Studies on cholecystokinin-containing neuronal pathways in rat cerebral cortex and striatum

Quantitative mass spectrometry reveals changes in SNAP-25 isoforms in schizophrenia

SNAP-25 and syntaxin are presynaptic terminal SNARE proteins altered in amount and function in schizophrenia. In the ventral caudate, we observed 32% lower SNAP-25 and 26% lower syntaxin, but greater interaction between the two proteins using an in vitro assay. SNAP-25 has two isoforms, SNAP-25A and B, differing by only 9 amino acids, but with different effects on neurotransmission. A quantitative mass spectrometry assay was developed to measure total SNAP-25, and proportions of SNAP-25A and B. The assay had a good linear range (50- to 150-fold) and coefficient of variation (4.5%). We studied ventral caudate samples from patients with schizophrenia (n=15) previously reported to have lower total SNAP-25 than controls (n=13). We confirmed 27% lower total SNAP-25 in schizophrenia, and observed 31% lower SNAP-25A (P=0.002) with 20% lower SNAP-25B amounts (P=0.10). Lower SNAP-25A amount correlated with greater SNAP-25-syntaxin protein-protein interactions (r=-0.41, P=0.03); the level of SNAP-25B did not. Administration of haloperidol or clozapine to rats did not mimic the changes found in schizophrenia. The findings suggest that lower levels of SNAP-25 in schizophrenia may represent a greater effect of the illness on the SNAP-25A isoform. This in turn could contribute to the greater interaction between SNAP25 and syntaxin, and possibly disturb neurotransmission in the illness.

Bulk regional viral injection in neonatal mice enables structural and functional interrogation of defined neuronal populations throughout targeted brain areas

The ability to label and manipulate specific cell types is central to understanding the structure and function of neuronal circuits. Here, we have developed a simple, affordable strategy for labeling of genetically defined populations of neurons throughout a targeted brain region: Bulk Regional Viral Injection (BReVI). Our strategy involves a large volume adeno-associated virus (AAV) injection in the targeted brain region of neonatal Cre driver mice. Using the mouse olfactory bulb (OB) as a model system, we tested the ability of BReVI to broadly and selectively label tufted cells, one of the two principal neuron populations of the OB, in CCK-IRES-Cre mice. BReVI resulted in labeling of neurons throughout the injected OB, with no spatial bias toward the injection site and no evidence of damage. The specificity of BReVI labeling was strikingly similar to that seen previously using immunohistochemical staining for cholecystokinin (CCK), an established tufted cell marker. Hence, the CCK-IRES-Cre line in combination with BReVI can provide an important tool for targeting and manipulation of OB tufted cells. We also found robust Cre-dependent reporter expression within three days of BReVI, which enabled us to assess developmental changes in the number and laminar distribution of OB tufted cells during the first three postnatal weeks. Furthermore, we demonstrate that BReVI permits structural and functional imaging in vivo, and can be combined with transgenic strategies to facilitate multi-color labeling of neuronal circuit components. BReVI is broadly applicable to different Cre driver lines and can be used to regionally manipulate genetically defined populations of neurons in any accessible brain region.

A novel mechanism and treatment target for presynaptic abnormalities in specific striatal regions in schizophrenia

Abnormalities of amount and function of presynaptic terminals may have an important role in the mechanism of illness in schizophrenia. The SNARE proteins (SNAP-25, syntaxin, and VAMP) are enriched in presynaptic terminals, where they interact to form a functional complex to facilitate vesicle fusion. SNARE protein amounts are altered in the cortical regions in schizophrenia, but studies of protein-protein interactions are limited. We extended these investigations to the striatal regions (such as the nucleus accumbens, ventromedial caudate (VMC), and dorsal caudate) relevant to disease symptoms. In addition to measuring SNARE protein levels, we studied SNARE protein-protein interactions using a novel ELISA method. The possible effect of antipsychotic treatment was investigated in parallel in the striatum of rodents that were administered haloperidol and clozapine. In schizophrenia samples, compared with controls, SNAP-25 was 32% lower (P=0.015) and syntaxin was 26% lower (P=0.006) in the VMC. In contrast, in the same region, SNARE protein-protein interactions were higher in schizophrenia (P=0.008). Confocal microscopy of schizophrenia and control VMC showed qualitatively similar SNARE protein immunostaining. Haloperidol treatment of rats increased levels of SNAP-25 (mean 24%, P=0.003), syntaxin (mean 18%, P=0.010), and VAMP (mean 16%, P=0.001), whereas clozapine increased only the VAMP level (mean 13%, P=0.004). Neither drug altered SNARE protein-protein interactions. These results indicate abnormalities of amount and interactions of proteins directly related to presynaptic function in the VMC in schizophrenia. SNARE proteins and their interactions may be a novel target for the development of therapeutics.

CCK/dopamine interactions in Fawn-Hooded and Wistar-Kyoto rat brain

The aim of this study was to compare the actions of CCK neuropeptides within the nucleus accumbens (N.Acc) of alcohol preferring (Fawn-Hooded, FH) and alcohol nonpreferring (Wistar-Kyoto, WKY) rats. CCK-8S (30-300 nM) facilitated the K(+) stimulated release of [(3)H]dopamine (DA) from N.Acc prisms in both rat strains, whereas CCK-4 (30 nM-1 microM) caused a significant decrease of evoked [(3)H]DA in the FH rat only. A scattered distribution of CCK-A and -B receptor immunopositive varicose fibers were visualized throughout the N.Acc of both rat strains along with a topographic distribution of CCK receptor positive cells throughout the ventral mesencephalon.

Cholecystokinergic innervation of nucleus accumbens subregions

Behavioral and pharmacological evidence has shown a different and opposite role of the neuropeptide cholecystokinin (CCK) on the dopamine (DA) function in the caudal versus rostral part of the nucleus accumbens. Previous reports have speculated that the caudal region of the nucleus accumbens would receive CCKergic innervation from dopaminergic neurons of the mesencephalic ventral tegmental area, whereas the CCKergic input to the rostral accumbens would originate in non-dopaminergic neurons from extra-mesencephalic areas of the brain. In the present study, this issue was addressed using retrograde tracing techniques in conjunction with immunocytochemistry. Retrograde tracers were injected in the three compartments of the accumbens (i.e., rostral pole, core and septal shell). In summary, our results demonstrate that 1) the main CCKergic input of the accumbens originates in the ventral mesencephalon; 2) the rostral pole is equally innervated by CCK neurons projecting from both substantia nigra pars compacta and ventral tegmental area; 3) the primary source of CCK innervation of the accumbal core is the substantia nigra pars compacta; and 4) whereas the CCKergic input to the septal shell originates primarily in the ventral tegmental area. Additionally, our results also showed that most of the CCKergic neurons projecting to any of the accumbal compartments also produce dopamine. These data constitute the first neuroanatomical evidence for the differential effects of CCK on dopamine actions in the different regions of the nucleus accumbens.

Cholecystokinin B receptor antagonists enhance the locomotor response to the N-methyl-D-aspartate antagonists phencyclidine and dizocilpine maleate

The cholecystokinin antagonists L-740,093, L-365,260, LY-288513 and CI988, which are all selective for the cholecystokininB receptor subtype, were examined for their ability to modulate locomotor activity induced by the non-competitive N-methyl-D-aspartate receptor antagonists phencyclidine and dizocilpine maleate (MK-801) in habituated rats. It was found that the locomotor effects (motility, locomotion) produced by subcutaneous administration of phencyclidine (2 mg/kg) were significantly potentiated by intraperitoneal (i.p.) administration of L-740,093 (1 mg/kg), L-365,260 (10 mg/kg), LY-288513 (10 mg/kg), but not CI-988 (10 mg/kg). Locomotor activity induced by subcutaneous administration of MK-801 (0.15 mg/kg) was potentiated by intraperitoneal L-740,093 (0.3, 1 and 3 mg/kg). L-740,093, L-365,260, LY-288513 and CI-988 administered alone did not alter spontaneous locomotor activity (motility) as compared to vehicle/saline controls. However, when these antagonists were administered to naive, unhabituated rats, L-365,260 and LY-288513 caused a significant reduction in motility compared to the vehicle control. These findings suggest that, although cholecystokinin may be involved in exploratory behaviour exhibited by rats in a novel environment (unhabituated rats), its role is negligible in rats subjected to a familiar environment (habituated rats). Furthermore, these results support the interpretation that cholecystokinin has a suppressant effect on locomotion elicited by phencyclidine and MK-801, and that this inhibitory action of cholecystokinin is mediated via the cholecystokininB receptor, since it can be eliminated by administration of cholecystokininB antagonists. It is suggested that the site of action of the cholecystokininB receptors involves mainly the cholecystokinin/glutamate projection from the cortex to the anterior nucleus accumbens and/or striatum. Finally, the present study provides two examples of endogenous release of a neuropeptide resulting in behavioural consequences.

Direct contractile effect of cholecystokinin octapeptide on caecal circular smooth muscle cells of guinea pig via both CCK-A and CCK-B/gastrin receptors

This study was designed to investigate the participation of cholecystokinin(CCK)-A and/or CCK-B/gastrin receptors in CCK-8-induced contraction of guinea pig caecal circular smooth muscle cells, using a novel selective CCK-A receptor antagonist, (S)-N-[1-(2-fluorophenyl)-3,4,6,7-tetrahydro-4-oxo-pyrrolo-[3,2,1-jk] [1,4]benzodiazepine-3-yl]-1H-indole-2-carboxamide (FK480), and a novel selective CCK-B/gastrin receptor antagonist, (R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo-5-phenyl-1H-1, 4-benzodiazepine-3-yl]-3-(3-methylphenyl)urea (YM022). Concentration-response curves for the contractile effect of CCK-8 alone and in the presence of 0.1nM FK480, 0.1 nM YM022, or a combination of 0.1 nM FK480 and 0.1 nM YM022 on isolated smooth muscle cells were determined. In addition, the inhibitory effects of various concentrations of FK480 or YM022 on 1 nM CCK-8-induced contraction were examined. At a concentration of 0.1 nM, both FK480 and YM022 shifted the concentration-response curve for CCK-8 to the right (about 100 times) with the same potency. In addition, a concentration-response curve for a combination of 0.1 nM FK480 and 0.1 nM YM022 was shifted to the right (about 100 times) of the curves for 0.1 nM FK480 alone or 0.1 nM YM022 alone. Both antagonists inhibited 1 nM CCK-8-induced contraction of caecal circular smooth muscle cells in a concentration-dependent manner, with the similar inhibitory potency. A significant inhibition was obtained at a concentration as low as 0.1 nM FK480 and 0.1 nM YM022. This study strongly suggested the presence of both CCK-A and CCK-B/gastrin receptors in caecal circular smooth muscle cells of guinea pig, and that the contractile effect of CCK-8 on these cells was mediated via both of these receptors.

Modulation of neurotransmitter release by cholecystokinin in the neostriatum and substantia nigra of the rat: regional and receptor specificity

The effect of cholecystokinin peptides on the release of dynorphin B, aspartate, glutamate, dopamine and GABA in the neostriatum and substantia nigra of the rat was investigated using in vivo microdialysis. Sulphated cholecystokinin-8S in the dialysis perfusate (1-100 microM) induced a concentration-dependent increase in extracellular dynorphin B and aspartate levels, both in the neostriatum and substantia nigra. Striatal dopamine levels were only increased by 100 microM of cholecystokinin-8S, while in the substantia nigra they were increased by 10-100 microM of cholecystokinin-8S. Extracellular GABA and glutamate levels were increased following 100 microM of cholecystokinin-8S only. Striatal cholecystokinin-8S administration also produced a significant increase in nigral dynorphin B levels. Local cholecystokinin-4 (100 microM) produced a moderate, but significant, increase of extracellular dynorphin B and aspartate levels in the neostriatum and substantia nigra. No effect was observed on the other neurotransmitters investigated. A 6-hydroxydopamine lesion of the nigrostriatal dopamine pathway did not affect the increases in dynorphin B and aspartate levels produced by local administration of cholecystokinin-8S. Basal extracellular GABA levels were increased significantly in both the neostriatum and substantia nigra ipsilateral to the lesion. Nigral glutamate and aspartate levels were also increased in the lesioned substantia nigra, but in the lesioned neostriatum aspartate levels were decreased. The cholecystokinin-B antagonist L-365,260 (20 mg/kg, s.c.), but not the cholecystokinin-A antagonist L-364,718 (devazepide; 20 mg/kg, s.c.), significantly inhibited the effect of cholecystokinin-8S on striatal dynorphin B and aspartate levels. In the substantia nigra, however, the effect of cholecystokinin-8S on dynorphin B and aspartate levels was inhibited to a similar extent by both L-365,260 and L-364,718. Pretreatment with L-364,718, but not with L-365.260, prevented the increase in nigral dopamine levels produced by nigral cholecystokinin-8S administration. Taken together, these results suggest that cholecystokinin-8S modulates dynorphin B and aspartate release in the neostriatum and substantia nigra of the rat via different receptor mechanisms. In the neostriatum, the effect of cholecystokinin-8S on dynorphin B and aspartate release is mediated via the cholecystokinin-B receptor subtype, while in the substantia nigra, cholecystokinin-8S modulates dynorphin B and aspartate release via both cholecystokinin-A and cholecystokinin-B receptor subtypes. Cholecystokinin-8S modulates dopamine release mainly in the substantia nigra, via the cholecystokinin-A receptor subtype.

Cholecystokinin-GABA interactions in rat striatum

The release of [3H]gamma-aminobutyric acid ([3H]GABA) from rat striatal slices before and during electrical field stimulation (EFS) was measured. Electrical stimulation (10 Hz) induced an increase of Ca(++)- and tetrodotoxin-sensitive [3H]GABA release from the striatal slices. In the presence of sulphated octapeptide of cholecystokinin, CCK-8S (10(-9) M, 10(-8) M and 10(-7) M) both the basal and the electrically (10 Hz)-evoked release of [3H]GABA were dose-dependently increased. These effects of CCK-8S were abolished by tetrodotoxin (10(-6) M) and were not influenced by the CCK-A receptor antagonist loxiglumide (CR1505) (10(-7) M and 10(-6) M). The stimulant effect of CCK-8S was antagonized by the newly synthesized CCK-B selective receptor antagonist PD134308 (10(-7) M and 10(-6) M). These findings suggest that CCK-8 plays a neuromodulatory role in the regulation of GABAergic neuronal activity in the striatum. The activation of CCK-B receptors located on GABAergic neurons is involved in the GABA release-potentiating effect of CCK-8S in rat striatum.

Cholecystokinin-induced release of dopamine in the nucleus accumbens of the spontaneously hypertensive rat

Changes in dopamine neurotransmission in the nucleus accumbens of the spontaneously hypertensive rat (SHR) may be involved in the pathogenesis of hypertension. This investigation tested the hypothesis that the sulfated octapeptide cholecystokinin (CCK8S) induced release of dopamine is greater in the SHR than in its normotensive control, the Wistar-Kyoto rat (WKY). Dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were sampled using microdialysis in the caudal half of the nucleus accumbens of 10-week-old anesthetized SHRs and WKYs. Samples were collected in the following order: 3 baseline, 3 CCK8S (10 mumol/l), and 3 postdrug samples. The samples were then analyzed using high pressure liquid chromatography with electrochemical detection. CCK8S increased dopamine and DOPAC levels in both the SHR and WKY with a larger increase in basal dopamine in the SHR (greater than 200%). Perfusion of the nucleus accumbens with 1 mumol/l of CCK8S or the nonsulfated form of CCK8 (CCK8US, 10 mumol/l) produced no significant increase in the release of dopamine in the SHR. These results indicate that CCK8S-induced release of dopamine in the nucleus accumbens is greater in the SHR. Changes in CCK8S neurotransmission/receptor function may be responsible for the alterations in dopaminergic function of the SHR and the pathogenesis of hypertension.

Time-dependent changes in dopamine agonist-induced striatal Fos immunoreactivity are related to sensory neglect and its recovery after unilateral prefrontal cortex injury

This study examined interactions between the corticostriatal glutamatergic system and the nigrostriatal dopaminergic system via immunocytochemical examination of dopamine (DA) agonist induction of the striatal immediate early gene product Fos following cortical injury. After unilateral aspiration of the medial agranular cortex (AGm) region of prefrontal cortex, rats were tested for orientation to visual, tactile, and auditory stimuli. Fos immunoreactivity induced by d-amphetamine (5 mg/kg) or apomorphine (5 mg/kg) was quantified in dorsolateral and ventrolateral regions of caudate-putamen (CPu) in rats still demonstrating sensory neglect (5 days postsurgery) and in rats recovered from sensory neglect produced by AGm ablation (29+ days postsurgery). The pattern of immunoreactivity of rats still demonstrating neglect differed from that of unlesioned rats or recovered AGm-ablated rats. In rats demonstrating sensory neglect, d-amphetamine or apomorphine induction of Fos in the ipsilateral CPu was reduced by about 40% compared to the contralateral CPu or to comparable readings in unlesioned controls. These asymmetries were restricted to dorsolateral CPu, the region receiving the densest input from AGm. In contrast, recovered AGm-ablated rats had DA agonist-induced striatal Fos immunoreactivity that was symmetrical between the two hemispheres and comparable to control values. These findings indicate that adaptations involving the striatal medium spiny neuron, a site of convergence of cortical glutamatergic and nigral dopaminergic afferents, may contribute to recovery from behavioral deficits resulting from neocortical injury.

Up-regulation of cholecystokinin receptors in the nucleus accumbens of the young prehypertensive spontaneously hypertensive rat

We employed receptor autoradiography to test the hypothesis that changes in cholecystokinin neurotransmission in the striatum of the young spontaneously hypertensive rat (SHR) is involved in the development of hypertension. The binding density of 125I-Bolton Hunter labelled cholecystokinin octapeptide (125I-BH-CCK8) in the striatum of 5-week-old prehypertensive SHRs and its normotensive control the Wistar-Kyoto rat (WKY) was determined using computer-assisted densitometry. We found a significant increase in 125I-BH-CCK8 binding density in the nucleus accumbens of the SHR. No difference between the binding density of 125I-BH-CCK8 was found in the caudate-putamen and the prefrontal cortex of SHRs and WKYs. These results suggest that changes in CCK8S neurotransmission or receptor function are not secondary to an increase in arterial blood pressure and, therefore, may be involved in the development of hypertension.

Co-storage in large 'dense-core' vesicles of dopamine and cholecystokinin in rat striatum

The subcellular localization of cholecystokinin in the striatum--an area where a high density of cholecystokinin containing terminals has been demonstrated--was studied using biochemical techniques. Cholecystokinin containing vesicles were partially purified using iso-osmotic Ficoll gradients. As judged from their size and their buoyant density in isopycnic gradients, cholecystokinin containing vesicles represent large 'dense-core' vesicles. Negative staining and subsequent immunolabelling for synaptophysin at the electron microscopical level, showed labelled vesicles of 50-70 nm. binding of dihydrotetrabenazine was detected in the cholecystokinin containing fractions. The results suggest that dopamine is co-stored with cholecystokinin in large dense vesicles in rat striatum.

Cholecystokinin in cortico-striatal neurons in the rat: immunohistochemical studies at the light and electron microscopical level

Using immunohistochemical techniques we have analysed the occurrence of cholecystokinin-like immunoreactivity (CCK-LI) in the cortex and striatum of the rat. In the cortex few CCK-immunoreactive cell bodies, mainly interneurons, could be visualized in normal brains, and a moderately dense network of CCK fibres was also observed. Injections of colchicine into the striatum led to an accumulation, in the surrounding cortex, of CCK-LI in the initial segment of the axon of numerous cells. In addition, with an antibody to pro-CCK several cell bodies, many of which with pyramidal shape, could be visualized. Furthermore, retrograde staining of cortical cells after unilateral injection of wheat germ agglutinin into the striatum revealed bilaterally in the cortex a number of labelled cells that also contained pro-CCK-LI. In the striatum CCK-LI was diffusely distributed in fine fibres as well as in patches of fibres located in the medial aspects. After decortication followed by callosotomy these patches disappeared on the side ipsilateral to the lesion, while the pattern of immunoreactivity of several other peptides in the striatum was unaffected. No change was observed on the contralateral side. Decortication or callosotomy alone did not affect the pattern of CCK-LI. At the ultrastructural level several CCK-immunoreactive terminals could be observed, mostly with clear, densely packed vesicles and straight asymmetric synaptic contacts with small spines, characteristic for terminals of cortical origin. The results are consistent with the presence of a major, partly crossed, CCK-containing cortico-striatal pathway.

Cholecystokinin corticostriatal pathway in the rat: evidence for bilateral origin from medial prefrontal cortical areas

The anterograde tracer Phaseolus vulgaris-leucoagglutinin was used to examine the organization of the projections to the striatum from medial prefrontal and frontal cortical areas in the rat with reference to their relation to cholecystokinin-like immunoreactivity in the striatum. Medial prefrontal cortical areas projected bilaterally, with an ipsilateral predominance, to the striatum. Most of the positive fibres were found in medial and ventral areas of the caudate-putamen and in the nucleus accumbens. Labelled fibres formed distinct patch-like arrangements throughout the dorsomedial striatum, whereas more ventrally the fibres were densely packed and spread to lateral areas. Almost no fibres were found in the dorsolateral aspects of the caudate-putamen. Cholecystokinin-like immunoreactivity in the striatum was diffusely distributed in the medial aspects, in fine punctate elements as well as in patches of fibres. Overlapping of corticostriatal clusters of fibres, from medial prefrontal cortex, with cholecystokinin-immunoreactive patches was found at all rostrocaudal levels studied, but predominantly in rostral areas. The overlap was present both in the ipsilateral and the contralateral side. Often the cluster of corticostriatal fibres was completely and precisely overlaid by a cholecystokinin-immunoreactive patch. At more caudal planes the overlap was only partial and in some instances cholecystokinin-positive patches "avoided" zones of dense corticostriatal fibre terminations. Frontal cortex injections of tracer gave rise to a network of fibres in the lateral aspects of the striatum, sparing the medial areas. No overlap with cholecystokinin-immunoreactive patches was found in these cases. These results suggest that a large number of cholecystokinin-containing striatal fibres originate in medial prefrontal cortical areas.

Distribution of mRNA for CCK-B receptor in the brain of Mastomys natalensis: abundant expression in telencephalic neurons

The distribution of cholecystokinin B (CCK-B) receptors in the Mastomys brain was studied using Northern blot analysis and in situ hybridization technique. By Northern blot analysis using 32P-labeled cDNA probe, the cortex had the highest hybridization signal of CCK-B receptor mRNA in the brain. The olfactory bulb and hippocampus showed a moderate level of signals. In situ hybridization using 35S-labeled cRNA probes revealed a wide and region-specific distribution of CCK-B receptor mRNA in the telencephalon. Throughout the cerebral cortex, labeled cells were found in all layers, with higher intensities in layers II, V and VI. Pyramidal cells of the layer II of the piriform cortex showed the highest level of signals in the brain. In the hippocampus, most of the pyramidal cells of the Ammon's horn were labeled, although labeled cells were not detected in other layers. Distinct signals were also detected in the various amygdaloid nuclei, caudate-putamen, reticular thalamic nucleus, hypothalamic ventromedial nucleus and inferior colliculus. This distribution pattern may further support the prominent existence of CCK-B receptors in the brain particularly in the telencephalon.

On the origin of striatal cholecystokinin release: studies with in vivo microdialysis

In the present study, extracellular levels of the neuropeptide cholecystokinin (CCK), of the monoamine dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and of the excitatory amino acids glutamate and aspartate were simultaneously monitored by microdialysis in the neostriatum of halothane-anesthetized rats under basal and K(+)-depolarizing conditions. Extracellular CCK and dopamine levels, but not glutamate and aspartate levels, were decreased by perfusion with a Ca(2+)-free medium, under both basal and K(+)-depolarizing conditions. HPLC revealed that the majority of the CCK-like immunoreactivity in the perfusates coeluted with CCK octapeptide. Striatal extracellular CCK levels were decreased by decortication plus callosotomy, with a parallel decrease in glutamate levels. Striatal extracellular levels of dopamine, DOPAC, and HVA were significantly decreased in animals treated previously with a unilateral 6-hydroxydopamine injection into the medial forebrain bundle. In these animals, however, the effect of decortication plus callosotomy on CCK and glutamate levels was not further augmented. Thus, this study supports the hypothesis of a neuronal origin of extracellular CCK and dopamine monitored with microdialysis in the striatum of the rat, and also supports the idea of a partly contralateral origin of corticostriatal CCK and glutamate inputs.

Regulation by the neuropeptide cholecystokinin (CCK-8S) of protein phosphorylation in the neostriatum

Despite physiological evidence that cholecystokinin (CCK) is an excitatory neurotransmitter in the brain, little is known about its mechanism of action. CCK immunoreactivity in the brain, including projections to the striatum, is primarily attributable to the sulfated octapeptide CCK-8S. We report here that CCK-8S abolishes cAMP-dependent phosphorylation of a dopamine- and cAMP-regulated 32-kDa phosphoprotein (DARPP-32) in striatal neurons. The effect of CCK-8S is prevented by antagonists of CCKB and N-methyl-D-aspartate receptors. Our results support a model in which CCK-8S, originating from CCK or CCK/glutamate corticostriatal neurons, promotes the release of an excitatory neurotransmitter that causes the dephosphorylation and inactivation of DARPP-32, a potent protein phosphatase inhibitor, thereby modulating neuronal excitability.

Immunohistochemical evidence for a crossed cholecystokinin corticostriatal pathway in the rat

Using the indirect immunofluorescence technique, the effects of decortication and callosotomy on the pattern of cholecystokinin (CCK)-like immunoreactivity were studied in the striatum of the rat. Decortication plus callosotomy, but not decortication alone, caused a strong decrease in the immunoreactivity on the side ipsilateral to the lesion. An almost complete disappearance of CCK immunoreactive patches in the medial-dorsal aspects of the striatum was observed. These results indicate that part of the striatal CCK immunoreactive fibres are of cortical origin, to a considerable extent from the contralateral side.

Distribution of cells containing mRNA encoding cholecystokinin in the rat central nervous system

The distribution of cells containing mRNA encoding cholecystokinin was studied in the rat central nervous system by in situ hybridization histochemistry. Cholecystokinin mRNA containing neurons were considerably more numerous than the cholecystokinin-like immunoreactive neurons detected by immunocytochemistry even after colchicine pretreatment and appeared to be heavily, moderately, or lightly labeled. Such neurons were present in the olfactory bulb, olfactory nuclei, layers II-III and V-VI of the cerebral cortex, amygdaloid nuclei, subiculum, hippocampus, claustrum, endopiriform nucleus, several hypothalamic nuclei, most of the thalamic nuclei, ventral tegmental area, substantia nigra, interfascicularis nucleus, linearis rostralis, central gray, Edinger-Westphal nucleus, superior and inferior colliculi, parabrachial nucleus, reticular formation, raphe nuclei, and spinal trigeminal nucleus. This distribution partly confirmed and partly extended the previous immunohistochemical descriptions. Several brain areas such as the thalamus and the colliculi contain cholecystokinin mRNA but are devoid of perikarya exhibiting cholecystokinin-like immunoreactivity. The cerebral cortex and the hippocampus present a far higher density of cholecystokinin mRNA containing cells, including pyramidal neurons, than of perikarya containing cholecystokinin-like immunoreactivity. These results suggest that cholecystokinin or cholecystokinin-related peptides could have a functional role in numerous cerebral pathways including long projections such as cortical or thalamic projections.

Cholecystokinin: Corelease with dopamine from nigrostriatal neurons in the cat

Halothane-anaesthetized cats were implanted with push-pull cannulae to demonstrate the in vivo release of cholecystokinin-like immunoreactivity (CCK-LI) in the substantia nigra and the ipsilateral caudate nucleus. The spontaneous and the calcium-dependent potassium-evoked release of CCK-LI were observed in both structures. In addition, the local application of tetrodotoxin (10-6 M) reduced the spontaneous release of the peptide. 6-OHDA lesions made in the substantia nigra pars compacta led to a complete destruction of nigrostriatal dopaminergic neurons. CCK-LI levels were not affected in the caudate nucleus but were reduced substantially in the substantia nigra. The activation of dopaminergic cells induced by the nigral application of alpha-methyl-para-tyrosine (10-4 M) stimulated the release of CCK-LI and dopamine in the ipsilateral caudate nucleus, whilst opposite effects were seen in the substantia nigra. Similar results were obtained when dopaminergic transmission was blocked in the caudate nucleus suggesting that the evoked release of CCK-LI by the alpha-methyl-para-tyrosine treatment originates from dopaminergic nerve terminals and not from other CCK-LI containing fibres in response to released dopamine. Dopamine (10-7 M) as well as the D1 agonist SKF 38393 (10-5 M) stimulated CCK-LI release when applied into the caudate nucleus while the D2 agonist, LY 171555 (10-6 M) slightly reduced peptide release. The local application of cholecystokinin-8 sulfate (CCK-8S) (10-8 M, for 30 min) into the substantia nigra pars compacta increased the firing rate of dopaminergic cells and stimulated the release of newly synthesized 3H-dopamine from dendrites and nerve terminals. These results suggest, but do not definitively prove, that, in the cat, CCK-LI and dopamine are coreleased from nigrostriatal mixed dopaminergic/CCK-LI neurons and that CCK-LI released from dendrites is, like dopamine, involved in the regulation of the activity of these cells.

Ventral mesencephalic neurons containing both cholecystokinin- and tyrosine hydroxylase-like immunoreactivities project to forebrain regions

The coexistence of cholecystokinin- and tyrosine hydroxylase-like immunoreactivities within neurons of the rat ventral mesencephalon was analyzed by using an indirect immunofluorescence technique for the simultaneous demonstration of two antigens in the same tissue section. A high degree of colocalization was observed in the substantia nigra pars compacta, in which 80-90% of all labeled neurons at rostral and up to 70% at intermediate levels contained both cholecystokinin and tyrosine hydroxylase. At caudal levels, the incidence of colocalization declined to approximately 30-50%. All of the immunoreactive perikarya in the substantia nigra pars lateralis were labeled with both substances. Other areas of the ventral midbrain that exhibited a moderate proportion of neurons immunoreactive for both cholecystokinin and tyrosine hydroxylase included the ventral tegmental area, interfascicular nucleus, and rostral and caudal linear nuclei. In addition, coexistence was occasionally observed within neurons of the central and ventral periaqueductal gray matter, supramammillary region, peripeduncular region, retrorubral field, and extremely rarely, within the substantia nigra pars reticulata. Cell bodies containing tyrosine hydroxylase-like immunoreactivity (indicative of dopamine) usually outnumbered those containing the peptide except in the supramammillary region and in the ventral periaqueductal gray matter, where the cholecystokinin perikarya were present in higher numbers. The double-labeling colocalization technique was combined with fluorescence retrograde tracing to determine some of the forebrain projections of these neurons. Ventral midbrain neurons containing both cholecystokinin and tyrosine hydroxylase were found to project to the caudate-putamen, nucleus-accumbens, prefrontal cortex, and amygdala. These projections originated from neurons located predominantly in the substantia nigra pars compacta and the ventral tegmental area. Thus, cholecystokinin occurs within the well-known dopaminergic nigrostriatal pathway in the rat. Overall, these results demonstrate that a significant proportion of the dopamine neurons giving rise to the ascending mesotelencephalic projections also contain the peptide cholecystokinin.

Forebrain projections from cholecystokininlike-immunoreactive neurons in the rat midbrain

The purpose of the present study was to analyze the distribution of cholecystokininlike-immunoreactive (CCK-I) neurons within the rat ventral mesencephalon which project to several forebrain areas. The peroxidase-antiperoxidase immunocytochemical technique was used to examine the anatomical localization of CCK-I within the ventral midbrain and in the following forebrain regions: caudate-putamen, nucleus accumbens, olfactory tubercle, bed nucleus of the stria terminalis, septum, amygdala, and prefrontal, anterior cingulate, and piriform cortices. CCK-I perikarya were distributed throughout the substantia nigra, ventral tegmental area, and several midline raphe nuclei to a greater extent than previously reported, particularly in the substantia nigra pars compacta. Terminallike immunoreactivity for CCK was observed in all of the above forebrain sites. In addition, infrequent CCK-I cell bodies were localized in the caudate-putamen, nucleus accumbens, olfactory tubercle, septum, and bed nucleus of the stria terminalis. To analyze forebrain projections of the ventral midbrain CCK-I neurons, indirect immunofluorescence was combined with fluorescence retrograde tracing. CCK-I neurons of the substantia nigra and/or ventral tegmental area were found to project, to varying extents, to all of the above CCK-I forebrain terminal fields. The nucleus accumbens, olfactory tubercle, and septal and prefrontal cortical projections arose primarily from CCK-I perikarya in the ventral tegmental area whereas the projections to the caudate-putamen and anterior cingulate cortex arose predominantly from immunoreactive neurons in the substantia nigra pars compacta. The amygdala received innervation mainly from CCK-I cell bodies located in the substantia nigra pars lateralis. CCK-I afferents to the bed nucleus of the stria terminalis and piriform cortex originated from perikarya distributed approximately equally across the ventral tegmental area and substantia nigra pars compacta. The general topography of CCK-I forebrain innervation observed in this study is similar to that previously reported for the ascending dopaminergic projections from ventral mesencephalic neurons. CCK-I neurons of the midline raphe nuclei were found to provide relatively minor afferents to the caudate-putamen, bed nucleus of the stria terminalis, septum, and prefrontal cortex and more substantial projections to the amygdala. The results of this study demonstrate that CCK-I neurons of the ventral midbrain supply a much broader innervation of forebrain regions than previously appreciated.(ABSTRACT TRUNCATED AT 400 WORDS)

Bilateral ablation of frontal cortex reduces concentration of cholecystokinin-like immunoreactivity in rat dorsolateral striatum

Rat striatum (caudatoputamen, CP) contains high concentrations of cholecystokinin-like immunoreactivity (CCK-LI) which is not synthesized in the CP itself, but is brought to it by afferent projections. Some of these have been reported to originate in the sensori-motor cortex. The source of the major part of the CCK-LI in the CP is not known. In the present study, it was investigated whether neurons in the frontal cortex send CCK-LI-containing fibers to the CP. Ablation of the frontal pole of one hemisphere did not decrease but significantly enhanced the CCK-LI in the dorsal CP. Unilateral ablation of the frontal pole combined with the ipsilateral severance of corpus callosum fibers reduced ipsilaterally the concentration of CCK-LI in the dorsolateral CP by approximately 60%. Also ablation of the frontal poles of both sides bilaterally reduced the concentration of CCK-LI in the dorsolateral CP by approximately 40%. It is concluded that the neuronal elements in the dorsolateral CP of one side, which contain CCK-LI, are in some way connected with neurons in the frontal poles of both hemispheres. This connection may be just functional or may be due to CCK-containing fibers, which originate in the frontal pole.

Comparison of the action of cholecystokinin, carbachol and vasoactive intestinal peptide on receptor-activated formation of cyclic GMP and cyclic AMP in the striatum and the pancreas

Sulphated cholecystokinin octapeptide (CCK-8S) and sodium nitroprusside (SNP) increased the formation of cyclic GMP in rat striatal slices with no effect on cyclic AMP. CCK-8S, SNP and carbachol increased the formation of cyclic GMP in guinea-pig pancreatic lobules, but had no effect on levels of cyclic AMP. Vasoactive intestinal peptide (VIP) significantly stimulated the formation of cyclic AMP in both striatal and pancreatic tissue without effect on levels of cyclic GMP in these tissues. In rat striatal slices carbachol significantly inhibited the VIP-stimulated increase in cyclic AMP.