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

Molecular forms of somatostatin, substance P and neurotensin in fresh human cerebral cortex

The molecular forms of somatostatin, substance P and neurotensin in fresh normal human cerebral cortex have been investigated using high performance liquid chromatography and radioimmunoassay. For each peptide most of the immunoreactivity measured corresponds to a single molecular form co-eluting with the authentic peptide. Small differences in the minor peaks of somatostatin and substance P immunoreactivity are seen when compared to the results of similar studies on post mortem human brain. A substantial difference in the molecular forms of neurotensin was seen which suggests that degradation of this peptide may occur post mortem.

Comparison of circling induced by unilateral intrastriatal microinjections of haloperidol, clozapine and CCK-8 in rats

The existence of the neuropeptide cholecystokinin (CCK) within a subpopulation of central dopamine (DA) neurons has led to speculations that the peptide may serve as an endogenous modulator of DA functions. To test this possibility, the present study examined the pharmacological action of CCK-8 by comparing its effects on DA-mediated circling behavior with those of a typical (haloperidol; HAL) and an atypical (clozapine; CLZ) dopamine antagonist neuroleptic drug. Rats received unilateral intrastriatal infusions of either sulfated CCK-8 (1, 2, or 8 micrograms), HAL (5 micrograms) or CLZ (5 or 20 micrograms) 15 minutes after systemic injection of d-amphetamine (1 mg/kg). Animals were then placed into rotational chambers where the number and direction of complete 360 degree turns was automatically recorded over a 1 hour session. HAL produced strong and almost exclusive ipsilateral circling while the responses after CLZ and CCK-8 were reliably more variable in rotational direction. More specifically, the results suggest that CLZ is only a weak antagonist of behaviors mediated by striatal DA activation while CCK seems to be devoid of antidopaminergic properties in the striatum.

Distribution of immunoreactive somatostatin (ISRIF) in the nervous system of the squid, Loligo pealei

Somatostatin (SRIF) is a neuropeptide with a widespread distribution in the mammalian CNS. In the present study we have examined the distribution of immunoreactive-like SRIF (ISRIF)-containing elements in the nervous system of the cephalopod mollusk Loligo pealei, or the Woods Hole squid. ISRIF was localized by light immunocytochemistry in sections of the squid-optic lobe, circumesophageal ganglia-and in stellate ganglion. In the optic lobe, ISRIF neurons were found in the internal granule cell layer and medulla and immunoreactive fibers were seen throughout the lobe and in the optic tract but were absent from the optic nerve, i.e., the projection between the retina and optic lobe. In the supraesophageal complex, ISRIF neurons were found in all lobes, but primarily in the vertical, subvertical, and frontal. In the subesophageal ganglion, ISRIF neurons were seen mainly following unilateral pallial nerve lesions; these neurons were primarily small-to-medium sized. ISRIF fibers were seen in many of the nerves exiting from the brain and in nerves extending between the sub- and supra-esophageal ganglia. In the stellate ganglion, ISRIF was present in many neurons as well as in a plexus of fibers within the ganglion; the peptide was absent from the second-order fibers and the giant axon. The data suggest that a molecule immunologically similar to vertebrate SRIF may be a major transmitter/modulator in this invertebrate. These results provide a foundation for further studies to evaluate the role of this molecule.

Enzyme immunoassay for cholecystokinin octapeptide sulfate and its application

A sensitive and specific enzyme-linked immunosorbent assay (ELISA) for cholecystokinin octapeptide sulfate (CCK-8S) has been developed using N-terminal specific antibody for CCK-8S. In this assay CCK-8S coupled with poly-L-Glu (CCK-poly-Glu), which is adsorbed on a solid phase, competes with CCK-8S for the binding sites of rabbit anti-CCK antibody, and the complex of the immobilized antibody and CCK-poly-Glu is measured using goat anti-rabbit immunoglobulin G conjugated with horseradish peroxidase. The total time for completion of the assay is less than 24 h. Near 50% bound levels, the intraassay coefficient of variation is 5.2-6.2% and the interassay coefficient of variation is 5.9-8.5%. This assay is sensitive enough to detect 9 pg of CCK-8S, and the data from rat brain regions using this ELISA are very similar to the data from those using radioimmunoassay (RIA). Therefore, this ELISA is simpler and more rapid in comparison with conventional RIA. In the preliminary experiments, we applied this method for determination of CCK content in the brain regions of adult rats treated with 6-hydroxy-dopamine or in newborn rats subjected to anoxia, and showed that this system is applicable to detection of changes of endogenous CCK content.

Behavioral changes following central injection of cysteamine in rats

When tested 3 days following 4 daily intracerebroventricular injections of 250 micrograms cysteamine, which depletes somatostatin, rats demonstrated a significant increase in locomotor activity that was not observed in animals treated similarly with 350 micrograms cysteamine. A significant deficit in passive avoidance was observed in animals treated with the 350-micrograms dose, but not in animals treated with 250 micrograms cysteamine. These data suggest that altered activity of the somatostatinergic system disrupts specific processes underlying neural integration of complex behaviors.

Effects of haloperidol on somatostatin-like immunoreactivity in the CSF of Schizophrenic patients

The levels of somatostatin-like immunoreactivity (SLI) were determined in the cerebrospinal fluid (CSF) of 14 schizophrenic patients before and after 3 weeks on haloperidol treatment. Baseline levels of SLI correlated negatively with psychopathological items on the Brief Psychiatric Rating Scale related to psychotic productivity. SLI levels increased after haloperidol treatment, but this increase did not correlate with psychopathological improvement. A difference in the ratio of larger and smaller molecular forms of the peptide was found before and after treatment. The drug-free samples showed a preponderance of the larger molecular forms, resulting in a ratio of 4:1, whereas the haloperidol-treated samples showed an equal distribution of both species.

Neuropeptides in the amygdala of controls, schizophrenics and patients suffering from Huntington's chorea: an immunohistochemical study

The location of the neuropeptides methionine-enkephalin (ME), neurotensin (NT), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) within the amygdaloid complex of healthy human individuals, schizophrenics and patients suffering from Huntington's chorea was studied qualitatively by means of immunohistochemistry. VIP-like immunoreactivity (IR) was present predominantly in a dense cluster of fibers and terminals in the central amygdaloid nucleus. ME-IR was observed in fibers, terminals and cell bodies in the same subnucleus, exhibiting a characteristical distribution pattern. NT-positive cell bodies were situated within the center of the central amygdaloid nucleus, fibers and terminals being encountered mainly at the periphery. NPY-IR was found to be evenly distributed throughout the amygdala. Distribution and staining intensity of ME, NPY and NT in the amygdala showed no qualitatively recognizable difference between the normal and schizophrenic specimens, whereas VIP-IR appeared to be slightly increased in the central amygdaloid nucleus of schizophrenics. In the choreic cases, the considerably shrunken amygdala exhibited only very low staining intensity of the four investigated neuropeptides.

A Negative Symptom Rating Scale

Renewed interest in the role of negative symptoms in "defect state" schizophrenia calls for the design of a standardized, easy to use, reliable, and valid instrument to assess these aspects of psychopathology. In order to measure negative symptoms, we developed the Negative Symptom Rating Scale (NSRS). We report on the design, interrater reliability, and construct-validation of NSRS against the most frequently used negative symptom scales or subscales. In summary, the NSRS is a short, sensitive, highly specific, reliable, and apparently valid instrument for measuring negative symptoms in schizophrenia.

Synthesis and biological activity of Boc [Nle28, Nle31]CCK27-33, a highly potent CCK8 analogue

A new CCK8 related peptide, Boc[Nle28,Nle31]CCK27-33 (Boc[diNle]CCK7) was synthesized and tested for cholecystokinic activity, at both the peripheral and the central level. This analogue, protected against both chemical oxidation and enzymatic degradation by aminopeptidases, was shown to be equipotent to CCK8 in releasing amylase from rat pancreas fragments. In addition, the EC50 values of Boc[diNle]CCK7 in the guinea pig gallbladder and ileum contraction assays (3.2 nM and 3.0 nM respectively) were similar to those of CCK8 (6.0 nM and 2.0 nM). Moreover both Boc[diNle]CCK7 and CCK8 elicited similar effects on the open field test over the same concentrations range. These results demonstrate the ability of Boc[diNle]CCK7 to be a suitable tool for investigating the physiological role of native CCK8.

Reduced high affinity cholecystokinin binding in hippocampus and frontal cortex of schizophrenic patients

Cholecystokinin (CCK) binding sites were assessed in post-mortem brain membrane preparations from controls and schizophrenic patients. 125I-BH CCK33 specific binding was reduced by 40% (p less than 0.02) in the hippocampus and by 20% (p less than 0.01) in the frontal cortex of schizophrenic patients compared with controls. There were no differences in 125I-BH CCK33 binding between the two groups in the amygdala, temporal cortex or caudate nucleus.

Neuropeptides in human brain--postmortem studies

Four neuropeptides (substance P, methionine-enkephalin, neurotensin and cholecystokinin) were measured by radioimmunoassays in a number of brain regions of deceased patients with mental illnesses and controls. The most striking finding in these studies was that methionine-enkephalin concentrations in caudate nuclei of chronic paranoid schizophrenic patients were reduced relative to several control groups. Neuroleptics had no obvious effects on any of the four measured neuropeptides. These findings are not inconsistent with the hypothesis that methionine-enkephalin may be involved in some of the pathology of the schizophrenic syndrome.

Cholecystokinin peptides, dopamine and schizophrenia--a review

CCK-IR is co-localized with DA in some DA neurons projecting to limbic structures. The extent of the co-localization is species dependent. The co-localization of CCK and DA is of interest in view of the DA hypothesis of schizophrenia and the putative role of limbic dysfunction in the pathophysiology of this disorder. In animals biochemical, electrophysiological and behavioural studies point to an interaction between CCK and DA. Whereas some investigations point to an inhibitory effect on DA function, which would be compatible with a potential antischizophrenic action, others point to an enhancement or no effect. CCK peptides show a neuroleptic-like profile in several screening tests for neuroleptics but not in all studies. In man there is endocrinological evidence for an inhibitory effect of CCK-33 and CCK-8 on DA function. However, alternate explanations are possible. CSF CCK-IR is unchanged or decreased in schizophrenia. Autopsy investigations have shown significant decreases, increases or no change in brain CCK-IR concentrations and a decrease in CCK-33 binding in schizophrenia. Eight of 11 clinical trials with CER, CCK-8 or CCK-33 have shown a therapeutic effect in schizophrenia; only two of these eight trials have been double-blind studies. The three controlled investigations which have shown no effect have used only small patient populations. None of the trials have used an active placebo. It is difficult to reconcile the apparent long duration of antipsychotic activity with the short half-life of the peptides and problems of the peptides in crossing the blood brain barrier. Despite these apparent anomalies information to date is sufficiently impressive to warrant further detailed investigation of CCK-DA-interactions and the evaluation of the clinical effects of a variety of CCK peptides and related compounds, natural and synthetic, which may more easily cross the blood brain barrier and which may show regional selectivity in site of action in brain.

Caerulein and its analogues: neuropharmacological properties

The decapeptide from the frog Hyla caerulea, caerulein (caerulein diethylammonium hydrate, ceruletide, CER) is chemically closely related to the C-terminal octapeptide of cholecystokinin (CCK-8). Like CCK-8, CER and some of its analogues produce many behavioural effects in mammals: inhibition of intake of food and water; antinociception; sedation; catalepsy; ptosis, antistereotypic, anticonvulsive and tremorolytic effects; inhibition of self-stimulation. Effects of CER in man comprise sedation, satiety, changes in mood, analgesia and antipsychotic effects. A modulation of central dopaminergic functions appears to be one possible mechanism of CER and its analogues. A common denominator for all effects of CER is, at present, not evident.

Effect of systemically administered caerulein on dopamine metabolism in rat brain

The effect of caerulein, a cholecystokinin-like peptide, on the dopamine (DA) system was examined in rat brain. Caerulein, when tested in vitro, had no significant influence on either D-1 or D-2 DA receptors. A single injection of caerulein (400 micrograms/kg, i.p.) reduced both homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum. No significant change in DA metabolites was found in the other 7 areas (polar and medial fields of prefrontal cortex, anterior cingulate cortex, nucleus accumbens, tuberculum olfactorium, septum and amygdala). After repeated injections of caerulein (200 micrograms/kg, i.p., daily for 5 days), the decreases in striatal HVA and DOPAC had disappeared, while the amount of HVA had increased in the nucleus accumbens. These results suggest that peripherally administered caerulein modulates the nigrostriatal and mesolimbic DA neuron systems in the different modes of action.

A neural plasticity hypothesis of schizophrenia

An extensive research effort has failed, thus far, to conclusively identify a specific disease process (or processes) underlying the behavioral symptoms of schizophrenia. The present paper will entertain the hypothesis that the structural and functional plasticity of the brain can constitute a "nonspecific" biological etiology of schizophrenia. This plasticity need not be accompanied by infectious processes or gross alterations in neurotransmitter levels, enzyme activities, etc. that are specific to schizophrenia. The monkey isolation syndrome provides a precedent for a causal relationship between brain plasticity and pathological behavior. In a speculative manner, it will be demonstrated that neural plasticity concepts can be invoked to potentially explain several aspects of schizophrenia: the various types of behavioral symptoms exhibited by schizophrenics, the regional alterations in brain structure and function seen in chronic schizophrenics, the involvement of genetic and environmental etiological factors, the pharmacological support for the dopamine hypothesis, and the delayed onset of neuroleptic antipsychotic action. Considering the explanatory potential of neural plasticity concepts, a research program which focuses on these concepts seems warranted.

Cholecystokinin-octapeptide in chronic schizophrenia: a double-blind placebo-controlled study

Antipsychotic properties of cholecystokinin have been suggested both in laboratory studies and in some open clinical trials, mainly in patients suffering from chronic schizophrenia. Eighteen patients (14 males, 4 females) meeting Research Diagnostic Criteria for schizophrenia had been receiving neuroleptics at a dosage that had not changed for 3 months, and to which the patients were at best only partially responsive. The patients were randomized into groups that received weekly intravenous injections of 10 micrograms of CCK-8 or normal saline over 8 weeks. Neuroleptic medication was unchanged for the study. Baseline and weekly assessments were carried out using the Brief Psychiatric Rating Scale (BPRS) and the Schizophrenia Subscale of the Present State Examination (SS-PSE). Analysis of covariance revealed significant differences between CCK-8 and placebo over the study period on the Thought Disturbance Factor and Total Score of the BPRS, and on the Nuclear Syndrome, Total Delusion Factor, and Total Score of the SS-PSE. No important side effects were noted. It is concluded that CCK-8 has definite antipsychotic properties in patients with chronic schizophrenia. Clinical trials in neuroleptic-free patients are warranted.