By K. Zarkos. Swarthmore College. 2018.
A after middle cerebral artery occlusion in the rat (49) order tadapox 80mg without prescription, a find- preliminary report on a P2X7 knockout has appeared (64) tadapox 80 mg line. Antisense to the P2X7 receptor or selec- tive receptor antagonists may represent a novel approach to PURINERGIC THERAPEUTICS the treatment of stroke. Three distinct classes of compound can modulate P1 and P2 receptor function: (a) conventional agonist, partial ago- Epilepsy nist and antagonist ligands; (b) allosteric modulators of re- ceptor function; and (c) modulators of the endogenous sys- Seizure activity is associated with rapid and marked increases tems that regulate the extracellular availability of ATP, in CNS adenosine concentrations in animals (68), as well adenosine, UTP, and their respective nucleotides. This last as in patients with epilepsy with spontaneous-onset seizures group includes the various ecto-ATPases that catalyze the (69). Seizure activity induced by a variety of chemical and degradation of nucleotides (5), ADA, AK, and the bidirec- electrical stimuli in animal models is reduced by adenosine tional member transporter systems that remove adenosine and related agonists (68) acting through A1receptors. From data on electrically kindled seizure models, adenosine agonists re- AK effects in brain tissue (22), it appears that modulation duce seizure severity and duration without significantly al- of endogenous adenosine levels by inhibition of AK is not tering seizure threshold. These anticonvulsant effects are a viable drug discovery approach. Adenosine antagonists including caffeine, the- hypoxia and focal ischemia, a finding providing additional ophylline, and BIIP 20 (Fig. Adenosine-receptor agonists such as CHA models by blocking the actions of endogenous adenosine. The clinic for their efficacy in cognitive disorders. Although pro- neuroprotective effects of adenosine are mediated by several vocative clinical data have been generated, neither com- P1 receptors: A1-receptor activation stabilizes neuronal pound showed sufficiently robust efficacy in larger AD trials Chapter 15: Purinergic Neurotransmission 201 to warrant continuation. However, aged patients with rheu- of the pars reticulata, which, turn, through a pars reticu- matoid arthritis who consume large quantities of antiinflam- lata–thalamic GABAergic pathway, inhibits the thalamic- matory agents such as indomethacin show an inverse corre- cortical glutaminergic pathway. Dysfunction of this path- lation for the incidence of AD, a finding highlighting the way may underlie the movement disorders seen in Hunting- pivotal role of inflammation in disease origin. A direct pathway originating in striatal agonists and AK inhibitors have marked antiinflammatory GABAergic–substance P–dynorphinergic neurons inhibits activity (67), inhibiting free radical production, and thus the internal segment of the pars reticulata to disinhibit the they may be effective in maintaining cell function in AD, ascending thalamic glutaminergic pathway and to activate in addition to modulating cytotoxic events. The balance between the direct (corti- Trophic factors in nervous tissue act to ensure neuronal cal activating) and indirect (cortical inhibiting) striatal do- viability and regeneration. Withdrawal of nerve growth fac- paminergic pathways provides a tonic regulation of normal tor, which exerts a tonic cell death–suppressing signal, leads motor activity. These studies indicate that striatal adenosine to neuronal death. Polypeptide growth factors linked to re- A2A receptors may play a pivotal role in neurologic disorders ceptor tyrosine kinases, such as fibroblast growth factors, involving basal ganglia dysfunction such as PD. The A2A epidermal growth factor, and platelet-derived growth factor, agonist, CGS 21680, given intrastriatally, attenuates the are increased with neural injury (70). ATP can act in combi- rotational behavior produced by dopamine agonists in uni- nation with various growth factors to stimulate astrocyte laterally lesioned rats. Mechanistically, radioligand-binding proliferation and to contribute to the process of reactive studies have shown an increased efficacy of CGS 21680 in astrogliosis, a hypertrophic-hyperplastic response typically reducing the binding affinity of supersensitive D2 receptors, associated with brain trauma, stroke and ischemia, seizures, a finding supporting the increased sensitivity of animals and various neurodegenerative disorders. In reactive astro- with supersensitive dopamine receptors to CGS 21680 gliosis, astrocytes undergo process elongation and express treatment. Repeated administration of the dopamine antag- glial fibrillary acidic protein, an astrocyte-specific intermedi- onist, haloperidol can up-regulate the density of both D2 ate filament protein with an increase in astroglial cellular and A2A receptors in rat striatum. ATP increases glial fibrillary acidic protein Adenosine A1 receptor activation can reduce the high- and activator protein-1 (AP-1) complex formation in astro- affinity state of striatal dopamine D1 receptors, the A1 re- cytes and mimics the effects of basic fibroblast growth factor ceptor agonist, and CPA blocking D1-receptor–mediated (70). Both ATP and guanosine triphosphate induce trophic locomotor activation in reserpinized mice (72). The nonse- factor (nerve growth factor, neurotrophin-3, fibroblast lective adenosine agonist, NECA, can attenuate the perioral growth factor) synthesis in astrocytes and neurons. The ef- dyskinesias induced by D1-receptor activation in rabbits. Nonetheless, these rectly modulates dopamine-receptor–mediated effects on studies have focused research on the hypoxanthine analogue, striatal GABA-enkephalinergic neurons and striatal neotrofin (AIT-082) (Fig. These adenosine trophin production and enhances working memory and re- agonist–mediated effects are independent of G-protein stores age-induced memory deficits in mice (71). This com- coupling and may involve an intramembrane modulatory pound has shown positive effects in early phase II trials for mechanism involving receptor heterooligimerization (26). The dynamic interactions between dopaminergic and In 1974, Fuxe showed that methylxanthines such as caf- purinergic systems in striatum suggest that dopaminergic feine could stimulate rotational behavior and could poten- dysfunction may be indirectly ameliorated by adenosine re- tiate the effects of dopamine agonists in rats with unilateral ceptor modulation. Selective adenosine A2A receptor antag- striatal lesions Conversely, adenosine agonists blocked the onists such as KF 17837 and KW 6002 (Fig.
Altered alpha2-adrenoceptor sensitivity in panic disor- 1341–1343 discount tadapox 80mg on line. Uncoupling of the noradren- vascular responses during phobic anxiety safe tadapox 80 mg. Psychosom Med 1985; ergic-hypothalamus-pituitary adrenal axis in panic disorder pa- 47:320–332. Persistence of blunted inephrine responsivity to orthostatic challenge in anxiety disor- human growth hormone response to clonidine in fluoxetine- ders: comparison of patients with panic disorder and social pho- treated patients with panic disorder. Am J Psychiatry 1995;152: bia and normal control subjects. Effects of thyrotropin-releas- phenylethylene glycol (MHPG) and growth hormone responses ing hormone on blood pressure and heart rate in phobic and in panic disorder patients and normal controls. Hypercortisolism and its possible Arch Psychiatry 1992;241:337–344. Effects of chronic stress ronal dysregulation in panic disorder: the effects of intravenous on plasma corticosterone, ACTH and prolactin. Physiol Behav yohimbine and clonidine in panic disorder patients. Effects of yohimbine rine and plasma corticosterone following acute and chronic on heart rate variability in panic disorder patients and normal stressors: influence of social isolation and handling. Pharmacol controls: a study of power spectral analysis of heart rate. PET measurement of ACTH secretion: effect of stress-induced corticosterone secre- tion on subsequent stress responses in the rat. Endocrinology central metabolic correlates of yohimbine administration in 1973;92:1367–1375. Temporal and social factors Psychiatry 1993;50:266–274. Psychoneuroendocrinology and serotonergic function in posttraumatic stress disorder. Abuse-related PTSD: evidence for campal glucocorticoid receptors and hypothalamic-pituitary- chronic neuroendocrine activation in women. Urinary catechola- thalamic corticotropin-releasing factor mRNA medial CRF con- mines and cortisol in recent-onset posttraumatic stress disorder text, and stress induced release in adult rats. Bennett Re- corticotropin releasing factor systems due to early life stress: search Award: developmental traumatology. Biological stress relationship to pathophysiology of major depression and post- systems. Changes in plasma releasing factor in adult nonhuman primates exposed to early- norepinephrine to combat-related stimuli among Vietnam vet- life stressors: implications for the pathophysiology of mood and erans with post traumatic stress disorder. Csf norepineph- handling on age-related impairments associated with the hippo- rine concentrations in posttraumatic stress disorder. Altered platelet alpha2 alters adrenocortical negative feedback sensitivity and hippo- Chapter 63: Neurobiological Basis of Anxiety Disorders 927 campal type II glucocorticoid receptor binding in the rat. Neu- cortisol excretion in patients with post-traumatic stress disorder roendocrinology 1989;50:597–604. The dexamethasone tion for understanding the states of fear and anxiety and allo- suppression test and thyrotropin-releasing hormone stimulation static load. Enhanced suppres- the amygdala and the parvocellular region of the paraventricular sion of cortisol following dexamethasone administration in post- nucleus of the hypothalamus. Enhanced dexametha- CRH mRNA and content in the bed nucleus of the stria termi- sone suppression of plasma cortisol in adult women traumatized nalis; comparison with the effects in the central nucleus of the by childhood sexual abuse. Initial posttrau- in the rat brain and pituitary by glucocorticoids and stress. Endo- matic urinary cortisol levels predict subsequent PTSD symp- crinology 1995;136:4517–4525. Elevated CSF corticotro- paraventricular nucleus: a hybridization histochemical study in pin-releasing factor concentrations in posttraumatric stress dis- the rat. Cerebrospinal fluid cortico- and urocortin in behavioral responses to stressors. Brain Res tropin-releasing hormone and adrenal cortical activity in post 1999;848:141–152.
Bremner and colleagues (20) also used script-driven imagery and PET to study rCBF in ten female survivors of childhood sexual abuse with Imaging Studies of Neurochemistry PTSD and 12 without PTSD buy 80mg tadapox. Consistent with the findings Schuff and colleagues used mMRI and MRS to study seven of Shin et al discount tadapox 80mg without prescription. Although these investigators found a nonsignificantly in the PTSD group. Liberzon and col- PTSD and 11 healthy comparison subjects without histories leagues (76) used SPECT to study rCBF in 14 Vietnam of maltreatment (37). The PTSD group had lower NAA/ veterans with PTSD, 11 veteran control subjects, and 14 creatine ratios in pregenual anterior cingulate gyrus. In separate scanning sessions, subjects result is consistent with those of symptom provocation PET listened to combat sounds and white noise. In the combat studies (20,23,129), which have reported failure to activate sounds versus white noise comparison, all three groups anterior cingulate in PTSD. Yohimbine administration was associated with increased anxiety and panic symptoms , as well as wide- spread decreases in cerebral glucose metabolism in the Summary PTSD group. Taken together, data from neuroimaging studies are consis- Shin and colleagues studied seven patients with combat- tent with the current neurocircuitry model of PTSD that related PTSD and seven matched trauma-exposed control emphasizes the functional relationship among the amygdala, subjects without PTSD in the context of a PET cognitive hippocampus, and medial prefrontal cortex. Subjects were required to make volumes and NAA levels appear to be decreased in persons judgments about pictures from three categories: neutral, with PTSD. These findings dovetail with animal research general negative, and combat-related. Subjects performed that points to a relationship among stress, HPA axis func- two types of tasks: one involved responding while actually tion, and cell viability within the hippocampus. Function- seeing the pictures (perception), and another involved re- ally, in comparison with control subjects, patients with sponding while recalling the pictures (imagery). During fMRI, subjects viewed fearful and happy faces temporally masked by neutral faces. Healthy persons are typically aware of seeing only the neutral faces, although they show amygdala activation to the masked fear- OBSESSIVE-COMPULSIVE DISORDER ful faces (142). Rauch and colleagues found greater amyg- Corticostriatal Model dala activation to masked fearful faces in persons with PTSD than in control subjects (108). Furthermore, the magnitude One current neuroanatomic model of OCD focuses on cor- of amygdala activation was correlated with PTSD severity. According to Chapter 65: Structural and Functional Imaging of Anxiety and Stress Disorders 959 this model, the primary disorder lies within the striatum as well as functional MRI (15) have also most consistently (specifically, the caudate nucleus). This leads to inefficient shown increased brain activity within anterior-lateral orbit- gating at the level of the thalamus, which results in hyperac- ofrontal cortex, anterior cingulate cortex, and caudate nu- tivity within orbitofrontal cortex (corresponding to the in- cleus during the OCD symptomatic state. In these studies, patients with OCD perform are performed to recruit the inefficient striatum ultimately an implicit (i. In both studies, patients with OCD failed to recruit stria- tum normally and instead activated medial temporal regions Structural Imaging Findings typically associated with conscious information processing. The results of several mMRI investigations of OCD have suggested volumetric abnormalities involving the caudate Imaging Studies of Neurochemistry nucleus, although the nature of the observed abnormalities has been somewhat inconsistent. Ebert and colleagues (41) found reduced in the OCD group. Glutamate is the principal transmitter mediat- mixed-gender cohort of 24 patients with OCD versus 21 ing frontostriatal communication. Interestingly, elevated matched controls and found no significant differences in striatal glutamate levels were attenuated toward normal after striatal volumes. These findings suggest that or- ment-naive pediatric subjects with OCD and 19 case- bitofrontal hyperactivity in OCD may be mirrored by ele- matched psychiatrically healthy comparison subjects. These vated glutamate at the site of orbitofrontal ramifications in investigators found reduced striatal volumes in the OCD striatum, and treatment-related attenuation of orbitofrontal group and an inverse correlation between striatal volume and OCD symptom severity. Functional Imaging Findings Neutral state paradigms employing PET and SPECT have Summary most consistently indicated that patients with OCD exhibit Taken together, these neuroimaging findings are consistent increased regional brain activity within orbitofrontal and with disorders in corticostriatothalamocortical circuitry. Observed dif- the striatum, MRI and MRS studies of OCD have shown ferences in regional activity within the caudate nucleus have been less consistent (6,113). PET studies have revealed hyperactivity within orbit- lated attenuation of abnormal regional brain activity within ofrontal cortex, and the magnitude of this hyperactivity pre- orbitofrontal cortex, anterior cingulate cortex, and caudate dicts response to treatment. In addition, in neurologically nucleus (8,9,61,95,124,137). In addition, both pharmaco- normal persons, the performance of repetitive motor rou- logic and behavioral therapies appear to be associated with tines does facilitate striatal recruitment in the service of thal- similar brain activity changes (8,124).
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