Characterization of [(125) I]epibatidine binding and nicotinic agonist-mediated (86) Rb(+) efflux in interpeduncular nucleus and inferior colliculus of beta2 null mutant mice

The beta2 nicotinic acetylcholine receptor subunit null mutation eliminated most high affinity [(3) H]epibatidine binding in mouse brain, but significant binding remained in accessory olfactory nucleus, medial habenula, inferior colliculus and interpeduncular nucleus. Residual [(125) I]epibatidine binding sites in the inferior colliculus and interpeduncular nucleus were subsequently characterized. Inhibition of [(125) I]epibatidine binding by 12 agonists and six antagonists was very similar in these regions. Most acetylcholine-stimulated (86) Rb(+) efflux is eliminated in thalamus and superior colliculus of beta2 null mutants, but significant activity remained in inferior colliculus and interpeduncular nucleus. This residual activity was subsequently characterized. The 12 nicotinic agonists tested elicited concentration-dependent (86) Rb(+) efflux. Epibatidine was the most potent agonist. Cytisine was also potent and efficacious. EC(50) values for quaternary agonists were relatively high. Cytisine-stimulated (86) Rb(+) efflux was inhibited by six classical nicotinic antagonists. Mecamylamine and D-tubocurarine were most potent, while decamethonium was the least potent. Agonists and antagonists exhibited similar potency in both brain regions. Alpha-bungarotoxin (100 nm) did not significantly inhibit cytisine-stimulated (86) Rb(+) efflux, while the alpha3beta4 selective antagonist, alphaConotoxinAuIB, inhibited a significant fraction of the response in both brain regions. Thus, beta2 null mutant mice express residual nicotinic activity with properties resembling those of alpha3beta4*-nAChR.     

Autoradiographic distribution of high affinity muscarinic and nicotinic cholinergic receptors labeled with [3H]acetylcholine in rat brain

The relative distribution of muscarinic and nicotinic cholinergic receptors labeled with [3H]acetylcholine was determined using autoradiography. [3H]Acetylcholine binding to high affinity muscarinic receptors was similar to what has been described for an M-2 distribution: highest levels of binding occurred in the pontine and brainstem nuclei, anterior pretectal area and anteroventral thalamic nucleus, while lower levels occurred in the caudate-putamen, accumbens nucleus and primary olfactory cortex. Nicotinic receptors were labeled with [3H]acetylcholine to the greatest extent in the interpeduncular nucleus, several thalamic nuclei, medial habenula, presubiculum and superior colliculus, and to the least extent in the hippocampus and inferior colliculus. By using autoradiography to localize cholinergic binding sites throughout the brain it was observed that the distributions of high affinity muscarinic and nicotinic sites labeled with the endogenous ligand, [3H]acetylcholine are different from each other and are different from distributions of muscarinic and nicotinic sites labeled with muscarinic and nicotinic antagonists.     

Chronic nicotine administration does not increase nicotinic receptors labeled by [125I]epibatidine in adrenal gland,superior cervical ganglia,pineal or retina

Neuronal nicotinic acetylcholine receptors (nAChRs) were measured in CNS and peripheral tissues following continuous exposure to saline or nicotine hydrogen tartrate (3.3 or 10 mg/kg/day) for 14 days via osmotic pumps. Initially, binding of [3H](-)nicotine, [3H]cytisine and [3H]epibatidine to nAChRs was compared to determine the suitability of each for these kinds of studies. The predominant nAChR labeled by agonists in the cerebral cortex is an alpha 4 beta 2 subtype, whereas the predominant nicotinic receptors in the adrenal gland, superior cervical ganglia and pineal gland contain an alpha 3 subunit, and they do not bind either [3H](-)nicotine or [3H]cytisine with high affinity. In retina some nAChRs bind all three ligands with high affinity, and others appear to bind only [3H]epibatidine. Thus, only [3H]epibatidine had high enough affinity to be useful for measuring the nAChRs in all of the tissues. The receptors from nicotine-treated rats were then measured using [125I]epibatidine, which has binding characteristics very similar to [3H]epibatidine. Treatment with the two doses of nicotine hydrogen tartrate increased binding sites in the cerebral cortex by 40% and 70%, respectively. In contrast, no significant changes in the density of receptor binding sites were found in the adrenal gland, superior cervical ganglia, pineal gland or retina. These data indicate that chronic administration of nicotine even at high doses does not increase all nicotinic receptor subtypes, and that receptors containing alpha 3 subunits may be particularly resistant to this nicotine-induced change.     

Nicotinic alpha5 subunit deletion locally reduces high-affinity agonist activation without altering nicotinic receptor numbers

Neuronal nicotinic acetylcholine receptor subunit alpha5 mRNA is widely expressed in the CNS. An alpha5 gene polymorphism has been implicated in behavioral differences between mouse strains, and alpha5-null mutation induces profound changes in mouse acute responses to nicotine. In this study, we have examined the distribution and prevalence of alpha5* nicotinic acetylcholine receptor in mouse brain, and quantified the effects of alpha5-null mutation on pre-synaptic nicotinic acetylcholine receptor function (measured using synaptosomal (86)Rb(+) efflux) and overall [(125)I]epibatidine binding site expression. alpha5* nicotinic acetylcholine receptor expression was found in nine of fifteen regions examined, although < 20% of the total nicotinic acetylcholine receptor population in any region contained alpha5. Deletion of the alpha5 subunit gene resulted in localized loss of function (thalamus, striatum), which was itself confined to the DHbetaE-sensitive receptor population. No changes in receptor expression were seen. Consequently, functional changes must occur as a result of altered function per unit of receptor. The selective depletion of high agonist activation affinity sites results in overall nicotinic function being reduced, and increases the overall agonist activation affinity. Together, these results describe the receptor-level changes underlying altered behavioral responses to nicotine in nicotinic acetylcholine receptor alpha5 subunit-null mutants.     

Autoradiographic localization of nicotinic receptor binding in rat brain using [3H]methylcarbamylcholine, a novel radioligand

Light microscopic autoradiography was used to visualize the neuroanatomical distribution of nicotinic receptors in rat brain using a novel radioligand, [3H]methylcarbamylcholine (MCC). Specific [3H]MCC binding to slide-mounted tissue sections of rat brain was saturable, reversible and of high affinity. Data analysis revealed a single population of [3H]MCC binding sites with a Kd value of 1.8 nM and Bmax of 20.1 fmol/mg protein. Nicotinic agonists and antagonists competed for [3H]MCC binding sites in slide-mounted brain sections with much greater potency than muscarinic drugs. The rat brain areas containing the highest densities of [3H]MCC binding were in thalamic regions, the medial habenular nucleus and the superior colliculus. Moderate densities of [3H]MCC binding were seen over the anterior cingulate cortex, the nucleus accumbens, the zona compacta of substantia nigra and ventral tegmental area. Low densities of [3H]MCC binding were found in most other brain regions. These data suggest that [3H]MCC selectively labels central nicotinic receptors and that these receptors are concentrated in the thalamus, the medial habenular nucleus and the superior colliculus of the rat brain.     

Effect of Chronic Nicotine Treatment on Nicotinic Autoreceptor Function and N-[3H]Methylcarbamylcholine Binding Sites in the Rat Brain

It has been reported that N-methylcarbamylcholine (MCC), a nicotinic agonist, binds to central nicotinic receptors and causes an increase of acetylcholine (ACh) release from certain central cholinergic nerve terminals. The present experiments determine whether these two phenomena change in response to the chronic administration of nicotine, a procedure known to result in an increase in nicotinic binding sites. Chronic nicotine caused a brain region-specific up-regulation of [3H]MCC sites; binding increased in the frontal cortex, parietal cortex, striatum, and hippocampus, but not in the occipital cortex or cerebellum. The effect of nicotine was selective to nicotinic binding sites, because muscarinic sites, both M1 ([ 3H]pirenzepine) and M2 ([3H]ACh), were unaffected by chronic nicotine treatment. MCC increased the release of ACh from the frontal cortex and hippocampus by a calcium-dependent mechanism; MCC did not alter ACh release from striatum or occipital cortex of control animals. The MCC-induced increase in ACh release was not apparent in those animals which had been treated with nicotine. There was a partial recovery of nicotinic autoreceptor function when animals were allowed to recover (4 days) following chronic nicotine treatment, but the density of binding sites remained increased compared to control. Chronic nicotine did not change the potassium-evoked release of ACh from the frontal cortex or hippocampus, but decreased this measure from striatum. It also decreased the ACh content of the striatum, but not that of the cortex or the hippocampus; the activity of choline acetyltransferase was not altered in any of the regions tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

The alpha4beta2alpha5 nicotinic cholinergic receptor in rat brain is resistant to up-regulation by nicotine in vivo

We used immunoprecipitation with subunit-specific antibodies to examine the distribution of heteromeric neuronal nicotinic acetylcholine receptors (nAChRs) that contain the α5 subunit in the adult rat brain. Among the regions of brain we surveyed, the α5 subunit is associated in ∼37% of the nAChRs in the hippocampus, ∼24% of the nAChRs in striatum, and 11–16% of the receptors in the cerebral cortex, thalamus, and superior colliculus. Sequential immunoprecipitation assays demonstrate that the α5 subunit is associated with α4β2* nAChRs exclusively. Importantly, in contrast to α4β2 nAChRs, which are increased by 37–85% after chronic administration of nicotine, the α4β2α5 receptors are not increased by nicotine treatment. These data thus indicate that the α4β2α5 nAChRs in rat brain are resistant to up-regulation by nicotine in vivo , which suggests an important regulatory role for the α5 subunit. To the extent that nicotine-induced up-regulation of α4β2 nAChRs is involved in nicotine addiction, the resistance of the α4β2α5 subtype to up-regulation may have important implications for nicotine addiction.     

In Vivo Regulation of [3H]Acetylcholine Recognition Sites in Brain by Nicotinic Cholinergic Drugs

The in vivo regulation of [3H]acetylcholine [( 3H]ACh) recognition sites on nicotinic receptors in rat brain was examined by administering drugs that increase stimulation of nicotinic cholinergic receptors, either directly or indirectly. After 10 days of treatment with the cholinesterase inhibitor diisopropyl fluorophosphate, [3H]ACh binding in the cortex, thalamus, striatum, and hypothalamus was decreased. Scatchard analyses indicated that the decrease in binding in the cortex was due to a reduction in the apparent density of [3H]ACh recognition sites. In contrast, after repeated administration of nicotine (5-21 days), the number of [3H]ACh recognition sites was increased in the cortex, thalamus, striatum, and hypothalamus. Similar effects were observed in the cortex and thalamus following repeated administration of the nicotinic agonist cytisin. The nicotinic antagonists mecamylamine and dihydro-beta-erythroidine did not alter [3H]ACh binding following 10-14 days of administration. Further, concurrent treatment with these antagonists and nicotine did not prevent the nicotine-induced increase in these binding sites. The data indicate that [3H]ACh recognition sites on nicotinic receptors are subject to up- and down-regulation, and that repeated administration of nicotine results in a signal for up-regulation, probably through protracted desensitization at the recognition site.     

Brain and pituitary receptors for corticotropin releasing factor: Localization and differential regulation after adrenalectomy

Specific receptors for corticotropin releasing factor (CRF) were identified in two functionally distinct systems within the brain, the cortex and the limbic system. Autoradiographic mapping of the CRF receptors in the brain revealed high binding density throughout the neocortex and cerebellar cortex, subiculum, lateral septum, olfactory tract, bed nucleus of the stria terminalis, interpeduncular nucleus and superior colliculus. Moderate to low binding was found in the hippocampus, nucleus accumbens, claustrum, nucleus periventricularis thalamus, mammillary bodies, subthalamic nucleus, periaqueductal grey, locus coeruleus and nucleus of the spinal trigeminal tract. As in the anterior pituitary gland, CRF receptors in the brain were shown to be coupled to adenylate cyclase. However, in contrast to the marked decrease in CRF receptors observed after adrenalectomy in the anterior pituitary gland, CRF receptor concentration in the brain and pars intermedia of the pituitary was unchanged. The presence of CRF receptors in areas involved in the control of hypothalamic and autonomic nervous system functions is consistent with the major role of CRF in the integrated response to stress.     

Calcium Modulation of Activation and Desensitization of Nicotinic Receptors from Mouse Brain

Abstract: The effects of extracellular calcium on functional properties of nicotinic receptors from mouse thalamus were investigated. Previous studies have reported that calcium modulates the function of several neuronal nicotinic receptors. A ⁸⁶Rb⁺ ion efflux assay was developed to measure nicotinic receptor function from brain tissue, and data indicate that α₄β₂ receptors may mediate this response. Using the ⁸⁶Rb⁺ efflux assay, calcium effects on receptor activation, desensitization induced by high, activating and low, subactivating concentrations of agonist, and recovery from desensitization were examined. Effects of calcium on the kinetics of ligand binding were also investigated. Calcium modulated receptor activation by increasing the maximal response to nicotine in a concentration-dependent manner, without affecting the EC₅₀ of nicotine. Barium, but not magnesium, mimicked the effects of calcium on receptor activation. The increase in receptor activation could not be explained by changes in the ratio of activatable to desensitized receptors as assessed by the kinetics of ligand binding. Desensitization following activation was unaffected by calcium. Calcium, barium, and magnesium, however, increased the potency of nicotine for desensitization induced by exposure to low, subactivating concentrations of nicotine. Recovery from desensitization was not modulated by calcium. These data suggest that calcium modulates various functional aspects of nicotinic receptors from mouse brain and may do so via different mechanisms.     

Nicotine exploits a COPI-mediated process for chaperone-mediated up-regulation of its receptors

Chronic exposure to nicotine up-regulates high sensitivity nicotinic acetylcholine receptors (nAChRs) in the brain. This up-regulation partially underlies addiction and may also contribute to protection against Parkinson’s disease. nAChRs containing the α6 subunit (α6* nAChRs) are expressed in neurons in several brain regions, but comparatively little is known about the effect of chronic nicotine on these nAChRs. We report here that nicotine up-regulates α6* nAChRs in several mouse brain regions (substantia nigra pars compacta, ventral tegmental area, medial habenula, and superior colliculus) and in neuroblastoma 2a cells. We present evidence that a coat protein complex I (COPI)-mediated process mediates this up-regulation of α6* or α4* nAChRs but does not participate in basal trafficking. We show that α6β2β3 nAChR up-regulation is prevented by mutating a putative COPI-binding motif in the β3 subunit or by inhibiting COPI. Similarly, a COPI-dependent process is required for up-regulation of α4β2 nAChRs by chronic nicotine but not for basal trafficking. Mutation of the putative COPI-binding motif or inhibition of COPI also results in reduced normalized Förster resonance energy transfer between α6β2β3 nAChRs and εCOP subunits. The discovery that nicotine exploits a COPI-dependent process to chaperone high sensitivity nAChRs is novel and suggests that this may be a common mechanism in the up-regulation of nAChRs in response to chronic nicotine.     

Autoradiographic distribution of I-galanin binding sites in the rat central nervous system

Galanin (GAL) binding sites in coronal sections of the rat brain were demonstrated using autoradiographic methods. Scatchard analysis of ¹²⁵I-GAL binding to slide-mounted tissue sections revealed saturable binding to a single class of receptors with a Kd of approximately 0.2 nM. ¹²⁵I-GAL binding sites were demonstrated throughout the rat central nervous system. Dense binding was observed in the following areas: prefrontal cortex, the anterior nuclei of the olfactory bulb, several nuclei of the amygdaloid complex, the dorsal septal area, dorsal bed nucleus of the stria terminalis, the ventral pallidum, the internal medullary laminae of the thalamus, medial pretectal nucleus, nucleus of the medial optic tract, borderline area of the caudal spinal trigeminal nucleus adjacent to the spinal trigeminal tract, the substantia gelatinosa and the superficial layers of the dorsal spinal cord. Moderate binding was observed in the piriform, periamygdaloid, entorhinal, insular cortex and the subiculum, the nucleus accumbens, medial forebrain bundle, anterior hypothalamic, ventromedial, dorsal premamillary, lateral and periventricular thalamic nuclei, the subzona incerta, Forel's field H₁ and H₂, periventricular gray matter, medial and superficial gray strata of the superior colliculus, dorsal parts of the central gray, peripeduncular area, the interpeduncular nucleus, substantia nigra zona compacta, ventral tegmental area, the dorsal and ventral parabrachial and parvocellular reticular nuclei. The preponderance of GAL-binding in somatosensory as well as in limbic areas suggests a possible involvement of GAL in a variety of brain functions.     

Nicotinic activation of mesolimbic neurons assessed by rubidium efflux in rat accumbens and ventral tegmentum

Dopaminergic mesolimbic neurons, with cell bodies in the ventral tegmental area (VTA) projecting to the nucleus accumbens (NAc), have been shown to be involved in the development of drug dependence. The application of nicotine to either the VTA or NAc produces an increase in dopamine release; however, the positive reinforcement produced by the systemic injection of nicotine is primarily due to stimulation of nicotinic acetylcholine receptors (nAChRs) in the VTA. Because the brain levels of nicotine would likely be the same in both brain areas, the nAChRs in the NAc may be less sensitive than those in the VTA. This study was undertaken to make a direct comparison of the native nAChRs in intact slices of NAc and VTA by measuring nicotine-stimulated efflux of (86)Rb(+) in a superfusion assay. The potency of nicotine and several other agonists was similar in both brain areas, but nicotine was somewhat more efficacious in the NAc. The effects of treatment duration, calcium and nicotinic antagonists were also determined. The results suggest that the predominant effect of nicotine in the VTA following systemic administration is due to differences in neuronal circuitry or firing patterns rather than inherent differences in the two nAChR populations.     

Chronic Nicotine Alters Nicotinic Receptor-induced Presynaptic Ca<Superscript>2+</Superscript> Responses in Isolated Nerve Terminals

Brain nicotinic receptors display pronounced permeability for Ca²⁺ and localize to presynaptic nerve terminals, in addition to postsynaptic sites. Chronic exposure to nicotine has been shown to alter brain nicotinic receptor expression, but the functional consequences for presynaptic Ca²⁺ have not been directly examined. Here, we used confocal imaging to assess Ca²⁺ responses in individual nerve terminals from cortices of mice treated up to 14 days with nicotine as compared to vehicle-treated controls. Chronic nicotine treatment led to substantially enhanced amplitudes of presynaptic Ca²⁺ responses to acute application of nicotine at concentrations of 50 nM (2-fold) and 500 nM (1.7-fold), but not 50 μM. In addition, increased expression of high-affinity nicotinic receptors on isolated terminals was observed following chronic treatment, as determined immunocytochemically and pharmacologically. These findings suggest that chronic exposure to nicotine may lead to enhanced sensitivity to nicotine at select presynaptic sites in brain via up-regulation of high-affinity nicotinic receptors.     

福尔马林致痛提高大鼠中枢μ阿片受体密度及电针的加强作用

用放射自显影方法观察到;（１）大鼠脚掌注射福尔马林后,某些与镇痛有关的脑区如尾核头部、伏隔核、杏仁核、中央灰质、脚间核、中缝大核、脊髓背角等结构中μ阿片受体密度明显增加（Ｐ＜０．０５,Ｐ＜０．０１）;（２）给予电针抑制痛反应的大鼠,在其大部分上述结构及扣带回、隔区、视前内侧区、内膝体、上丘、中缝背核及中央上核受体密度明显增加;与福尔马林注射组相比,脚间核、中央灰质尾端腹外侧区、腰膨大背角的受体密度进一步增加。从而在受体水平支持伤害性刺激可以激活体内内阿片肽能活动,而电针可以加强这一活动的设想。     

Up-regulation of nicotinic receptors by nicotine varies with receptor subtype

Recent evidence suggests that in addition to alpha4beta2 and alpha3-containing nicotinic receptors, alpha6-containing receptors are present in midbrain dopaminergic neurons and involved in the nicotine reward pathway. Using heterologous expression, we found that alpha6beta2, like alpha3beta2 and alpha4beta2 receptors, formed high affinity epibatidine binding complexes that are pentameric, trafficked to the cell surface, and produced acetylcholine-evoked currents. Chronic nicotine exposure up-regulated alpha6beta2 receptors with differences in up-regulation time course and concentration dependence compared with alpha4beta2 receptors, the predominant high affinity nicotine binding site in brain. The alpha6beta2 receptor up-regulation required higher nicotine concentrations than for alpha4beta2 but lower than for alpha3beta2 receptors. The alpha6beta2 up-regulation occurred 10-fold faster than for alpha4beta2 and slightly faster than for alpha3beta2. Our data suggest that nicotinic receptor up-regulation is subtype-specific such that alpha6-containing receptors up-regulate in response to transient, high nicotine exposures, whereas sustained, low nicotine exposures up-regulate alpha4beta2 receptors.     

Mu-opioid receptors are involved in the tolerance to nicotine antinociception

Several studies have shown the participation of the endogenous opioid system on the antinociceptive effects and addictive properties of nicotine. The aim of the present study was to explore the involvement of the mu-opioid receptors in the development of tolerance to nicotine antinociception. Chronic treatment of C57BL/6 mice with nicotine (5 mg/kg s.c., three times daily during 12 days) resulted in tolerance to its antinociceptive responses in the tail-immersion test. We investigated the possible existence of adaptive changes in the expression and/or functional activity of mu-opioid receptors in these tolerant mice by using autoradiography of [(3)H]D-Ala(2)-MePhe(4)-Gly-ol(5) enkephalin ([(3)H]DAMGO) binding and DAMGO-stimulated guanosine [(35)S]5'-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) binding. The density of mu-opioid receptors in the spinal cord was not modified in nicotine-tolerant mice, whereas a decrease was found in the caudate-putamen, as well as in the core and the shell of the nucleus accumbens. However, the functional activity of these receptors was significantly increased in the spinal cord as a consequence of nicotine treatment. To further investigate the role of mu-opioid receptors in the tolerance to nicotine-induced antinociception, we evaluated this response in C57BL/6 mu-opioid receptor knockout mice. Chronic nicotine treatment produced tolerance in both wild-type and knockout animals, but tolerance developed faster in mice lacking mu-opioid receptors. These results indicate that mu-opioid receptors play an important role in the development of tolerance to nicotine antinociceptive effects.     

Chronic nicotine differentially affects the function of nicotinic receptor subtypes regulating neurotransmitter release

It is known that nicotine can activate several subtypes of release-regulating presynaptic nicotinic receptors (nAChRs) including those situated on central noradrenergic, dopaminergic, cholinergic and glutamatergic axon terminals. The objective of this study was to investigate the effects of chronic administration of (-)nicotine on the function of the above autoreceptors and heteroreceptors using rat superfused synaptosomes. In hippocampal synaptosomes prelabelled with [3H]noradrenaline (NA) the nicotine-evoked overflow of [3H]NA was higher in rats treated with nicotine for 10 days (via osmotic mini-pumps) than in vehicle-treated rats. In striatal synaptosomes, prelabelled with [3H]dopamine (DA), chronic nicotine did not modify the releasing effect of nicotine. No significant change was observed in experiments with synaptosomes from nucleus accumbens prelabelled with [3H]DA. Exposure of hippocampal synaptosomes prelabelled with [3H]choline to nicotine elicited release of [3H]acetylcholine; this effect was almost abolished in synaptosomes from animals administered nicotine for 10 days, suggesting down-regulation of nicotinic autoreceptors. In hippocampal synaptosomes prelabelled with [3H]D-aspartate, the releasing effect of epibatidine following chronic nicotine treatment did not differ from that in controls. The K+-evoked exocytotic release of the neurotransmitters tested was not modified by long-term nicotine administration. The results show that chronic nicotine differentially affects the function of release-regulating nAChR subtypes.     

Autoradiographic Visualization of the Receptor Subclasses for Vasoactive Intestinal Polypeptide (VIP) in Rat Brain

Vertongen, P., S. N. Schiffmann, P. Gourlet and P. Robberecht. Autoradiographic visualization of the receptor subclasses for Vasoactive Intestinal Polypeptide (VIP) in rat brain. Peptides 18(10) 1547–1554, 1997.—Vasoactive Intestinal Polypeptide (VIP) exerts its biological effects through interaction with two high affinity receptors named the VIP₁- and the VIP₂ receptors. Their messenger RNAs have been mapped in rat brain by in situ hybridization. A cyclic peptide (RO 25-1553) and a secretin analogue ([R¹⁶]chicken secretin) were identified as selective agonist peptides for the VIP₂- and VIP₁ receptors, respectively. The iodinated peptides retained the high affinity and selectivity of the unlabelled peptides and were used for the mapping of each receptor subclass in rat brain. VIP₁ receptors were present in the cerebral cortex, the piriform cortex, the claustrum, the caudate-putamen, the dentate gyrus, the lateral amygdaloïd nucleus, the anteroventral thalamic nucleus, the rhomboïd nucleus, the supraoptic nucleus and the choroïd plexus. VIP₂ receptors were present in the cerebral cortex, the claustrum, the caudate-putamen, the nucleus accumbens, the lateral septal nuclei, the bed nucleus of the stria terminalis, the basolateral amygdaloïd nucleus, the Ammon’s horn, the thalamic nuclei except some centromedial nuclei, the medial habenula, the suprachiasmatic nucleus, the periventricular nucleus, the mammilary nucleus, the superior colliculus and the choroïd plexus.     

Protein kinase C regulation of dopamine transporter initiated by nicotinic receptor activation in slices of rat prefrontal cortex

We previously reported that activation of nicotinic receptors causes an enhancement in amphetamine-stimulated release of dopamine via its transporter from slices of prefrontal cortex, but no such enhancement of release from slices of nucleus accumbens or striatum. The nicotinic receptors mediating the enhancement most likely contain alpha4 and beta2 subunits based upon pharmacological characterization. In this study, we sought to characterize the second messenger systems associated with the nicotine-mediated response. Sodium channel involvement was confirmed by the observation that tetrodotoxin blocked nicotine-mediated enhancement, whereas veratridine or elevated K(+) mimicked the enhancement seen with nicotine. Inclusion of EGTA blocked nicotine-mediated enhancement, suggesting that, even though no exogenous Ca(2+) was added, endogenous stores were required for the enhancement. The enhancement by nicotine was also abolished by the L-type voltage-dependent calcium channel (VDCC) antagonist nitrendipine, but not by the N-type VDCC antagonist omega-conotoxin GVIA. Finally, inhibition of protein kinase C also abolished the nicotine-mediated enhancement of amphetamine-stimulated dopamine release, whereas inhibitors of Ca(2+)/calmodulin kinase II did not. These findings establish that nicotine can exert selective effects on dopamine transporter activity in prefrontal cortex, an area involved in cognition and learning.