PHARMACOKINETICS,ABSORPTION, DISTRIBUTION AND DISPOSITION OF [125I]-OLIGOTIDE FOLLOWING INTRAVENOUS OR ORAL ADMINISTRATION IN THE RAT

Oligotide (O) was labelled with ¹²⁵I. The radiolabelled compound ([¹²⁵I]-Oligotide ([¹²⁵I]-O)) retained the biological activity of parent O. Following single intravenous administration the half lives of radioactivity associated with O and/or O related components in plasma were 9–10 min and 9–10 h for α and β phases respectively. Following single oral administration the half life of radioactivity associated with O and/or O related components in plasma was 11.45 – 12.76 h for β fase. Following multiple oral administration once daily for 7 days, the half life of radioactivity associated with O and/or O related components following the 7th dose was 10–12 h for β phase. The areas under plasma total radioactivity versus time curves were dose-dependent. Following single intravenous administration the major proportion of the administered dose was excreted via urine, while following single oral administration excretion via urine and faeces accounted for similar proportions of the administered dose. Following both single and oral administration the levels of radioactive components derived from [¹²⁵I]-O in organs examined were generally highest in highly perfused organs. © 1997 Elsevier Science Ltd     

Endocytosis of nerve growth factor by ‘differentiated’ PC12 cells studied by quantitative ultrastructural autoradiography

The endocytosis of [¹²⁵I]nerve growth factor (NGF) by rat pheochromocytoma cells (PC12 line), previously exposed to the growth factor (‘differentiated’ or ‘primed’ cells), was studied by ultrastructural quantitative autoradiography. Cells previously grown in the presence of NGF were incubated at 37 °C with [¹²⁵I]NGF for periods of up to 24 h. Under these culture conditions, PC12 cells have a rich network of neurites.

At the commencement of the experiment, after incubation of cells with [¹²⁵I]NGF for 1 min at room temperature, the plasma membranes of perikarya and processes showed similar levels of labeling by [¹²⁵I]NGF of0.186 ± 0.03grains/μm and0.152 ± 0.013grains/μm respectively.

The density of grains per micron of plasma membrane of perikarya reached a plateau between 15 min to 2 h of incubation of cells at 37 °C with [¹²⁵I]NGF (0.58 ± 0.15grains/μm and0.65 ± 0.18grains/μm, respectively).

The endocytosis of [¹²⁵I]NGF in perikarya of cells incubated for 6 h at 37 °C was studied by the ‘mask’ analysis method of Salpeter et al.²². At this time, the greatest amount of endocytosis was observed, corresponding to 28.4% of total grain counts. The following optimized computed source densities, or relative specific activities± standard errors of measurement (S.E.M.), were obtained: plasma membrane,16.52 ± 0.86; multivesicular bodies,9.58 ± 2.84; endosomes,5.00 ± 0.97; smooth vesicles and tubules,1.66 ± 0.38; lysosomes,1.13 ± 0.20; mitochondria,0.46 ± 0.10; nuclear membranes or envelopes,0.32 ± 0.14; nuclei,0.06 ± 0.01; the Golgi apparatus,0.08 ± 0.06; and other cytoplasmic elements0.07 ± 0.03.

Our findings indicate that smooth vesicles and tubules, endosomes, multivesicular bodies and lysosomes are part of the pathway(s) of endocytosis of NGF, while all other cytoplasmic and nuclear elements, including the nuclear membrane, are not.

The heavy plasma membrane labeling of NGF and the relatively low degree of its endocytosis are consistent with the hypothesis that the NGF action is mediated through plasma membrane activated second messenger(s).     

The opiate receptor: a single 110 kDa recognition molecule appears to be conserved in Tetrahymena, leech, and rat

We compared the molecular nature of the rat brain opiate receptor with that of the invertebrate leech, Haemopis marmorata, and the protozoan, Tetrahymena, in order to examine the issue of apparent receptor heterogeneity with respect to biochemical structure. A binding study with rat brain membrane verified that [¹²⁵I]β-endorphin ([¹²⁵I]βE), a broad specificity ligand, is displaced by the antagonist (-)-naloxone, but not the inactive stereoisomer (+)-naloxone; agonists considered prototypes for μ, δ, and κ opiate receptors all displayed stereospecific binding displacement. For SDS-PAGE analysis of the opiate receptor [¹²⁵I]β-endorphin was covalently affixed to its recognition molecule with the cross-linking reagent DSS. Primary reaction products occur at 110, 58/55, and 29 kDa. Cross-linking products of all 3 molecular weights are effectively reversed by opiate ligands, regardless of their μ, δ, or κ specificities. Peptide mapping studies in SDS gels, using limited proteolysis, showed that the 110 kDa band can be digested into 58 and 29 kDa fragments and the 58 kDa band into a 29 kDa fragment. Additional smaller molecular weight fragments were generated from the 110, 58/55, and 29 kDa bands which shared their molecular weights. Two possible explanations for the extensive homology between the three major cross-linking products are: (1) the 110 kDa species is the opiate receptor, and the 58 and 29 kDa species are proteolytic fragments; and (2) one of the lower molecular weight species is the opiate receptor, and adjacent receptors are aggregated into the 110 kDa complex through cross-linking. An evolutionary conservation of the opiate receptor is suggested by the presence of the same 3 major cross-linking products in Tetrahymena, leech, and rat.     

Vasopressin binds to microvessels from rat hippocampus

Recent evidence suggests that vasopressin may influence the permeability of the endothelium of brain capillaries. We measured the binding of [¹²⁵I]arginine-8-vasopressin ([¹²⁵I]AVP) to microvessels isolated from different regions of the rat brain. The study revealed saturable and specific binding of [¹²⁵I]AVP to microvessels isolated from hippocampus. Scatchard analysis confirmed a single class of high affinity sites with an equilibrium dissociation constant,K_d, of 3.2 nM and an apparent maximal binding capacity of 205 fmol/mg protein. No binding was observed to microvessels from neocortex and striatum.     

Homologous desensitization of human corticotropin-releasing factor, receptor in stable transfected mouse fibroblast cells

Previous radioligand binding and second messenger studies have shown that corticotropin-releasing factor (CRF) modulates its receptor following both in vivo and in vitro treatment. In the present study, we determined the sequence of events leading to CRF-induced downregulation and desensitization of cloned CRF receptors in murine fibroblast cells (Ltk⁻) stably transfected with CRF, DNA (from human pituitary). Treatment of cells with rat/human CRF produced a dose- and time-dependent decrease in [¹²⁵I]Tyr^o-ovine CRF ([¹²⁵I]oCRF) binding and a concomitant decrease in CRF-stimulated adenylate cyclase activity. Significant decreases in [¹²⁵I]oCRF binding and agonist-stimulated cAMP production were evident minutes after CRF treatment with maximal (60–80%) reductions seen following 1 h of CRF treatment. Scatchard analysis revealed that the decrease in [¹²⁵I]oCRF binding was due to the downregulation of the receptor with no significant alteration seen in the affinity of the ligand. Since the transfected cell line is engineered using an artificial promoter, we did not detect any significant changes in CRF₁ receptor mRNA levels following CRF treatment for up to 24 h.     

Kinetics and distribution of [Fe–I]transferrin injected into the ventricular system of the rat

We examined the kinetics and distribution of [⁵⁹Fe–¹²⁵I] rat Tf and unlabelled human Tf injected into a lateral cerebral ventricle (i.c.v. injection) in the rat. [⁵⁶Fe–¹³¹I]Tf injected intravenously served as a control of blood–brain barrier (BBB) integrity. In CSF of adult rats, ⁵⁹Fe and [¹²⁵I]Tf decreased to only 2.5% of the dose injected after 4 h. In brain parenchyma, [¹²⁵I]Tf had disappeared after 24 h, whereas approximately 18% of i.c.v.-injected ⁵⁹Fe was retained even after 72 h. The elimination pattern of [¹²⁵I]Tf from the CSF corresponded to that of [¹³¹I]albumin injected i.c.v., suggesting a nonselective washout of CSF proteins. [¹³¹I]Tf was hardly detectable in the brain, reflecting an unimpaired BBB during the experiments. Morphologically, ⁵⁹Fe and i.c.v. injected human Tf were confined to the ventricular surface and meningeal areas, whereas grey matter regions at distances more than 2–3 mm from the ventricles and the subarachnoid space were unlabelled. However, accumulation of ⁵⁹Fe was observed in the anterior thalamic and the medial habenular nuclei, and in brain regions with synaptic communications to these areas. In the newborn rats aged 7 days (P7) injected i.c.v. with [⁵⁹Fe–¹²⁵I]Tf and examined after 24 h, the amounts of [¹²⁵I]Tf in CSF were approximately 3.5 times higher than in adult rats collected after the same time interval, whereas the amounts of ⁵⁹Fe in CSF were at the same level in P7 and adult rats. In the brain tissue of the i.c.v. injected P7 rats, both [¹²⁵I]Tf and ⁵⁹Fe were retained to a significantly higher degree compared to that seen in adult brains. The rapid washout and lack of capability for i.c.v. injected [¹²⁵I]Tf to penetrate deeply into the brain parenchyma of the adult brain question the importance of Tf of the CSF, and choroid plexus-derived Tf, for Fe neutralization and delivery of Fe–Tf to TfR-containing neurons and other cells in the CNS. However, it may serve these functions in young animals due to a lower rate of turnover of CSF.     

A radioisotopic method for the simultaneous quantitation of regional cerebral blood flow and glucose utilization in small dissected samples: Validation studies and values in the nitrous oxide-anesthetized rat

A method is described for the simultaneous determination of the rates of regional cerebral blood flow (rCBF) and regional cerebral glucose utilization (rCMRgl) in 6–7 mg brain samples dissected from multiple areas of interest. The method utilizes [¹³¹I]-iodoantipyrine ([¹³¹l]IAP) to measure rCBF by indicator fractionation, and [¹⁴C]2-deoxyglucose to measure rCMRgl. [¹³¹I]IAP was synthesized with specific activity exceeding 350 Ci/mmol and radiochemical purity greater than 99.5% by the radioiodination of antipyrine with Na¹³¹I. A triple-counting strategy was developed to quantitate¹⁴C activity of the dissected brain samples in the presence of¹³¹I. The factors contributing to the propagated error of the double-label separation strategy were defined and optimal assay parameters were determined. The separation strategy was validated by measuring rCBF simultaneously with both [¹³¹I]IAP (x) and [¹⁴C]IAP (y) in a series of rats. The equation of the regression line was y = 1.025 x −0.065 (correlation coefficient 0.985), denoting excellent agreement. In another series of 5 normocapnic rats anesthetized with nitrous oxide, rCBF and rCMRgl were measured simultaneously. In individual animals, the rates of rCBF within 14–16 brain areas were closely coupled to their respective rates of glucose metabolism. For the group data, the linear regression equation relating rCBF (y) to rCMRgl (x) was y = 1.76 x + 0.13 (correlation coefficient 0.93,P < 0.001). These studies provide direct evidence, based upon data obtained in the same brain, of a close coupling of regional metabolic rate and blood flow.     

Loss of muscarinic M4 receptors in hippocampus of Alzheimer patients

We assessed muscarinic M₁, M₂ and M₄ receptor subtypes in the hippocampus of Alzheimer’s and control brains by receptor autoradiography using ligands such as [¹²⁵I]muscarinic toxin-1 ([¹²⁵I]MT-1, M₁ selective), [³H]AFDX-384 (M₂ partially selective) and [¹²⁵I]muscarinic toxin 4 ([¹²⁵I]M₄ toxin-1, M₄ selective). Our results revealed a significant decrease in muscarinic M₄ receptor binding in the dentate gyrus and CA4 regions of brain sections from Alzheimer’s patients compared to controls. No changes in the density of M₁ or M₂ receptor binding were observed. Our findings suggest that, relative to other muscarinic receptor subtypes, the M₄ receptor could be the subtype which is selectively compromised in Alzeheimer’s disease (AD).     

Reduction of insulin binding in the arcuate nucleus of the rat hypothalamus after 6-hydroxydopamine treatment

Insulin receptors are present in the hypothalamus, but the cell types bearing them are unknown. In order to test the hypothesis that some insulin receptors in the hypothalamus are associated with catecholamine terminals, rats were injected with 50 μg or 75 μg doses (intracerebroventricular) of 6-hydroxydopamine (6-OHDA). Control rats received vehicle only. The animals were sacrificed 7 days after injection, and catecholamine and indolamine levels in the hypothalamus were measured by high performance liquid chromatography with electrochemical detection. Localization of specific binding sites for [¹²⁵I]-insulin in the arcuate (ARC), dorsomedial (DMN) and ventromedial (VMN) nuclei were determined by quantitative film autoradiography. Treatment with 6-OHDA resulted in a 70% reduction in hypothalamic norepinephrine content as compared to vehicle-treated controls (P < 0.01). A slight depletion of epinephrine, dopamine and indolamines was also detected. Computerized image analysis of the autoradiograms was used to determine radioactivity bound (DPM/mm²) in each nucleus. Highest binding was in the ARC and DMN, with much lower binding in the VMN. Insulin binding in the ARC of the 6-OHDA-treated group was decreased by 25% compared to controls (P < 0.01). No significant change in insulin binding was observed in the DMN or VMN. The 6-OHDA treatment had no significant effect on weight gain or on plasma insulin levels. The reduction of insulin binding in the ARC after 6-OHDA treatment supports the hypothesis that some insulin binding sites are located on catecholamine terminals in the arcuate nucleus.     

Photoperiodic effects on puberty and specific 2-[I]iodomelatonin binding sites in Siberian hamsters

When juvenile male Siberian hamsters are transferred from a long photoperiod to a short photoperiod, sexual maturation is greatly delayed by a pineal-dependent process. We hypothesized that the eventual onset of puberty during short photoperiod exposure may be caused by a loss of receptors for the pineal hormone, melatonin. This study quantitated specific 2-[¹²⁵I]iodomelatonin binding sites in the suprachiasmatic nuclei and pars tuberalis of Siberian hamsters exposed to short photoperiod (10 h light per day) for either 12 or 30 weeks and in hamsters exposed to long photoperiod (16 h light per day) for the same time intervals. Photoperiodic exposure significantly affected testes weight. The hamsters exposed to long photoperiod for either 12 or 30 weeks had mean testes weights > 700 mg, in contrast to hamsters in short photoperiod for 12 weeks (mean testes weights < 30 mg) or 30 weeks (mean testes weights approximately 350 mg). The affinity of specific 2-[¹²⁵I]iodomelatonin binding sites in both regions was significantly lower in hamsters exposed to short photoperiod as compared to hamster exposed to long photoperiod, at either 12 or 30 weeks. In contrast, there were no effects of photoperiod or duration of exposure on the density of specific 2-[¹²⁵I]iodomelatonin binding sites in either the suprachiasmatic nuclei or the pars tuberalis. Furthermore, a change in the affinity of the specific 2-[¹²⁵I]iodomelatonin binding sites in the suprachiasmatic nuclei was observed between the hamsters housed in short photoperiod for 12 weeks (sexually immature) and the hamsters housed in short photoperiod for 30 weeks (undergoing puberty). These results demonstrate that although the onset of puberty after long-term exposure to short photopoeriod does not involve a loss of specific 2-[¹²⁵I]iodomelatonin binding sites in the suprachiasmatic nuclei or pars tuberalis, it is associated with a decrease in the affinity of specific 2-[¹²⁵I]iodomelatonin binding sites in these regions.     

Pharmacological characterization of grooming induced by a selective NK-1 tachykinin receptor agonist

Bilateral intranigral administration of the selective NK-1 tachykinin receptor agonist [AcArg⁶, Sar⁹, Met(O₂)¹¹]SP_6–11 (0–11 nmol total bilateral dose) selectively induced grooming in rats. This response was blocked by concurrent intranigral administration of the NK-1 tachykinin receptor antagonist RP 67580 (2 nmol), but not by NK-2 (L-659, 877) or NK-3 ([Trp⁷, β-Ala⁸]NKA_4–10) antagonists. Pretreatment with systemic opioid (naloxone 1.5 mg/kg) and D₁ dopamine (SCH 23390 100 μg/kg) receptor antagonists also attenuated tachykinin-induced grooming, which was unaffected by D₂ dopamine (sulpiride 30 mg/kg) or 5-HT_2A+C (ritanserin 2 mg/kg) antagonists. Grooming induced by intranigral [AcArg⁶, Sar⁹, Met(O₂)¹¹]SP_6–11 was also attenuated by bilateral 6-hydroxydopamine lesions of te substantia nigra. These findings indicate that grooming induced by intranigral tachykinins reflects activation of NK-1 receptors and is dependent upon endogenous dopamine and consequent selective stimulation of D₁ dopamine receptors.     

Cross-reactivities of neuropeptide Y and peptide YY with pancreatic polypeptide antisera: evidence for the existence of pancreatic polypeptide in the brain

Highly purified neuropeptide Y (NPY) and peptide YY (PYY) did not cross-react in our human pancreatic polypeptide (hPP) radioimmunoassay, nor did ¹²⁵I-labelled NPY and PYY, even with anti-hPP serum at low dilution (1:1000). However, both [¹²⁵I]NPY and [¹²⁵I]PYY significantly cross-reacted with anti-bovine PP (bPP) serum at low dilution (1:1000, similar to that used in immunohistochemistry). These results suggest that radioassayable hPP-like peptide in the porcine or canine brain is probably pancreatic polypeptide itself, otherwise immunohistochemically detected bPP-like peptide may represent both NPY and PP.     

Glucocorticoid regulation of hippocampal oxytocin receptor binding

The effects of glucocorticoid hormones on oxytocin receptors in rat hippocampus were investigated. Oxytocin receptor autoradiography (using 0.1 and 1.2 nM concentrations of [¹²⁵I]OVTA) revealed a significant (P < 0.02) decrease in oxytocin receptor binding in adrenalectomized animals 7 days after the surgery. Corticosterone replacement at the time of adrenalectomy prevented the decrease in oxytocin binding. The findings were significant in hippocampus and subiculum. These findings suggest regulation of oxytocin receptors, and possibly oxytocin-regulated behaviors by glucocorticoids.     

Stimulated release of [H]β-alanine from the rabbit retina

The efflux of [³H]β-alanine from rabbit retina after intravitreal injection has been studied.

The site of uptake of [³H]β-alanine into retina was checked by autoradiography and was found mainly in the inner plexiform layer and in cells with the position of amacrines and in some ganglion cells.

When the preloaded retina was stimulated by light flashes the release of radioactivity increased significantly. Chromatography of the superfusate demonstrated a single radioactive spot which cochromatographed with authentic β-alanine.

The efflux of [³H]β-alanine was affected by raising the K⁺ concentration. The rate of efflux was also immediately increased when unlabelled β-alanine or GABA was added to the superfusion medium. Glycine was much less effective.

The present study shows that light stimulation releases [³H]β-alanine from the retina and that β-alanine may use the same transport system as GABA. This further supports the suggestion that β-alanine may act as a ‘false transmitter’ replacing GABA in the retina.     

Interactions of poly (L-lysine) with human platelets. Correlation of binding with induction of platelet aggregation

Poly(L-lysine) (PLL) was iodinated with ¹²⁵I by use of the Bolton and Hunter reagent. Use of ¹²⁵I-PLL permitted demonstration of the binding of this cationic polymer to platelets. ¹²⁵I-PLL binds to freshly isolated viable platelets, paraformaldehyde-fixed platelets, isolated platelet plasma membrane preparations, and fixed plasma membrane preparations. Determination of affinities of binding suggests the possibility of at least two classes of binding sites for PLL. The binding is inhibited competitively by unlabeled PLL but displacement of bound PLL is complicated by the aggregation of platelets that occurs in the presence of large amounts of added unlabeled PLL. Succinylation of ε-amino groups of PLL results in complete loss of binding of the polymer to platelets. Binding of ¹²⁵I-PLL is not affected by the presence of EDTA, adenosine, prostaglandin E₁, cyclic 2′3′ AMP, or acetyl-salicyclic acid, and none of these agents have an effect on PLL-induced platelet aggregation. When studies were conducted with PLLs of different average molecular weights (MW), it was observed that 68,000 MW PLL has a significantly greater binding affinity than either 30,000 MW or 6,200 MW PLLs. When the platelet aggregation-inducing abilities of different MW PLLs were compared with their binding affinities, it was observed that the molecular size of PLL that caused maximal aggregation at minimal molar concentration also exhibited the greatest deqree of binding.     

Postnatal development of functional dopamine, opioid and tachykinin receptors that regulate acetylcholine release from rat neostriatal slices. Effect of 6-hydroxydopamine lesion

In the present work we have studied the postnatal development of functional dopamine, opioid and tachykinin receptors, which regulate cholinergic activity in the neostriatum. The release of endogenous acetylcholine from rat striatal slices was measured using a chemiluminescent method. We have observed that the inhibition mediated by dopamine through D₂ receptors was not detectable until postnatal day 10, whereas the inhibition mediated by opioid receptors was detectable at postnatal day 15 for δ-receptors ([D-Pen², D-Pen⁵]-enkephalin) and at postnatal day 21 for μ-receptors ([D-Ala², Gly(ol)⁵]-enkephalin). Excitatory effect mediated by tachykinins through NK₁ ([Sar⁹, Met(O2)¹¹]-Substance P), NK₂ ([Nle¹⁰]-Neurokinin A_4–10), or NK₃ (senktide) receptors was already detectable at postnatal day 5.

In order to examine the influence of dopamine in the development of tachykinin and opioid systems in the neostriatum, we induced dopamine deficiency by intraventricular injection of 6-hydroxydopamine at postnatal day 3. We observed an increase in senktide-evoked acetylcholine release at postnatal day 30. The effect produced by [Sar⁹, Met(O₂¹¹]-Substance P and [Nle¹⁰]-Neurokinin A_4–10 was not modified. Furthermore, at postnatal day 35, we could observed that the two opioid receptor agonists have no effect.

Our results show that dopamine, tachykinins and opioids are already able to mediate the modulation of acetylcholine release in early stages of development with a different pattern of postnatal development. Furthermore, the integrity of a dopaminergic system plays an important role in the functional development of the neostriatal cholinergic neurons which are differentially modulated by opioids or tachykinins.     

Photoaffinity labeling of the β-adrenergic receptor in synaptic membranes of rat cerebral cortex and cerebellum

The β-adrenergic receptor polypeptides in synaptic membranes of rat cerebral cortex and cerebellum have been identified using the photoaffinity label[¹²⁵I]iodoazidobenzylpindolol. The major receptor polypeptides possess apparent molecular weights of 62, 000 and 49,000 (cerebral cortex) or 59,000 and 46,000 (cerebellum). Treatment of the membranes with endoglycosidase F caused the receptor polypeptides from both tissues to exhibit lower apparent molecular weight (51,000) on sodium dodecyl sulfate polyacrylamide gels, indicating that β-adrenergic receptors in mammalian brain are glycoproteins as are the receptors in peripheral tissues.     

Reactivity of heparin with the human plasma heparin-binding proteins thrombin, antithrombin III, and apolipoproteins E and B-100

The heparin-binding properties of human plasma apolipoproteins B-100 and E (apoB-100 and E) of low density lipoproteins (LDL), thrombin, and antithrombin-III (AT-III) were investigated. A highly reactive heparin (HRH) to apoB-100 was isolated by chromatography of crude heparin on a column of LDL immobilized to Affi-Gel 10. This HRH showed a high, Ca²⁺-dependent precipitating activity towards LDL; 1 μg HRH uronic acid precipitated 50–70 μg LDL-protein. HRH was fractionated further by chromatography on a column of AT-III bound to concanavalin A-Sepharose. The unretained fraction of heparin (HRH₁)had a low affinity for AT-III. The bound heparin (HRH₂) had a high affinity for AT-III and precipitated LDL in the presence of Ca²⁺. To assess further their heparin-binding properties, the proteins were subjected to gradient-gel electrophoresis under denaturing conditions, transferred to nitrocellulose by electrophoresis, and then assayed for their ability to bind [¹²⁵I]-labeled HRH₂. Autoradiographic analysis showed that thrombin, apolipoproteins E and B-100, and the AT-III-thrombin covalent complex bound HRH₂. Denatured AT-III did not bind HRH₂, indicating that its heparin recognition site may depend on conformation.     

The neuroleptic-like peptide desenkephalin-γ-endorphin does not antagonize the dopamine receptor agonist-induced inhibition of the release of [H]dopamine from rat nucleus accumbens slices in vitro

In rats, the non-opioid β-endorphin (βE) fragment desenkephalin-γ-endorphin (DEγE, βE_6–17) antagonizes the hypomotility induced by a small dose of dopamine (DA) receptor agonists. It has been suggested that DEγE might act in this respect by a direct or indirect blockade of presynaptically located DA receptors in the nucleus accumbens, thereby causing an increase of DA release. Therefore in the present study the effect of DEγE was examined on DA receptor agonist-induced inhibition of the electrically evoked release of previously accumulated [³H]DA from rat nucleus accumbens slices in vitro. The DA receptor agonists apomorphine, LY 171555 andn,n-di-n-propyl-7-hydroxy-2-aminotetralin (DP-7-AT) inhibited in a concentration-dependent manner the electrically evoked release of [³H]DA. The selective D₂ receptor antagonist (−)-sulpiride blocked the effects of apomorphine, corroborating that the DA receptor involved is of a D₂ type. DEγE was tested at several concentrations (10⁻⁹–10⁻⁶) and under various experimental conditions. DEγE, by itself, did not affect either the electrically stimulated or the basal release of [³H]DA. The inhibiting effect of DA receptor agonists was slightly reduced by DEγE, but this effect was present in some experiments only. It is concluded that DEγE does not function as an antagonist for the DA receptor mediating DA release and that the interaction observed in behavioural experiments between DA agonists and DEγE does not occur at the level of this receptor.     

Regulation of neurotensin-containing neurons in the rat striatum. Effects of unilateral striatal lesions with quinolinic acid and ibotenic acid on neurotensin content and its binding site density

Recently, we reported bilateral increases in striatal neurotensin (NT) levels following unilateral 6-hydroxydopamine lesion of the nigrostriatal dopaminergic pathway. In the present study, the effect of unilateral striatal lesions with quinolinic acid (QA, 300 nmol) or ibotenic acid (IBO, 130 nmol) on striatal NT levels and binding site densities were analyzed in order to investigate other possible regulations of NT systems. QA and IBO injection decreased γ-aminobutyric acid (GABA) levels and [¹²⁵I]iodosulpride (a specific D2 receptor antagonist) binding site densities in the lesioned striatum, indicating degeneration of striatal intrinsic neurons. Striatal dopaminergic terminals were not altered by QA as shown by the lack of changes in [³H]dihydrotetrabenazine ([³H]TBZOH, a specific ligand of the vesicular monoamine transporter) binding site densities. Moreover, QA lesion induced an increase in NT levels and a decrease in NT binding sites in the lesioned striatum without any change in the contralateral structure. In contrast to QA, IBO might destroy a certain proportion of dopaminergic terminals in the lesioned striatum, as shown by a 54% decrease in [³H]TBZOH binding. Furthermore, IBO lesion enhanced striatal NT levels bilaterally, while NT binding sites decreased in the lesioned striatum and increased in the contralateral side. The present results suggest that not only dopaminergic neurons but also striatal intrinsic neurons may control NT systems in the striatum.