ABCG2/BCRP transport mechanism revealed through kinetically excited targeted molecular dynamics simulations

ABCG2/BCRP is an ABC transporter that plays an important role in tissue protection by exporting endogenous substrates and xenobiotics. ABCG2 is of major interest due to its involvement in multidrug resistance (MDR), and understanding its complex efflux mechanism is essential to preventing MDR and drug-drug interactions (DDI). ABCG2 export is characterized by two major conformational transitions between inward- and outward-facing states, the structures of which have been resolved. Yet, the entire transport cycle has not been characterized to date. Our study bridges the gap between the two extreme conformations by studying connecting pathways. We developed an innovative approach to enhance molecular dynamics simulations, ‘kinetically excited targeted molecular dynamics’, and successfully simulated the transitions between inward- and outward-facing states in both directions and the transport of the endogenous substrate estrone 3-sulfate. We discovered an additional pocket between the two substrate-binding cavities and found that the presence of the substrate in the first cavity is essential to couple the movements between the nucleotide-binding and transmembrane domains. Our study shed new light on the complex efflux mechanism, and we provided transition pathways that can help to identify novel substrates and inhibitors of ABCG2 and probe new drug candidates for MDR and DDI.

Substance P-Immunoreactive Fiber Varicosities Appear to Innervate Galaninergic Perikarya in the Human Hypothalamus

Introduction: Substance P (SP) is a member of the tachykinin family. In the central nervous system, SP participates among others, in the regulation of pain, learning, memory, emotion, and sexual functions. In the periphery, SP affects the gastrointestinal, cardiovascular, and urinary systems. Galanin, similarly to SP, appears to be involved in wide range of physiologic functions, including cognition, waking and sleep, feeding, mood, blood pressure, reproduction, and development, where acts as a trophic factor. The similar distribution of SP-immunoreactive (SP-IR) fibers and galanin-IR perikarya in the human hypothalamus suggests functional interaction between these neuropeptides. Methods: We have utilized double-label immunohistochemistry to reveal these putative juxtapositions. Results: The majority of galanin-IR neurons receive contacting SP-IR fibers that often cover a significant area of the galaninergic perikarya forming multiple en passant type contacts. These SP-galanin juxtapositions are located mainly in the basal part of the infundibulum/median eminence, populating the basal periventricular region as well as the basal perifornical area. Discussion: The density and the morphology of these associations suggest that these contacts are functional synapses and therefore may represent the morphological substrate of the control of SP on multiple functions regulated/modulated by galanin. SP via galanin may modulate anterior pituitary hormone secretion, as contrary to SP, high density of galanin immunoreactivity is present in the median eminence, and by innervating galanin-IR neurons projecting to other parts of the brain, SP can modulate indirectly their activities. Impact statement The present study is the first describing juxtapositions between the substance P (SP)-immunoreactive (IR) and galanin-IR neurons in the human hypothalamus. These juxtapositions may be functional synapses and they may represent the morphological substrate of the control of SP on the galaninergic system. SP via galanin may modulate anterior pituitary hormone secretion, as contrary to SP, high density of galanin immunoreactivity is present in the median eminence. Galanin, released into the hypothalamo-hypophyseal circulation, can reach the anterior pituitary and function as a hypophysiotropic substance and regulates anterior pituitary hormone secretion. SP by innervating galanin-IR neurons, which project to other parts of the brain, can modulate indirectly their activities.

Thyrotropin-releasing hormone axonal varicosities appear to innervate dopaminergic neurons in the human hypothalamus

Thyrotropin-releasing hormone (TRH) has a critical role in the central regulation of thyroid-stimulating hormone (TSH) from the anterior pituitary, and subsequently, thyroid hormone secretion from the thyroid gland. In addition to its role in the regulation of HPT axis, TRH is a potent regulator of prolactin (PRL) secretion by stimulating PRL secretion either directly from lactotrophs or indirectly via its action on the tuberoinfundibular dopamine (TIDA) neurons. In rodents, the TRH neurons which regulate TSH and thyroid hormone secretion, called hypophysiotropic TRH neurons, are in the medial subdivision of the parvicellular paraventricular nucleus (PVN). In humans, the PVN also contains a large population of TRH neurons, especially in its medial part, but the location of hypophysiotropic TRH neurons is not yet known. In addition to regulating TSH and PRL secretion, TRH also functions as a neurotransmitter/neuromodulator. In rodents and teleosts, TRH axons densely innervate TIDA neurons to inhibit tyrosine hydroxylase (TH) biosynthesis, neuronal firing, and dopamine turnover which may contribute to increasing PRL secretion. No such connections have been reported in humans, although dopaminergic neurons express TRH receptors and TRH also regulates PRL secretion. The objectives of this study were to map TRH-IR and TH-IR structures in the human hypothalamus with single-label light microscopic immunocytochemistry and study their interaction with double-label light microscopic immunocytochemistry. We show that TRH-IR nerve terminals densely surround TH-IR neurons (perikarya and dendrites) in the infundibulum of the human hypothalamus. The micrographs illustrating these juxtapositions were taken by Olympus BX45 microscope equipped with a digital camera and with 100X oil immersion objective. Composite images were created from the consecutive micrographs if the neurons were larger than the frame of the camera, using Adobe Photoshop software. As no gaps between TRH-IR and TH-IR elements were seen, these contacts may be functional synapses by which TRH regulates the activity of dopaminergic neurons and subsequently TSH and PRL secretion.

Intimate associations between the endogenous opiate systems and the growth hormone-releasing hormone system in the human hypothalamus

Although it is a general consensus that opioids modulate growth, the mechanism of this phenomenon is largely unknown. Since endogenous opiates use the same receptor family as morphine, these peptides may be one of the key regulators of growth in humans by impacting growth hormone (GH) secretion, either directly, or indirectly, via growth hormone-releasing hormone (GHRH) release. However, the exact mechanism of this regulation has not been elucidated yet. In the present study we identified close juxtapositions between the enkephalinergic/endorphinergic/dynorphinergic axonal varicosities and GHRH-immunoreactive (IR) perikarya in the human hypothalamus. Due to the long post mortem period electron microscopy could not be utilized to detect the presence of synapses between the enkephalinergic/endorphinergic/dynorphinergic and GHRH neurons. Therefore, we used light microscopic double-label immunocytochemistry to identify putative juxtapositions between these systems. Our findings revealed that the majority of the GHRH-IR perikarya formed intimate associations with enkephalinergic axonal varicosities in the infundibular nucleus/median eminence, while endorphinergic-GHRH juxtapositions were much less frequent. In contrast, no significant dynorphinergic-GHRH associations were detected. The density of the abutting enkephalinergic fibers on the surface of the GHRH perikarya suggests that these juxtapositions may be functional synapses and may represent the morphological substrate of the impact of enkephalin on growth. The small number of GHRH neurons innervated by the endorphin and dynorphin systems indicates significant differences between the regulatory roles of endogenous opiates on growth in humans.

Glycosaminoglycans and neuroprotection

Glycosaminoglycans (GAGs) are basic building blocks of the ground substance of the extracellular matrix and present at the cellular level as an important component of the glycocalyx covering the cell membrane. In addition to the general role of GAGs in maintaining the integrity of the cell and extracellular matrix by retaining water, certain GAGs exhibit anticoagulant and neuroprotective properties and serve as cell-surface receptors for various molecules. Although heparin, a highly sulfated GAG, has been used as a drug for more than 70 years due to its anticoagulant attributes, the neuroprotective properties of GAGs came into focus only in recent years. The discovery of some of the roles GAGs play in the pathomechanism of numerous neurodegenerative disorders as well as shedding light on the neuroprotective properties of these compounds in animal studies raised the possibility that GAGs may provide an entirely new avenue in the treatment of neurodegenerative diseases. Indeed, some GAGs were successfully used to improve the cognitive function of patients with various neurodegenerative conditions (Ban et al. (1991, 1992); Conti et al. (1989a, b); Passeri and Cucinotta, (1989); Santini (1989). Although the mechanism by which the GAGs exhibit neuroprotective properties is not entirely clear, there is a general consensus that the major factors of the neuroprotective attributes of GAGs include the impact of GAGs on amyloidogenesis and the regulatory action of GAGs in the apoptotic pathway.

Catecholaminergic axonal varicosities appear to innervate growth hormone-releasing hormone-immunoreactive neurons in the human hypothalamus: the possible morphological substrate of the stress-suppressed growth

CONTEXT

Stress is considered to be a major factor in the regulation of growth. Psychosocial dwarfism, characterized with short stature, delayed puberty, and depression, is typically preceded by psychological harassment or stressful environment. It has been observed that stress suppresses GH secretion, possibly via the attenuation of GHRH secretion. However, the exact mechanism of the impact of stress on growth has not been elucidated yet.

OBJECTIVE

Our previous studies revealed intimate associations between neuropeptide Y (NPY)-immunoreactive (IR) axonal varicosities and GHRH-IR perikarya in the human hypothalamus. Because NPY is considered to be a stress molecule, NPY-GHRH juxtapositions may represent an important factor of stress-suppressed GHRH release. In addition to NPY, catecholamines are among the major markers of stress. Thus, in the present study, we examined the putative juxtapositions between the catecholaminergic tyrosine hydroxylase (TH)-/dopamine-β-hydroxylase-/phenylethanolamine N-methyltransferase-IR and GHRH-IR neural elements in the human hypothalamus. To reveal these juxtapositions, double-label immunohistochemistry was used.

RESULTS

Our findings revealed that the majority of the GHRH-IR perikarya formed intimate associations with TH-IR fiber varicosities. The majority of these juxtapositions were found in the infundibular nucleus/median eminence.

CONCLUSIONS

The lack of phenylethanolamine N-methyltransferase-GHRH associations and the small number of dopamine-β-hydroxylase-GHRH juxtapositions suggest that the vast majority of the observed TH-GHRH juxtapositions represent dopaminergic associations. The density of the abutting TH-IR fibers on the surface of the GHRH perikarya suggests that these juxtapositions may be functional synapses, and thus, in addition to NPY, catecholamines may regulate GHRH secretion via direct synaptic mechanisms.

A putative morphological substrate of the catecholamine-influenced neuropeptide Y (NPY) release in the human hypothalamus

Neuropeptide Y (NPY) is a 36 amino acid peptide, which among others, plays a pivotal role in stress response. Although previous studies confirmed that NPY release is increased by stress in several species, the exact mechanism of the stress-induced NPY release has not been elucidated yet. In the present study, we examined, with morphological means, the possibility that catecholamines directly influence NPY release in the human hypothalamus. Since the use of electron microscopic techniques is virtually impossible in immunostained human samples due to the long post mortem time, double-label immunohistochemistry was utilised in order to reveal the putative catecholaminergic-NPY associations. The present study is the first to demonstrate juxtapositions between the catecholaminergic, tyrosine hydroxylase (TH)/dopamine-beta hydroxylase (DBH)-immunoreactive (IR) and NPY-IR neural elements in the human hypothalamus. These en passant type associations are most numerous in the infundibular and periventricular areas of the human diencephalon. Here, NPY-IR neurons often form several contacts with catecholaminergic fibre varicosities, without any observable gaps between the contacting elements, suggesting that these juxtapositions may represent functional synapses. The lack of phenylethanolamine N-methyltransferase (PNMT)-NPY juxtapositions and the relatively few observed DBH-NPY associations suggest that the vast majority of the observed TH-NPY juxtapositions represent dopaminergic synapses. Since catecholamines are known to be the crucial components of the stress response, the presence of direct, catecholaminergic (primarily dopaminergic)-NPY-IR synapses may explain the increased NPY release during stress. The released NPY in turn is believed to play an active role in the responses that are directed to maintain the homeostasis during stressful conditions.

Distribution and morphology of the juxtapositions between growth hormone-releasing hormone-(ghrh)-immunoreactive neuronal elements

Previous studies revealed that growth hormone-releasing hormone (GHRH)-immunoreactive (IR) neurons form a circumscribed cell group in the basal infundibulum/median eminence of the human hypothalamus. GHRH from these neurons is released into the hypothalamo-hypophyseal portal circulatory system in a pulsatile manner. It is a common consensus that the pulsatile release of GHRH is the main driving force behind the pulsatile release of growth hormone (GH) and may contribute to the regulation of other hypothalamic functions. The pulsatile release of GHRH requires synchronized activity of GHRH-IR neurons. However, the morphological basis of this synchronization between the GHRH-IR neural elements has not been elucidated yet. Since the utilization of electron microscopy combined with immunohistochemistry is virtually impossible in the human brain due to the long post mortem period, immunohistochemistry, evaluated with oil immersion light microscopy, was used in order to reveal the associations between the GHRH elements. Numerous GHRH-GHRH juxtapositions have been detected in the infundibular area/median eminence, where GHRH-IR axonal varicosities often formed multiple contacts with GHRH-IR perikarya. Examination of these associations with high magnification oil immersion light microscopy revealed (1) axonal swellings at the site of the contacts and (2) no gaps between the contacting elements suggesting that these juxtapositions may be functional synapses. The large number of GHRH-GHRH juxtapositions in the infundibular area/median eminence suggests that these synapse-like structures may represent the morphological substrate of the synchronized activity of GHRH neurons that in turn may result in the pulsatile release of GHRH in human.

Distribution and morphology of the catecholaminergic neural elements in the human hypothalamus

Previous studies have demonstrated that catecholaminergic, tyrosine hydroxylase (TH)-immunoreactive (IR) perikarya and fibers are widely distributed in the human hypothalamus. Since TH is the key and rate-limiting enzyme for catecholaminergic synthesis, these IR neurons may represent dopaminergic, noradrenergic or adrenergic neural elements. However, the distribution and morphology of these neurotransmitter systems in the human hypothalamus is not entirely known. Since the different catecholaminergic systems can be detected by identifying the neurons containing the specific key enzymes of catecholaminergic synthesis, in the present study we mapped the catecholaminergic elements in the human hypothalamus using immunohistochemistry against the catecholaminergic enzymes, TH, dopamine beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT). Only a few, PNMT-IR, adrenergic neuronal elements were found mainly in the infundibulum and the periventricular zone. DBH-IR structures were more widely distributed in the human hypothalamus occupying chiefly the infundibulum/infundibular nucleus, periventricular area, supraoptic and paraventricular nuclei. Dopaminergic elements were detected by utilizing double label immunohistochemistry. First, the DBH-IR elements were visualized; then the TH-IR structures, that lack DBH, were detected with a different chromogen. In our study, we conclude that all of the catecholaminergic perikarya and the majority of the catecholaminergic fibers represent dopaminergic neurons in the human hypothalamus. Due to the extremely small number of PNMT-IR, adrenergic structures in the human hypothalamus, the DBH-IR fibers represent almost exclusively noradrenergic neuronal processes. These findings suggest that the juxtapositions between the TH-IR and numerous peptidergic systems revealed by previous reports indicate mostly dopaminergic synapses.

Isolation and characterization of nodulation genes from Bradyrhizobium sp. (Vigna) strain IRc 78

An 11.76-kilobase-pair (kb) segment of DNA from Bradyrhizobium sp. (Vigna) strain IRc 78 that hybridizes to nodulation genes of Rhizobium meliloti strain 41 was isolated. Hybridization of the 11.76-kb DNA fragment to DNA from other Bradyrhizobium species revealed a high degree of sequence conservation in this region. Transfer of the 11.76-kb segment to nodulation-defective (Nod(-)) mutants of R. meliloti restored their ability to induce nodules on Medicago sativa (alfalfa). Mutants of strain IRc 78 generated by Tn5 mutagenesis of the 11.76-kb segment fell into three classes according to their symbiotic reaction with Vigna unguiculata (cowpea). Class I mutants of strain IRc 78 were unable to induce root-hair curling or to nodulate; class II induced small, ineffective nodules; and class III showed delayed and decreased nodulation with reduction in amount of nitrogen fixed. Furthermore, in contrast to the wild-type strain, class I mutants could not induce nodules on Glycine max (soybean), Cajanus cajan (pigeon pea), or Arachis hypogaea (peanut). This finding suggests a common function of the 11.76-kb region in the infection of host plants by Bradyrhizobium either through root hairs or by "crack entry."

Putative proprioceptive function of the pelvic ligaments: biomechanical and histological studies

The sacrospinous (SS) and sacrotuberous (ST) ligaments of the pelvic ring are known as mechanical stabilisers of the pelvic girdle, primarily against rotational forces in the sagittal and horizontal planes. Earlier studies, however, raised the possibility that ST/SS ligaments possess significant proprioceptive function, while the mechanical role of these ligaments in maintaining the structural integrity of the pelvis is of less importance. The aim of this study is to determine whether the function of these ligaments is strictly to provide mechanical stability or if they have any additional functional properties, i.e., proprioception. In order to reveal the function of the SS/ST ligaments, biomechanical studies of cadaver pelvis were used along with the histological analysis of the ligaments. Following measurements to determine the accurate mechanical role of the pelvic ligaments, the strength of these ligaments was significantly less than we earlier expected. For this reason other functions of the SS/ST ligaments were considered, including the proprioceptive role. Indeed, histological studies revealed ramifying nerve terminals in the SS/ST ligaments. These terminals may represent the morphological substrate of the proprioceptive function associated with the ligaments. Our studies revealed that SS/ST ligaments might have a significant proprioceptive function providing information of the position of the pelvis. Consequently, the mechanical role of the ligaments in maintaining the structural integrity of the pelvis may be significantly less than previously assumed. Understanding the function of the SS/ST ligaments is crucial for providing more precise guidelines for patient management with injuries to the posterior pelvic region.

Neuroprotective properties of glycosaminoglycans: potential treatment for neurodegenerative disorders

Previous studies suggest that proteoglycans and glycosaminoglycans (GAGs) may play an important role in the pathogenesis and/or alleviation of neurodegenerative disorders, including Alzheimer's disease (AD). Proteoglycans increase the formation of neurofibrillary tangles, and stimulate the aggregation of beta-amyloid (Abeta). This effect, on the other hand, is believed to be competitively inhibited by certain GAGs. Over the past few years, we have examined the neuroprotective properties of Neuroparin (C3), a low-molecular-weight GAG (approx. 2.1 kDa), in animal models of lesions characteristic of AD. Neuroparin is composed of 4-10 oligosaccharides, and it is derived from heparin involving depolymerization of heparin by gamma irradiation. In our experiments, Neuroparin protected against cholinergic lesions induced by intracerebroventricular injection of a specific cholinotoxin, AF64A, in rats. Administration of Neuroparin attenuated AF64A-stimulated, low-affinity nerve growth factor receptor-immunoreactive axonal varicosities in the rat septum, and increased arborization of hippocampal CA1 neurons. Neuroparin also reduced the septal caspase 3 immunoreactivity induced by AF64A treatment. Moreover, Neuroparin reduced tau 2 immunoreactivity in the rat hippocampus, stimulated by intra-amygdaloid injection of Abeta(25-35). These findings are in good agreement with our previous data indicating a neuroprotective role of GAGs. These results, plus others, all suggest that Neuroparin may possess neuroprotective properties against many of the characteristic neural lesions in AD. Since our pharmacokinetic studies revealed that Neuroparin is capable of crossing the blood-brain barrier, Neuroparin may, conceivably, open an entirely new avenue in the treatment of neurodegenerative disorders. Phase I studies have been completed, and have proven to be extremely supportive in that regard.

Vascular anomalies in a case of situs inversus

Situs inversus is a developmental condition in which the thoracic and abdominal organs fail to negotiate their normal migration patterns and the result is a mirror-image arrangement of these viscera. The literature provides evidence that individuals with this condition have a higher incidence of other congenital malformations (e.g. heart anomalies). Here we describe the dissection of a 71 year-old female cadaver with situs inversus, in which we discovered multiple anomalous vessels associated with the coeliac trunk directed toward the liver. In addition, we identified the inferior vena cava on the left side and a persistent supracardinal vein on the right, constituting a double inferior vena cava. Finally, we identified multiple abnormal venous channels associated with the sub-renal inferior vena cava. These vascular patterns are indeed a rare finding and have surgical implications but may indicate a higher incidence of vascular anomalies in cases of situs inversus.

Three-dimensional representation of the neurotransmitter systems of the human hypothalamus: inputs of the gonadotrophin hormone-releasing hormone neuronal system

The gonadotrophin-releasing hormone (GnRH) represents the final common pathway of a neuronal network that integrates multiple external and internal factors to control fertility. Among the many inputs GnRH neurones receive, oestrogens play the most important role. In females, oestrogen, in addition to the negative feedback, also exhibits a positive feedback influence upon the activity and output of GnRH neurones to generate the preovulatory luteinising hormone surge and ovulation. Until recently, the belief has been that the GnRH neurones do not contain oestrogen receptors and that the action of oestrogen upon GnRH neurones is indirect, involving several, oestrogen-sensitive neurotransmitter and neuromodulator systems that trans-synaptically regulate the activity of the GnRH neurones. Although this concept still holds for humans, recent studies indicate that oestrogen receptor-beta is expressed in GnRH neurones of the rat. This review provides three dimensional stereoscopic images of GnRH-immunoreactive (IR) and some peptidergic (neuropeptide Y-, substance P-, beta-endorphin-, leu-enkaphalin-, corticotrophin hormone-releasing- and galanin-IR) and catecholaminergic neurones and the communication of these potential oestrogen-sensitive neuronal systems with GnRH neurones in the human hypothalamus. Because the post-mortem human tissue does not allow the electron microscopic identification of synapses on GnRH neurones, the data presented here are based on light microscopic immunocytochemical experiments using high magnification with oil immersion, semithin sections or confocal microscopy.

Low intracerebroventricular doses of cholinotoxin AF64A do not affect the morphology of gonadotropin hormone-releasing hormone (GnRH)-immunoreactive fibers in the rat septum

Ethylcholine aziridinium (AF64A) induces cholinergic lesion in animal models of AD. Although higher concentrations of AF64A are known to induce nonspecific, cholinergic, and non-cholinergic lesions, low concentrations are believed to be selectively cholinotoxic. However, morphological evidence of this phenomenon has not been demonstrated yet. The present study demonstrates that while AF64A damaged septal cholinergic fibers, periventricular GnRH-immunoreactive fibers remained intact, confirming the highly selective cholinotoxicity of AF64A at appropriate concentrations.

Low molecular weight glycosaminoglycan C3 attenuates AF64A-stimulated, low-affinity nerve growth factor receptor-immunoreactive axonal varicosities in the rat septum

Glycosaminoglycans (GAGs) play a pivotal role in the pathogenesis of Alzheimer's disease (AD). Although, as we have shown earlier, a low molecular weight GAG, C3, protects against ethylcholine aziridinium (AF64A)-induced cholinergic damage, and against A(beta)-induced tau-2-immunoreactivity (IR), the mechanism of the neuroprotective effect of GAGs is not yet known. Several clues exist. Previous studies in rats revealed that continuous NGF infusion (icv) after AF64A injection increases septal ChAT and AChE activities. Moreover, C3 increases axonal outgrowth in the rat hippocampus, raising the possibility of a NGF-receptor mediated neuroprotection. Furthermore, it has been reported that NGF expression is increased in the septum following AF64A administration. To study the question regarding the mechanism of neuroprotective action of GAGs, AF64A, a selective cholinotoxin, was administered stereotaxically, bilaterally, into the lateral ventricles of Fischer albino male rats (1 nmol/2 microl/side). In order to establish the effect of C3 on the expression of the NGF receptor-IR elements, C3 was administered orally (25 mg/kg, once a day), by gavage, 7 days before, and 7 days after the AF64A injection. NGF receptor immunohistochemistry revealed that AF64A induced the appearance of NGF-receptor-IR axonal varicosities in the rat medial septum. These varicose fibers were attenuated by 14 days' administration of C3. The possible explanation of our data may be that C3 increases NGF synthesis in the lateral septum. The increased level of NGF could suppress the increased, AF64A-induced NGF receptor expression in the medial septal nucleus. These results further accentuate our earlier observations that C3 may have potential as a therapeutic agent in AD and other neurodegenerative disorders.

Glycosaminoglycan C3 protects against AF64A-induced cholinotoxicity in a dose-dependent and time-dependent manner

Several studies revealed that proteoglycans (PGs) and glycosaminoglycans (GAGs) play a pivotal role in the pathogenesis of Alzheimer's disease (AD). PGs have affinity to amyloid beta (Abeta) and protect it against proteolysis, and the consequent aggregation is the cause of neurotoxicity. This effect is believed to be attenuated by GAGs. Moreover, a low-molecular-weight GAG C3 derived from unfractionated heparin has been reported to protect against Abeta-induced tau-2 immunoreactivity and cholinergic damage induced by a cholinotoxin, AF64A, in rat. However, the optimal dose and the timeframe of administration of C3 are still unknown. In our studies, we revealed the concentration-dependent and time-dependent effects of C3 on AF64A-induced cholinergic lesion in rat. C3 was administered orally in 5, 10, and 25 mg/kg/day concentration, 7 days before and/or 7 days after intracerebroventricular (i.c.v.) AF64A administration. Our results have shown that 25 mg/kg/day C3 effectively protects against AF64A-generated cholinotoxicity if administered both 7 days before and 7 days after the AF64A injection. In contrast to these findings, administration of 5 or 10 mg/kg/day C3 or 25 mg/kg/day C3, given 7 days before or 7 days after stereotaxic AF64A injection, did not show cholinoprotective effects. In conclusion, the time-dependent effects of C3 on AF64A-induced cholinergic lesion suggest that C3 may act via the processes of both neuroprotection and neurorepair. Moreover, the effects of C3 depend largely on the administered dose of this low-molecular-weight GAG. The present findings also indicate that C3, administered in the effective concentration and timeframe, may play a pivotal role in the treatment of AD.

Desensitization of 5-HT1A receptors by 5-HT2A receptors in neuroendocrine neurons in vivo

An imbalance between serotonin-2A (5-HT2A) and 5-HT1A receptors may underlie several mood disorders. The present studies determined whether 5-HT2A receptors interact with 5-HT1A receptors in the rat hypothalamic paraventricular nucleus (PVN). The sensitivity of the hypothalamic 5-HT1A receptors was measured as oxytocin and adrenocorticotropic hormone (ACTH) responses to the 5-HT1A receptor agonist (+)-8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide [(+)8-OH-DPAT] (40 microg/kg s.c.). The 5-HT(2A/2C) receptor agonist (-)DOI [(-)-1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane HCl] (1 mg/kg s.c.) injected 2 h prior to (+)8-OH-DPAT significantly reduced the oxytocin and ACTH responses to (+)8-OH-DPAT, producing a heterologous desensitization of the 5-HT1A receptors. Microinjection of the 5-HT2A receptor antagonist MDL100,907 [(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol; 0, 10, or 20 nmol, 15 min prior to (-)DOI] into the PVN dose-dependently prevented the desensitization of 5-HT1A receptors induced by the 5-HT2A receptor agonist (-)DOI. Double-label immunocytochemistry revealed a high degree of colocalization of 5-HT1A and 5-HT2A receptors in the oxytocin and corticotropin-releasing factor neurons of the PVN. Thus, activation of 5-HT2A receptors in the PVN may directly induce a heterologous desensitization of 5-HT1A receptors within individual neuroendocrine cells. These findings may provide insight into the long-term adaptation of 5-HT1A receptor signaling after changes in function of 5-HT2A receptors; for example, during pharmacotherapy of mood disorders.

Protection against inflammatory neurodegeneration and glial cell death by 7β-hydroxy epiandrosterone, a novel neurosteroid

It has been demonstrated that neuroprotective effects of dehydroepiandrosterone (DHEA) may be mediated by its 7alpha- and 7beta-hydroxy derivatives. Epiandrosterone is also converted to 7beta-hydroxy epiandrosterone (7beta-OH EPIA) in numerous tissues. The aim of the present study was to establish whether treatment with 7beta-hydroxy epiandrosterone has a neuroprotective effect in animal models of Alzheimer's disease (AD) lesions. Intra-amygdaloid administration of amyloid beta [Abeta(25-35)] increased the number of tau-positive cells in the ipsilateral hippocampus. Intracerebroventricular administration of ethylcholine aziridinium (AF64A) caused cholinergic damage in the septum, and glial lesions in the lateral septal nucleus and in the lateral zones of the hippocampus. These effects were almost completely prevented when animals were treated subcutaneously (b.i.d.) for 10 days with 0.1 mg/kg 7beta-hydroxy epiandrosterone. These findings indicate that 7beta-hydroxy epiandrosterone has powerful cytoprotective effects suggesting that (a) this neurosteroid may have therapeutic potential in various neurodegenerative conditions such as Alzheimer's disease, and (b) 7beta-hydroxy steroids may constitute a novel class of endogenous neuroprotective agents.

Protective effect of the heparin-derived oligosaccharide C3, on AF64A-induced cholinergic lesion in rats

Alzheimer's disease (AD) literature indicates that glycosaminoglycans (GAGs) may prevent proteoglycan-induced amyloid-beta (Abeta) aggregation, decrease Abeta-induced tau-2 immunoreactivity, and increase the axonal growth and arborization of hippocampal neurons. However, there is no information about the impact of GAGs on cholinergic lesions. Here, AF64A was administered stereotaxically into the lateral ventricles of rats, at doses that are selective for cholinotoxicity (1 and 2 nmol). The heparin-derived oligosaccharide (HDO), C3 (25mg/kg), was administered orally, once daily for 7 days before, and 7 days after AF64A administration. Choline acetyltransferase (ChAT) immunohistochemistry revealed that C3 administration reduced AF64A-induced cholinergic damage in the septum and cingulum bundle. Quantitative neuronal cell counts showed that C3 attenuated, by 60%, the decrease in cell number in the medial septum. Enzyme analysis showed that C3 also significantly restored ChAT (30%) and acetylcholinesterase (AChE) enzyme activity (45%), which had been diminished by AF64A. Our data suggest that, in addition to its effects of anti-Abeta aggregation, anti-Abeta-induced tau-2 immunoreactivity, and neurotrophic effects, C3 also effectively reduces AF64A-induced cholinergic damage; hence it may have potential therapeutic value in AD patients.

Dose-dependent effect of cholinotoxin AF64A on the cholinergic elements of the cingulum bundle in rat

Previous studies revealed that cholinergic neurons possessing long axons are extremely sensitive to ethylcholine aziridinium ion (AF64A) administration [Neuropharmacology 31 (1992) 397]. In the present paper we examined the effect of AF64A on the cholinergic elements of the cingulum bundle. Seven days after AF64A administration choline acetyltransferase (ChAT)-immunoreactive fibers were extensively damaged on the dorsal part of cingulum bundle. These findings are the first reporting damage by AF64A to this brain region.

Evidence that 5-HT2A receptors in the hypothalamic paraventricular nucleus mediate neuroendocrine responses to (-)DOI

The present study determined whether the serotonin2A (5-HT2A) receptors in the hypothalamic paraventricular nucleus mediate the neuroendocrine responses to a peripheral injection of the 5-HT2A/2C receptor agonist (-)DOI [(-)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane]. The 5-HT2A receptor antagonist MDL100,907 ((+/-)-alpha(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol), the 5-HT2C receptor antagonist SB-242084 (6-chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-indoline), or vehicle were microinjected bilaterally through a chronically implanted double-barreled cannula into the hypothalamic paraventricular nucleus 15 min before a peripheral injection of (-)DOI in conscious rats. (-)DOI significantly elevated plasma levels of oxytocin, prolactin, ACTH, corticosterone, and renin. Neither the 5-HT2A receptor antagonist nor the 5-HT2C receptor antagonist, injected alone, altered the basal levels of these hormones. MDL100,907 (0.748, 7.48, and 18.7 nmol) dose dependently inhibited the (-)DOI-induced increase in all of the hormones except corticosterone. In contrast, SB-242084 (10 nmol) did not inhibit (-)DOI-increased hormone levels. To confirm the presence of 5-HT2A receptors in the hypothalamic paraventricular nucleus, 5-HT2A receptors were mapped using immunohistochemistry. Densely labeled magnocellular neurons were observed throughout the anterior and posterior magnocellular subdivisions of the hypothalamic paraventricular nucleus. Moderately to densely labeled cells were also observed in parvicellular regions. Thus, it is likely that 5-HT2A receptors are present on neuroendocrine cells in the hypothalamic paraventricular nucleus. These data provide the first direct evidence that neuroendocrine responses to a peripheral injection of (-)DOI are predominantly mediated by activation of 5-HT2A receptors in the hypothalamic paraventricular nucleus.

The blood-brain barrier accessibility of a heparin-derived oligosaccharides C3

Although heparin-derived oligosaccharide(s) (HDO) have been clinically used for the management of neurological disorders, such as stroke and Alzheimer's disease (AD), very little information on the mechanism of their therapeutic action is known. To test the hypothesis that HDO may pass through the blood-brain barrier (BBB) to mediate their effects, a pharmacodynamic (PD) model was developed and the presence of HDO in the cerebrospinal fluid (CSF) was used as a BBB accessibility index. Rats were treated with an ultralow molecular weight (MW) heparin fragment C3 via the intravenous or subcutaneous routes at 5-10 mg/kg. At varying periods, the plasma, CSF, and brain samples were collected, and functional anti-factor Xa activities were measured to quantitate the CSF/plasma ratios (CPR) and the brain uptake. C3 showed CPR of 1.7% and 0.8% after intravenous and subcutaneous injections, respectively. These findings were verified by intravenous administration of tritium-labeled C3 followed by detection of the radioactivity in the CSF and brain homogenates. These data suggest that ultralow MW HDO may pass through the BBB.

Molecular and biochemical profiling of a heparin-derived oligosaccharide, C3

This study was designed to characterize a heparin-derived oligosaccharide (HDO), C3, using chemical and biochemical methods. Although previous studies have suggested C3 as a promising compound in the treatment of Alzheimer's disease (AD), its molecular and biochemical properties are still unknown. In this study, the molecular profiles and anticoagulant effects of C3 were investigated. To characterize the molecular and biochemical properties of C3, gel permeation chromatography (GPC), polyacrylmide gel electrophoresis (PAGE), radiolabeling and anticoagulant assays, such as activated partial thromboplastin time (APTT), Heptest, and anti-factor Xa assay, were used. The GPC profile revealed that C3 was an ultra-low-molecular-weight (MW) heparin mixture. The multiple components in C3 were studied with PAGE analysis. Tritium-labeled C3 exhibited similar biological properties as nonlabeled materials. The biological assays showed that C3 and its components exhibited weak anticoagulant effect. These results demonstrated the applicability of the combination of GPC, PAGE, and coagulation assays to characterize the molecular and biochemical profile of HDO. In addition, the low anticoagulant effect of C3 suggests that this compound could be a relatively low-risk adjunct in the treatment of AD.

Oral and subcutaneous administration of the glycosaminoglycan C3 attenuates Abeta(25-35)-induced abnormal tau protein immunoreactivity in rat brain

High molecular weight glycosaminoglycans (GAG) and proteoglycans (PG) affect pathological changes of the brain in Alzheimer's disease (AD). PG stimulate the processing and aggregation of amyloid-beta (Abeta), protect the protein from proteolysis, and increase the formation of neurofibrillary tangles by inducing the hyperphosphorylation of tau protein. These effects may be competitively inhibited by GAG. We have studied the effects of orally (by gavage) and subcutaneously (s.c.) administered low molecular weight heparin, C3 (4-10 oligosaccharides; MW = 2.1 kDa; USP value = 12 U/mg), on abnormal tau-2 protein immunoreactivity in the rat hippocampus following a single, unilateral intra-amygdaloid administration of Abeta(25-35). Oral administration of C3 (25 mg/kg; once daily) was initiated 3 days prior to Abeta(25-35) administration, and was continued daily for an additional 14 days. S.c. administration of C3 (2.5 mg/kg, twice daily), was started 3 days prior to, and was continued for 32 days after, Abeta(25-35) administration. Animal brains were subsequently processed for tau-2, ChAT-immunoreactivity, choline acetyltransferase (ChAT) activity and acetylcholinesterase (AChE) activity. Both oral and s.c. administration of C3 attenuated Abeta(25-35) induced appearance of tau-2-immunoreactive (IR) perikarya in the ipsilateral hippocampus (P < 0.05). Hippocampal cholinergic enzyme activity in C3 treated animals was not significantly different from control animals. The present findings suggest that C3 might be used successfully to prevent abnormal tau protein formation in chronic neurologic diseases, such as AD. Moreover, our data demonstrate that the mechanism of this effect does not appear to influence the cholinergic system of the brain.

Agrobacterium-mediated transformation of white clover using direct shoot organogenesis

White clover (Trifolium repens L.) plants from the cultivars Grasslands Huia and Grasslands Tahora have been transformed using Agrobacterium-mediated T-DNA transfer. Transgenic plants regenerated directly from cells of the cotyledonary axil. To transform white clover, shoot tips from 3 day old seedlings were co-cultivated with A. tumefaciens strain LBA4404 carrying the plasmid vector pPE64. This vector contains the neomycin phosphotransferase II gene (nptII) and β-glucuronidase reporter gene (gus) both under the control of the CaMV 35S promoter. Kanamycin-resistant plants regenerated within 42 days after transfer onto selective media. Integration of the nptII and gus genes into the white clover genome was confirmed using Southern blotting, and histochemical analysis indicated that the gus gene was expressed in a variety of tissues. In reciprocal crosses between a primary transformant and a non-transformed plant the introduced gus gene segregated as a single dominant Mendelian trait.