Specificity of Neurotensin Metabolism by Regional Rat Brain Slices

Regional differences in neurotensin metabolism and the peptidases involved were studied using intact, viable rat brain microslices and specific peptidase inhibitors. Regional brain slices (2 mm x 230 microns) prepared from nucleus accumbens, caudate-putamen, and hippocampus were incubated for 2 h in the absence and presence of phosphoramidon, captopril, N-[1(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate, and o-Phenanthroline, which are inhibitors of neutral endopeptidase 24.11, angiotensin-converting enzyme, metalloendopeptidase 24.15, and nonspecific metallopeptidases, respectively. Neurotensin-degrading proteolytic activity varied by brain region. Significantly less (35.0 +/- 1.6%) neurotensin was lost from hippocampus than from caudate-putamen (45.4 +/- 1.0%) or nucleus accumbens (47.8 +/- 1.1%) in the absence of inhibitors. Peptidases responsible for neurotensin metabolism on brain slices were found to be predominantly metallopeptidases. Metalloendopeptidase 24.15 is of major importance in neurotensin metabolism in each brain region studied. The relative contribution of specific peptidases to neurotensin metabolism also varied by brain region; angiotensin-converting enzyme and neutral endopeptidase 24.11 activities were markedly elevated in the caudate-putamen as compared with the nucleus accumbens or hippocampus. Interregional variation in the activity of specific peptidases leads to altered neurotensin fragment formation. The brain microslice technique makes feasible regional peptide metabolism studies in the CNS, which are impractical with synaptosomes, and provides evidence for regional specificity of neurotensin degradation.     

Circadian rhythms in catecholamine metabolites and cyclic nucleotide production

Circadian rhythms in noradrenergic (NE) and dopaminergic (DA) metabolites and in cyclic nucleotide production were measured in discrete regions of rat brain. A circadian rhythm was found in the concentration of the NE metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), in the hippocampus. No MHPG rhythm was found in frontal, cingulate, parietal, piriform, insular or temporal cortex, or in hypothalamus. Circadian rhythms in the concentration of the NE metabolite, 3,4-dihydroxyphenylglycol (DHPG), occurred in occipital and parietal cortex and hypothalamus, with no rhythm observable in temporal or insular cortex, hippocampus, pons-medulla or cerebellum. The 24-hr mean concentration of MHPG varied 3.5-fold, highest in cingulate and lowest in parietal, temporal and occipital cortex. The 24-hr mean concentration of DHPG varied 6-fold, highest in hypothalamus and lowest in parietal cortex. Circadian rhythms in the concentration of the DA metabolite, homovanillic acid (HVA), were found in olfactory tubercle, amygdala and caudate-putamen, but not in nucleus accumbens. A circadian rhythm in the concentration of the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), occurred in nucleus accumbens, but not in olfactory tubercle or caudate-putamen. The mean 24-hr concentration of HVA was highest in caudate-putamen, intermediate in nucleus accumbens, and lowest in olfactory tubercle and amygdala. The mean 24-hr concentration of DOPAC was highest in nucleus accumbens and lower in olfactory tubercle and caudate-putamen. Circadian rhythms were found in the concentration of cyclic GMP (cGMP) in all regions measured except parietal cortex. The mean 24-hr concentration varied 128-fold, highest in nucleus accumbens, frontal poles, and hypothalamus and lowest in cingulate cortex. Circadian rhythms in cyclic AMP (cAMP) concentration were found in piriform, temporal, occipital, cingulate, and parietal cortex, amygdala and nucleus accumbens. No rhythms were found in frontal or insular cortex, hypothalamus, hippocampus, caudate-putamen or olfactory tubercle. The 24-hr mean cAMP concentration varied 4-fold, highest in parietal cortex and lowest in caudate-putamen and amygdala. Norepinephrine metabolites and dopamine metabolites were rhythmic in few regions. It is, therefore, unlikely that the rhythmicity measured in adrenergic receptors is, in general, a response to rhythmic changes in adrenergic transmitter release. The putative second messenger response systems, especially cGMP, were more often rhythmic. The rhythms in cGMP are parallel in form and region to those in the alpha 1-adrenergic receptor and may act as 2nd messenger for that receptor.(ABSTRACT TRUNCATED AT 400 WORDS)     

Degradation of human gastrin and CCK by endopeptidase 24.11: differential behaviour of the sulphated and unsulphated peptides

The degradation of human sulphated heptadecapeptide gastrin (G17s) by human endopeptidase 24.11 was studied in vitro. The products of degradation were characterized by HPLC, region-specific gastrin radioimmunoassay and amino acid analysis. The enzyme cleaved G17s at four sites, Trp4-Leu5, Ala11-Tyr12, Gly13-Trp14 and Asp16-Phe17. The patterns of fragments produced when sulphated and unsulphated G17s are hydrolysed by endopeptidase 24.11 indicate that the enzyme cleaves both substrates at the same four bonds. However, the sulphated G17 was 3-times less rapidly degraded than the unsulphated G17 (G17ns). In contrast, the rate of cleavage of the octapeptide cholecystokinin (CCK8) was faster when the peptide was sulphated. The kinetic data of endopeptidase 24.11 indicated similar Km values for sulphated or unsulphated gastrin and CCK; sulphated CCK8 exhibited a 2-fold higher kcat/Km value compared to unsulphated CCK8, whereas G17s exhibited a 2-fold lower kcat/Km value compared to G17ns. The results indicate that the presence of a sulphate group causes a marked reduction in the rate of hydrolysis of gastrin by endopeptidase 24.11, whereas sulphation enhances cholecystokinin degradation by the same enzyme. They also suggest that endopeptidase 24.11 may be responsible for the difference in metabolism of sulphated and unsulphated G17, previously observed in human circulation.     

Influence of Region-Specific Alterations of Neuropeptidase Content on the Catabolic Fates of Neuropeptides in Alzheimer's Disease

Abstract: We established the cartography of 11 exo- and endopeptidases in the frontal and parietal cortices and in the cerebellum of brains of patients diagnosed with a senile dementia of the Alzheimer's type (SDAT). Comparison with those of four subjects who had died without known neurologic or psychiatric illness indicated that there existed a region-specific alteration of the peptidase contents in the disease. In the frontal area of SDAT brains, postproline dipeptidyl aminopeptidase and aminopeptidase M activities were significantly reduced. In the parietal cortex of SDAT brain, activities of three additional endopeptidases—angiotensin-converting enzyme, proline endopeptidase, and endopeptidase 24.15—were also drastically reduced. In contrast, the cerebellum displayed a set of proteolytic activities that remained unaffected in SDAT brain. The putative influence of the disease on the catabolic fates of neurotensin, neuropeptide Y, and somatostatin(1–14) was investigated. Neurotensin was catabolized at identical rates in the frontal and parietal cortices in nondemented and SDAT brains. In contrast, neuropeptide Y metabolism was slowed down in SDAT brains in the frontal but not in the parietal cortex. Finally, the degradation velocities of somatostatin(1–14) were lowered in both cortical areas of SDAT brains. It is interesting that, by means of specific peptidase inhibitors, we demonstrated that endopeptidase 24.15 participated in somatostatin(1–14) inactivation in the parietal but not in the frontal cortex. It is suggested that the lowering of the rate of somatostatin(1–14) inactivation in the parietal cortex of SDAT brains likely results from the depletion of endopeptidase 24.15 in this brain region.     

Circadian rhythms in neurotransmitter receptors in discrete rat brain regions

Circadian rhythms were measured in alpha 1-, alpha 2- and beta-adrenergic, acetylcholine muscarinic (ACh), and benzodiazepine (BDZ) receptor binding in small regions of rat brain. Rhythms in alpha 1-receptor binding were measured in olfactory bulb, frontal, cingulate, piriform, parietal, temporal and occipital cortex, hypothalamus, hippocampus, pons-medulla, caudate-putamen and thalamus-septum. No rhythm was found in cerebellum. Rhythms in alpha 2-receptor binding were measured in frontal, parietal and temporal cortex, and pons-medulla. No rhythm was found in cingulate, piriform or occipital cortex, or hypothalamus. Rhythms in binding to beta-receptors were measured in olfactory bulb, piriform, insular, parietal and temporal cortex, hypothalamus and cerebellum. No rhythms were found in frontal, entorhinal, cingulate, or occipital cortex, hippocampus, caudate-putamen, or pons-medulla. Rhythms in ACh receptor binding were measured in olfactory bulb, parietal cortex and caudate-putamen. No rhythms were found in frontal or occipital cortex, nucleus accumbens, hippocampus, thalamus-septum, pons-medulla or cerebellum. Rhythms in BDZ receptor binding were measured in olfactory bulb, olfactory and occipital cortex, olfactory tubercle, nucleus accumbens, amygdala, caudate-putamen, hippocampus and cerebellum. No rhythms were found in parietal cortex, pons-medulla or thalamus-septum. The 24-hr mean binding to receptors varied between 3- and 10-fold, the highest in cortex and the lowest, usually, in cerebellum. The piriform cortex was particularly high in alpha 1- and alpha 2-adrenergic receptors; the nucleus accumbens and caudate, in ACh receptors; and the amygdala, in BDZ receptors. Most adrenergic and ACh receptor rhythms peaked in subjective night (the period when lights were off under L:D conditions), whereas most BDZ receptor rhythms peaked in subjective day (the time lights were on in L:D). Perhaps in the rat, a nocturnal animal, the adrenergic and ACh receptors mediate activity and the functions that accompany it, and the BDZ receptors mediate rest, and with it, sleep.     

Stress-Induced Sensitization of Dopamine and Norepinephrine Efflux in Medial Prefrontal Cortex of the Rat

Abstract: We examined whether prior exposure to chronic cold (17–28 days, 5°C) alters basal or stress-evoked (30-min tail shock) catecholamine release in medial prefrontal cortex, nucleus accumbens, and striatum, using in vivo microdialysis. Basal norepinephrine (NE) concentrations in medial prefrontal cortex did not differ between chronically cold-exposed rats and naive control rats (2.7 ± 0.3 vs. 2.5 ± 0.2 pg/20 µl, respectively). Basal dopamine (DA) efflux in any of the brain regions was not significantly different between chronically cold-exposed rats and naive rats. However, a trend for lower basal DA efflux in the cold-exposed relative to naive rats was observed in medial prefrontal cortex (1.5 ± 0.2 vs. 2.2 ± 0.3 pg/20 µl, respectively), nucleus accumbens (3.7 ± 0.8 vs. 5.4 ± 0.9 pg/20 µl, respectively), and striatum (4.4 ± 0.5 vs. 7.2 ± 1.5 pg/20 µl, respectively). In medial prefrontal cortex of rats previously exposed to cold, tail shock elicited a greater increase from baseline in both DA and NE efflux relative to that measured in naive rats (DA, 2.3 ± 0.3 vs. 1.2 ± 0.1 pg, respectively; NE, 3.8 ± 0.4 vs. 1.4 ± 0.2 pg, respectively). However, in nucleus accumbens or striatum of rats previously exposed to cold, the stress-induced increase in DA efflux was not significantly different from that of naive rats (nucleus accumbens, 1.8 ± 0.7 vs. 1.5 ± 0.3 pg, respectively; striatum, 1.9 ± 0.4 vs. 2.6 ± 0.7 pg, respectively). Thus, both cortical NE projections and cortically projecting DA neurons sensitize after chronic exposure to cold. In contrast, subcortical DA projections do not sensitize under these conditions.     

Hydrolysis of the C-terminal octapeptide of cholecystokinin by rat kidney membranes: characterization of the cleavage by solubilized endopeptidase-24.11

Rat kidney membranes were solubilized by Triton X-100 and the CCK-8 degrading peptidases were resolved by chromatography on DEAE-cellulose. Four proteases were detected: two phosphoramidon-sensitive endopeptidases (EC 3.4.24.11), a bestatin-sensitive aminopeptidase and an unidentified enzyme. The pattern of cleavage of CCK-8 and shorter C-terminal fragments by endopeptidase 24.11 was investigated and indicated that the Gly29-Trp30, Trp30-Met31 and Asp32-Phe33 were scissile bonds. However, the cleavage pattern differed markedly from one CCK peptide to another: in the penta- and hexapeptide of CCK the bonds hydrolyzed were either Asp-Phe and Trp-Met or, Asp-Phe and Gly-Trp, respectively. The presence of the sulfate group on the tyrosine residue of CCK-8 influence markedly the nature of the major cleavage fragments produced by the endopeptidase. The major bonds cleaved were Asp-Phe, Trp-Met and Gly-Trp for unsulfated CCK-8, whilst for the sulfated octapeptide, the Trp-Met bond became a minor cleavage site.     

CCK nerve terminals in the rat striatal and limbic areas originate partly in the brain stem and partly in telencephalic structures

After direct injection of colchicine into the rat rostral caudateputamen, levels of cholecystokinin-like immunoreactive (CCK-IR) material in this part of the nucleus are significantly lowered, and CCK-IR neuronal cell bodies are not demonstrable in the caudateputamen, although numerous ones are revealed in some adjacent telencephalic regions. Direct injection of kainic acid into the rostral caudate-putamen is not followed by a decrease of CCK-IR material in the lesioned region. Twenty one days after injection of 6-hydroxydopamine into the rat ventral mesencephalon, a significant decrease of CCK-IR material is observed in the frontal pole, the pyriform cortex, the nucleus accumbens and the ventral mesencephalon itself, but not in the caudate-putamen. After brain stem hemitransection, no decrease in CCK-IR material is observed in the rostral caudate-putamen.     

Autoradiography of CCK receptors in the rat brain using [H]Boc[Nle]CCK27–33 and [I]bolton-hunter CCK8. Functional significance of subregional distributions

[³H]Boc[Nle^28,31]CCK₂₇–₃₃ ([³H]BDNL-CCK₇) is a new ligand for cholecystokinin (CCK) receptors, endowed with a high specific activity (100 Ci/mmol). Binding sites for this ligand were visualized in the rat brain by autoradiography [³H]BDNL-CCK₇ binds specifically to an apparent single class of CCK receptors on rat striatum sections with a K_d of 1.76 nM and a B_max of 57 fmol/mg protein. Unsulfated CCK₈ was two times less potent than sulfated CCK₈ to displace binding of [³H]BDNL-CCK₇. Binding sites for [³H]BDNL-CCK₇ were present in many brain regions, the highest concentrations occurring in cortex, olfactory bulbs, nucleus accumbens, and medium to high concentrations in striatum, hippocampus, and several nuclei of thalamus, hypothalamus and amygdala. In the same experimental conditions, the binding sites for [¹²⁵I]BH-CCK₈ showed similar specificity and localization. We thus used both ligands to investigate the subregional distributions of CCK receptors in nucleus accumbens and hippocampus, where a highly organized topography of action of CCK has been reported. In nucleus accumbens, the CCK binding sites were concentrated in the anterior portion of the nucleus, whereas very low densities were observed within medial posterior nucleus accumbens, where injection of CCK has been shown to potentiate dopamine-induced hyperlocomotion. p]In hippocampus, CCK receptors were concentrated in the polymorphic zone of the hilus of the dentate gyrus and in stratum lacunosum moleculare of Ammon's horn. Very few receptors were observed in other regions of hippocampus, including stratum pyramidale and stratum moleculare. This is in contrast with the presence of numerous CCK terminals and the potent effect of CCK in these areas. The distributions of CCK receptors reported here in both nucleus accumbens and hippocampus were discussed in correlation with the distribution of CCK neurons and terminals, the related anatomical pathways, and the pharmacological profiles of the effects of CCK in these regions.     

3-Methoxytyramine Is the Major Metabolite of Released Dopamine in the Rat Frontal Cortex: Reassessment of the Effects of Antipsychotics on the Dynamics of Dopamine Release and Metabolism in the Frontal Cortex, Nucleus Accumbens, and Striatum by a Simple Two Pool Model

Abstract: 3-Methoxytyramine (3-MT) and 3,4-dihydroxyphenylacetic acid (DOPAC) rates of formation were used, respectively, to assess the dynamics of dopamine (DA) release and turnover in the rat frontal cortex, nucleus accumbens, and striatum. Assuming total (re)uptake and metabolism of released DA are relatively uniform among the three brain regions, a simplified two pool model was used to assess the metabolic fate of released DA. Under basal conditions, 3-MT formation was found to comprise >60% of total DA turnover (sum of 3-MT plus DOPAC rates of formation) in the frontal cortex, and not more than 15% in the nucleus accumbens and striatum. Haloperidol increased the 3-MT rate of formation to a greater extent in the frontal cortex than in the two other regions. Clozapine increased the 3-MT rate of formation in the frontal cortex and decreased it in the striatum. Both drugs increased DOPAC rate of formation in the frontal cortex and nucleus accumbens. It was elevated by haloperidol but not clozapine in the striatum. It is concluded that (1) O -methylation is a prominent step in the catabolism of DA in the frontal cortex under both physiological conditions and after acute treatment with antipsychotics, (2) 3-MT is the major metabolite of released DA in the frontal cortex and possibly also in the nucleus accumbens and striatum, (3) in contrast to the frontal cortex, most of the DOPAC in the nucleus accumbens and striatum appear to originate from intraneuronal deamination of DA that has not been released, (4) because presynaptic uptake and metabolism of DA give rise to DOPAC, whereas postsynaptic uptake and metabolism produced both DOPAC and 3-MT, the ratio of 3-MT to DOPAC rates of formation can be a useful index of reuptake inhibition.     

Effect of neonatal handling on brain enkephalin-degrading peptidase activities.

Neonatal handling decreases neutral endopeptidase 24.11 activity in the amygdala. However, this procedure does not affect aminopeptidase activities in any of the brain areas studied. Neonatal handling has been one of the most commonly used strategies to study the plasticity of the nervous system. The crucial role of the opioids in the control of different aspects of behaviour and development has been well documented. Regarding this subject, the endogenous opioid system might mediate some of the effects induced by neonatal handling. In this work, we have studied the effects of neonatal handling on several enkephalin-degrading peptidases, including soluble and membrane-bound aminopeptidases (puromycin-sensitive and -insensitive) and neutral endopeptidase 24.11 in different rat brain areas. Tyrosine aminopeptidase activities were measured fluorimetrically using tyrosine-beta-naphthylamide as substrate and puromycin as selective inhibitor of one of the membrane-enzymes. Dansyl-D-Ala-Gly-Phe(pNO2)-Gly was the fluorogenic substrate for neutral endopeptidase. The reduced neutral endopeptidase 24.11 activity in the amygdala of neonatal handled rats could reduce enkephalin catabolism in this area and it could be responsible for some of the effects induced by neonatal handling.     

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.     

Degradation of human atrial natriuretic peptide by human brain membranes

Human atrial natriuretic peptide (Ser 99-Tyr 126) was rapidly degraded by both choroid plexus and hypothalamic membranes with a complex pattern of cleavage. The use of protease inhibitors allowed a preliminary characterization of the enzymes involved in the hydrolysis of the Ser-Phe and Phe-Arg bonds of iodine-labelled atrial natriuretic peptide.The C-terminal tripeptide was generated by three different enzymatic activities acting on the Ser-Phe bond: endopeptidase 24.11, a phosphoramidon-insensitive metallopeptidase and a thiol protease. Peptides like substance P, neurotensin, bradykinin inhibited the cleavage of the Ser-Phe bond of atrial natriuretic peptide. The C-terminal tripeptide was further degraded by aminopeptidases. Cleavage of the C-terminal dipeptide was inhibited by aprotinin, suggesting the contribution of brain kallikrein in the formation of this metabolite.These results show that many different proteases were involved in the hydrolysis of the C-terminal sequence of atrial natriuretic peptide, at least in vitro and underline the complexity of neuropeptide catabolism by brain preparations.     

Effect of stress and ACTH on dopamine metabolism in the nucleus accumbens and frontal cortex

The effect of ACTH and electric foot shock stress on DOPAC content were determined in the frontal cortex and nucleus accumbens. Twenty min of stress enhanced DOPAC levels in the frontal cortex and in the nucleus accumbens by about 80% and 35%, respectively. On the other hand, a single dose of ACTH failed to change DOPAC concentration in the above brain areas. The present results show that the activation of mesolimbic and mesocortical dopaminergic systems is not mediated by ACTH secretion.     

Neurotensin and Neuromedin N Are Differently Metabolized in Ventral Tegmental Area and Nucleus Accumbens

Whole homogenates and membrane-bound and cytosoluble fractions prepared from rat ventral tegmental area (VTA) and nucleus accumbens were examined for their content of peptidasic activities and for their ability to metabolize neurotensin and its natural related hexapeptide neuromedin N. No qualitative differences were observed between these two brain regions concerning the presence and the subcellular distribution of a series of activities able to hydrolyze various specific fluorimetric enzymatic substrates. However, aminopeptidase B, endopeptidase 24-15, and endopeptidase 24-11 were significantly lower in the VTA than in the nucleus accumbens membrane preparations, while proline endopeptidase was detected in significantly higher amount only in the cytosolic fraction prepared from nucleus accumbens. Both neurotensin and neuromedin N were metabolized more rapidly in the nucleus accumbens than in the VTA. Furthermore, the degradation rate of neuromedin N was considerably faster than that of neurotensin whatever the cerebral area examined. Studies carried out with highly specific peptidase inhibitors revealed that endopeptidase 24-15 mainly contributed to the catabolism of neurotensin in homogenates and membrane-bound preparations of nucleus accumbens and VTA, while aminopeptidase B appeared predominantly responsible for the rapid disappearance of neuromedin N in both cerebral tissues. The possibility that the different metabolic processes of the two peptide congeners could explain their distinct pharmacological profiles observed after their microinjection in the nucleus accumbens and in the VTA is discussed.     

Region - specific alterations in tyrosine hydroxylase activity in rats exposed to lead

Previous studies from our laboratory showed that subchronic exposure to low levels of Pb resulted in significant decrease in dopamine (DA) content, attenuation of stimulus-induced release of DA in the dopaminergic projection area of nucleus accumbens (NA), and alterations in tyrosine hydroxylase (TH) activity in rat whole brain homogenates. The present study reported here was conducted to assess the functional integrity of DA synthesis in different brain regions of rats subchronically (90-days) exposed to 50 ppm Pb by measuring the activity of the rate limiting enzyme, tyrosine hydroxylase, in seven brain regions. In Pb-exposed rats, TH activity was reduced in two of the seven brain regions investigated, i.e., nucleus accumbens (42% reduction) and frontal cortex (61% reduction) when compared to controls. In contrast, Pb exposure did not affect the TH activity in cerebellum, brainstem, hippocampus, hypothalamus and striatum. The changes in TH activity in nucleus accumbens (NA) and frontal cortex (FC) in Pb-exposed rats were further confirmed by Western blot analysis using TH polyclonal antibody. Collectively, these results indicate that low level subchronic Pb exposure may affect TH protein in these brain regions.     

Differential effects of chronic treatment with haloperidol and clozapine on the level of preprosomatostatin mRNA in the striatum,nucleus accumbens,and frontal cortex of the rat

1. The goal of this work was to determine the effects of typical and atypical neuroleptics on the level of preprosomatostatin messenger RNA (mRNA) in regions of the rat brain innervated by dopaminergic neurons. 2. Quantitative in situ hybridization histochemistry was used to measure the levels of mRNA encoding preprosomatostatin in neurons of the striatum, the nucleus accumbens, and the medial and lateral agranular areas of the frontal cortex in adult rats treated with either haloperidol or clozapine. 3. In untreated animals, the density of neurons containing preprosomatostatin mRNA was higher in the nucleus accumbens than in the striatum and frontal cortex. The intensity of labeling per neuron, however, was higher in the striatum than in the two other areas examined, suggesting that the expression of preprosomatostatin mRNA is differentially regulated in these brain regions. Chronic administration of haloperidol (1 mg/kg for 28 days) induced a significant decrease in the labeling for preprosomatostatin mRNA in neurons of the nucleus accumbens, frontal cortex, and medial but not lateral striatum. Treatment with clozapine (20 mg/kg for 28 days) increased the levels of preprosomatostatin mRNA in the nucleus accumbens but not in the striatum or the frontal cortex. 4. These results support a role for dopamine in the regulation of central somatostatinergic neurons. The differences in the effects of haloperidol, a neuroleptic which induces extrapyramidal side effects, and clozapine, which does not, suggest that somatostatinergic neurons may play an important role in the regulation of motor behavior.     

Lack of Change in Basal Ganglia Neuropeptide Content Following Subacute 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Treatment of the Common Marmoset

Treatment of common marmosets with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 1-4 mg/kg for up to 4 days) caused a profound parkinsonian state. Ten days from the start of MPTP treatment, all animals showed marked motor impairment, consisting of bradykinesia and akinesia, limb rigidity, postural abnormalities, loss of vocalisation and blink reflex, and, on occasions, postural tremor. Measurement of caudate-putamen monoamine content at this time showed a profound loss in 3,4-dihydroxyphenylethylamine, homovanillic acid, and 3,4-dihydroxyphenylacetic acid concentrations. Measurement of neuropeptide concentrations in the caudate-putamen, internal and external segments of the globus pallidus, nucleus accumbens, substantia nigra, frontal cortex, and hippocampus showed met-enkephalin, leu-enkephalin, and cholecystokinin (CCK-8) concentrations to be unaffected by MPTP treatment. There was a small decrease in the substance P content of frontal cortex, but otherwise the content of this neuropeptide was unaltered. Parkinsonism in the marmoset, induced by MPTP treatment 10 days earlier, does not alter neuropeptide concentrations in the manner observed in Parkinson's disease.     

Neurotensin-Metabolizing Peptidases in Rat Fundus Plasma Membranes

The mechanisms by which neurotensin (NT) was inactivated by rat fundus plasma membranes were characterized. Primary inactivating cleavages occurred at the Arg8-Arg9, Pro10-Tyr11, and Ile12-Leu13 peptidyl bonds. Hydrolysis at the Arg8-Arg9 bond was fully abolished by the use of N-[1(R,S)-carboxy-2-phenylethyl]-alanyl-alanyl-phenylalanine-p- aminobenzoate, a result indicating the involvement at this site of a recently purified soluble metallopeptidase. Hydrolysis of the Pro10-Tyr11 bond was totally resistant to N-benzyloxycarbonyl-prolyl-prolinal and thiorphan, an observation suggesting that the peptidase responsible for this cleavage was different from proline endopeptidase and endopeptidase 24.11 and might correspond to a NT-degrading neutral metallopeptidase recently isolated from rat brain synaptic membranes. The enzyme acting at the Ile12-Leu13 bond has not yet been identified. Secondary cleavages occurring on NT degradation products were mainly generated by bestatin-sensitive aminopeptidases and post-proline dipeptidyl aminopeptidase. The content in NT-metabolizing peptidases present in rat fundus plasma membranes is compared with that previously established for purified rat brain synaptic membranes.     

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

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