Reduced cholecystokinin-like and somatostatin-like immunoreactivity in limbic lobe is associated with negative symptoms in schizophrenia

Enkephalin, dynorphin and substance P in postmortem substantia nigra from normals and schizophrenic patients

Three peptide neuromodulators that are found in high concentration in the substantia nigra: dynorphin A 1-8, met5-enkephalin-arg6-gly7-leu8 and substance P, were measured by specific radioimmunoassays in nigral tissue from normals and schizophrenics postmortem. Substance P and dynorphin were unchanged between the two groups. However, the proenkephalin-derived peptide was significantly elevated in the schizophrenic group. The immunoreactivity was identified as authentic met5-enkephalin-arg6-gly7-leu8 by high pressure liquid chromatography. The data suggest that a different set of regulatory controls exists for nigral enkephalin peptides as compared to dynorphin and substance P, and that the former system may be disordered in schizophrenia.

Carbachol infusion into the dentate gyrus disrupts sensorimotor gating of startle in the rat

Prepulse inhibition (PPI) is the decrease in a startle response that occurs when the startling stimulus is preceded by a weaker stimulus or "prepulse". Schizophrenic patients exhibit abnormally low levels of PPI when the prepulse precedes the startle stimulus by less than 500 ms. A similar deficit in sensorimotor gating can be demonstrated in rats after stimulation of D2 dopamine (DA) receptors by systemic administration of DA agonists or by infusion of DA directly into the nucleus accumbens. We now demonstrate that carbachol infusion into the dentate gyrus of the hippocampal formation disrupts PPI in the rat. This disruption of sensorimotor gating occurs when the startling stimulus is either acoustic or tactile. Carbachol infusion into the neocortex has no effect on PPI. While pretreatment with the D2 DA receptor antagonist spiperone reverses the disruption of PPI caused by systemic administration of apomorphine, this pretreatment fails to reverse the disruption of PPI induced by carbachol infusion into the hippocampus. These results demonstrate that pharmacologic stimulation of the hippocampus disrupts sensorimotor gating in the rat by a mechanism distinct from that of DA agonists. Prepulse inhibition of the startle reflex is an animal model in which pharmacologic stimulation of the hippocampus mimics the deficits in sensorimotor gating observed in schizophrenic patients.

Distribution of cholecystokinin mRNA and peptides in the human brain

Expression of preprocholecystokinin mRNA was studied in regions of post mortem human brain using RNA blot analysis (Northern blot) and in situ hybridization. Northern blot analysis using a cDNA probe showed high levels of an approximately 0.8 kb preprocholecystokinin mRNA in all regions of neocortex examined. Lower levels of preprocholecystokinin mRNA were detected in amygdaloid body and thalamus. In situ hybridization analysis using the same cDNA probe revealed numerous weakly labelled neurons in different areas of human neocortex and less numerous neurons in hippocampus and amygdaloid body. High-performance liquid-chromatography and gel-chromatography combined with radioimmunoassay of cholecystokinin-like immunoreactivity from human cerebral cortex and caudate nucleus revealed two major forms, one coeluting with sulphated cholecystokinin-8 and the other coeluting with sulphated cholecystokinin-58. Two minor components coeluting with cholecystokinin-4 and cholecystokinin-5 were also detected. The finding of cholecystokinin-like immunoreactivity corresponding to cholecystokinin-8 and cholecystokinin-58 in caudate nucleus where no preprocholecystokinin mRNA was found, indicates the presence of these peptides in afferent nerve terminals.

Astrocytosis in the molecular layer of the dentate gyrus: a study in Alzheimer's disease and schizophrenia

Recently, several authors have claimed prominent abnormalities in the entorhinal cortex of both patients with Alzheimer's disease (AD) and schizophrenia. The entorhinal cortex is the origin of the perforant pathway, a major input to granule cells of the dentate gyrus of the hippocampus. The present study explored the possibility of a lesion in the entorhinal cortex of both AD and schizophrenic patients by quantitating astrocytic markers within the terminal fields of the perforant pathway. An increase in fibrillary astrocytes was found in half (3/6) of the AD patients while none of the schizophrenic (n = 6) or control (n = 7) brains exhibited gliosis. Since the redistribution and hyperplasia of astrocytes within the molecular layer of the partially deafferented dentate gyrus depend on the chronicity of the entorhinal lesion, the abnormalities observed in AD patients are consistent with the progressive course of the illness. Furthermore, the presence of gliosis in the subiculum of three out of six AD patients suggested pathology secondary to projections from the entorhinal region, amygdala, or prepyriform cortex. The absence of similar changes in schizophrenic patients does not disprove previous claims of entorhinal pathology but suggests that the lesion, if it exists, is either static in nature or occurred long before death.

Organization of peptidergic and catecholaminergic efferents from the nucleus of the solitary tract to the rat amygdala

Previous studies have focused on the role of the central nucleus of the amygdala (CeA) in cardiovascular and other amygdaloid functions. The combined retrograde tracing/immunohistochemical method was used to test for the presence of enkephalin, neurotensin, neuropeptide Y, and catecholamine neurons within the nucleus of the solitary tract that send efferents to the CeA. After injections of retrograde tracer into the CeA, retrogradely labeled neurons were observed within the caudal, medial nucleus of the solitary tract. Most CeA-projecting neurons were located ipsilaterally within the medial nucleus of the solitary tract at the level of the area postrema. Retrogradely labeled enkephalin- and neurotensin-immunoreactive neurons were found within the medial nucleus of the solitary tract at this level, while retrogradely labeled neuropeptide Y-immunoreactive neurons were found within the medial nucleus of the solitary tract rostral to the area postrema. About 60-74% of CeA-projecting cells were also immunoreactive for tyrosine hydroxylase. Approximately 9% of retrogradely neurons were phenylethanolamine-N-methyltransferase immunoreactive. The results provide evidence that within the nucleus of the solitary tract, peptidergic CeA-projecting neurons have a topographic distribution. In addition, noradrenergic neurons within the A2 group, rather than adrenergic neurons of the C2 group, provide the bulk of catecholaminergic input to the CeA from the nucleus of the solitary tract. Cell counts indicate that each of these peptides may be colocalized (to varying extents) within catecholamine-producing neurons. Also the catecholaminergic and enkephalinergic contribution to the ascending pathway from the nucleus of the solitary tract to the CeA distinguishes it neurochemically from the descending pathway. Thus, although there are afferent and efferent connections between the nucleus of the solitary tract and CeA, their peptidergic/neurotransmitter connections are not necessarily reciprocal. Input from nucleus of the solitary tract peptidergic and catecholaminergic neurons to the CeA may be important in the etiology of a number of pathophysiological conditions including hypertension, gastric ulcers, and schizophrenia.

The relationship of negative schizophrenia to parkinsonism

The positive-negative distinction of schizophrenia has emerged as a valid means of clarifying its heterogeneity. Despite evidence that the two symptom classes may reflect different dimensions of the disease, there is presently no integrated model for understanding of the pathophysiology of these symptoms and their co-occurrence in schizophrenia. We propose that negative phenomena of schizophrenia may be a variant of Parkinsonism. This view is supported by the overlap with Parkinsonism in terms of clinical features, neurochemistry, pharmacology, as well as neuroradiological and neuropathological aspects. As such, negative symptoms may be a manifestation of disease of the basal ganglia and constitute the core pathology in schizophrenia. Positive symptoms, conversely, may reflect an "accessory" process related to a compensatory increase in striatal and limbic dopamine activity following an injury to the dopaminergic system. In the present communication we present a series of studies that support the association of negative schizophrenia and Parkinsonism. Based on this evidence, we suggest that schizophrenic patients with prominent negative symptoms might be managed like patients with Parkinson's disease, namely, with dopaminergic drugs and MAO-B inhibitors. Finally, the association of negative schizophrenia with Parkinsonism raises the possibility that adrenal medullary tissue transplantation, which may benefit a selected group of Parkinsonian patients, may be a future promising therapy for refractory negative schizophrenia.

Decreased somatostatin-like immunoreactivity in the cerebrospinal fluid of chronic schizophrenic patients with cognitive impairment

The level of cerebrospinal fluid somatostatin-like immunoreactivity (CSF SLI) was determined for 11 chronic schizophrenic patients with moderate cognitive impairment and for 8 controls. The CSF SLI was significantly reduced (37%) in schizophrenic patients, but this decrease did not correlate with the degree of cognitive decline measured by the Mini-Mental State Examination, with psychotic symptoms estimated by the Brief Psychiatric Rating Scale, or with the neuroleptic dose. Although a reducing effect of long-term neuroleptic treatment cannot be totally excluded, the present study suggests that the CSF SLI level is decreased in cognitively impaired schizophrenic patients, as in many other disorders with cognitive impairment.

Deficit and hemispheric asymmetry of GABA uptake sites in the hippocampus in schizophrenia

There is increasing evidence of a deficit or disturbance of neurons in the brains of schizophrenic patients--evidence that particularly implicates the frontal or temporal lobes. As yet there is no direct neurochemical correlate of the transmitter systems involved, although changes in some neurotransmitters in the temporal lobe have been reported. Radiolabeled nipecotic acid, a specific inhibitor of uptake sites to gamma-aminobutyric acid (GABA), has provided a marker of GABAergic neurons. The binding of this ligand to brain tissue taken at autopsy has demonstrated a decreased density of GABA uptake sites in the hippocampus in schizophrenia. This decrease was found to correlate in the left hemisphere with increased concentration of dopamine in the amygdala, providing a link between neuropathology, evidence of laterality, and the dopamine hypothesis of the disease.

Regional distribution of the messenger RNA coding for the neuropeptide cholecystokinin in the human brain examined by in situ hybridization

The regional localization of mRNA coding for the neuropeptide cholecystokinin (CCK) has been studied in the human brain by in situ hybridization using a 32P-labelled synthetic oligonucleotide. Autoradiograms were quantified using computer-assisted microdensitometry. Positive hybridizing cells were seen in the neocortex, the claustrum, the hippocampus and the amygdala with the highest densities observed in the claustrum, some cortical layers and the CA2 and CA3 regions of the hippocampus. No significant hybridization signal was observed in the substantia nigra, caudate nucleus, putamen, globus pallidus, nucleus accumbens, thalamus, hypothalamus, medulla oblongata and cerebellum. The topographic distribution of neurons expressing CCK mRNA correlates well with that previously reported by immunocytochemistry or radioimmunoassay in brain areas such as the neocortex, the amygdala and the hippocampus. However, some discrepancies were also found, particularly in the basal ganglia, the midbrain, the thalamus and the hypothalamus. These results show that in situ hybridization with oligonucleotide probes together with a semiquantitative analysis can be used to map the distribution of cells expressing CCK mRNA in human postmortem materials.

The human amygdaloid complex: a cytologic and histochemical atlas using Nissl, myelin, acetylcholinesterase and nicotinamide adenine dinucleotide phosphate diaphorase staining

We examined the distribution of acetylcholinesterase and nicotinamide adenine dinucleotide phosphate diaphorase enzyme activity in the human amygdala using histochemical techniques. Both methods revealed compartments of higher or lower enzyme activity, in cells or neuropil, which corresponded to the nuclear subdivisions of the amygdala as defined with classical Nissl and myelin methods. The boundaries between the histochemical compartments were usually so sharp that the identification of these nuclear subdivisions was enhanced. There was also variation of staining intensity within many of the nuclear subdivisions, such as the lateral and central nuclei, anterior amygdaloid area and the intercalated groups. This histochemical difference corresponded to more subtle differences in Nissl and myelin staining patterns, and suggests further structural subdivisions of potential functional significance. We present a revised scheme of anatomical parcellation of the human amygdala based upon serial analysis with all four techniques. Our expectation is that this will allow the delineation of a clearer homology between the cytoarchitectonic subdivisions of the human amygdala and those of experimental animals.

Reduced GABA uptake sites in the temporal lobe in schizophrenia

The binding of [3H]nipecotic acid, a ligand for labelling GABA uptake sites in brain, was measured in left and right frontal cortex, polar temporal cortex, hippocampus and amygdala from control and schizophrenic postmortem brains. In schizophrenic brains, single concentration [3H]nipecotic acid binding was reduced bilaterally in amygdala and hippocampus and on the left side only in polar temporal cortex. These data suggest that GABA neurones are involved in the cerebral atrophy of schizophrenia and, in agreement with other studies, that this process is most pronounced in left temporal cortex.

Monoclonal antibodies to study the brain in schizophrenia

Twelve monoclonal antibodies were developed which show selective reactivity with brain tissue homogenates from 4 patients with schizophrenia compared to 4 normal controls. Certain antibodies were more reactive with tissue from cases with schizophrenia, others with control tissue. Patterns of reactivity also depended on brain region tested. Differences in reactivity generally ranged from 2- to as much as 8-fold. This panel of monoclonal antibodies may be useful to investigate the pathophysiology of schizophrenia.

Beyond the dopamine hypothesis. The neurochemical pathology of schizophrenia

The dopamine hypothesis still provides a valuable approach to the study of schizophrenia and its treatment by drugs. Although the neuroleptic drugs appear to act via an inhibition of dopamine receptors, measurements of dopamine metabolites in vivo, or of the transmitter and its receptors in post-mortem brain tissue, do not provide unequivocal evidence of a hyperactivity of dopaminergic neurotransmission in the disease. Nevertheless, increased dopamine function might be a consequence of a primary neuronal abnormality in another system. Recent imaging studies and neuropathological reports suggest that, in some patients, there may be a deficit and/or disturbance of neurons in certain temporal limbic regions, and this is supported by some neurochemical investigations, particularly of neuropeptide and amino-acid transmitter systems. A loss of such neurons could conceivably lead to a disinhibition of limbic dopamine neurons, providing the means whereby neuroleptic drug treatment might ameliorate the effects of a neuronal deficit in schizophrenia.

Approaches for finding new types of antipsychotic compounds

There is strong evidence that pharmacological interaction with central dopamine transmission at several levels may induce antipsychotic effects in psychiatric patients. All the pharmacological principles interacting with other systems have so far not been established with regard to antipsychotic potential. Besides the dopamine system pharmacological manipulation of central serotonergic, gabaergic and noradrenergic mechanisms may also be of therapeutic value in schizophrenia. The interaction of peptidergic mechanisms and central dopaminergic mechanisms is another avenue for further exploration regarding to pathophysiology of psychosis and its treatment. Elucidation of the heterogeneity and molecular structure of central dopamine receptors seems the most rational approach for creating new dimensions for further development of drug design for pharmacotherapy of psychosis. The detailed mapping of afferent and efferent systems coupled to central dopamine neurons is also an approach that may give guide-lines for finding new types of antipsychotic drugs.

A mechanism for the involvement of colocalized neuropeptides in the actions of antipsychotic drugs

Evidence has accumulated to implicate neuropeptides localized within midbrain dopamine neurons (cholecystokinin, neurotensin, acetylcholinesterase) in synaptic transmission, mental disease, and pharmacotherapy. We suggest a means by which antipsychotic drugs alter the dynamics between dopamine and colocalized peptides: the intrinsic ability of these agents to stimulate dopamine neuronal activity while blocking dopamine receptors modulates the ratio of catecholaminergic to peptidergic transmission within the mesotelencephalic system. Imbalances of peptide and dopamine cotransmission and their modulation by neuroleptics may be relevant to the pathogenesis and pharmacotherapy of schizophrenia.

Cholecystokinin binding sites in the rat forebrain: effects of acute and chronic methamphetamine administration

Using the in vitro quantitative receptor autoradiographical technique, changes in the binding parameters of [propionyl-3H] propionylated CCK-8 [( 3H]pCCK-8) binding sites in the rat forebrain were investigated following acute and chronic administration of methamphetamine (MAP). The (Kd)app values of [3H]pCCK-8 binding sites in the frontal medial cortex and anterior cingulate cortex were significantly reduced after a single injection of 4mg/kg MAP. On the other hand, chronic treatment (14 days) with MAP at this dose significantly decreased the Bmax value of [3H]pCCK-8 binding sites in the anterior cingulate cortex accompanied by supersensitivity of locomotor effects to MAP. These findings suggest that dopamine (DA) neurons in these two regions are functionally related to intrinsic CCK-containing cortical neurons, and that CCK subsensitivity, perhaps due to an alteration in DA transmission, is involved in MAP sensitization. These findings may be relevant to the DA hypothesis of schizophrenia.

Temporal lobe structure as determined by nuclear magnetic resonance in schizophrenia and bipolar affective disorder

Temporal lobe structure has been assessed by magnetic resonance imaging in groups of patients with schizophrenia (n = 21) bipolar affective disorder (n = 20) and normal controls (n = 21). In the temporal lobe area a significant (p less than 0.05) diagnosis by side interaction was present, the area being less on the left than on the right side in patients with schizophrenia in contrast to findings in the two other groups. Lateral ventricular and temporal horn area did not distinguish the groups as a whole. However, there was a significant (p less than 0.05) relationship between lateral ventricular area and poor outcome, and in an analysis confined to males, patients with schizophrenia (n = 15) were found to have significantly (p less than 0.05) enlarged temporal horns.

Brain CCK-B receptors mediate the suppression of dopamine release by cholecystokinin

The sulfated octapeptide of cholecystokinin (CCK-8S) and CCK fragments were administered to mice to determine the subtype and central versus peripheral location of the CCK receptor that modulates dopamine release in the neostriatum. Dopamine release was decreased when unsulfated CCK (CCK-8U) or the butoxycarbonyl tetrapeptide of CCK (t-boc-CCK-4) was infused into the brain ventricles but not when injected subcutaneously. These CCK fragments bind to the brain-type (CCK-B) but not alimentary-type (CCK-A) receptor. Centrally or peripherally administered CCK-8S also lowered dopamine release and this action was not blocked by the selective CCK-A receptor antagonist, L 364,718. The increase in dopamine release following amphetamine administration was attenuated by central injections of t-boc-CCK-4, CCK-8U, or CCK-8S, and this action of CCK-8S was not prevented by L 364,718. These data are the first to demonstrate that CCK-B receptors in brain mediate the suppression of dopamine release by cholecystokinin, especially when release is augmented. CCK-B receptor agonists should be useful for the treatment of psychiatric conditions that result from hyperactive dopamine neurons.

Fluphenazine treatment reduces CSF somatostatin in patients with schizophrenia: correlations with CSF HVA

CSF somatostatin and homovanillic acid (HVA) were measured in 14 schizophrenic patients while they were drug-free and during chronic fluphenazine treatment. CSF somatostatin was significantly reduced and CSF HVA was significantly elevated (p less than 0.002) during fluphenazine treatment. There was a trend toward correlation between CSF somatostatin and CSF HVA in the 14 schizophrenic patients when drug-free (r = 0.49, p less than 0.07) and fluphenazine-treated (r = 0.47, p less than 0.08). When examined in a larger group (n = 46) of drug-free schizophrenics, this relationship was highly significant (r = 0.59, p less than 0.001). These clinical data are consistent with preclinical evidence indicating a functional interaction between CNS somatostatin and dopamine systems.

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.

Cholecystokinin receptor subtypes and neuromodulation

The sulfated octapeptide of cholecystokinin (CCK-8S) and CCK fragments have been administered to mice to determine the subtype and location of the CCK receptor that modulates the release of dopamine (DA) in brain. 1. Centrally (i.c.v.) or peripherally (s.c.) administered CCK-8S lowers DA release, and to a lesser extent, metabolism, in the neostriatum and olfactory tubercle. 2. DA release is decreased when the CCK-B selective compounds, unsulfated CCK-8 (CCK-8U) or the butoxycarbonyl tetrapeptide of CCK (t-boc-CCK-4), are given i.c.v. but not when injected s.c. 3. The increase in DA release following amphetamine administration is attenuated by i.c.v. but not s.c. injections of t-boc-CCK-4 or CCK-8U and by CCK-8S given via either route. 4. None of the s.c. actions of CCK-8S are prevented by the CCK-A receptor antagonist, L 364,718. CCK-B receptors in brain mediate the suppression by CCK of basal and augmented DA release. CCK-B receptor agonists may be useful for the treatment of psychiatric conditions that result from excessive DA release.

Anatomical distribution of somatostatin immunoreactivity in the infant brainstem

The distribution of somatostatin-immunoreactive structures in the infant brainstem was investigated using the peroxidase-antiperoxidase technique. A wide distribution of somatostatin-immunoreactive cell bodies and fibers was observed throughout the brainstem. Numerous somatostatin-immunoreactive cell bodies and fibers were present in several areas of the brainstem including the substantia grisea centralis and the reticular formation. Some immunoreactive cell bodies were seen in cranial nerve nuclei such as the nucleus praepositus, the nucleus nervi hypoglossi and the vestibular nuclei. Immunoreactive fibers were seen in the nucleus cuneatus, the locus coeruleus, the nucleus tractus solitarius, the nucleus ambiguus, the nucleus tractus spinalis nervi trigemini and the dorsal horn of the spinal cord. These data were in agreement with previous works on the human adult. However, a high density of somatostatin-immunoreactive cell bodies and fibers in the interpeduncular nucleus and in the nucleus centralis superior, and a dense network of somatostatin-immunoreactive fibers in the dorsal part of the nucleus inferior olivarius, were also observed. The role of somatostatin in some brainstem nuclei and its probable implication in some specific neuropathological diseases of the infant brainstem is discussed.

Regional distribution of cholecystokinin receptors in macaque medial temporal lobe determined by in vitro receptor autoradiography

Cholecystokinin (CCK) binding sites were localized in the hippocampus, amygdala, and medial temporal cortices of macaque monkeys by using techniques of in vitro receptor autoradiography. Binding sites were labeled with 3H-CCK-8 and 125I-CCK-33, and nonspecific binding was assessed in the presence of 1 microM CCK-8. Comparison of autoradiograms with Nissl-stained sections allowed precise correlation of autoradiographic grain distribution with cytoarchitecture. CCK binding in the amygdala varied among nuclear subdivisions. It was dense in the lateral, basomedial, endopiriform, and cortical nuclei, in the parvicellular portion of the accessory basal nucleus, the periamygdaloid cortex, the cortical transition area, and in the amygdalohippocampal area. Labeling was sparse in the central, medial, and basolateral nuclei as well as in the magnocellular accessory basal nucleus. In the hippocampal formation, a single dense band of CCK binding was observed over the granule cell layer and adjacent few millimeters of the molecular layer of the dentate gyrus, while in the polymorph and remaining portions of this layer binding was of very low density. Prominent label over the pyramidal layer in the presubiculum clearly distinguished this region from the adjacent subiculum in which binding just exceeded background levels. Moderate to light label was observed in the hilus and stratum pyramidale of CA3, CA2, and CA1, while other hippocampal layers showed minimal specific binding. Variation in CCK binding in the medial temporal cortex showed close correspondence to cytoarchitectonic subdivisions. In entorhinal cortex, for example, binding was concentrated in layers III-VI while label in area 35 was prominent in all laminae except layer IV. Area TH of von Bonin and Bailey ('47) was distinguished from other regions by evenly distributed binding across all layers, while in area TF a bilaminar pattern of label in layers II and IV was observed. The highly specific patterns of CCK binding in amygdala and transitional cortices of the medial temporal lobe can be related to terminal fields of neo- and allocortical afferents to these regions, while label in the hippocampal formation coincides with the terminals of intrinsic neurons which ramify among the somata of cells that are targets of neocortical afferents. Thus, in all structures of the medial temporal lobe the disposition of peptidergic binding sites suggests that CCKergic systems may be important in the modulation of cortical afferents.

New perspectives in basal forebrain organization of special relevance for neuropsychiatric disorders: the striatopallidal, amygdaloid, and corticopetal components of substantia innominata

The basal forebrain is critically involved in functions representing the highest levels of integration. Only recently has a relatively clear anatomical picture of this important area begun to emerge. The territory that has generally been referred to as the "substantia innominata" appears to be composed of portions of three recognizable forebrain structures: the ventral striatopallidal system, the extended amygdala and the magnocellular corticopetal system. (1) Rostrally, the striatopallidal system reaches ventrally to the base of the brain. (2) Caudal to the ventral extension of the striatopallidal system elements of the centromedial amygdala and bed nucleus of the stria terminalis are merged so that these two areas together with this subpallidal corridor form a large forebrain unit that might be described as an "extended amygdala". (3) Large cholinergic and non-cholinergic corticopetal neurons form a more or less continuous aggregate that is interwoven with the striatopallidal and extended amygdala systems in basal forebrain. Consideration of morphological and connectional characteristics of basal forebrain suggests that the corticopetal cell groups, together with magnocellular elements of the striatum, serve similar functional roles for the striatopallidal system, the extended amygdala, and the septal-diagonal band complex. Specifically, the output of medium spiny neurons in striatum, extended amygdala, and lateral septum are directed toward somewhat larger sparsely or moderately spiny neurons with radiating dendrites which in turn project to diencephalon and brainstem or provide either local feedback (e.g. in striatum) or distal feedback to cortex. The functional implications of this parallel processing of descending forebrain afferents are discussed.

Cholecystokinin attenuates basal and drug-induced increases of limbic and striatal dopamine release

Subcutaneous administration to mice of the sulfated octapeptide of cholecystokinin (CCK; 0.2-1 mg/kg) lowered dopamine release and metabolism in the caudate-putamen and frontal cortex in a dose- and time-related manner. Twelve-fold higher doses of CCK were required to lower dopamine release and metabolism in the olfactory tubercle. Amphetamine-induced increases in dopamine release but not metabolism in the caudate-putamen and olfactory tubercle were attenuated in a dose-related manner by CCK. Increases in dopamine release and metabolism following haloperidol were also attenuated by CCK. These data are consistent with the potential antipsychotic action of CCK receptor agonists. CCK appears to be a suppressor of striatal, limbic and cortical dopamine release, especially when release is augmented.

Functional expression of brain cholecystokinin and bombesin receptors in Xenopus oocytes

Total RNA was extracted from 15-day-old whole rat brains. Microinjection of the RNA into Xenopus laevis oocytes induced electrophysiological responsiveness to cholecystokinin-8 (CCK) and bombesin (BBS) but not to corticotropin-releasing factor (CRF) or somatostatin. The responses to CCK and BBS were similar in shape, time course, and reversal potential to that induced by receptor mediated phospholipid breakdown and that which is induced by intracellular injection of IP3. These responses were not blocked by atropine or by mianserin, did not require extracellular Ca2+ and were completely suppressed by intracellular injection of EGTA.

The use of cholecystokinin in schizophrenia: a review

Cholecystokinin (CCK) is a peptide originally isolated from the gut. It has been investigated as a candidate treatment for schizophrenia on the assumption that the illness is associated with an imbalance between CCK and dopamine in the mesolimbic dopamine system. Many of the studies to assess the efficacy of CCK used open designs and are prone to observer bias and over-optimistic reporting. Most of the studies used CCK as an adjunct to standard neuroleptic treatment and are too small to be able to demonstrate extra efficacy above that of the active compound. Only three out of ten studies using CCK or placebo as an adjunct to neuroleptics reported limited efficacy. Of the 14 placebo-controlled reports only three were in drug-free patients. These were unfortunately too small, or too brief, to draw valid conclusions of efficacy. A summary of these data suggests that although 500 patients have received CCK, its efficacy in the treatment of schizophrenia has not been properly tested.

Cholecystokinin

1. CCK-peptides are distributed throughout the whole brain with the exception of the cerebellum. 2. There is strong evidence that they act as neuromodulators on the noradrenergic, opioid and mainly dopaminergic system. 3. CCK reduces food-intake. However, tolerance occurs, when chronically given. Thus, potential benefits in the treatment of obesity seem unlikely. 4. CCK increases threshold and tolerance to electrically and thermally induced cutaneous pain. CCK yields relief of pain in colic and ischaemic pain. 5. To date, results about CCK-content in CSF and post-mortem-brain in various psychiatric and neurological diseases related to the dopaminergic system are equivocal. 6. Treatment studies do not provide evidence for beneficial effects of CCK-peptides in schizophrenia.

The distribution of somatostatin-immunoreactive neurons and fibers in the rat cerebral cortex: light and electron microscopic studies

The distribution of somatostatin (SOM)-immunoreactive neurons in rat motor and somatosensory cortices was studied by immunohistochemistry at both light and electron microscopic levels. Three types of SOM-positive neurons were described. Type A cells are large to medium in size, multipolar in shape and have 3-5 long primary cell processes. Type B cells are medium to small, fusiform in shape and have two primary processes. These two subtypes show abundant subcellular organelles and are heavily stained throughout their cytoplasm. Type C cells are small, ovoid or fusiform in shape and are lightly stained. These previously undescribed cells are the largest SOM-immunoreactive population in the cortex. Ultrastructurally they have few subcellular organelles and only a patchy immunostaining in the cytoplasm. SOM-immunoreactive neurons occur in all cortical layers except I, and are most numerous in layer V of the somatosensory and motor cortex. In SOM-positive dendrites, electron-dense immunoreactive/peroxidase end product is primarily associated with microtubules. Fine deposits also occur deep to the postsynaptic membrane asymmetric synapses making contact with such dendrites.

Prednisone decreases CSF somatostatin in healthy humans: implications for neuropsychiatric illness

Several neuropsychiatric illnesses, including depression and Alzheimer's disease, are reported to be characterized by hypercortisolemia and by reduced levels of cerebrospinal fluid somatostatin-like immunoreactivity (CSF-SLI). To investigate a possible causal linkage between these abnormalities we administered prednisone, 80 mg orally per day for 5 days, to 9 healthy volunteers. We observed significant prednisone-induced reductions in CSF-SLI. Moreover, the magnitude of these reductions was inversely related to the magnitude of prednisone-induced reductions in plasma ACTH levels, suggesting a functional interaction between circulating corticosteroids, central somatostatin and pituitary ACTH release.

Dopaminergic agents affected neuronal transmission of cholecystokinin in the rat brain

In order to study the interaction between cholecystokinin (CCK) and dopamine (DA), we prepared an anti-CCK-8 antibody with low cross reactivity, and observed effects of administered various dopaminergic agents on CCK-immunoreactivity (CCK-IR) in discrete brain regions of rats. CCK-8 IR (boiling water extraction) and CCK-33 IR (acetic acid extraction) were also measured in the same sample. A single administration of haloperidol decreased the CCK-8 IR in the corpus striatum and that of racemic sulpiride significantly decreased the CCK-8 IR in the frontal cortex and the limbic system. In contrast, a single administration of apomorphine or methamphetamine increased the CCK-8 IR in the same regions. These findings suggest that an acute response of the CCK system to administered dopaminergic agents may be due to a change in the rate of release of CCK-8, but not to a change in its synthesis in areas in which DA neurons originating in the midbrain innervate. After chronic administration of racemic sulpiride or methaphetamine, CCK-8 IR in various brain regions exhibited a tendency close to that of control.

Selective decreases in MAO-B activity in post-mortem brains from schizophrenic patients with type II syndrome

The activities of the A and B forms of the enzyme monoamine oxidase (MAO, E.C. 1.4.3.4) have been assessed with the substrates 5-hydroxytryptamine and benzylamine respectively in seven areas of the brains of 39 patients with schizophrenia and 44 control subjects. Whereas previous studies have found the enzyme unchanged in brain in schizophrenia, in this study there was a modest but significant decrease in the activity of MAO-B in frontal and temporal cortices and in amygdala. This decrease could not be accounted for by neuroleptic medication, age, sex or post-mortem variables. In a series of 22 patients who had been assessed in life, the reduction in MAO-B activity was found to be associated specifically with the presence of negative symptoms (flattening of affect and paucity of speech). The findings are therefore consistent with other evidence for structural and neurochemical change in the temporal lobe that have been associated with the type II (defect state) syndrome of schizophrenia. The change in enzyme activity is unlikely to be related to a change in monoamine metabolism but may reflect a disturbance in glial function. The change in MAO-B activity in brain in this study is confined to particular areas of brain and a subgroup of patients; it is thought to be entirely unrelated to earlier reports of reductions of enzyme activity in platelets, which are probably attributable to prolonged neuroleptic medication.

Distribution of immunoreactive cholecystokinin in the human hippocampus

The distribution of cholecystokinin immunoreactive (CCK-IR) nerve cell bodies and processes is reported in the human hippocampus by using the peroxidase-antiperoxidase technique of Sternberger. The CCK-immunoreactivity occurs in three major classes of interneurons: small (10-20 microns) horizontal multipolar neurons of the alveus and stratum oriens; small vertically oriented bipolar or multi-polar neurons in the stratum oriens and stratum pyramidale of Ammon's horn, layers II and III of the subicular system and the entorhinal area; large (20-35 microns) bipolar neurons in the hilus. Each region of the hippocampus is distinct in its CCK-IR nerve fibers content. Those fibers are particularly abundant around pyramidal cells of the CA2 and CA3 subfields of the Ammon's horn and around granular cells suggesting synaptic interaction between the CCK nerve terminals and glutamate neurons of these two regions. No CCK-IR fiber is detected in the fimbria and only a few number of CCK-IR beaded fibers are seen in the angular bundle. These anatomical data suggest that CCK interacts in the functional circuitry of the human hippocampus.

Characterization of [3H]cholecystokinin octapeptide binding to mouse brain synaptosomes: effects of neuroleptics

The presence of high concentrations of both dopamine and cholecystokinin (CCK) in the striatum and in various limbic structures suggests that the CCK may not only influence dopaminergic transmission, but it also may be relevant to the psychopathology of schizophrenia and to the therapeutic effects of neuroleptics. By using a synaptosomal fraction isolated from the mouse cerebral cortex and [propionyl-3H]CCK8-sulphate ([3H]CCK8S) as a ligand, a single binding site for [3H]CCK8 with a KD value of 1.04 nM and a Bmax value of 42.9 fmol/mg protein was identified. The competitive inhibition of [3H]CCK8S binding by related peptides produced an order of potency of CCK8-sulphated (IC50 = 5.4 nM) greater than CCK8-unsulfated (IC50 = 40 nM) and greater than CCK4 (IC50 = 125 nM). The regional distribution of [3H]CCK8S binding in the mouse brain was highest in the olfactory bulb (34.3 +/- 5.6 fmol/mg protein) greater than cerebral cortex greater than cerebellum greater than olfactory tubercle greater than striatum greater than pons-medulla greater than mid brain greater than hippocampus greater than hypothalamus (12.4 +/- 2.1 fmol/mg protein). The repeated administration of haloperidol (2.5 mg/kg/tid) increased the binding of [3H]CCK8S in cerebral cortex from 31.8 +/- 1.7 to 38.9 +/- 5.2 fmol/mg protein. The varied distribution of CCK8S receptors may signify nonuniform functions for the octapeptide in the brain.

Somatostatin and neuropeptide Y are unaltered in the amygdala in schizophrenia

Although a biochemical abnormality has been postulated in the etiology of schizophrenia, evidence supporting this hypothesis has been conflicting. Because of the presence of somatostatin-like immunoreactivity (SLI) in limbic system nuclei of the brain, we examined postmortem concentrations of SLI in patients dying with schizophrenia and in normal controls. Concentrations of SLI in Brodmann cortical area 38, hippocampus, caudate, putamen, nucleus accumbens, and both segments of the globus pallidus were not significantly different from controls. In addition, we examined both SLI and neuropeptide-Y-like immunoreactivity (NPYLI) in subnuclei of the amygdala and the substantia innominata. There were no significant alterations in either neuropeptide as compared with controls.

Cholecystokinin-induced inhibition of dopamine neurotransmission: comparison with chronic haloperidol treatment

A dose-dependent inhibition of DA release was observed by in vivo electrochemical techniques after acute i.v. injections of CCK8-S (1.0-8.0 micrograms/kg). The threshold dose was 1.0 microgram/kg, and maximum inhibition of release (90%) was obtained with doses of 4 and 8 micrograms/kg. Injections of CCK8-US (4-20 micrograms/kg) had no effect on DA release. Repeated treatment with haloperidol (0.5 mg/kg s.c.) for 21 days produced a 47% inhibition of DA release in the nucleus accumbens. Apomorphine (50 micrograms/kg) reversed the inhibitory effects of both acute injections of CCK8-S and prolonged haloperidol treatment on DA release. In contrast, apomorphine (50 micrograms/kg) administered alone inhibited DA release, presumably via hyperpolarization of DA neurons. The attenuation of DA release by either an acute injection of CCK8-S or repeated treatment with haloperidol is attributed to the induction of depolarization block in mesolimbic DA neurons. These data may be indicative of antipsychotic properties of CCK8-S.

On the distribution of cholecystokinin receptor binding sites in the human brain: an autoradiographic study

Cholecystokinin (CCK) binding sites were localized by in vitro autoradiography in human postmortem brain materials from 12 patients without reported neurological diseases using [125I]Bolton-Hunter CCK octapeptide (BHCCK-8) as a ligand. The pharmacological characteristics of BHCCK-8 binding to mounted tissue sections were comparable to those previously reported in the rat. CCK-8 being the most potent displacer, followed by caerulein, CCK-4, and gastrin I. The distribution of BHCCK-8 binding sites was heterogeneous. These sites were highly concentrated in a limited number of gray matter areas and nuclei. The highest binding densities were seen in the glomerular and external plexiform layers of the olfactory bulb. BHCCK-8 binding sites were also enriched in the neocortex, where they presented a laminar distribution with low levels in lamina I, moderate concentration in laminae II to IV, high density in lamina V, and low levels in lamina VI. A different laminar distribution was seen in the visual cortex, where a low receptor density was observed in lamina IV but higher density in laminae II and VI. In the basal ganglia the nucleus accumbens, caudatus, and the putamen presented moderate to high densities of binding sites, while the globus pallidus lacked sites of BHCCK-8 binding. In the limbic system the only area presenting moderate to high density was the amygdaloid complex, particularly in the granular nucleus, while most of the thalamic nuclei were extremely poor or lacked BHCCK-8 binding. The hippocampal formation showed low (CA1-3) to moderate (subiculum) densities. Midbrain areas generally disclosed very low levels of BHCCK-8 binding sites. The pontine gray and the nucleus reticularis tegmenti pontis showed a relatively high density of CCK-8 receptor specific binding. Moderate to very high densities were found in few nuclei of the lower brainstem and spinal cord as the inferior olives and their accessory nuclei, the arcuate nuclei, the striae medullares, the efferent (motor) nucleus of the vagus, and the substantia gelatinosa of the cervical and thoracic spinal cord. These results are discussed in relation to the distribution of endogenous peptide and to the known physiological and pharmacological effects of substances acting on these receptors.

Neuropeptides in neurological disease

Neuropeptides are widely distributed in the central nervous system, where they serve as neuroregulators. Recent interest has focused on their role in degenerative neurological diseases. We describe the normal anatomy of neuropeptides in both the cerebral cortex and basal ganglia as a framework for interpreting neuropeptide alterations in Alzheimer's disease (AD), Huntington's disease, and Parkinson's disease. Concentrations of cortical somatostatin are reduced in AD and in dementia associated with Parkinson's disease. Concentrations of neuropeptide Y and corticotropin-releasing factor are also reduced in AD cerebral cortex. The reduced cortical concentrations of somatostatin and neuropeptide Y in AD cerebral cortex may reflect a loss of neurons or terminals in which these two peptides are co-localized. In Huntington's disease, basal ganglia neurons in which somatostatin and neuropeptide Y are co-localized are selectively preserved. Cerebrospinal fluid concentrations of neuropeptides in AD reflect alterations in cortical concentrations. Improved understanding of neuropeptides in degenerative neurological illnesses will help define which neuronal populations are specifically vulnerable to the pathological processes, and this could lead to improved therapy.

Cholecystokinin-immunoreactive boutons in synaptic contact with hippocampal pyramidal neurons that project to the nucleus accumbens

Neurons in the hippocampal formation of the rat that project to the medial nucleus accumbens were identified following the retrograde transport of a conjugate of horseradish peroxidase with wheat germ agglutinin. The great majority of such projecting neurons were located in the ventral subiculum and were pyramidal in shape; the pyramidal nature of 25 such retrogradely labelled neurons was established by Golgi impregnation. In material processed to reveal both retrogradely labelled cells and cholecystokinin-immunoreactivity, no immunoreactive projecting neurons were found. However, 48 identified projecting neurons, probably pyramidal, were found to receive input from cholecystokinin-immunoreactive boutons that formed symmetrical synaptic contacts with the soma or proximal dendrites. It is suggested that one function of cholecystokinin-immunoreactive neurons in the hippocampal formation might be to influence the output of the pyramidal neurons that project to the nucleus accumbens. Since this pathway is one of the main links between the limbic system and the basal ganglia, it is conceivable that changes in the cholecystokinin levels in the hippocampus, as found in schizophrenia, might influence behaviour through the pathway connecting the hippocampus with the nucleus accumbens.

Distribution of somatostatin receptors in the human brain: an autoradiographic study

High affinity somatostatin receptors have been measured in postmortem brains from 18 neurologically asymptomatic patients (mean age: 67 years) using the stable somatostatin analog 125I-204-090, DPhe-Cys-Tyr-DTrp-Lys-Thr-Cys-Thr(ol), as radioligand. In homogenates from human frontal cortex, high affinity (Kd = 0.52 nM; Bmax = 557 fmol/mg protein) receptors with pharmacological specificity for somatostatin, [D-Trp8]somatostatin and somatostatin-28 were found. The CNS distribution of these receptors was studied by autoradiography. Somatostatin receptors were distributed in varying densities throughout the whole brain. High concentrations are found in all cortical layers, the deeper layers (V-VI) being usually more dense than the superficial layers (I-III). The limbic system is heavily labeled, in particular hippocampus (CA1, dentate gyrus), most of the nuclei of the amygdala, and the habenula. Also parts of the basal ganglia are very rich in somatostatin receptors: the nucleus caudatus as well as the nucleus accumbens are very dense, whereas the globus pallidus is virtually unlabeled. Interestingly, significant amounts of somatostatin receptors are found in the human cerebellum, which is devoid of endogenous somatostatin. Other discrete areas of the CNS are enriched with somatostatin receptors: locus coeruleus, tuberal nuclei of the hypothalamus, claustum, tuberculum olfactorium as well as spinal trigeminal nucleus and substantia gelatinosa of the spinal cord. The substantia innominata is poor in somatostatin receptors. In general there is a good correlation in the distribution of somatostatin receptors in the human and rat brain and there is a reasonable correlation with endogenous somatostatin levels in human brain tissue, particularly in the larger structures. The very high density and the specific localization of somatostatin receptors in strategic key points in the CNS such as cortex, basal ganglia, limbic system and substantia gelatinosa suggests an important role of somatostatin in cognitive, sensory and extrapyramidal motor functions. The significance of somatostatin receptors in the human cerebellum remains to be elucidated.