Neurokinin2-R in medial septum regulate hippocampal and amygdalar ACh release induced by intraseptal application of neurokinins A and B

The neurokinin receptors (NK-R), NK(2)- and NK(3)-R, have been implicated in behavioral processes, but apparently in opposite ways: while NK(2)-R agonism disrupts memory and has anxiogenic-like action, NK(3) -R agonists facilitate memory and display anxiolytic-like effects. Systemic application of NK(2)-R antagonists block the release of acetylcholine (ACh) in the hippocampus, which is induced by intraseptal administration of the NK(2)-R ligand, neurokinin A (NKA). We investigated the effects of medial septal injection of NKA and a preferred ligand of NK(3)-R, neurokinin B (NKB), on the activity of cholinergic neurons of the basal forebrain and assessed the role of the medial septal NK(2)-R in the control of extracellular ACh levels in cholinergic projection areas. ACh was dialysed in the frontal cortex, amygdala and hippocampus of anesthetized animals and was analysed by HPLC-EC. ACh levels in hippocampus and amygdala, but not in frontal cortex were increased after intraseptal injection of either NKA or NKB (0.1, 1, 10 μM). Application of the nonpeptidic NK(2)-R antagonist, saredutant SR48968 (1, 10, 100 pM), followed by NKA (1 μM) or NKB (10 μM) injection into the medial septum, blocked the ACh increase in hippocampus and amygdala. These results indicate that medial septal NK(2)-R have an important role in mediating ACh release, for one, via the septal-hippocampal cholinergic projection and, secondly, via direct or indirect route to the amygdala, but not frontal cortex. They also support the hypothesis that hippocampal cholinergic neurotransmission controls amygdala function suggesting that this interaction is regulated via NK(2)-R in the medial septum.     

Effect of denervation of the locus coeruleus projections by DSP-4 treatment on [3H]-raclopride binding to dopamine D(2) receptors and D(2) receptor-G protein interaction in the rat striatum

Changes in the control of dopaminergic neurotransmission by noradrenergic locus coeruleus (LC) projections has been implicated in such disorders as depression, drug addiction, and Parkinson's disease. In the present study, the effect of DSP-4, a neurotoxin highly selective for LC projections, on D(2) receptor abundance as assessed by [3H]-raclopride binding in the striatum was studied in rats after administration in doses of 10 and 50 mg/kg either 3 days or 1 month before decapitation. Three days after DSP-4 the levels of noradrenaline in the frontal cortex were dose-dependently reduced; after 1 month, noradrenaline levels were lowered only by the higher dose. DOPAC levels were dose-dependently reduced in the frontal cortex and striatum 3 days but not 1 month after DSP-4 treatment. Cortical 5-HIAA levels were reduced 3 days but not 1 month after DSP-4. The apparent number of D(2) receptor binding sites in the striatum was higher 1 month after either dose of DSP-4. DSP-4 treatment had no effect on [3H]-raclopride binding affinity, the ability of dopamine (DA) to compete with [3H]-raclopride binding and to activate [35S]GTPgammaS binding or on the binding affinities of GDP and [35S]GTPgammaS for corresponding G proteins 1 month after administration of the neurotoxin. These data suggest that after administration of DSP-4, short-term reduction in DA and 5-HT metabolism occurs. Subsequently, an upregulation of D(2) receptor binding sites develops in the striatum even after a minor denervation of the LC projections. Thus, alterations in the LC projection systems elicit lasting adaptive changes in DA-ergic neurotransmission that can serve as a substrate for psychiatric disorders.     

Specificity and efficacy of noradrenaline, serotonin depletion in discrete brain areas of Swiss mice by neurotoxins

The aim of this work is to define neurotoxins doses to have efficient and specific depletion of noradrenaline (NA), serotonin (5-HT) neurotransmission in cortex, striatum, hippocampus and hypothalamus of Swiss mice after intraperitoneal administration of, respectively, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) and para-chlorophenylalanine methyl ester hydrochloride (PCPA). The neurotransmitters concentrations were determined by high performance liquid chromatography with amperometric detection. The minimal single dose necessary to produce a highly significant decrease of NA levels (p<0.01 in comparison with control group) in hypothalamus (-44%), hippocampus (-91%), striatum (-40%) and cortex (-68%) was 50mg/kg but DA and 5-HT levels were modified, respectively, in hypothalamus and striatum. Three doses of PCPA 300 mg/kg over 3 consecutive days involve a profound depletion of 5-HT transmission in all discrete brain areas but NA and DA levels were also significantly reduced. In conclusion, DSP-4 has a different efficacy in discrete brain areas with a noradrenergic specificity which is not absolute, PCPA has a similar efficacy in all brain areas but is unspecific of 5-HT transmission.     

Dopaminergic regulation of cortical acetylcholine release.

The extent to which the activity of basal forebrain cholinergic neurons is influenced by dopamine (DA) was investigated using in vivo microdialysis of cortical acetylcholine (ACh). Systemic administration of the DA receptor agonist apomorphine significantly increased dialysate concentrations of ACh. Systemic, but not local, administration of d-amphetamine produced similar effects. Both D1 (SCH 23390) and D2 (haloperidol, raclopride) DA receptor antagonists attenuated the amphetamine-induced increase in cortical ACh release; however, only the D1 antagonist significantly reduced basal output of cortical ACh. These findings suggest that the activity of cortically projecting cholinergic neurons in the nucleus basalis is regulated in an excitatory manner by central dopaminergic neurons and that both D1 and D2 receptors are involved.     

Modulation of acetylcholine release by D1, D2 dopamine receptors in rat striatum under freely moving conditions

Using in vivo brain dialysis under freely moving conditions, we have studied the effects of dopamine (DA) agonists and antagonists on acetylcholine (ACh) and DA release in rat striatum. The striatal infusion of the D1 DA receptor specific agonist, SKF38393, increased striatal ACh release in a dose-dependent manner (10(-6) to 10(-4) M), and 3 x 10(-5) M SKF38393 elicited a 60% augmentation in the level of ACh release. The level of ACh was increased with perfusion of 10(-4) M SCH23390, a D1 specific antagonist, but decreased with 10(-3) M SCH23390. The D2 specific agonist, LY171555, and the antagonist, sulpiride, slightly altered the level of ACh in the striatum. On the other hand the level of DA dramatically increased in a dose-dependent manner with SKF38393 or SCH23390 and decreased with LY171555. LY171555 inhibited the effect of 10(-4) M SKF38393 on ACh release, and enhanced the effect of SKF38393 on DA release. These results suggest that the D1 DA receptor mainly mediates ACh release and the D2 DA receptor modifies the effects of the D1 receptor.     

Regulation of Dopamine D1 and D2 Receptors on Striatal Acetylcholine Release in Rats

The effects of dopamine (DA) D₁ and D₂ receptors on striatal acetylcholine (ACh) releases were investigated by in vivo microdialysis. All drugs were applied via dialysis membrane directly to the striatum. The levels of ACh release were increased by 10⁻⁴ M SKF38393, a D₁ receptor agonist. Although 10⁻⁴ M SCH23390, a D₁ receptor antagonist, exhibited an increase in the levels of ACh release, the agonist (10⁻⁴ M) induced-increase in the levels of ACh release was suppressed by coperfusion of the antagonist (10⁻⁴ M). In contrast, the levels of ACh release were decreased by the D₂ receptor agonist, N-434, in a dose-dependent manner (10⁻⁵ M to 10⁻⁷ M) and increased by the D₂ receptor antagonist, sulpiride, in a dose-dependent manner (10⁻⁵ M to 10⁻⁷ M). The agonist (10⁻⁵ M) induced-decrease in the levels of ACh release was suppressed by coperfusion of the antagonist (10⁻⁶ M). Coperfusion of D₁ (10⁻⁴ M) and D₂ (10⁻⁵ M) agonists blocked both effects of respective drug alone. In order to clarify the effect of endogenous DA, two drugs with different mechanisms for enhancing DA concentration in the synaptic cleft, the DA release-inducer methamphetamine, and the DA uptake inhibitor nomifensine were perfused separately. Both (10⁻⁴ M to 10⁻⁶ M) produced a dose- and a time-dependent decrease in the levels of ACh release. Significant higher levels of ACh release were observed in the striatum of the 6-hydroxydopamine (8

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)-treated rats with significant depletion of striatal DA content. These results suggest that in striatal DA-ACh interaction ACh release, as cholinergic interneuron's activity, is tonically inhibited via the D₂ receptor, mainly by dopaminergic input, and the D₁ receptor probably modifies the effect of the D₂ receptor indirectly.     

Lack of localization of 5-HT6 receptors on cholinergic neurons: implication of multiple neurotransmitter systems in 5-HT6 receptor-mediated acetylcholine release

The involvement of the cholinergic system in learning and memory together with the cognitive enhancing properties of 5-HT6 receptor antagonists led us to study the relationship between 5-HT6 receptors and cholinergic neurotransmission. A selective cholinergic lesion, induced by injection of the immunotoxin 192-IgG-Saporin into the nucleus basalis magnocellularis, failed to alter the density of 5-HT6 receptor mRNA or protein expression in the deafferentated frontal cortex, suggesting that 5-HT6 receptors are not located on cholinergic neurons. The 5-HT6 receptor antagonist SB-357134 (0.001-1 microM) induced a concentration-dependant K+-evoked [3H]acetylcholine (ACh) release in vitro in rat cortical and striatal slices, which was blocked by tetrodotoxin. SB-357134, up to 1 microM, stimulated glutamate release in cortical and striatal slices. In the cortex, riluzole (1 microM) blocked the SB-357134-induced K+-stimulated [3H]ACh release, and simultaneous administration of MK-801 (1 microM) and SB-357134 (0.05 microM) elicited an increase in K+-evoked ACh release. In the striatum, SB-357134, 1 microM, decreased dopamine release, and the increase in K+-evoked [3H]ACh release induced by 5-HT6 receptor blockade was reversed by the D1 receptor antagonist, SCH23390 (1 microM). In both the frontal cortex and striatum, bicuculline, 1 microM, showed no effect on SB-357134-evoked [3H]ACh. These results are discussed in terms of neurochemical mechanisms involved in 5-HT6 receptor functions.     

Cholinergic activity in autism: abnormalities in the cerebral cortex and basal forebrain.

OBJECTIVE: Measures of cholinergic transmitter activity were investigated in patients with autism because of reported neuropathological abnormalities in cholinergic nuclei in the basal forebrain. METHOD: Levels of cholinergic enzyme and receptor activity were measured in the frontal and parietal cerebral cortex of deceased autistic adults, similarly aged normal adults without mental retardation, and nonautistic mentally retarded adults. The immunoreactivity levels of brain-derived neurotrophic factor and nerve growth factor were measured in the basal forebrain. RESULTS: There were no differences between the autistic and comparison groups in choline acetyltransferase or acetylcholinesterase activity in the cerebral cortex and basal forebrain or in muscarinic M(2) receptor or alpha-bungarotoxin binding within the cortex. Cortical M(1) receptor binding was up to 30% lower than normal in the autistic subjects, and the difference reached significance in the parietal cortex. In both the parietal and frontal cortices, differences in nicotinic receptors assessed by [(3)H]epibatidine binding were significant and extensive (65%-73% lower in the autistic group than in the normal subjects); there were no differences in nicotine binding in the basal forebrain. Immunochemical analysis indicated lower levels of both the alpha(4) and beta(2) nicotinic receptor subunits in the parietal cortex. The M(1) receptor abnormality was not evident in the nonautistic group with mental retardation, although the lower [(3)H]epibatidine binding was apparent. In the basal forebrain, the level of brain-derived neurotrophic factor in the autistic group was three times as high as the level of the normal group. CONCLUSIONS: These neurochemical abnormalities implicate the cholinergic system in developmental disorders such as autism and suggest the potential for intervention based on cholinergic receptor modulation.     

Postnatal development of D1 dopamine receptors in the medial prefrontal cortex, striatum and nucleus accumbens of normal and neonatal 6-hydroxydopamine treated rats: a quantitative autoradiographic analysis.

The postnatal development of dopamine (DA) D1 receptors in the medial prefrontal cortex (mPFC), striatum (STR) and nucleus accumbens (NAC) of control and perinatally 6-hydroxydopamine (6-OHDA) lesioned rats was examined using quantitative autoradiography of 3H-SCH 23390 binding. D1 receptors are present at one week and increase only slightly to a stable level by 2 weeks in the STR and NAC. Their ontogeny is not altered by intracisternal injection of 6-OHDA 5 days after birth. A biphasic pattern of appearance of D1 receptors was found in the mPFC. D1 receptors are present in the mPFC at 1 week, increase 3-fold by 2-3 weeks, and then decline at 4 and 6 weeks. 6-OHDA lesions do not significantly alter this pattern. At all postnatal ages. D1 receptor binding in the mPFC exhibits a laminar distribution with increased receptor density in deep cortical layers (V, VI) compared to more superficial cortical layers (I, II). Both superficial and deep layers of D1 receptors in the mPFC show similar postnatal developmental patterns. DA turnover rates are consistently about 10-fold higher in frontal pole compared to remainder of forebrain at all postnatal ages. Early 6-OHDA lesions increase DA turnover in forebrain, but lead to a persistent reduction in DA turnover in frontal pole by 2 weeks of age.     

Physiological release of striatal acetylcholine (in vivo): effect of somatostatin on dopaminergic-cholinergic interaction

The effects of somatostatin (SOM) on the release of acetylcholine (ACh) and dopamine (DA) from striatum of freely moving rats were studied by transversal microdialysis. Acetylcholine (ACh) and dopamine (DA) were detected by high performance liquid chromatography (HPLC) with electrochemical detection. Somatostatin (0.1, 0.5 and 1 microM), administered locally through the microdialysis probe to the striatum, was able to release dose-dependently ACh from the cholinergic neurons of the striatum. The increase in the extracellular levels of ACh produced by 1 microM SOM in the striatum reached a maximum of 200%. ACh-releasing effect of SOM was completely inhibited by tetrodotoxin indicating that neuronal firing is involved in its effect. Local infusion of sulpiride, 10 microM, D(2) receptor antagonist, potentiated (about 100%) the SOM (1 microM)-induced release of ACh. SOM, 1 microM, was more effective in enhancing the release of ACh in the striatum (two-fold increase) after degeneration of the nigrostriatal DA pathway with 6-hydroxydopamine (6-OHDA) (250 microg/animal, i.c.v.). The D(2) receptor agonists bromcriptine, 10 microM, or apomorphine, 10 microM, completely antagonize SOM-induced release. SOM, 1 microM, enhanced the release of DA (about 400%). These findings indicate that SOM is capable of releasing both ACh and DA in the striatum, however, its effect on ACh release is partially masked unless the D(2) receptor-mediated tonic inhibitory effect of released DA from the nigro-striatal pathway is attenuated.     

Rotational behaviour produced in rats by unilateral electrolytic lesions of the ascending noradrenergic bundles

Marked differences were found in the activity of choline acetylase (ChAc) in various discrete areas of the rat striatum. The richest cholinergic innerbation was observed in the centrolateral part of the structure. A similar distribution was obtained by measuring acetylcholine (ACh) levels in punches taken from frozen frontal serial slices. As revealed by the analysis of the topographical distributions of ChAc activity, ACh, 5-HT and DA, the regional cholinergic innervation differed markedly from that of aminergic terminals.Changes in ACh levels induced by drugs could be estimated in microdiscs of tissues punched from frozen slices. Apomorphine and haloperidol, which increased and decreased ACh levels respectively, induced similar effects in the various striatal areas examined. By contrast quipazine, a drug acting on 5-HT uptake and release and on serotoninergic recptors, selectively increased ACh levels in some areas of the striatum but not in others. The regional changes in ACh levels induced by quipazine were satisfactorily correlated with the regional distribution of 5-HT but not with that of DA.These results suggest that a limited population of striatal cholinergic neurons is under the inhibitory control of serotoninergic neurons. They also indicate that some striatal cholinergic neurons influenced by dopaminergic neurons are not controlled by serotoninergic neurons.     

Differential changes in cholinergic markers from selected brain regions after specific immunolesion of the rat cholinergic basal forebrain system

The aim of this study was to characterize the effects of cortical cholinergic denervation on cholinergic parameters in the cerebral cortex and basal forebrain using a novel immunotoxin (conjugate of the monoclonal antibody 192IgG against the low-affinity nerve growth factor receptor armed with cytotoxin saporin) to efficiently and selectively lesion cholinergic neurons in rat basal forebrain. Seven days following an intracerebroventricular injection of the cholinergic immunotoxin 192IgG-saporin the binding levels of nicotinic and M¹- and M₂-muscarinic acetylcholine receptors (mAChR), high-affinity choline uptake sites, as well as the m1-m4 mAChR mRNA were determined in coronal brain sections by both receptor autoradiography and in situ hybridization, and quantified by image analysis. Hemicholinium-3 binding to high-affinity choline uptake sites was decreased by up to 45% in all cortical regions and in the hippocampus after a single injection of the immunotoxin compared to controls. In contrast, M₁-mAChR sites were increased over the corresponding control value in the anterior parts of cingulate, frontal, and piriform cortex by about 20%, in the hindlimb/forelimb areas (18%), in the parietal cortex (35%), in the occipital cortex area 2 (17%), as well as in the temporal cortex (25%) following immunolesion. M₂-mAChR levels were found to be significantly increased in the posterior part of the parietal cortex area 1 (by about 22%) and in the occipital cortex area 2 (20%) only. With respect to laminar cortical localization, M₂-mAChRs and choline uptake sites were altered in all cortical layers, whereas M₁-mAChRs were preferentially affected in the upper cortical layers by the immunolesion. The increase in M₁-mAChR binding in the temporal and occipital cortex as a consequence of the immunolesion was complemented by an increase in the amount of m1 and m3 mAChR mRNA of about 20% in these regions. The elevated levels of M₂-mAChR sites in the occipital and temporal cortex following immunolesion were accomplanied by an increase in the m4 (by 25%) but not m2 mAChR mRNA. There was no effect of the immunolesion on the m1-m4 mAChR mRNA in frontal cortical regions. In the basal forebrain, however, immunolesioning caused about a 40% decrease in the level of m2 mAChR mRNA in the medial and lateral septum as well as in the vertical and horizontal limb of the diagonal band, whereas M₁- and M₂-mAChR binding and the levels of m1, m3, and m4 mAChR mRNA were not affected by the immunolesion in any of the basal forebrain nuclei studied. Seven days after a single dose of the 192IgG-saporin immunotoxin there was no change in the level of cortical nicotinic acetylcholine receptor sites in any of the regions studied compared to corresponding controls. The region-specific changes in the level of M₁- and M₂-mAChRs, as well as corresponding receptor gene expression and the lack of effects on cortical nicotinic receptors, may be part of an adaptive mechanism in response to cholinergic degeneration. These data further support the usefulness of the 192IgG-saporin conjugate as an appropriate tool to produce cortical cholinergic dysfunction. © 1995 Wiley-Liss, Inc.     

Cortico-hippocampal APP and NGF levels are dynamically altered by cholinergic muscarinic antagonist or M1 agonist treatment in normal mice

To determine whether altered cholinergic neurotransmission can modify the long-term secretion of amyloid precursor protein (APP), endogenous levels of APP and nerve growth factor (NGF), we administered a selective M1 muscarinic receptor agonist (RS86) or the muscarinic antagonist, atropine, for 7 days in vivo into young adult mice (C57BL/6j). The levels of NGF and total APP in the hippocampus, frontal cortex, striatum, parietal cortex and cerebrospinal fluid (CSF) were examined by ELISA and Western blot. We found that this repeated i.m. administration of M1 receptor agonist resulted in decreased total APP levels in the hippocampus, frontal cortex and parietal cortex, and increased secreted alpha-APPs levels in the CSF. M1 agonist treatment also resulted in decreased NGF levels in the hippocampus and CSF. These effects of the M1 muscarinic agonist could be blocked by atropine, which by itself elevated tissue levels of total APP. Interestingly, we found that the decrease of total APP in the hippocampus and striatum after M1 agonist treatment inversely correlated with the change in NGF levels. These data suggest that a sustained increased cholinergic, M1-mediated neurotransmission will enhance secretion of alpha-APPs in CSF and adaptively reduce the levels of total APP and NGF in the corticohippocampal regions of normal mice. The dynamic and adaptive regulation linking total APP and NGF levels in normal adult mice is relevant for understanding the pathophysiology of conditions with cholinergic and APP related pathologies, like Alzheimer's disease and Down's syndrome.     

The disruption of spatial cognition and changes in brain amino acid, monoamine and acetylcholine in rats with transient cerebral ischemia

We investigated the disruption of spatial cognition due to transient forebrain ischemia using an 8-arm radial arm maze task in rats. Five or 10 min of ischemia did not affect the task acquisition. When rats established spatial cognition by daily training of the task, 10 min of ischemia significantly decreased the number of correct choices and increased the errors in the task when performed 24 h after reperfusion. These changes, however, returned to the normal level after about 4 days of daily training. Glutamic acid (Glu) and acetylcholine (ACh) release from the dorsal hippocampus (DH) was observed to transiently increase during ischemia. However, neither the content of noradrenaline (NA) nor the release of NA in the DH changed during ischemia. The NA and ACh release from the DH, however, gradually decreased during reperfusion, and the decrease became significant at 24 h after reperfusion. The NA content of the frontal cortex (FO and the DH increased 7 days after reperfusion. These results suggest that the disruption of spatial cognition induced by 10 min of ischemia may be attributed to a greater degree to the dysfunction of the hippocampal ACh and NA, and cortical NA systems, rather than to the development of neuronal cell death in these areas.     

Dopamine D1 autoreceptor function: possible expression in developing rat prefrontal cortex and striatum.

Synthesis-modulating dopamine (DA) autoreceptor function was studied in vivo using gamma-butyrolactone (GBL) to block propagation along DA axons. DA synthesis was measured by the accumulation of L-3,4-dihydroxyphenylalanine (L-DOPA) after inhibition of aromatic L-amino acid decarboxylase. GBL treatment markedly increased DOPA accumulation in both the striatum and prefrontal cortex of developing rats. The selective DA partial D1 agonist SKF-38393 inhibited this GBL-induced rise in DA synthesis in both the striatum and prefrontal cortex of 15- and 22-day-old rats, but not in adults. The effects of SKF-38393 in developing rats were mimicked by the non-catechol D1 partial agonist CY-208-243, and were blocked by the D1 antagonist SCH-23390, suggesting receptor mediation. The mixed D2/D3 agonist quinpirole attenuated DA synthesis in striatum of both two-week-old and adult rats, but failed to inhibit the GBL-induced increase in DA synthesis in the developing prefrontal cortex. These findings suggest that synthesis-modulating D1-like receptor function may emerge transiently in the developing mammalian forebrain. In the adult striatum these functions appear to be subsumed by D2-like receptors, whereas all synthesis-modulating DA receptor function in prefrontal cortex appears to be essentially lost with maturation.     

Enhancement of [3H]dopamine release and its [3H]metabolites in rat striatum by nicotinic drugs

Recent evidence has identified directly muscarinic acetylcholine receptor (m-ACh R) and nicotinic acetylcholine receptor (n-ACh R) in the brain utilizing receptor binding assay. Several studies suggest that release of dopamine (DA) in the striatum is regulated by presynaptic receptors present on dopaminergic terminals. In the present study, the effects of cholinergic drugs on [3H]DA release were examined using micropunched tissue and synaptosomes obtained from rat striatum. ACh (5 x 10(-4) M) significantly increased spontaneous [3H]DA release, and the overflow was partially inhibited by D-tubocurarine (1 mM) but not atropine. Nicotine, lobeline, coniine and spartein, nicotinic agonists, significantly increased spontaneous and 25 mM K + evoked [3H]DA release almost in a dose-dependent manner. In contrast, oxotremorine (2 x 10(-4) M), muscarinic agonist, did not any change in [3H]DA efflux. Furthermore, the metabolites of [3H]DA were separated by column chromatography. The main metabolite of [3H]DA in the spontaneous release from rat striatal synaptosomes was [3H]DOPAC (3,4-dihydroxyphenylacetic acid). Lobeline (5 x 10(-5) M) accelerated the outflow of [3H]DOPAC and [3H]OMDA metabolites (O-methylated and deaminated metabolites). These results could give rise to the suggestion that there was n-ACh R on the dopaminergic nerve terminals in the striatum and n-ACh R might have related to a directly excitatory effect on the DA release.     

Time-related effects of stress on cholinergic sensitivity

The effect of the administration of the muscarinic cholinergic agonist oxotremorine on locomotor activity was investigated in DBA/2 mice subjected to chronic restraint stress of different durations (120 min daily for 10, 14 or 18 days). Oxotremorine induced a depressant effect on locomotion, which was reduced after 10 and 14 days of restraint, but not after a 18-day restraint stress. Acetylcholine (ACh) content was significantly reduced in prefrontal cortex after 10 and 14 days of stress but returned to control values after 18 days of restraint. No changes in ACh content were observed in nucleus accumbens and striatum. These results are discussed in terms of possible changes in muscarinic receptor sensitivity.     

Cortical and nigral deafferentation and striatal cholinergic markers in the rat dorsal striatum: different effects on the expression of mRNAs encoding choline acetyltransferase and muscarinic m1 and m4 receptors

The regulation of the striatal m1 and m4 muscarinic receptor mRNA as well as the choline acetyltransferase (ChAT) mRNA expression by nigral dopaminergic and cortical glutamatergic afferent fibres was investigated using quantitative in situ hybridization histochemistry. The effects induced by a unilateral lesion of the medial forebrain bundle and a bilateral lesion of the sensorimotor (SM) cortex were analysed in the dorsal striatum 3 weeks after the lesions. Dopaminergic denervation of the striatum resulted in a marked decrease in the levels of m4 mRNA throughout the striatum, while the levels of muscarinic m1 mRNA and ChAT mRNA in cholinergic neurons were unaffected by the lesion. In contrast, following bilateral cortical ablation, the levels of the muscarinic m1 mRNA were significantly increased in the striatal projection area of the SM cortex, whereas the expression of m4 mRNA remained unchanged. Single cholinergic cell analysis by computer-assisted grain counting revealed a decreased labelling for ChAT mRNA per neuron following cortical ablation. However, in contrast to the topographical m1 mRNA changes, the decreased ChAT mRNA expression was evenly distributed within the striatum, suggesting an indirect cortical control upon striatal cholinergic interneurons. Altogether, these data suggest that dopaminergic nigral and glutamatergic cortical afferents modulate differentially cholinergic markers, at the pre- and post-synaptic levels. Beside the fact that nigral and cortical inputs exert an opposite control on cholinergic neurotransmission, our study further shows that this control involved different muscarinic receptor subtypes: the m4 and m1 receptors, respectively.     

Regulation of cerebral cortical blood flow by the basal forebrain cholinergic fibers and aging

This article reviews the study of neural vasodilator mechanisms of the cerebral cortex by basal forebrain cholinergic nerve fibers and their age-related function in rats. During the last decade, we have demonstrated a neural regulatory system of cerebral blood flow in rats involving intracerebral cholinergic vasodilator nerve fibers originating in the basal forebrain and projecting to the cerebral cortex. Activation of these cholinergic vasodilator fibers results in the release of acetylcholine (ACh) within the cortex, activation of both nicotinic and muscarinic ACh receptors, and vasodilatation without coupling to glucose metabolic rates. This cholinergic vasodilator system has been shown to decline with age in rats mainly due to age-related declines of nicotinic ACh receptor activity. However, muscarinic ACh receptor activity and the release of ACh into the extracellular space in the cortex are well maintained during aging. The present age-related decline of the intracerebral cholinergic vasodilator system found in rats seems to affect cognitive function during aging, although this cholinergic vasodilator system has not yet been demonstrated in humans.     

Differential effects of phencyclidine and methamphetamine on dopamine metabolism in rat frontal cortex and striatum as revealed by in vivo dialysis

We have examined the effects of schizophrenomimetic drugs including phencyclidine (PCP) and methamphetamine (MAP) on cortical and striatal dopamine (DA) metabolism using an in vivo dialysis technique in the rat. An acute systemic injection of PCP (2.5–10 mg/kg, intraperitoneally (i.p.)) dramatically increased concentrations of DA, 3,4-dihydroxy-phenylacetic acid, and homovanillic acid in the dialysates from the medial frontal cortex in a dose-dependent fashion. However, PCP (2.5–10 mg/kg, i.p.) caused a much lower augmentation of extracellular DA release, with a significant decrease in dialysate DOPAC levels in the striatum. Moreover, continuous infusion of tetrodotoxin (TTX, 10⁻⁵ M) into the prefrontal or striatal region through the microdialysis tube completely blocked the ability of PCP (10 mg/kg, i.p.) to alter the extracellular release of DA and its metabolites in the respective areas. In contrast, MAP (4.8 mg/kg, i.p.) elicited a marked and tetrodotoxin-resistant increase in DA levels with a significant loss of DOPAC contents in the extracellular space of both the frontal cortex and the striatum. The present results clearly demonstrate the differential effects of PCP on cortical and striatal DA transmission, suggesting that PCP may facilitate DA release in the medial frontal cortex by increasing impulse flow in the DA neurons projecting to the cortical area, whereas PCP-induced elevation of extracellular DA in the striatum may be caused mainly by reuptake inhibition of DA liberated by basal activity of the striatal DA neurons. The regional variation in PCP-induced DA release would be due to the combination of NMDA (N-methyl-D-aspartate) receptor blocking and DA reuptake inhibition by the drug. The uniform and TTX-resistant nature of MAP-induced changes in brain DA metabolism may result from the direct actions of MAP at DA nerve terminals. © 1996 Wiley-Liss, Inc.