PET ligands [18F]LSN3316612 and [11C]LSN3316612 quantify O-linked-β-N-acetyl-glucosamine hydrolase in the brain

We aimed to develop effective radioligands for quantifying brain O-linked-β-N-acetyl-glucosamine (O-GlcNAc) hydrolase (OGA) using positron emission tomography in living subjects as tools for evaluating drug target engagement. Posttranslational modifications of tau, a biomarker of Alzheimer's disease, by O-GlcNAc through the enzyme pair OGA and O-GlcNAc transferase (OGT) are inversely related to the amounts of its insoluble hyperphosphorylated form. Increase in tau O-GlcNAcylation by OGA inhibition is believed to reduce tau aggregation. LSN3316612, a highly selective and potent OGA ligand [half-maximal inhibitory concentration (IC50) = 1.9 nM], emerged as a lead ligand after in silico analysis and in vitro evaluations. [3H]LSN3316612 imaged and quantified OGA in postmortem brains of rat, monkey, and human. The presence of fluorine and carbonyl functionality in LSN3316612 enabled labeling with positron-emitting fluorine-18 or carbon-11. Both [18F]LSN3316612 and [11C]LSN3316612 bound reversibly to OGA in vivo, and such binding was blocked by pharmacological doses of thiamet G, an OGA inhibitor of different chemotype, in monkeys. [18F]LSN3316612 entered healthy human brain avidly (~4 SUV) without radiodefluorination or adverse effect from other radiometabolites, as evidenced by stable brain total volume of distribution (VT) values by 110 min of scanning. Overall, [18F]LSN3316612 is preferred over [11C]LSN3316612 for future human studies, whereas either may be an effective positron emission tomography radioligand for quantifying brain OGA in rodent and monkey.

Peripheral and central nervous system distribution of the CGRP neutralizing antibody [125I] galcanezumab in male rats

Objective

The objective of this investigation was to examine the distribution of galcanezumab and a control immunoglobulin 4 antibody containing the same constant regions as galcanezumab, into peripheral and central tissues.

Methods

Galcanezumab and a control immunoglobulin 4 antibody were radioiodinated with Iodine-125 to specific activities of 0.11 mCi/mg and 0.16 mCi/mg, respectively. At 24, 72, and 168 hours following subcutaneous injection of either antibody (4 mg/kg), cerebrospinal fluid and plasma were obtained followed by saline perfusion to remove residual blood and collection of selected tissues for determination of Iodine-125 content by gamma counting.

Results

The peak plasma levels of Iodine-125 galcanezumab and Iodine-125 control immunoglobulin 4 were observed at 72 hours and remained high at 168 hours post-dose. The rank order of tissue levels was dura mater = spleen > trigeminal ganglia ≫hypothalamus = spinal cord = prefrontal cortex = cerebellum. Iodine-125 galcanezumab levels in peripheral tissue (dura mater, spleen, and trigeminal ganglia) averaged 5% to 11% of plasma, whereas all of the central nervous system (CNS) tissue levels and the cerebrospinal fluid levels were < 0.4% of plasma. Distribution of the antibodies into the dura mater and the trigeminal ganglia was similar to that observed in the spleen and significantly greater than exposure in the brain or spinal cord.

Conclusions

The central levels of galcanezumab were relatively low, which would favor the dura mater and trigeminal ganglia as sites of action for its observed clinical efficacy. However, a central site of action cannot be excluded.

Human mast cells release the migraine-inducing factor pituitary adenylate cyclase-activating polypeptide (PACAP)

Background Many patients with migraines suffer from allergies and vice versa, suggesting a relationship between biological mechanisms of allergy and migraine. It was proposed many years ago that mast cells may be involved in the pathophysiology of migraines. We set out to investigate the relationship between mast cell activation and known neurogenic peptides related to migraine. Methods Cultured human mast cells were assayed for the presence of neuropeptides and their receptors at the RNA and protein level. Immunohistochemistry analyses were performed on tissue resident and cultured mast cells. Mast cell degranulation assays were performed and pituitary adenylate cyclase-activating polypeptide (PACAP) activity was measured with a bioassay. Results We found that cultured and tissue resident human mast cells contain PACAP in cytoplasmic granules. No other neurogenic peptide known to be involved in migraine was detected, nor did mast cells express the receptors for PACAP or other neurogenic peptides. Furthermore, mast cell degranulation through classic IgE-mediated allergic mechanisms led to the release of PACAP. The PACAP released from mast cells was biologically active, as demonstrated using PACAP receptor reporter cell lines. We confirmed existing literature that mast cell degranulation can also be induced by several neurogenic peptides, which also resulted in PACAP release. Conclusion Our data provides a potential biological explanation for the association between allergy and migraine by demonstrating the release of biologically active PACAP from mast cells.

An Allosteric Potentiator of the Dopamine D1 Receptor Increases Locomotor Activity in Human D1 Knock-In Mice without Causing Stereotypy or Tachyphylaxis

Allosteric potentiators amplify the sensitivity of physiologic control circuits, a mode of action that could provide therapeutic advantages. This hypothesis was tested with the dopamine D1 receptor potentiator DETQ [2-(2,6-dichlorophenyl)-1-((1S,3R)-3-(hydroxymethyl)-5-(2-hydroxypropan-2-yl)-1-methyl-3,4-dihydroisoquinolin-2(1H)-yl)ethan-1-one]. In human embryonic kidney 293 (HEK293) cells expressing the human D1 receptor, DETQ induced a 21-fold leftward shift in the cAMP response to dopamine, with a K_b of 26 nM. The maximum response to DETQ alone was ∼12% of the maximum response to dopamine, suggesting weak allosteric agonist activity. DETQ was ∼30-fold less potent at rat and mouse D1 receptors and was inactive at the human D5 receptor. To enable studies in rodents, an hD1 knock-in mouse was generated. DETQ (3–20 mg/kg orally) caused a robust (∼10-fold) increase in locomotor activity (LMA) in habituated hD1 mice but was inactive in wild-type mice. The LMA response to DETQ was blocked by the D1 antagonist SCH39166 and was dependent on endogenous dopamine. LMA reached a plateau at higher doses (30–240 mg/kg) even though free brain levels of DETQ continued to increase over the entire dose range. In contrast, the D1 agonists SKF 82958, A-77636, and dihydrexidine showed bell-shaped dose-response curves with a profound reduction in LMA at higher doses; video-tracking confirmed that the reduction in LMA caused by SKF 82958 was due to competing stereotyped behaviors. When dosed daily for 4 days, DETQ continued to elicit an increase in LMA, whereas the D1 agonist A-77636 showed complete tachyphylaxis by day 2. These results confirm that allosteric potentiators may have advantages compared with direct-acting agonists.

Effects of corticotropin-releasing factor 1 receptor antagonism on the hypothalamic-pituitary-adrenal axis of rodents

Corticotropin-releasing factor (CRF) is the major hypothalamic neuropeptide responsible for stimulation of the hypothalamic-pituitary-adrenal axis (HPAA), resulting in the synthesis and release of glucocorticoids from the adrenal cortex. In a recent study, we reported the discovery of the CRF1 receptor antagonist, 3-(4-chloro-2-morpholin-4-yl-thiazol-5-yl)-8-(1-ethylpropyl)-2,6-dimethyl-imidazo[1,2-b]pyridazine (MTIP), which has efficacy in preclinical models of stress-induced alcohol consumption. Because CRF1 is important in HPAA activation, we evaluated the effects of MTIP administration on rodent HPAA function. Initial studies established the MTIP doses required for brain and pituitary CRF1 occupancy and those associated with the inhibition of intracerebroventricular CRF on the HPAA in mice. Then, rat basal plasma corticosterone (CORT) concentrations were measured hourly by radioimmunoassay for 24 h after three daily doses of MTIP or vehicle. In these studies, the early phase of the nocturnal CORT surge was reduced; however, the area under the CORT curve was identical for the 24-h period. In subsequent studies, increases in plasma CORT due to direct pharmacological manipulation of the HPAA axis or by stressors were evaluated after MTIP treatment in mice. MTIP attenuated CORT responses generated by immediate bolus administration of insulin or ethanol; however, MTIP did not affect activation of the HPAA by other stressors and pharmacological agents. Therefore, MTIP can modulate basal HPAA activity during the CORT surge and reduced activation after a select number of stressors but does not produce a lasting suppression of basal CORT. The ability of MTIP to modulate plasma CORT after hyperinsulinemia may provide a surrogate strategy for a target occupancy biomarker.

Distribution of NPY Y5-Like Immunoreactivity in the Rat Brain

The pharmacology and brain mRNA distribution of the neuropeptide Y (NPY) rat Y5 (rY5) receptor has led to the hypothesis that this receptor might mediate the hypothalamic feeding response to NPY in addition to many other physiologic functions. However, through the use of autoradiographic techniques, only very low levels of Y5-like immunoreactive (Y5-ir) binding are detected in the rat brain. To localize the Y5 protein in the rat brain, polyclonal antibodies were raised to the carboxyl terminus of the rY5 receptor. The resulting antisera were affinity purified and characterized by specific binding to HEK293 cells that had been stably transfected with the rY5 receptor. Utilizing immunohistochemical techniques, we found a discrete pattern of Y5-ir in the rat brain. In initial studies, very low levels of Y5-ir were detected, and TSA amplification was required to visualize the staining. Areas with the highest levels of expression include the piriform cortex, supraoptic nucleus, and hippocampus. Areas with moderate levels of expression include the lateral septum, amygdala, arcuate nucleus, paraventricular hypothalamic nucleus, locus coeruleus, and cerebellum. With several exceptions, this pattern of distribution is consistent with earlier reports of rY5 mRNA and receptor protein expression.

Stress and central Urocortin increase anxiety-like behavior in the social interaction test via the CRF1 receptor

Corticotropin releasing factor (CRF) and Urocortin are important neurotransmitters in the regulation of physiological and behavioral responses to stress. Centrally administered CRF or Urocortin produces anxiety-like responses in numerous animal models of anxiety disorders. Previous studies in our lab have shown that Urocortin infused into the basolateral nucleus of the amygdala produces anxiety-like responses in the social interaction test. Subsequently, in the current study we prepared a specific CRF1 receptor antagonist (N-Cyclopropylmethyl-2,5-dimethyl-N-propyl-N'-(2,4,6-trichloro-phenyl)-pyrimidine-4,6-diamine, NBI3b1996) to examine in this paradigm. This CRF1 receptor antagonist inhibited the ex vivo binding of 125I-sauvagine to rat cerebellum with an ED50 of 6 mg/kg, i.p. NBI3b1996 produced a dose-dependent antagonism of Urocortin-induced anxiety-like behavior in Social Interaction test with an ED50 of 6 mg/kg, i.p. The compound had no effect on baseline social interaction. In addition, the CRF1 receptor antagonist prevented the stress-induced decrease in social interaction. These results provide further support for the CRF1 receptor in anxiety-like behavior and suggest this pathway is quiescent in unstressed animals.

Atomoxetine increases extracellular levels of norepinephrine and dopamine in prefrontal cortex of rat: a potential mechanism for efficacy in attention deficit/hyperactivity disorder

The selective norepinephrine (NE) transporter inhibitor atomoxetine (formerly called tomoxetine or LY139603) has been shown to alleviate symptoms in Attention Deficit/Hyperactivity Disorder (ADHD). We investigated the mechanism of action of atomoxetine in ADHD by evaluating the interaction of atomoxetine with monoamine transporters, the effects on extracellular levels of monoamines, and the expression of the neuronal activity marker Fos in brain regions. Atomoxetine inhibited binding of radioligands to clonal cell lines transfected with human NE, serotonin (5-HT) and dopamine (DA) transporters with dissociation constants (K(i)) values of 5, 77 and 1451 nM, respectively, demonstrating selectivity for NE transporters. In microdialysis studies, atomoxetine increased extracellular (EX) levels of NE in prefrontal cortex (PFC) 3-fold, but did not alter 5-HT(EX) levels. Atomoxetine also increased DA(EX) concentrations in PFC 3-fold, but did not alter DA(EX) in striatum or nucleus accumbens. In contrast, the psychostimulant methylphenidate, which is used in ADHD therapy, increased NE(EX) and DA(EX) equally in PFC, but also increased DA(EX) in the striatum and nucleus accumbens to the same level. The expression of the neuronal activity marker Fos was increased 3.7-fold in PFC by atomoxetine administration, but was not increased in the striatum or nucleus accumbens, consistent with the regional distribution of increased DA(EX). We hypothesize that the atomoxetine-induced increase of catecholamines in PFC, a region involved in attention and memory, mediates the therapeutic effects of atomoxetine in ADHD. In contrast to methylphenidate, atomoxetine did not increase DA in striatum or nucleus accumbens, suggesting it would not have motoric or drug abuse liabilities.

Adolescents' perceptions of discipline within intact families and stepfamilies

This study examined adolescents' perceptions of discipline in intact families and stepfamilies. Forty-five adolescents, ranging in age from 15 to 19 years, completed the Adolescent Discipline Perception Survey (ADPS). They responded to questions related to their own discipline experiences as well as their views on how they would discipline an adolescent. Results indicated that adolescents from intact families and stepfamilies identified loss of privileges and grounding as the primary discipline methods used by their families. In addition, adolescents from intact families and stepfamilies reported house rules and peers as the most common discipline issues. Twenty-six percent of adolescents from intact families and 44% of those from stepfamilies reported that grounding was the most severe form of punishment they had received.

Injection of muscimol in dorsomedial hypothalamus and stress-induced Fos expression in paraventricular nucleus

Prior microinjection of the GABA(A)-receptor agonist muscimol into the dorsomedial hypothalamus (DMH) in conscious rats attenuates the increases in heart rate, blood pressure, and circulating adrenocorticotrophic hormone seen in air stress. Here, we examined the effect of similar treatment on air stress- or hemorrhage-induced Fos expression in the paraventricular nucleus (PVN). Muscimol (80 pmol/100 nl per side) or saline (100 nl per side) was microinjected bilaterally into the DMH in conscious rats before either air stress, an emotional or neurogenic stressor, or graded hemorrhage, a physiological stressor. Each stressor evoked a characteristic pattern of Fos expression in the parvocellular and magnocellular PVN after saline. Injection of muscimol into the DMH suppressed Fos expression in the PVN associated with air stress but not with hemorrhage. Injection of muscimol at sites anterior to the DMH and closer to the PVN had no effect on Fos expression in the PVN after air stress. Thus activation of neurons in the DMH is necessary for excitation of neurons in the PVN during air stress but not during hemorrhage.

Differential distribution of urocortin- and corticotropin-releasing factor-like immunoreactivities in the rat brain

Urocortin, a novel 40 amino acid neuropeptide, is a member of the corticotropin-releasing factor family. With 45% homology to corticotropin-releasing factor, urocortin binds with similar affinity to the corticotropin-releasing factor- and corticotropin-releasing factor-2 receptors and may play a role in modulating many of the same systems as corticotropin-releasing factor. To assess whether urocortin and corticotropin-releasing factor are localized in the same regions of the brain, we compared the distribution of urocortin- and corticotropin-releasing factor-like immunoreactivities in the rat central nervous system. Polyclonal antibodies to rat corticotropin-releasing factor and rat urocortin were generated and utilized to map the distribution of corticotropin-releasing factor- and urocortin-like immunoreactivities throughout the rat forebrain and brainstem. Characterization of the antibodies by radioimmunoassay showed no cross-reactivity with related peptides. Male Sprague-Dawley rats were treated with colchicine for 18-24 h. Following colchicine treatment, the rats were perfused with paraformaldehyde-lysine-periodate fixative and their brains removed. Serial coronal sections were taken throughout the rat brain and processed for either corticotropin-releasing factor- or urocortin-like immunoreactivity. Urocortin-like immunoreactivity shows a discrete localization within several regions including the supraoptic nucleus, the median eminence, Edinger-Westphal nucleus and the sphenoid nucleus. This is in contrast to the more abundant corticotropin-releasing factor-like immunoreactivity. Regions containing high levels of corticotropin-releasing factor immunoreactivity include the lateral septum, paraventricular nucleus of the hypothalamus, median eminence and locus coeruleus. There are a few regions that contain both urocortin-immunoreactive and corticotropin-releasing factor-immunoreactive cells, such as the supraoptic nucleus and the hippocampus. Therefore, urocortin and corticotropin-releasing factor appear to have different distribution patterns which may be indicative of their respective physiological functions.

Antiinflammatory activity of the platelet-activating factor receptor antagonist A-85783

Accumulating evidence suggests an important role for the lipid mediator, platelet-activating factor (PAF), in cutaneous inflammation. In these studies the antiinflammatory effects of the potent and selective lipophilic PAF receptor antagonist A-85783 topically applied to the ventral ears of male Wistar rats were assessed. Intradermal injections of PAF into rat ears resulted in cutaneous inflammation as assessed by both ear thickness measurements and histological evaluation. Pretreatment of the ears with A-85783 resulted in an inhibition of subsequent PAF-induced inflammation. A-85783 treatment also inhibited phorbol myristic acetate-induced cutaneous inflammation, suggesting that the PAF receptor is involved in the etiology of this experimental dermatitis. These findings demonstrate that epicutaneous A-85783 is an appropriate tool to study the role of the PAF receptor in cutaneous inflammation, and suggest the possible clinical utility of this new class of antiinflammatory agents.

Identification and pharmacological characterization of platelet-activating factor and related 1-palmitoyl species in human inflammatory blistering diseases

Through its pro-inflammatory effects on leukocytes, endothelial cells, and keratinocytes, the lipid mediator platelet-activating factor (PAF) has been implicated in cutaneous inflammation. Although the 1-alkyl PAF species has been considered historically the most abundant and important ligand for the PAF receptor (PAF-R), other putative ligands for this receptor have been described including 1-acyl analogs of sn-2 acetyl glycerophosphocholines. Previous bioassays have demonstrated a PAF-like activity in lesions of the autoimmune blistering disease bullous pemphigoid. To assess the actual sn-2 acetyl glycerophosphocholine species that result in this PAF agonistic activity, we measured PAF and related sn-2 acetyl GPCs in fresh blister fluid samples from bullous pemphigoid and noninflammatory (suction-induced) bullae by mass spectrometry. We report the presence of 1-hexadecyl as well as the 1-acyl PAF analog 1-palmitoyl-2-acetyl glycerophosphocholine (PAPC) in inflammatory blister fluid samples. Because PAPC is the most abundant sn-2 acetyl glycerophosphocholine species found in all samples examined, the pharmacological effects of this species with respect to the PAF-R were determined using a model system created by transduction of a PAF-R-negative epidermoid cell line with the PAF-R. Radioligand binding and intracellular calcium mobilization studies indicated that PAPC is approximately 100x less potent than PAF. Though a weak agonist, PAPC could induce PAF biosynthesis and PAF-R desensitization. Finally, intradermal injections of PAF and PAPC into the ventral ears of rats demonstrated that PAPC was 100x less potent in vivo. These studies suggest possible involvement of PAF and related species in inflammatory bullous diseases.

Effect of microinjection of muscimol into the dorsomedial or paraventricular hypothalamic nucleus on air stress-induced neuroendocrine and cardiovascular changes in rats

The paraventricular nucleus (PVN) contains neurons that release corticotrophin-releasing factor (CRH) and thus provide the stimulus for the release of adrenocorticotrophic hormone (ACTH), the neuroendocrine hallmark of the response to stress. However, inhibition of neuronal activity in the nearby dorsomedial hypothalamic nucleus (DMH) by microinjection of the GABA(A) receptor agonist muscimol suppresses cardiovascular changes seen in air stress in conscious rats, while similar treatment in the PVN has no effect. Because the DMH projects to the PVN and also contains CRH neurons, we decided to investigate the role of neuronal activity in the DMH in the neuroendocrine response to stress. In control rats or after microinjection of saline vehicle into either the PVN or the DMH, air stress resulted in equivalent increases in plasma levels of ACTH, heart rate, and arterial pressure. Bilateral microinjection of muscimol 80 pmol/100 nl/side into either the PVN or the DMH prior to air stress reduced the associated increases in plasma ACTH (-37% and -71%, respectively), while only injection into the DMH attenuated the accompanying tachycardia (-62%) and pressor (-83%) effects. Thus, neurons in the DMH, but not in the PVN, play a role in both the cardiovascular and neuroendocrine response to air stress.

Role of the dorsomedial hypothalamus in the cardiovascular response to stress

1. Disinhibition of the dorsomedial hypothalamus (DMH) in rats by local microinjection of GABAA receptor antagonists evokes behavioural and physiological changes resembling those seen in acute experimental stress. 2. Conversely, similar microinjection of muscimol, a potent agonist at inhibitory GABAA receptors, virtually abolishes stress-induced increases in heart rate and arterial pressure. 3. Blockade of excitatory amino acid (EAA) receptors in the DMH also attenuates [correction of attentuates] stress-induced cardiovascular changes and microinjection of kainate, AMPA or NMDA at low doses elicits cardiovascular effects resembling those seen in stress. Paradoxically, injection of higher doses of NMDA or of glutamate into this region has no consistent effect. 4. The cardiovascular effects of bicuculline methiodide, a GABAA receptor antagonist, as well as those of NMDA and/or kainate were assessed after identical injection into either the DMH, the paraventricular nucleus (PVN) or the area between the two nuclei in both anaesthetized and conscious rats. For each agent, a similar pattern was seen, with the largest increases in heart rate and arterial pressure occurring after injection into the DMH and the smallest changes resulting from injection into the PVN. 5. In a parallel study, bilateral microinjection of muscimol into the DMH dramatically reduced air stress-induced cardiovascular changes; similar injection into the area of the PVN had no effect, while injection into the area between the nuclei produced an intermediate effect. 6. Our findings suggest that activation of neurons in the region of the DMH mediates stress-induced cardiovascular changes and that the activity of these neurons may be determined by the balance of tone at inhibitory GABAA receptors and EAA receptors.

Adolescents' perceptions and experiences of death and grieving

Although there is a considerable body of knowledge regarding adolescent grief, little research has focused on adolescents' perceptions and experiences of death and grief from those who are not currently in the bereavement process. Thirty-two adolescents between the ages of 13 to 18 were interviewed about their experiences of death and loss. Nineteen of the subjects attended suburban public high school, while 13 resided in a facility for adjudicated urban youth. Findings indicated that subjects were aware of death by age nine. In this sample, urban adolescents' perception of death involved reference to violence (25%) or religion (16.6%) in contrast to the suburban youths who referred less frequently to violence (0%) and religion (5.3%). The most distasteful aspect of death to the suburban students was suffering (31.6%), while it was loss of loved ones to the adjudicated youths (25%). Since talking and listening as comforting strategies were used by both groups (66.7%), background environment must be considered when examining adolescents' experiences and perceptions of death.

Hypothalamic sites mediating cardiovascular effects of microinjected bicuculline and EAAs in rats

Microinjection of gamma-aminobutyric acidA receptor antagonist bicuculline methiodide (BMI) into either the dorsomedial hypothalamic nucleus (DMH) or the nearby paraventricular hypothalamic nucleus (PVN) has been reported to evoke marked tachycardia and modest pressor effects. We compared the effects of microinjecting BMI and excitatory amino acids (EAAs) into 1) the DMH, 2) the PVN, and 3) an intermediate area between the two nuclei. In conscious rats, microinjection of (in pmol) 10 BMI, 0.5 kainic acid, or 5 N-methyl-D-aspartate into the DMH markedly increased heart rate and slightly elevated arterial pressure, whereas injections into other regions provoked changes that progressively declined in magnitude with increasing distance from the nucleus. A similar pattern was evident in urethan-anesthetized rats, where the shortest latency to onset of BMI-induced increases in heart rate was seen after injection into the DMH. These findings demonstrate that the cardiovascular changes seen after microinjection of BMI or EAAs into the medial hypothalamus result from an action in the DMH and not from spread to the PVN.