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Associations between cues associated with smoking generic citalopram 20mg line, times greater than venous levels (11) effective citalopram 40 mg. Within 10 to 20 sec- anticipated nicotine effects and the resulting urge to use onds after each puff purchase 40 mg citalopram, relatively high levels of nicotine reach tobacco (craving) become all important in maintaining the brain buy citalopram 10 mg online. Nicotine levels in plasma and in brain tissue then smoking safe citalopram 40mg. By midafternoon, relatively constant, steady- associated with pleasurable effects. Unpleasant or dysphoric state, venous plasma levels, 20 to 40 ng/mL, are reached, moods come to serve as conditioned cues for smoking. For but with transient 50-ng/mL increments in arterial and example, an adolescent smoker, usually within the first year brain levels after each cigarette. During sleep, plasma con- of smoking, learns that not having a cigarette available is centration of nicotine falls progressively but is still measur- associated with feelings of irritability and learns that just a able on awakening when the first cigarette of the next day few puffs from a cigarette diminish irritability and other is smoked, typically within 30 minutes of awakening. After hundreds smoking results in exposure of brain to nicotine 24 hours of repeated experiences, irritability from any source serves of each day but with regular brain level perturbations after as a cue for smoking. Left to nature, it is unlikely that many people would Smokers regulate smoked nicotine intake to maintain make or find a cigarette, light it, and smoke it (49). Condi- their preferred range of concentrations by varying puff and tioning and learning linking nicotine pharmacology and en- vironmental contingencies are facilitated by advertising en- inhalation timing, volume, and number (49). Nicotine in- couraging, often in subtle ways, the use of tobacco. Smokers can compen- beginning, teenage smokers teach each other. Quickly, links sate for differing machine-determined nicotine yields to ob- between the pharmacologic actions of nicotine and associ- tain a preferred dose of nicotine whether smoking a high- ated behaviors become powerful (7). Nicotine delivered by cigarettes power only gradually without nicotine delivered in the right offers smokers individualized control of nicotine dose unat- dose and context. Conditioning is a major factor in relapse tainable by other nicotine delivery systems (49). Dealing with it is important attributes of smoked nicotine dosimetry are relevant when in any therapeutics for nicotine addiction. Cigarette smoking or nicotine ad- placement therapies (NRTs). In contrast to smoking, chew- ministration improves attention, reaction time, and prob- ing tobacco and snuff deliver nicotine through oral or nasal lem-solving, particularly in recently abstinent smokers (55, mucosa. Plasma and brain nicotine concentrations rise more 74). Smokers typically report enhanced pleasure and re- gradually, reach plateau levels after about 30 minutes, and duced anger, tension, depression, and stress after a cigarette. Whether enhanced performance and improved mood after smoking are mostly or entirely the result of the relief of abstinence symptoms or rather are intrinsic effects of nico- NICOTINE RECEPTOR–BASED NEURAL tine on the brain remains unclear (49). Improvement in the MECHANISMS RELEVANT TO performance of nonsmokers after nicotine suggests at least THERAPEUTICS some direct enhancement (8). Nicotine binds stereoselectively to a diverse family of nico- NICOTINE PHARMACOKINETICS AND tinic cholinergic receptors widely distributed in brain, auto- METABOLISM nomic ganglia, adrenal medulla, and neuromuscular junc- tions (15,16). Nicotinic cholinergic multiple neuronal systems remains to be determined (49). Re- which nicotine is needed to maintain normal neurotrans- ceptor diversity probably accounts for the diverse effects mission. As nicotine levels decrease, diminished neurotrans- of nicotine experienced by smokers (19). The undoubtedly mitter release or altered modulation of neurotransmitter sys- complex relationships between specific nicotinic cholinergic tems (17) contributes to a relative deficiency state and in receptor subtypes and release of specific neurotransmitters humans, symptoms of lethargy, irritability, restlessness, in- are still to be fully characterized (92). Neurotransmitter re- ability to concentrate, depressed mood, and other symptoms lease is assumed to mediate nicotine effects such as arousal, making up the nicotine withdrawal syndrome. Plasma con- relaxation, cognitive enhancement, relief of stress, and centrations of nicotine in smokers are sufficient to desen- depression. Thus, self-adminis- ion channel, with five subunits.

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Amygdala N-methyl-D-aspartate not impair pavlovian fear conditioning but regulates when and receptors participate in the induction of long-term potentiation where fear is expressed purchase citalopram 20 mg line. J Exp Psychol Anim Behav Process 1999; in the dentate gyrus in vivo buy citalopram 40 mg free shipping. Neurotoxic lesions of basolateral amygdala facilitates the induction of long-term po- basolateral generic citalopram 10 mg line, but not central generic citalopram 20mg, amygdala interfere with pavlovian tentiation in the dentate gyrus in vivo buy generic citalopram 10mg. Neurosci Res 1995;22: second-order conditioning and reinforcer devaluation effects. Norepinephrine infused into the ba- neuron activity for the induction of long-term potentiation in solateral amygdala posttraining enhances retention in the spatial the dentate gyrus in vivo. Anxiolytic-like action of vation detected with echo-planar functional magnetic resonance neuropeptide Y: mediation by Y1 receptors in amygdala, and imaging. Intrinsic neurons in sive consequences of morphine withdrawal. Behav Pharmacol the amygdala field projected to by the medial geniculate body 1995;6:74–80. Disorders of facial recognition, social behaviour and rats via direct neurotropic action. Neural encoding of individual tractotomy: a clinical and experimental study. Psychol Med words and faces by the human hippocampus and amygdala. The amygdala is essential for the expression of nucleus lesions: effect on heart rate conditioning in the rabbit. Effects of electrical stimula- performance of conditional fear. Physiol Behav 1992;51: tion of the amygdaloid central nucleus on neocortical arousal 1271–1276. Stress-induced hypoalgesia and defensive freez- 141. Amygdaloid contribu- ing are attenuated by application of diazepam to the amygdala. Antinociception emotion, memory and mental dysfunction. New York: Wiley–Liss, following opioid stimulation of the basolateral amygdala is ex- 1992:229–254. Neurocomputation and learning: foundations Physiol Psychol 1980;94:313–323. Facilitation and inhibition of gastric pathology after 143. MK-801 protects condi- lesions in the amygdala in rats. Attenuation of shock-induced ulcers after lesions brane preparation. Administration of amygdaloid lesions on flight and defensive behaviors of wild thyrotropin-releasing hormone into the central nucleus of the black rats (Rattus rattus). Different types of fear- responding but not on discrimination. Psychopharmacology conditioned behaviour mediated by separate nuclei within 1987;92:491–504. Fear response and aggressive sions interfere with pavlovian negative ossasion setting. Modality-specific retrograde amnesia of campus impairs contextual retrieval of fear memory. Infusion of the non- Chapter 64: Neural Circuitry of Anxiety and Stress Disorders 949 NMDA receptor antagonist CNQX into the amygdala blocks 169. Human amygdala activa- latory systems and memory storage: role of the amygdala. Behav tion during conditioned fear acquisition and extinction: a Brain Res 1993;58:81–90. Infusion of the dopamine D1 recep- of the amygdala in neuromodulatory influences on memory tor antagonist SCH 23390 into the amygdala blocks fear expres- storage. The amygdala: neurobiological as- sion in a potentiated startle paradigm.

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At another extreme cheap citalopram 20mg with visa, some efficacy and that keep them in contact with clinicians habit reversal therapy involves the application of cognitive who can monitor their overall medical condition citalopram 40mg visa. Ulti- and behavioral therapy principles to TS (136) 20 mg citalopram overnight delivery, analogous mately purchase citalopram 10 mg otc, it is critically important for these alternative treat- to the successful use of these therapies in the treatment of ments to be tested in controlled trials discount citalopram 40mg without prescription, in which their tolera- OCD. Although studies with habit reversal therapy are only bility, safety, and efficacy can be established in an objective now being completed, initial results appear promising, of- manner. Unfortunately, the cost of such studies is often fering the possibility of a true, 'nonpharmacologic' ap- prohibitive, and they are generally not a high priority for proach to this disorder. Conceptually, once it is effectively funding from the pharmaceutical industry. Clinicians learned, habit reversal therapy may be easy to apply over a should ask patients and parents whether alternative thera- period of years, to a variety of different types of tics. Proponents of As is true with most neuropsychiatric conditions, comorbid- rTMS emphasize that the procedure can be administered on ity of TS with affective disorders deserves special attention, an outpatient basis, at relatively low cost, without apparent owing to the insidious and often profound morbidity im- significant side effects. More heroic efforts for intractable parted by depression. Comorbid affective illness accompa- TS and OCD have included psychosurgical interventions, nying TS is generally sensitive to standard pharmacothera- Chapter 117: Tourette Syndrome and Related Tic Disorders 1693 pies for these disorders. These can often be used in matched control tissue is also being collected, to diminish combination with anti-tic regimens, but the possibility of variability across different studies. These systematic efforts, iatrogenic depression from dopamine antagonists should al- combined with the judicious but timely distribution of ways be considered, because this may dictate a reduction in brain tissue for studies, should help to overcome many of neuroleptic dose rather than the addition of an antidepres- the limitations of past TS neuropathologic studies. As with comorbid OCD or ADHD, it appears that ity to utilize this material effectively and to interpret the comorbid depression can often cause a worsening of tics in information that it provides depends entirely on our TS, and there are reports of severe, refractory, mood-depen- progress in understanding the complex interconnections dent tics in comorbid TS and depression that show dramatic within CSPT circuitry. Although we have useful maps of the sensitivity to electroconvulsive therapy (138,139). Whereas major thoroughfares within CSPT circuitry, we will need more representative epidemiologic data are necessary, the to be equally knowledgeable regarding the detailed input- lifetime prevalence of comorbid mood disorders in TS pa- output relationships of functionally and neurochemically tients seen in specialty clinics may be as high as 70%, com- distinct striatal subterritories. Important pathologic find- parable to that reported in patients with OCD (140). Neuroimaging efforts in TS will focus on two strategies FUTURE DIRECTIONS that have been so informative in studies of OCD: pretreat- ment versus posttreatment repeated measures and on-line Several lines of inquiry are positioned to make major ad- behavioral or psychophysiologic probes in conjunction with vances in our understanding of the etiology and treatment functional imaging. Nonpharmacologic treatment effects of TS, based on the tremendous progress that has already on regional brain metabolism or brain activation may be been made in each of these areas: studied before and after habit reversal therapy, similar to The clinical 'phenotype' of TS has been particularly well such studies using cognitive and behavior therapy in OCD characterized. Appropriate on-line probes for fMRI studies must tics, sensory phenomena in TS are relatively less well under- be carefully developed. Optimally, these probes should stood and are more difficult to study. A full understanding either (a) detect deficits in patients with TS, or (b) in healthy of the TS phenotype will clearly enhance research efforts, persons, selectively activate relevant brain substrates, includ- by permitting stratification in measures from all levels of ing the basal ganglia or frontal circuitries. Event-related analysis, from genetics to neuropsychology. Detailed clinical fMRI techniques appear especially promising as investiga- characterization, and the experimental analysis that it facili- tors seek to identify the sequence of neural events that pre- tates, will also be important in clarifying the potentially cede and follow tics. This issue has tremendous im- the most promising regions is planned. Verification and portance, because these two 'types' of TS are not generally extension of this work within several extended TS families (and often cannot be) segregated in genetic, neuroimaging, are also anticipated. Parallel efforts will continue in targets or other biological measures in this disorder. For example, of opportunity, including informative chromosomal trans- it may not be appropriate to generalize to all forms of TS the locations. Ultimately, genes conferring a risk of TS will be biology that is described by neurochemical brain imaging identified and cloned. Experience from similar efforts that studies, which, because of ethical concerns, exclusively in- are already completed with the Huntington disease gene volve adults with TS. At another level, current TS studies suggest that identification of the TS genes will be followed that include children will likely involve both 'types' of TS, by a substantial amount of work designed to understand without any clear way to stratify this heterogeneous sample. These markers could greatly enhance and the Harvard Brain Tissue Resource Center, approxi- the power of linkage analyses, by allowing a 'physiologic' mately three new, optimal TS brains are collected each year, parsing of the phenotype of affected and at-risk individuals. A common 'library' of antisaccade measures (74), eyeblink measures of prepulse 1694 Neuropsychopharmacology: The Fifth Generation of Progress inhibition of startle (73) or condition-test paired pulse para- Although several new therapeutic approaches to TS are digms (76), and measures of cortical silent periods after being developed, as discussed earlier, there is clearly a signifi- rTMS (80).

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A direct pathway originating in striatal agonists and AK inhibitors have marked antiinflammatory GABAergic–substance P–dynorphinergic neurons inhibits activity (67) cheap 10 mg citalopram free shipping, inhibiting free radical production buy cheap citalopram 40mg online, and thus the internal segment of the pars reticulata to disinhibit the they may be effective in maintaining cell function in AD order 10mg citalopram free shipping, ascending thalamic glutaminergic pathway and to activate in addition to modulating cytotoxic events order citalopram 10 mg overnight delivery. 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 buy 40 mg citalopram with amex. 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. Anatomic links be- shown positive effects in 1-methyl-4-[henyl-1,2,3,6-tetra- tween central dopamine and adenosine systems are well es- hydropyridine–lesioned marmosets and cynomolgus mon- tablished; adenosine A2A receptors are highly localized in keys, well characterized animal models of PD, enhancing striatum, nucleus accumbens, and olfactory tubercle, brain the effects of L-dopa (73,74). KW-6002 has successfully regions that also have high densities of dopamine D1 and completed human phase I trials. In men who drank no coffee, the incidence to the globus pallidus that originates from striatal GABA- of PD was 10. Through GABAergic relays, this 10,000 person-years in men drinking at least 28 oz of coffee pathway interacts with a glutaminergic pathway from the per day (75). Dopamine–adenosine (ADO) interactions in the substantia nigra. An indirect path- way dopaminergic pathway arises from the striatal GABA-enkephalinergic dopaminergic neurons on which both dopamine D1 and adenosine A2A receptors are co-localized. Through a GABAergic interneuron originating in the external globus pallidus, the indirect pathway connects to a gluta- minergic pathway arising in the subthalamic nucleus. This, in turn, can activate the internal seg- ment of the pars reticulata and, through another GABA pathway, inhibit ascending glutaminegic neurons arising from the thalamus that innervate the cortex. The direct pathway arises from striatal GABA–substance P–dynorphinergic neurons that, through a GABAergic relay, inhibit the internal segment of the pars reticulata to disinhibit the ascending thalamic-cortical glutaminergic pathway. The balance between the direct (activating) and indirect (inhibitory) striatal dopami- nergic pathways can then tonically regulate normal motor activity. Dopaminergic inputs arising from the substantia nigra pars compacta can facilitate motor activity, inhibiting the indirect path- way by activation of D2 receptors and activating the direct pathway by D1 receptor activation. Distribution, biochemistry and function of striatal adenosine A2A receptors. Prog Neurobiol 1999;59:355–396; and Richardson PJ, Kase H, Jenner PG.

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