neurons harbored aberrant hyperactivity and exhibited early neurodegeneration in 5xFAD mice compared with lateral MB neurons in wild-type littermates. Inducing hyperactivity in lateral MB neurons in wild-type mice impaired performance on memory tasks, whereas attenuating aberrant hyperactivity in lateral MB neurons ameliorated memory deficits in 5xFAD mice. Our findings suggest that neurodegeneration may be a result of genetically distinct, projection-specific cellular dysfunction and that dysregulated lateral MB neurons may be causally linked to memory deficits in AD.

High ethanol preference and dissociated memory are co-occurring phenotypes associated with hippocampal GABAAR-δ receptor levels

Alcohol use disorder (AUD) frequently co-occurs with dissociative disorders and disorders with dissociative symptoms, suggesting a common neurobiological basis. It has been proposed that facilitated information processing under the influence of alcohol, resulting in the formation of dissociated memories, might be an important factor controlling alcohol use. Access to such memories is facilitated under the effect of alcohol, thus further reinforcing alcohol use. To interrogate possible mechanisms associated with these phenotypes, we used a mouse model of dissociative amnesia, combined with a high-alcohol preferring (HAP) model of AUD. Dissociated memory was induced by activation of hippocampal extrasynaptic GABA type A receptor delta subunits (GABA_AR-δ), which control tonic inhibition and to which ethanol binds with high affinity. Increased ethanol preference was associated with increased propensity to form dissociated memories dependent on GABA_AR-δ in the dorsal hippocampus (DH). Furthermore, the DH level of GABA_AR-δ protein, but not mRNA, was increased in HAP mice, and was inversely correlated to the level of miR-365-3p, suggesting an miRNA-mediated post-transcriptional mechanism contributing to elevated GABA_AR-δ. The observed changes of DH GABA_AR-δ were associated with a severe reduction of excitatory projections stemming from GABA_AR-δ-containing pyramidal neurons in the subiculum and terminating in the mammillary body. These results suggest that both molecular and circuit dysfunction involving hippocampal GABA_AR-δ receptors might contribute to the co-occurrence of ethanol preference and dissociated information processing.

Heterogeneity of the supramammillary-hippocampal pathways: evidence for a unique GABAergic neurotransmitter phenotype and regional differences

The supramammillary nucleus (SuM) provides substantial projections to the hippocampal formation. This hypothalamic structure is involved in the regulation of hippocampal theta rhythm and therefore the control of hippocampal-dependent cognitive functions as well as emotional behavior. A major goal of this study was to characterize the neurotransmitter identity of the SuM-hippocampal pathways. Our findings demonstrate two distinct neurochemical pathways in rat. The first pathway originates from neurons in the lateral region of the SuM and innervates the supragranular layer of the dorsal dentate gyrus and, to a much lesser extent, the ventral dentate gyrus. This pathway displays a unique dual phenotype for GABAergic and glutamatergic neurotransmission. Axon terminals contain markers of GABAergic neurotransmission, including the synthesizing enzyme of GABA, glutamate decarboxylase 65, and the vesicular GABA transporter and also a marker of glutamatergic neurotransmission, the vesicular glutamate transporter 2. The second pathway originates from neurons in the most posterior and medial part of the SuM and innervates exclusively the inner molecular layer of the ventral dentate gyrus and the CA2/CA3a pyramidal cell layer of the hippocampus. The axon terminals from the medial part of the SuM contain the vesicular glutamate transporter 2 only. These data demonstrate for the first time the heterogeneity of the SuM-hippocampal pathways, not only from an anatomical but also a neurochemical point of view. These pathways, implicated in different neuronal networks, could modulate different hippocampal activities. They are likely to be involved differently in the regulation of hippocampal theta rhythm and associated cognitive functions as well as emotional behavior.

Calcium increase in the mammillary bodies with aging

To elucidate compositional changes of the mammillary body with aging, the authors investigated age-related changes of elements, relationships among their elements, and gender differences in the mammillary bodies by direct chemical analysis. After ordinary dissection at Nara Medical University was finished, the mammillary bodies were resected from the cerebra of the subjects. The subjects consisted of 19 men and 25 women, ranging in age from 70 to 101 years (average age = 83.8 +/- 7.2 years). After ashing of the mammillary bodies with nitric acid and perchloric acid, element contents were determined by inductively coupled plasma-atomic emission spectrometry. It was found that the Ca content increased slightly and significantly in the mammillary bodies with aging, but the P, S, Mg, Zn, Fe, and Na contents did not change significantly with aging. Regarding the relationships among elements, significant correlations were found among the contents of Ca, P, S, and Mg in the mammillary bodies, with one exception between P and Mg contents. With regard to the seven element contents, no significant gender differences were found in the mammillary bodies.

A neuromodulatory role for oxytocin within the supramammillary nucleus

Oxytocin functions as both a neurohypophysial hormone and central neuromodulatory peptide, and has been implicated in reproductive behaviours, anxiety and reward, as well as facilitation of the neuroendocrine milk-ejection reflex. A potential substrate for oxytocin is the supramammillary nucleus (SuM), a structure that contains oxytocin binding sites and serves as an important relay within the limbic system. Hence, this study investigated the neuromodulatory role of oxytocin within the SuM. Firstly, the effect of oxytocin on neuronal firing within the SuM was studied, using in vitro brain slices from virgin female rats. Oxytocin (10(-6)M) excited approximately 50% of SuM neurones, and similar results were obtained with the selective oxytocin agonist, Thr(4) Gly(7) oxytocin (TGOT) (10(-6) and 10(-7)M). The remaining neurones were unaffected. The TGOT response was blocked by application of the oxytocin antagonist, [d(CH(2))51,Tyr(Me)(2),Thr(4),Orn(8),Tyr-NH29]-vasotocin. Repeat doses of TGOT caused diminution of the response, indicative of desensitisation. In the second series of experiments, immunocytochemical techniques were used to study the oxytocinergic innervation of the SuM. The supramammillary decussation was found to contain numerous oxytocinergic fibres, and some could be seen coursing ventrally to enter the SuM. Whereas, some were clearly "en passant" fibres innervating the neurohypophysis, others followed a more convoluted and branching course, and appeared to terminate within the nucleus. Finally, in vivo microinfusion studies investigated whether oxytocin injected into the SuM facilitated the milk-ejection reflex, a well known action of central oxytocin. Oxytocin microinfusion in the region of the SuM caused a pronounced facilitation of the reflex, contrasting with the much smaller effects of microinfusions made rostral or caudal to the nucleus. Collectively, these results strongly support a neuromodulatory role for oxytocin within the SuM. This could have important implications for understanding the diverse neuroendocrine and behavioural functions of central oxytocin, including its role in reward.

The supramammillo-septal-hippocampal pathway mediates sensorimotor gating impairment and hyperlocomotion induced by MK-801 and ketamine in rats

RATIONALE

Ketamine or MK-801 induced sensorimotor gating deficit, but the underlying neural mechanisms are not completely known. We have previously demonstrated that the medial septum (MS) mediated the phencyclidine-induced deficit in prepulse inhibition of the acoustic startle (PPI) in rats.

OBJECTIVES

We investigated the involvement of the supramammillary area (SUM) to MS pathway in PPI impairment and behavioral hyperlocomotion induced by MK-801 or ketamine in rats and correlated the behavioral deficits with hippocampal gamma wave increase.

MATERIALS AND METHODS

Ketamine (6 mg/kg, s.c.) or MK-801 (0.5 mg/kg, i.p.) was administered after infusion of saline or the GABA(A) receptor agonist, muscimol (0.25 microg), into the MS or SUM. Locomotion, PPI, and hippocampal electroencephalogram (EEG) were recorded.

RESULTS

MK-801 or ketamine induced PPI impairment and behavioral hyperlocomotion, accompanied by an increase in hippocampal gamma waves (30-100 Hz). The changes in behavior and gamma waves induced by ketamine or MK-801 were antagonized by pre-infusion of muscimol, but not saline, into the SUM or MS. Infusion of muscimol into the SUM alone did not significantly affect PPI, but it suppressed spontaneous locomotor behavior and hippocampal EEG. Infusion of ionotropic glutamate receptor antagonists into the MS did not affect the PPI deficit or the gamma wave increase after MK-801.

CONCLUSIONS

A non-glutamatergic component of the supramammillo-septal pathway mediates the hyperlocomotion and the deficits in PPI induced by MK-801 or ketamine. Inactivation of the MS or SUM normalized both the hippocampal gamma waves and the behavioral deficits (PPI impairment and hyperlocomotion).

Alpha N-catenin deficiency causes defects in axon migration and nuclear organization in restricted regions of the mouse brain

Alpha N-catenin is a cadherin-binding protein, widely expressed in the nervous system; and it plays a crucial role in cadherin-mediated cell-cell adhesion. Here we report the effects of alpha N-catenin gene deficiency on brain morphogenesis. In addition to the previously reported phenotypes, we found that some of the axon tracts did not normally develop, in particular, axons of the anterior commissure failed to cross the midline, migrating, rather, to ectopic places. In restricted nuclei, a population of neurons was missing or their laminar arrangement was distorted. The ventricular structures were also deformed. These results indicate that alpha N-catenin has diverse roles in the organization of the central nervous system, but only in limited portions of the brain.

Female odors stimulate CART neurons in the ventral premammillary nucleus of male rats

Olfactory information is known to influence both male and female sexual behavior. Chemosensory compounds known as pheromones activate distinct brain pathways, inducing innate and stereotyped behaviors, as well as hormonal changes. Studies have shown that female odors induce Fos expression in various brain nuclei of conspecific males, including the ventral premammillary nucleus (PMV). Although poorly investigated, previous studies have suggested that the PMV plays a role in aggressive and sexual behavior. In this study, we used Fos protein expression as a marker for neurons responsive to female odors in sexual inexperienced male rats exposed to soiled bedding. We observed that female odors induced intense Fos immunoreactivity throughout the PMV. Most of these neurons also express cocaine- and amphetamine-regulated transcript (CART) immunoreactivity. In addition, we used in situ hybridization and observed that, following exposure to female odors, CART mRNA increased only in the ventral PMV. Our results suggest that female odors stimulate CART production in the PMV of inexperienced males. Considering that the PMV CART neurons also express the leptin receptor, as well as the fact that they project to areas related to reproduction, we hypothesize that PMV CART neurons integrate nutritional and environmental (olfactory) information, being apt to modulate male reproductive behavior.

Distribution of urocortin 3 neurons innervating the ventral premammillary nucleus in the rat brain

Urocortin 3 (Ucn 3) is a recently described peptide of the corticotropin-releasing factor family. Neurons expressing Ucn 3 mRNA and peptide are distributed in specific brain areas, including the median preoptic nucleus, the perifornical area (PFx), and the medial nucleus of the amygdala (MEA). Fibers immunoreactive to Ucn 3 are confined to certain brain nuclei, being particularly dense in the ventral premammillary nucleus (PMV). In studies involving electrolytic lesions and analysis of Fos distribution according to behavioral paradigms, the PMV has been potentially implicated in conspecific aggression and sexual behavior. However, the role that Ucn 3 plays in this pathway has not been explored. Therefore, we investigated the origins of the urocortinergic innervation of the PMV of Wistar rat in an attempt to map the brain circuitry and identify likely related functions. We injected the retrograde tracer cholera toxin b subunit into the PMV and found that 88% of the Ucn 3-immunoreactive fibers in the PMV originate in the dorsal MEA, and that few originate in the PFx. As a control, we injected the anterograde tracer biotin dextran amine into both regions. We observed that the PMV is densely innervated by the MEA, and scarcely innervated by the PFx. The MEA is a secondary relay of the vomeronasal system and projects amply to hypothalamic nuclei related to hormonal and behavioral adjustments, including the PMV. Although physiological studies should also be performed, we hypothesize that Ucn 3 participates in such pathways, conveying sensory information to the PMV, which in turn modulates behavioral and neuroendocrine responses.

Astroglial distribution and sexual differences in neural metabolism in mammillary bodies

The sexual differences in cerebral nuclei are produced by the organizational and the activational function of gonadal hormones. The different performances by male and female rats in memory tasks requiring use of the mammillary bodies (MBs), could be due to structural and functional sexual dimorphic differences. Our work quantifies the number of glial fibrillary acidic protein immunoreactive (GFAP-IR) astrocytes, and neuronal metabolic activity measured by the cytochrome oxidase (CO) histochemistry in the MBs in rats of both sexes. We find that there is no difference in astroglial number in the medial mammillary nucleus (MMN) and in the lateral mammillary nucleus (LMN) of males, females in estrus and diestrus adult rats. However, we do find statistically significant differences between the sexes in the neuronal oxidative metabolism influenced by the estrous cycle. We, therefore, conclude that there are functional and not structural sex differences in the MBs.

Sim1 and Sim2 are required for the correct targeting of mammillary body axons

The mammillary body (MB), and its axonal projections to the thalamus (mammillothalamic tract, MTT) and the tegmentum (mammillotegmental tract, MTEG), are components of a circuit involved in spatial learning. The bHLH-PAS transcription factors SIM1 and SIM2 are co-expressed in the developing MB. We have found that MB neurons are generated and that they survive at least until E18.5 in embryos lacking both Sim1 and Sim2 (Sim1(-/-);Sim2(-/-)). However, the MTT and MTEG are histologically absent in Sim1(-/-);Sim2(-/-) embryos, and are reduced in embryos lacking Sim1 but bearing one or two copies of Sim2, indicating a contribution of the latter to the development of MB axons. We have generated, by homologous recombination, a null allele of Sim1 (Sim1(tlz)) in which the tau-lacZ fusion gene was introduced, allowing the staining of MB axons. Consistent with the histological studies, lacZ staining showed that the MTT/MTEG is barely detectable in Sim1(tlz/tlz);Sim2(+/-) and Sim1(tlz/tlz);Sim2(-/-) brains. Instead, MB axons are splayed and grow towards the midline. Slit1 and Slit2, which code for secreted molecules that induce the repulsion of ROBO1-producing axons, are expressed in the midline at the level of the MB, whereas Robo1 is expressed in the developing MB. The expression of Rig-1/Robo3, a negative regulator of Slit signalling, is upregulated in the prospective MB of Sim1/Sim2 double mutants, raising the possibility that the growth of mutant MB axons towards the midline is caused by a decreased sensitivity to SLIT. Finally, we found that Sim1 and Sim2 act along compensatory, but not hierarchical, pathways, suggesting that they play similar roles in vivo.

Experimental study of the connections of the preglomerular nuclei and corpus mamillare in the rainbow trout, Oncorhynchus mykiss

The preglomerular complex of trout consists of the anterior (aPGN) and medial (mPGN) preglomerular nuclei and the corpus mamillare (CM). In order to improve knowledge on this complex, we applied a lipophilic neuronal tracer (DiI) to the three nuclei. These nuclei received afferents from the medial part of the dorsal telencephalic area (Dm), the ventral part of the ventral telencephalic area (Vv), the preoptic nucleus, the periventricular layer of the rostral optic tectum and the central posterior thalamic nucleus. The aPGN also received numerous toral projections and, sent efferents to the anterior tuberal nucleus. In addition, both the aPGN and the mPGN nuclei gave rise to efferents to the dorsal region of the dorsal telencephalic area (Dd), whereas the medial preglomerular nucleus and the CM sent fibers to the torus lateralis and the diffuse nucleus, as confirmed by reciprocal labeling. A small mPGN/CM subgroup projected to the optic tectum. These results suggest close functional inter-relationship between the trout preglomerular complex and two telencephalic regions (Dm and Vv). In addition, all nuclei of the complex receive preoptic, tectal and dorsal thalamic afferents, whereas the aPGN and mPGN are related with acoustic-lateral ascending pathways, and the mPGN and CM with the central region of the dorsal telencephalic area and visceral/gustatory pathways.

Galanin immunohistochemistry and electron microscopic studies in developing human fetal mammillary bodies

Development and maturation of nuclear groups in the mammillary complex of second and third trimester human fetal hypothalamus were studied using Nissl stain, galanin immunocytochemistry and transmission electron microscopy. While the identity of the supra and medial mammillary nucleus was established at 24 weeks of gestation (w.g.) in Nissl stained preparation, galanin immunoreactive (Gal-ir) neurons were seen in the supra and medial mammillary nucleus of 27 through 39 w.g. fetuses. Immunoreactive perikarya in the lateral mammillary nucleus appear later at 34 w.g. and show relatively meager population. Gal-ir neurons of the supramammillary nucleus were divisible in dorsal and ventral subgroups. There was a progressive increase in galanin expressing neurons in more and more ventral positions, along the medial margin of either mammillary body so that in term fetal specimens, the ventral subgroup appeared to be continuous with the medial mammillary nucleus. Galanin positive neurons were relatively sparse in the core of the mammillary bodies. Transmission electron micrographs revealed neurons with varying degree of indentation of the nuclear envelope. Vigorous synaptogenesis was seen in the supramammillary region of the mammillary bodies. The height and width of the synaptic complex also showed a progressive increase. Although galanin neurons were reported from the supramammillary nucleus of adult human mammillary complex, no immunoreactivity was detected in the medial and lateral components of the mammillary body. We suggest that expression of galanin in the medial and lateral components may be of transient occurrence and may serve a significant role in the synaptogenesis.

Repeated 4-aminopyridine seizures reduce parvalbumin content in the medial mammillary nucleus of the rat brain

Parvalbumin (Pv) containing fast spiking neurons play a crucial role in synchronizing the activity of excitatory neuronal circuits in the brain. Alterations of parvalbumin content in these neurons can affect their spike characteristics and, ultimately, may increase the susceptibility of neuronal circuits to epileptic seizures. In the present study, we examined whether repeated 4-aminopyridine (4-AP)-induced seizures modify the regional parvalbumin contents in the rat brain. 4-Aminopyridine was injected intraperitoneally in adult rats, controls received the solvent. Animals were sacrificed at 3 h after a single acute treatment, or following repeated, daily treatments of 12 days. In situ hybridization (ISH) indicated significantly decreased parvalbumin mRNA level in the medial mammillary nucleus (MM) at 12 days. Western blotting revealed 20.1% significant decrease of parvalbumin content in the medial mammillary area, while parvalbumin immunohistochemistry indicated no change of the number of immunoreactive cells in the medial mammillary nucleus. The results reveal the downregulation of the transcription of the parvalbumin gene and the decrease of parvalbumin synthesis in medial mammillary nucleus neurons in response to experimental seizures.

Bsx, an evolutionary conserved Brain Specific homeoboX gene expressed in the septum, epiphysis, mammillary bodies and arcuate nucleus

Shaping and orchestrating the genetic program involved in embryonic modelling of brain structures is a major function played by homeobox containing genes. Recently, analysis of conditional mouse mutants has pointed out additional roles in supporting adult brain functional activities. During a search for novel homeobox genes in the public released genomic sequences derived by the Human and Mouse genome projects, we were able to identify the mouse homologue of the Drosophila brain specific homeobox gene. We named it Bsx and characterized its expression in embryonic and post-natal mouse brain. Interestingly, Bsx shows an expression pattern restricted to a few specific developing brain structures. Pineal gland, telencephalic septum, hypothalamic pre-mammillary body and arcuate nucleus are the only brain structures where we detected Bsx transcriptional activity, which is maintained also after birth. In particular, Bsx might be considered an important molecular marker for early embryonic stages of epiphysis development, being specifically expressed in this neural structure from E9.5 onwards.

Rewarding effects of AMPA administration into the supramammillary or posterior hypothalamic nuclei but not the ventral tegmental area

We examined whether injections of the excitatory amino acid AMPA are rewarding when injected into the posterior hypothalamus and ventral tegmental area. Rats quickly learned to lever-press for infusions of AMPA into the supramammillary or posterior hypothalamic nuclei but failed to learn to lever-press for similar injections into the ventral tegmental areas. AMPA injections into the supramammillary nucleus, but not the ventral tegmental area, induced conditioned place preference. The rewarding effects of AMPA appear to be mediated by AMPA receptors, because coadministration of the AMPA antagonist CNQX blocked the rewarding effects of AMPA, and administration of the enantiomer R-AMPA did not mimic the rewarding effects. AMPA injections into the supramammillary nucleus, but not the ventral tegmental area, also increased extracellular dopamine concentrations in the nucleus accumbens. Pretreatment with the D1 dopamine antagonist SCH 23390 [R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine] led to extinction of AMPA self-administration. These findings implicate posterior hypothalamic regions in reward function and suggest that reward mechanisms localized around the ventral tegmental area are more complex than has been assumed recently.

Characterization of gabaergic neurons within the human medial mamillary nucleus

The morphology, distribution and relative frequency of GABAergic neurons in the medial mamillary nucleus (MMN) of normal human individuals was studied using a glutamic acid decarboxylase (GAD) antiserum. GAD-immunoreactive (GAD-IR) neurons were found sparsely distributed throughout the MMN and most displayed a simple bipolar morphology. A small population of large diameter GAD-IR neurons was found in the white matter capsule adjacent to the ventral border of the MMN. Results of double-labeling experiments revealed no evidence of calretinin, parvalbumin or calbindin immunoreactivities co-localizing with GAD-IR neurons. GAD-IR neurons of the MMN had an average somal area of 138+/-41 microm2, compared with the average somal area of 384+/-137 microm2 for the population of MMN neurons as a whole. GAD-IR neurons had a tendency to cluster in groups of two (and occasionally three) and showed a distribution gradient across the MMN with higher densities being found near the insertion of the fornix, the origin of the mamillo-thalamic tract and toward the medial MMN border. Quantitative estimates of GAD-IR neuron frequency revealed the GAD-IR phenotype to constitute an average of 1.7% percent of the total neuron population within the human MMN. These findings suggest that inhibitory activity within the human MMN is regulated in part by a small population of intrinsic GABAergic interneurons.

Changes in metabolic activity and estrogen receptors in the human medial mamillary nucleus: relation to sex, aging and Alzheimer's disease

The medial mamillary nucleus (MMN) is situated caudally in the human hypothalamus and is involved in memory processes. In search for putative sites of action in estrogen replacement therapy on memory both in aging and Alzheimer's disease (AD), we aimed at determining whether changes would occur in estrogen receptors (ER) or metabolic activity in the MMN neurons under these conditions in a sex-dependent way. The Golgi apparatus (GA) and cell size, that were previously shown to be good measures of changes in neuronal metabolic activity, were measured in the MMN of 10 young (20-50 years old), 11 elderly (56-76 years old) control men and women and 11 AD patients (54-78 years old). In addition, we investigated whether estrogen receptor alpha or beta (ERalpha or ERbeta) immunoreactivity was altered in the MMN in aging or AD. There were no sex- or AD-related differences in the GA or cell size in the MMN. Both the GA and cell size of the MMN neurons were found to be increased in postmenopausal compared to young control women accompanied by a decrease in the amount of nuclear ERbeta. The percentage of nuclear ERalpha-positive MMN neurons was markedly enhanced in AD patients compared to controls and most prominently in AD men. In AD patients the proportion of nuclear ERalpha-positive neurons was positively correlated to the Braak stages that indicate the progression of the disease. No differences in the proportion of ERbeta-positive neurons were observed between AD and control patients. We propose that estrogens play an inhibitory role with respect to the metabolic activity of human MMN, which is mediated via ERbeta. This inhibitory effect is diminished in postmenopausal women. The role of the enhanced nuclear ERalpha staining in AD, that was also found in other brain areas, remains to be elucidated.

Distribution of melanin-concentrating hormone neurons projecting to the medial mammillary nucleus

The melanin-concentrating hormone and neuropeptide glutamic acid-isoleucine are expressed in neurons located mainly in the hypothalamus that project widely throughout the CNS. One of the melanin-concentrating hormone main targets is the medial mammillary nucleus, but the exact origin of these fibers is unknown. We observed melanin-concentrating hormone and neuropeptide glutamic acid-isoleucine immunoreactive fibers coursing throughout the mammillary complex, showing higher density in the pars lateralis of the medial mammillary nucleus, while the lateral mammillary nucleus showed sparse melanin-concentrating hormone innervation. The origins of these afferents were determined by using implant of the retrograde tracer True Blue in the medial mammillary nucleus. Double-labeled neurons were observed in the lateral hypothalamic area, rostromedial zona incerta and dorsal tuberomammillary nucleus. A considerable population of retrogradely labeled melanin-concentrating hormone perikaryal profiles was also immunoreactive to neuropeptide glutamic acid-isoleucine (74+/-15% to 85+/-15%). The afferents from the lateral hypothalamic area, rostromedial zona incerta and dorsal tuberomammillary nucleus to the medial mammillary nucleus were confirmed using implant of the anterograde tracer Phaseolus vulgaris leucoagglutinin. In addition, using double-labeled immunohistochemistry, we found no co-localization between neurons expressing melanin-concentrating hormone and adenosine deaminase (histaminergic marker) in the dorsal tuberomammillary nucleus. We hypothesize that these melanin-concentrating hormone projections participate in spatial memory process mediated by the medial mammillary nucleus. These pathways would enable the animal to look for food during the initial moments of appetite stimulation.

c-Fos expression in supramammillary and medial mammillary nuclei following spatial reference and working memory tasks

To investigate brain substrates of spatial memory, neuronal expression of c-Fos protein was studied. Two groups of rats were trained in two spatial memory tasks in the Morris water maze, where the rats have to apply a reference memory rule or a working memory rule. In addition to the experimental groups, two control groups were used to study c-fos activation not specific to the memory processes studied. After immunohistochemical procedures, the number of c-Fos positive neuronal nuclei was quantified in the mammillary body (MB) region (medial mammillary nucleus [MMn] and supramammillary nucleus [SuM]). The results have shown that some MMn neurons expressed c-Fos nuclear immunoreactivity related to spatial working memory but not to spatial reference memory. The increased number of c-Fos immunoreactive neuronal nuclei in the SuM was related to spatial training but not to either working or reference memory demands of the tasks.

Estrogen receptor-alpha distribution in the human hypothalamus in relation to sex and endocrine status

The present study reports the first systematic rostrocaudal distribution of estrogen receptor-alpha immunoreactivity (ERalpha-ir) in the human hypothalamus and its adjacent areas in young adults. Postmortem material taken from 10 subjects (five male and five female), between 20 and 39 years of age, was investigated. In addition, three age-matched subjects with abnormal levels of estrogens were studied: a castrated, estrogen-treated 50-year-old male-to-female transsexual (T1), a 31-year-old man with an estrogen-producing tumor (S2), and an ovariectomized 46-year-old woman (S8). A strong sex difference, with more nuclear ERalpha-ir in women, was observed rostrally in the diagonal band of Broca and caudally in the medial mamillary nucleus. Less robust sex differences were observed in other brain areas, with more intense nuclear ERalpha-ir in men, e.g., in the sexually dimorphic nucleus of the medial preoptic area, paraventricular nucleus, and lateral hypothalamic area, whereas women had more nuclear ERalpha-ir in the suprachiasmatic nucleus and ventromedial nucleus. No nuclear sex differences in ERalpha were found, e.g., in the central part of the bed nucleus of the stria terminalis. In addition to nuclear staining, ERalpha-ir appeared to be sex-dependently present in the cytoplasm of neurons and was observed in astrocytes, plexus choroideus, and other non-neuronal cells. ERalpha-ir in T1, S2, and S8 suggested that most of the observed sex differences in ERalpha-ir are "activational" (e.g., ventromedial nucleus/medial mamillary nucleus) rather than "organizational." Species similarities and differences in ERalpha-ir distribution and possible functional implications are discussed.

Possible glutamatergic/aspartatergic projections to the supramammillary nucleus and their origins in the rat studied by selective [(3)H]D-aspartate labelling and immunocytochemistry

The supramammillary neurons projecting directly to the hippocampus or indirectly via the septum participate in the regulation of hippocampal theta activity. Inputs to the supramammillary nucleus are only partly specified neurochemically. Glutamate appears to be an excitatory transmitter in this cell group, however, the origin of the glutamatergic afferents is unknown. The present investigations were devoted to study this question. The transmitter-selective [(3)H]D-aspartate retrograde transport method was used injecting the tracer into the lateral subregion of the nucleus. The radioactive tracer was visualized by autoradiography. Non-selective retrograde tracing experiments were also performed for reference injecting wheat germ agglutinin-conjugated colloidal gold into the same supramammillary region. Retrogradely radiolabelled neurons in various numbers were detected in several brain regions including medial septum-diagonal band complex, lateral septum, rostral part of medial and lateral preoptic areas, lateral habenula, ventral premammillary nucleus, apical subregion of interpeduncular nucleus, laterodorsal tegmental nucleus, and dorsal and median raphe nuclei. Radiolabelled neurons in the mentioned raphe nuclei were serotonin-immunonegative. In the non-selective retrograde tracing experiments combined with immunocytochemistry, about 50% of the retrogradely labelled neurons in the raphe nuclei was serotonin-immunonegative, showing that not only serotonergic raphe neurons project to the supramammillary nucleus. The findings indicate that a significant part of the afferents from telencephalic, diencephalic and brainstem regions to the supramammillary nucleus may contain glutamate/aspartate as neurotransmitter. The most important functional implications of these observations concern the role of the supramammillary nucleus in controlling the electrical activity of the hippocampus, and in particular the generation and maintenance of the theta rhythm.

Sex differences in androgen receptors of the human mamillary bodies are related to endocrine status rather than to sexual orientation or transsexuality

In a previous study we found androgen receptor (AR) sex differences in several regions throughout the human hypothalamus. Generally, men had stronger nuclear AR immunoreactivity (AR-ir) than women. The strongest nuclear labeling was found in the caudal hypothalamus in the mamillary body complex (MBC), which is known to be involved in aspects of cognition and sexual behavior. The present study was carried out to investigate whether the sex difference in AR-ir of the MBC is related to sexual orientation or gender identity (i.e. the feeling of being male or female) or to circulating levels of androgens, as nuclear AR-ir is known to be up-regulated by androgens. Therefore, we studied the MBC in postmortem brain material from the following groups: young heterosexual men, young homosexual men, aged heterosexual castrated and noncastrated men, castrated and noncastrated transsexuals, young heterosexual women, and a young virilized woman. Nuclear AR-ir did not differ significantly between heterosexual and homosexual men, but was significantly stronger than that in women. A female-like pattern of AR-ir (i.e. no to weak nuclear staining) was observed in 26- to 53-yr-old castrated male-to-female transsexuals and in old castrated and noncastrated men, 67--87 yr of age. In analogy with animal studies showing strong activational effects of androgens on nuclear AR-ir, the present data suggest that nuclear AR-ir in the human MBC is dependent on the presence or absence of circulating levels of androgen. The group data were, moreover, supported by the fact that a male-like AR-ir (i.e. intense nuclear AR-ir) was found in a 36-yr-old bisexual noncastrated male-to-female transsexual and in a heterosexual virilized woman, 46 yr of age, with high levels of circulating testosterone. In conclusion, the sexually dimorphic AR-ir in the MBC seemed to be clearly related to circulating levels of androgens and not to sexual orientation or gender identity. The functional implications of these alterations are discussed in relation to reproduction, cognition, and neuroprotection.

Expression of Foxb1 reveals two strategies for the formation of nuclei in the developing ventral diencephalon

Fork head b1 (Foxb1; also called Fkh5, HFH-e5.1, Mf3) is a winged helix transcription factor gene whose widespread early expression in the developing neural tube is soon restricted to the ventral and caudal diencephalon. During diencephalic neurogenesis, Foxb1 is expressed in one patch of neuroepithelium comprising a large mammillary portion and a smaller tuberal portion. The labeled cells coming from this patch contribute to nuclear formation by means of two different strategies: (1) caudally, the young neurons aggregate and settle immediately, giving rise to the nuclei of the mammillary body; (2) rostrally, the young neurons separate from the neuroepithelium forming a trail of cells which spans the mantle layer mediolaterally and which will give rise to two separate cell groups (the dorsal premammillary and part of the lateral hypothalamic area). Our results show the elaborate, regionalized histogenetic mechanisms necessary for the differentiation of the caudal diencephalon; moreover, they suggest that specifically labeled populations, arising from specifically labeled neuroepithelial patches and giving place to specific brain nuclei could be a common mechanism to build complex, nonlaminar regions of the forebrain.

Behavior and brain uptake of fluorodeoxyglucose in mature and aged C57BL/6 mice

This paper describes regional brain energy metabolism, sensorimotor, and memory functions in mature (12 months) and old (24 months) C57BL/6 mice. Male mice were tested across a variety of sensorimotor procedures and in the Morris water maze before evaluating brain uptake of fluorodeoxyglucose (FDG) in the resting state. Mature mice outperformed older mice during the difficult sensorimotor and memory tasks, but not the easier tasks. This suggested that the greater sensorimotor and memory demands of a task compromised the performance of the older mice. This conclusion was consistent with the relative FDG uptake decreases found in regions mediating sensorimotor coordination (vestibular, cerebellar, ventral thalamic regions) and some limbic regions linked to memory (mammillary body, posterior cingulate, and piriform cortices). The inferior colliculus and flocculus had the greatest metabolism in mature mice, as shown by resting FDG uptake, and these regions showed the most marked hypometabolism in the older mice. The data also showed that the neurobehavioral correlative pattern in older mice was modified. In conclusion, brain regions with higher energy metabolism, and the behaviors to which they are related, were affected most greatly by aging in C57BL/6 mice-suggesting that these areas are more metabolically vulnerable to aging effects.

Benzodiazepine binding sites in the human hypothalamus. Autoradiographic study

Using in vitro labelling and autoradiographic techniques, we have analyzed the fine and the detailed distribution of benzodiazepine binding sites in the post-mortem human hypothalamus. Binding sites were labelled in mounted tissue sections from adult brains, using the selective high affinity ligand [3H]-Flunitrazepam. A heterogeneous distribution of benzodiazepine binding sites was found throughout the rostrocaudal extent of human hypothalamus. The autoradiographic labelling was shown in the three hypothalamic parts, i.e., anterior, mediobasal and posterior levels. At the anterior level, the highest densities were present in the diagonal band of Broca, the preoptic area (medial and lateral parts) and the septohypothalamic nucleus. At the mediobasal hypothalamic level, the highest densities were mainly localized in the ventromedial nucleus, whereas the other structures were moderately labelled with [3H]-Flunitrazepam. The mammillary complex as well as the posterior hypothalamic area represented the most heavily labelled structures in the posterior hypothalamus. The results obtained in this study, indicate the presence of a large and heterogeneous distribution of benzodiazepine binding sites in human adult hypothalamus. This could support their implication in the control of distinct neural functions (like neuroendocrine role).

Group II selective metabotropic glutamate receptor agonists and local cerebral glucose use in the rat

The novel mGluR agonist LY354740 and a related analogue LY379268 are selective for mGluR2/3 receptors and are centrally active after systemic administration. In this study, rates of local cerebral glucose use were measured using the [14C]2-deoxyglucose autoradiographic technique to examine the functional consequences of their systemic administration in the conscious rat. Both LY354740 (0.3, 3.0, 30 mg/kg) and LY379268 (0.1, 1.0, 10 mg/kg) produced dose-dependent changes in glucose use. After LY354740 (3.0mg/kg), 4 of the 42 regions measured showed statistically significant changes from vehicle-treated controls: red nuclei (-16%), mammillary body (-25%), anterior thalamus (-29%), and the superficial layer of the superior colliculus (+50%). An additional 15 regions displayed significant reductions in function-related glucose use (P < .05) in animals treated with LY354740 (30 mg/ kg). LY379268 (0.1, 1.0, 10 mg/kg) produced changes in glucose metabolism in 20% of the brain regions analyzed. Significant increases (P < .05) in glucose use were evident in the following: the superficial layer of the superior colliculus (+81%), locus coeruleus (+57%), genu of the corpus callosum (+31%), cochlear nucleus (+26%), inferior colliculus (+20%), and the molecular layer of the hippocampus (+14%). Three regions displayed significant decreases: mammillary body (-34%), anteroventral thalamic nucleus (-28%), and the lateral habenular nucleus (-24%). These results show the important functional involvement of the limbic system together with the participation of components of different sensory systems in response to the activation of mGluR2 and mGluR3 with LY354740 and LY379268.

Estrogen receptor immunoreactivity is present in the majority of central histaminergic neurons: evidence for a new neuroendocrine pathway associated with luteinizing hormone-releasing hormone-synthesizing neurons in rats and humans

The central regulation of the preovulatory LH surge requires a complex sequence of interactions between neuronal systems that impinge on LH-releasing hormone (LHRH)-synthesizing neurons. The reported absence of estrogen receptors (ERs) in LHRH neurons indicates that estrogen-receptive neurons that are afferent to LHRH neurons are involved in mediating the effects of this steroid. We now present evidence indicating that central histaminergic neurons, exclusively located in the tuberomammillary complex of the caudal diencephalon, serve as an important relay in this system. Evaluation of this system revealed that 76% of histamine-synthesising neurons display ERalpha-immunoreactivity in their nucleus; furthermore histaminergic axons exhibit axo-dendritic and axo-somatic appositions onto LHRH neurons in both the rodent and the human brain. Our in vivo studies show that the intracerebroventricular administration of the histamine-1 (H1) receptor antagonist, mepyramine, but not the H2 receptor antagonist, ranitidine, can block the LH surge in ovariectomized estrogen-treated rats. These data are consistent with the hypothesis that the positive feedback effect of estrogen in the induction of the LH surge involves estrogen-receptive histamine-containing neurons in the tuberomammillary nucleus that relay the steroid signal to LHRH neurons via H1 receptors.

The distribution of melanin-concentrating hormone in the monkey brain (Cebus apella)

Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemical and in situ hybridization. MCH-immunoreactive neurons were found in the lateral hypothalamus and dorsolateral zona incerta. MCH-ir fibers were seen in the medial mammillary nucleus, and in the median eminence, and very few fibers in the globus pallidus. This is the first report describing the MCH-ir cell and fiber distribution in the monkey brain.

Placement in a novel environment induces fos-like immunoreactivity in supramammillary cells projecting to the hippocampus and midbrain

Injections of fluorescent retrograde tracers into either the hippocampal formation or the midbrain raphe nuclei resulted in retrograde labeling of many cells in the supramammillary region of the hypothalamus. Double labeling studies indicated that these two projections originate from different populations of supramammillary cells. Expression of the proto-oncoprotein Fos could be induced in some retrogradely labeled cells by placing rats in a novel open field before sacrifice. Although seen in both cell types, Fos-like immunoreactivity was significantly more common in supramammillary cells projecting to the hippocampus than in those projecting to the midbrain. These findings suggest that the supramammillary region may contain several populations of neurons which are differentially responsive to certain behavioral manipulations.

Amyloid beta-protein (A beta) accumulation in the putamen and mammillary body during aging and in Alzheimer disease

Immunocytochemical studies clearly showed that amyloid beta-protein (A beta) deposits are widely distributed in the subcortical regions as well as the cortices of normal aged and Alzheimer disease (AD) brains. To investigate the temporal profile of A beta accumulation in the subcortical region, we quantitated A beta40 and A beta42 levels, using sensitive enzyme immunoassays, in the putamen and mammillary bodies of normal individuals aged 24 to 87 years and of AD patients. In these two regions, A beta42 was the predominant species; in particular, A beta42 was the only A beta species detected in the putamen. In several cases the mammillary body contained only A beta40, but not A beta42. Although the extent of A beta accumulation in the 2 subcortical regions was much less than that in the cortex of the same subject, A beta42 appears to accumulate in both subcortical regions at the same time as in the cortex and leptomeninges. In addition, the A beta42 levels in the putamen or in the mammillary body correlated with those in the occipitotemporal cortex. This strongly suggests that the extent of A beta42 accumulation in the brain is determined not only by the duration of A beta accumulation but also by other unknown regional factors. Western blotting showed that the initial A beta species to accumulate in the putamen or mammillary body varied among individuals. In some cases, an A beta42 stable dimer was the most predominant species, while in other cases a 3 or 4 kD A beta42 monomer was more abundant, suggesting that the clearance rates of the A beta42 stable dimer and monomer are different in vivo.

Chronic administration of cannabinoids regulates proenkephalin mRNA levels in selected regions of the rat brain

This study was designed to examine the interactions between the cannabinoid and enkephalinergic systems in the rat brain. To this aim, we have examined the effects of subchronic (5 days) administration (10 mg.kg-1.day-1; i.p.) of delta 9 -tetrahydrocannabinol (THC) or R-methanandamide (AM356) and chronic (18 days) administration with the synthetic cannabinoid receptor agonist CP-55,940 (1 mg.kg-1.day-1; i.p) on proenkephalin (PENK) mRNA levels in several brain regions of the rat. Twenty micrometer brain sections from striatum, nucleus accumbens, paraventricular nucleus, ventromedial nucleus, periaqueductal grey matter and mammillary nucleus were hybridized with an oligonucleotide probe complementary to PENK using in situ hybridization technique. Subchronic administration of THC or AM356 increased PENK mRNA levels in the ventromedial nucleus of the hypothalamus, (82%) and (39%), in the periaqueductal grey matter, (97%) and (49%), and mammillary nucleus, (43%) and (9%), respectively. In contrast, both drugs were without effect in the striatum and nucleus accumbens. On the other hand, chronic administration of CP-55,940 increased PENK mRNA levels in the striatum (44%), nucleus accumbens (25%), paraventricular (31%) and ventromedial nuclei of the hypothalamus (41%). These results revealed that chronic cannabinoid administration increases opioid gene expression in the rat central nervous system and suggest an interaction between the cannabinoid and enkephalinergic systems that may be part of a molecular integrative response to behavioral and neurochemical alterations that occur in cannabinoid drug abuse.

Topographic localization of calretinin, calbindin, VIP, substance P, CCK and metabotropic glutamate receptor immunoreactive neurons in the supramammillary and related areas of the rat

A detailed description of the localization of neurons containing various neuropeptides in the supramammillary complex (SUM) is provided. Further, the neurochemical character of supramammillohippocampal and supramammilloseptal projecting neurons was investigated. The following experiments were performed: (a) immunocytochemistry for each of the eight different neuropeptides investigated, in animals pretreated or not with colchicine, and perfused in fixative containing or lacking acrolein; (b) a thorough mapping study of the localization of immunolabelled neurons at three rostrocaudal levels; (c) double-tracing retrograde labelling for two-directional neuronal projections combined with immunocytochemistry, to study neurochemical character of the projecting neurons. The observations are: (1) each type of immunolabelled elements, such as calretinin, calbindin, VIP, substance P, CCK and metabotropic glutamate receptor 1a immunopositive neurons has a characteristic localization; (2) no parvalbumin- and enkephalin-containing neurons are present in the SUM; and (3) a small population of calretinin-containing and a small number of calretinin-negative supramammillohippocampal neurons located in the lateral area also project to the medial septum-diagonal band region of the septal complex.

Fkh5-deficient mice show dysgenesis in the caudal midbrain and hypothalamic mammillary body

The murine winged helix gene Fkh5 is specifically expressed in the developing central nervous system (CNS). Early embryonic Fkh5 expression is restricted to the mammiliary body region of the caudal hypothalamus, midbrain, hindbrain and spinal cord. Postnatally, signals persist in specific nuclei of the mammillary body and in the midbrain. We generated Fkh5 deficient mice by homologous recombination to assess its in vivo function. At birth, Fkh5-deficient mice are viable and indistinguishable from wild-type and Fkh5 heterozygous littermates. However, about one third die within the first two days and another fifth before weaning. Surviving Fkh5-deficient mice become growth retarded within the first week and remain smaller throughout their whole life span. Fkh5-deficient females on 129Sv × C57BL/6 genetic background are fertile, but do not nurture their pups. More detailed analysis of Fkh5-deficient brains reveals distinct alterations in the CNS. In the midbrain, mutant mice exhibit reduced inferior colliculi and an overgrown anterior cerebellum. Furthermore, the hypothalamic mammillary body of Fkh5-deficient brains lacks the medial mammillary nucleus. These results suggest that Fkh5 plays a major role during CNS development.

Distinct substance P- and calretinin-containing projections from the supramammillary area to the hippocampus in rats; a species difference between rats and monkeys

Our recent studies showed the co-existence of substance P and calretinin in the supramammillo-hippocampal pathway of monkeys, as well as species differences in the synaptic targets of extrinsic substance P fibers in the hippocampi of monkeys and rats. Experiments used: (1) single and multiple stereotaxic injection of wheat germ agglutinin-conjugated HRP into the hippocampus and immunostaining for substance P in the supramammillary area; (2) colocalization of substance P and calretinin in supramammillary area cells; and (3) colocalization of these two neurochemicals in retrogradely labeled supramammillary projective cells of both male and female rats. These demonstrated: (a) many calretinin- and fewer substance P-immunoreactive neurons retrogradely labeled in the ipsilateral supramammillary area; (b) approximately 74% of all substance P cells contain calretinin and 9% of the calretinin neurons co-contain substance P; and, most importantly (c) none of the retrogradely labeled supramammillary cells colocalize calretinin and substance P. These results indicate the presence of two distinct supramammillo-hippocampal projections in the rat, one that contains substance P and the other calretinin. The latter innervates the same areas as those in the monkey, and the former terminates only in the CA2 hippocampal subfield.

Wernicke's encephalopathy with ballooned neurons in the mamillary bodies: an immunohistochemical study

Two cases of Wernicke's encephalopathy with the rare phenomenon of ballooned neurons in the mamillary bodies are reported. Both patients suffered from acute Wernicke's symptoms starting approximately two weeks before death. The mamillary bodies contained grossly enlarged, ballooned neurons, in one case associated with focal necrosis. The affected neurons were immunoreactive for phosphorylated neurofilament (160 and 200 kDa), and synaptophysin. Ubiquitin and alpha beta-crystallin expression were not detected. The mamillo-thalamic tract appeared normal in both cases. There was a marked associated microglial reaction, as shown by the antibody Ki-MIP. It is concluded that the ballooning of mamillary neurons reflects an acute retrograde reaction to primarily axonal damage. Rather than being a rare manifestation of the disease, these cases may constitute a typical intermediate early stage (10-15 days) in the development of Wernicke's encephalopathy).

A population of supramammillary area calretinin neurons terminating on medial septal area cholinergic and lateral septal area calbindin-containing cells are aspartate/glutamatergic

The excitatory amino acid, aspartate/glutamate content of septal complex calretinin (CR)-, choline acetyltransferase plus substance P-, and Leu-enkephalin (Leu-enk)-containing extrinsic afferents was examined. Experiments were carried out using the transmitter-specific [3H]-D-aspartate retrograde tracer technique in combination with immunostaining for CR, choline acetyltransferase, and Leu-enk. The extrinsic and intrinsic CR innervation of the same brain areas were elucidated on control rats and on animals in which the septum was surgically separated from its ventral afferents. Correlated light and electron microscopic double-immunostaining experiments were used to determine the synaptic connections between CR axon terminals and lateral septal area calbindin (CB)- and medial septal area choline acetyltransferase-immunoreactive neurons. Furthermore, to determine the synaptic power of supramammilloseptal aspartate/glutamatergic neurons on the septal complex, semiquantitative analyses were performed in the supramammillary area on retrogradely (1) [3H]-D-aspartate-radiolabeled and (2) HRP-labeled material. The results demonstrated that a population of the extrinsic CR axons originating in the supramammillary area are aspartate/glutamatergic. These fibers forming asymmetric synaptic contacts terminate on both CB and cholinergic neurons. Intraseptal CR neurons, which establish symmetric synapses, innervate only lateral septal area neurons, including the CB-containing cells. These observations, together with other published data, raise the possibility of a hippocampus-lateral septal (GABAergic CB-containing neurons)-supramammillary area (aspartate/glutamatergic cells)-medial septal (cholinergic neurons)-hippocampus signal loop, which might be involved in the generation and regulation of hippocampal theta rhythm activity.

Fos-like immunoreactivity in the mamillary body and thalamus following injections of muscimol into the ventral tegmental nucleus of Gudden in the rat

In many neurons, increased rates of firing are accompanied by expression of the proto-oncoprotein Fos. The current study examined Fos-like immunoreactivity in the mamillary body and the anterior thalamus following unilateral injections of the inhibitory GABA-A agonist muscimol into the ventral tegmental nucleus of Gudden (VTN). These injections resulted in a marked increase in Fos-like immunoreactivity ipsilaterally in both the medial mamillary nucleus and in its principle thalamic projection targets, the anteroventral and anteromedial thalamic nuclei. Since the projection from the VTN to the mamillary body has been shown to contain a substantial GABAergic component, these results are likely to reflect a disinhibition of mamillothalamic circuitry resulting from suppression of tonic inhibitory inputs arising in the VTN.

Reserpine- and tetrabenazine-sensitive transport of (3)H-histamine by the neuronal isoform of the vesicular monoamine transporter

The transport of (3)H-histamine by the endocrine-specific (VMAT1) and neuronal (VMAT2) isoforms of the vesicular monoamine transporter has been evaluated in digitonin-permeabilized fibroblasts transfected with either VMAT1 or VMAT2. Transport of (3)H-histamine by both VMAT1 and VMAT2 was reserpine-sensitive but only transport by VMAT2 was inhibited by tetrabenazine. Maximal equilibrated levels of (3)H-histamine accumulation by VMAT2 (K(m) 300 mu M) were approximately three times greater than that mediated by VMAT1 when using a subsaturating concentration of exogenous (3)H-histamine (50 mu M). The expression of VMAT2 in histaminergic neurons in the rat brain was examined with polyclonal antipeptide antibodies specific for VMAT1 or VMAT2. VMAT2-positive and tyrosine hydroxylase-negative immunoreactive cell bodies were localized to the ventral part of the posterior hypothalamus in the region of the mamillary nuclei. The transport properties of VMAT2 and the distribution of VMAT2 in cell bodies in the tuberomammillary nucleus of the posterior hypothalamus reported here and the apparent absence of VMAT1 and VMAT2 in tissue mast cells support previous findings of reserpine-sensitive and reserpine-resistant pools of histamine in brain and peripheral tissues.

A persistent sodium current in acutely isolated histaminergic neurons from rat hypothalamus

Histamine neurons acutely dissociated from the tuberomammillary nucleus of the rat hypothalamus were studied in whole-cell and cell-attached patch-clamp experiments. Electrophysiological properties of dissociated cells were found to be similar to those recorded in slice experiments using microelectrodes. Tuberomammillary neurons fired spontaneously and this activity persisted when Cs+ (1.5 mM) was added to, or when K+ was removed from the extracellular solution. In whole-cell experiments a persistent tetrodotoxin-sensitive inward current was recorded. In cell attached recordings voltage-gated sodium channels displayed either normal or non-inactivating behavior. These results provide a further analysis of the properties of histaminergic neurons and indicate that spontaneous activity is intrinsic to individual neurons. Evidence for a non-inactivating tetrodotoxin-sensitive sodium current is presented. Single channel recordings indicate that this current is the result of non-inactivating behavior of sodium channels. Such a current is well suited for biasing tuberomammillary neurons toward spontaneous activity.

Neuronal IFN-gamma in tuberomammillary neurones

Neuronal interferon-gamma (N-IFN-gamma), recently isolated from the nervous system, has a molecular weight distinct from that of lymphocyte-derived IFN-gamma, but crossreacts immunologically and shares certain bioactivities with this cytokine. In the rat brain N-IFN-gamma-immunoreactive perikarya were concentrated in the hypothalamic tuberomammillary nuclei; some immunostained neurones were also detected in the dorsal pontine tegmentum. Immunopositive nerve fibres were profusely distributed through the periventricular hypothalamus and midline thalamus. Scattered fibres occurred diffusely through the brain, ramified in the subpial layer and also surrounded intrathecal vessels. A dense concentration of puncta was detected in the suprachiasmatic nuclei and in the molecular layer of the hippocampal dentate gyrus. A role of N-IFN-gamma in immunological reactions and in modulation of selective brain functions is suggested.

Immunohistochemical localization of GABA in the mammillary complex of the rat

The distribution and synaptic organization of GABAergic elements in the mammillary nuclei of rats have been examined by the immunocytochemical localization of GABA at the light and electron microscope levels. The distribution of GABA-immunoreactive fibres and terminals in the mammillary body is non-homogeneous. By light microscopy, small scattered immunoreactive terminals are observed in the pars medianus, pars posterior and ventral region of the pars medialis of the medial mammillary nucleus. Larger labelled terminals are found in the pars lateralis, the dorsal region of the pars medialis of the medial mammillary nucleus and the lateral mammillary nucleus. At the ultrastructural level, GABA-immunoreactive synaptic endings in the different subdivisions of the medial mammillary nucleus exhibit a widespread somadendritic distribution. By contrast, GABA-immunoreactive terminals within the lateral mammillary nucleus are located predominantly in the neuropil and less frequently on neuronal somata. GABA-immunoreactive synaptic endings contain pleiomorphic synaptic vesicles and have symmetrical synaptic contact zones with the somata and dendrites in the lateral and medial mammillary nuclei. After in vivo inhibition of GABA metabolism with amino-oxyacetic acid, light microscopic examination of the mammillary nuclei reveals numerous small GABA-immunoreactive cells in various subdivisions of the medial mammillary nucleus. No immunoreactive cells are observed, however, in the lateral mammillary nucleus. Electron microscopic examination demonstrates that the GABA-immunoreactive cells are astrocytes. In the labelled astrocytes, immunohistochemical reaction product is localized throughout the nucleus and cytoplasm of the cells, in thin sheet-like processes surrounding neuronal elements and in end-feet lining the basal lamina of capillaries. The results indicate that the mammillary nuclei in the rat receive a strong GABAergic innervation. Most if not all, of the GABA-immunoreactive synaptic endings in the mammillary nuclei probably arise from extrinsic inhibitory sources. The possible sources of the GABA-immunoreactive input to the mammillary complex are discussed.

Multiple neurotransmitters in the tuberomammillary nucleus: comparison of rat, mouse, and guinea pig

Tuberomammillary neurons in the posterior hypothalamus are the sole source of neuronal histamine in adult mammalian brain. In the rat, these cells are reported to contain immunoreactivity for gamma-aminobutyric acid (GABA) and several neuropeptides. We compared the presence of these substances in the tuberomammillary cells of the rat, mouse, and guinea pig. In all three species, all histamine-immunoreactive neuronal cell bodies were positive for GABA. This suggests that GABAergic transmission may be important in tuberomammillary function. No cell bodies immunoreactive for thyrotropin releasing hormone (TRH) were found in the guinea pig or mouse tuberomammillary area. In contrast, about 14% of the histamine-immunoreactive tuberomammillary cells in the rat were TRH-positive. These cells were small or medium-sized and were located only in the medial part of the tuberomammillary complex. An antibody against porcine galanin stained about 45% of the tuberomammillary cell bodies in the rat and about 28% in the mouse, but none in the guinea pig. A large proportion of the cells in the rat and mouse, but none in the guinea pig, were positive for met-enkephalin-arg-phe. In contrast, all histamine-containing tuberomammillary cells in the guinea pig, but none in the rat or mouse, were immunoreactive for met-enkephalin. This may indicate a different expression of proenkephalin-derived peptides in the tuberomammillary neurons in these species. Some substance P-immunoreactive cell bodies were located in the tuberomammillary area in all three species. However, only 3% of the histamine-immunoreactive cell bodies in the rat and mouse but none in the guinea pig were substance P-positive. The neurochemical properties of the tuberomammillary nucleus that exhibited species commonality deserve to be studied neurochemically and electrophysiologically in order to determine the functional relevance of coexisting transmitters in this nucleus.

Distribution of substance P-immunoreactive elements in the preoptic area and the hypothalamus of the rat

The localization and morphology of neurons, processes, and neuronal groups in the rat preoptic area and hypothalamus containing substance P-like immunoreactivity were studied with a highly selective antiserum raised against synthetic substance P. The antiserum was thoroughly characterized by immunoblotting; only substance P was recognized by the antiserum. Absorption of the antiserum with synthetic substance P abolished immunostaining while addition of other hypothalamic neuropeptides had no effect on the immunostaining. The specificity of the observed immunohistochemical staining pattern was further confirmed with a monoclonal substance P antiserum. The distribution of substance P immunoreactive perikarya was investigated in colchicine-treated animals, whereas the distribution of immunoreactive nerve fibers and terminals was described in brains from untreated animals. In colchicine-treated rats, immunoreactive cells were reliably detected throughout the preoptic area and the hypothalamus. In the preoptic region, labeled cells were found in the anteroventral periventricular and the anteroventral preoptic nuclei and the medial and lateral preoptic areas. Within the hypothalamus, immunoreactive cells were found in the suprachiasmatic, paraventricular, supraoptic, ventromedial, dorsomedial, supramammillary, and premammillary nuclei, the retrochiasmatic, medial hypothalamic, and lateral hypothalamic areas, and the tuber cinereum. The immunoreactive cell groups were usually continuous with adjacent cell groups. Because of the highly variable effect of the colchicine treatment, it was not possible to determine the actual number of immunoreactive cells. Mean soma size varied considerably from one cell group to another. Cells in the magnocellular subnuclei of the paraventricular and supraoptic nuclei were among the largest, with a diameter of about 25 microns, while cells in the supramammillary and suprachiasmatic nuclei were among the smallest, with a diameter of about 12 microns. Immunoreactive nerve fibers were found in all areas of the preoptic area and the hypothalamus. The morphology, size, density, and number of terminals varied considerably from region to region. Thus, some areas contained single immunoreactive fibers, while others were innervated with such a density that individual nerve fibers were hardly discernible. During the last decade, knowledge about neural organization of rodent hypothalamic areas and mammalian tachykinin biochemistry has increased substantially. In the light of these new insights, the present study gives comprehensive morphological evidence that substance P may be centrally involved in a wide variety of hypothalamic functions. Among these could be sexual behavior, pituitary hormone release, and water homeostasis.

Alterations of atrial natriuretic factor in mammillary bodies and median eminence from hypertensive and experimental brain hemorrhage rats

The results of the present study demonstrate that atrial natriuretic factor (ANF) in the mammillary bodies has a dynamic change, while ANF in the median eminence is relatively constant in the course of the increase of blood pressure. It suggests that ANF in the mammillary bodies might take part in the regulation of blood pressure and ANF in the median eminence mainly participates in the functional regulation of the adenohypophysis.

Patterns of histamine release in the brain

The pattern of histamine release has been investigated in various brain areas of anaesthetized cats and conscious, freely moving rats by the push-pull technique. In the hypothalamus, medial amygdaloid nucleus and mamillary body of the anaesthetized cat, histamine was found to be released according to an ultradian rhythm with a frequency of 1 cycle per 1-2 h. Additionally, oscillations have been observed in the medial amygdaloid nucleus and mamillary body with a frequency of 1 oscillation per 10 min. In the posterior hypothalamus of the conscious rat, histamine is also released rhythmically with a frequency of 1 cycle per 1.5 h. Moreover, the release rate of histamine is increased in the night.