Trimethyltin-induced loss of NMDA and kainate receptors in the rat brain

Summary Adult rats exposed acutely to trimethyltin (TMT) manifest a number of behavioral alterations, in conjunction with neuronal degeneration in the limbic system. In the present study, changes in³H-TCP binding to N-methyl-D-aspartate (NMDA) receptors and³H-kainic acid (KA) binding to kainate receptors were studied by autoradiographic methods following TMT exposure (8 mg/kg, i.p.) in adult Sprague Dawley rats. No significant alterations were found at 4 hours after exposure. An extensive loss of³H-TCP and³H-KA binding was seen in the hilar region of the CA3 field at 2 and 12 weeks after TMT exposure. Also, the³H-TCP binding was decreased in piriform cortex and in striatum. Thus, TMT exposure leads to a major and regional selective loss of NMDA and kainate receptors in the limbic system, alterations that may be involved in the neuropathology and behavioral sequelae of TMT toxicity.Abbreviations TMT trimethyltin - NMDA N-methyl-D-aspartate - KA Kainic acid - TCP N-(1-2-thienylcyclohexyl)-3,4-piperidine     

Dose-related effect of the oxytocin fragment (prolyl-leucyl-glycinamide) on α-MPT-induced catecholamine disappearance and serotonin level in rat brain

Graded doses of Pro-Leu-Gly-NH₂ (3.5 × 10⁻¹², 3.5 × 10⁻¹¹, 3.5 × 10⁻¹⁰ or 3.5 × 10⁻⁹ mol) were administered into the lateral cerebral ventricle of rats. The noradrenaline level of the dorsal hippocampus was increased 30 min after a dose of 3.5 × 10⁻¹⁰ mol Pro-Leu-Gly-NH₂. The dopamine level was increased in the dorsal hippocampus and in the striatum. The serotonin level was increased in the hypothalamus, in the striatum and decreased in the dorsal hippocampus.The catecholamine disappearance following 350 mg/kg of α-methyl-p-tyrosine indicated an accelerated dopamine disappearance in the striatum for each dose studied, while the hypothalamic noradrenaline disappearance was inhibited by a dose of 3.5 × 10⁻¹¹ mol of Pro-Leu-Gly-NH₂.The data indicate that Pro-Leu-Gly-NH₂ induces dose and region-dependent changes in the cerebral monoamine metabolism. The striatal dopamine and hypothalamic serotonin metabolism appeared to be the most sensitive for intraventricular Pro-Leu-Gly-NH₂.     

Subchronic Treatment with Methamphetamine and Phencyclidine Differentially Alters the Adenosine A1 and A2A Receptors in the Prefrontal Cortex,Hippocampus, and Striatum of the Rat

Subchronic treatment with MAP (4.6 mg/kg, i.p., once daily for 11 days) significantly decreased the K_d, but not B_max, values of [³H]1,3-dipropyl-8-cyclopentylxanthine ([³H]DPCPX) binding to adenosine A₁ receptors in the prefrontal cortex and hippocampus, but not striatum, of rat brain. However, subchronic treatment with PCP (10 mg/kg, i.p., once daily for 11 days) did not alter the K_d and B_max values of [³H]DPCPX binding to adenosine A₁ receptors in these three regions. Subchronic treatment with MAP or PCP did not alter the B_max and K_d values of [³H]2-p-(2-carboxyehyl)phenethylamino-5-N-ethylcarboxyamidoadenosine ([³H]CGS21680) binding to adenosine A_2A receptors in the striatum. Furthermore, subchronic treatment with MAP or PCP significantly decreased the specific binding of [³H]CGS21680 to adenosine A_2A receptors in the hippocampus, but not in the prefrontal cortex. Thus, these results suggest that MAP and PCP may produce differential effects on the adenosine A_2A receptors, but not adenosine A₁ receptors in rat brain.     

Brain neurotransmitter receptors after long-term haloperidol: dopamine, acetylcholine, serotonin, alpha-noradrenergic and naloxone receptors.

Since long-term neuroleptic therapy is known to alter brain dopaminergic sensitivity, we tested the effects of chronic haloperidol administration (10 mg/kg/day for over 3 weeks) on the amount of the dopamine receptors (using ³H-apomorphine and ³H-haloperidol) in various regions of the rat brain. To test whether the changes in dopamine receptors were selectively produced, we also assayed acetylcholine receptors (with ³H-quinuclidinyl benzilate or ³H-QNB), alpha-noradrenergic receptors (with ³H-WB-4101), ³H-serotonin receptors and ³H-naloxone receptors.The specific binding of ³H-haloperidol increased significantly by 34% in the striatum and by 45% in the mesolimbic region after long-term haloperidol. The specific binding of ³H-apomorphine also increased significantly by 77% in the striatum and 55% in the mesolimbic area. Although there was a small significant increase of 20% in specific ³H-serotonin binding in the striatum, no such increment occurred in the hippocampus or the cerebral cortex. No significantly different binding occurred for the other ³H-ligands in these brain regions except for a 13% increase in alpha-noradrenergic binding in the cerebral cortex. These results indicate that long-term haloperidol treatment produces rather selective increases in dopamine/neuroleptic receptors, without much change in 4 other types of receptors. Such relatively selective increments in these receptors may be the basis of dopaminergic supersensitivity (e.g. tardive dyskinesia) after long-term haloperidol.     

Ligand Binding to CNS Muscarinic Receptor Is Transiently Modified by Convulsant 3-Mercaptopropionic Acid Administration

The administration of convulsant drugs has proven a powerful tool to study experimental epilepsy. We have already reported that the administration of convulsant 3-mercaptopropionic acid (mp) at 150 mg/kg enhances binding affinity of muscarinic antagonist [³H]quinuclidinyl benzilate ([³H]QNB) to certain rat CNS membranes during seizure and postseizure without affecting site number. Results obtained with a 100-mg/kg dose of mp have shown reversible increases in [³H]QNB binding to cerebellum and hippocampus, whereas a delayed response has been found in striatum. Neither a subconvulsant dose nor in vitro addition modifies binding. In order to evaluate preseizure, seizure as well as early (30 min) and late (24 h) postseizure stages, we employed a 50 mg/kg dose and tested [³H]QNB binding to CNS membranes. Changes in binding were as follows (in %): in cerebellum, +37, +86, and +40 at preseizure, seizure and early postseizure stages, respectively, but there was a decrease at late postseizure; in hippocampus, +27 at pre- and seizure stages, but a decrease at early and late postseizure. No changes were found in striatum or cerebral cortex membranes at any stage studied. Saturation curves analysed by Scatchard plots indicated that changes in [³H]QNB binding to cerebellar membranes are attributable to an increase in ligand affinity at seizure, followed by a decrease in binding site number at postseizure. A similar profile was observed for hippocampus except that the decrease in binding site number, though lower than at postseizure, was already evident at seizure stage. Results confirm a region-specific response to the convulsant and transient changes provide an example of neuronal plasticity.     

Distinct alpha-noradrenergic receptors differentiated by binding and physiological relationships.

Adult mice received two 70 μg doses of 6-hydroxydopamine intracisternally 72 hours apart, and the muscarinic binding properties of discrete brain regions were then investigated at various time intervals. Three days after the second injection, ³H-norepinephrine uptake was drastically reduced in all brain regions studied, and a distinct decrease in muscarinic receptor density was observed in the striatum (?18%), medulla-pons (?17%) and cerebellum (?15%) of lesioned animals as compared with controls. No changes were detected in muscarinic receptor density in the cortex or the hippocampus of treated animals, nor were any changes seen in the affinity of the labelled ligand for its receptor or in the displacement properties of the muscarinic binding by agonists in any of the regions studied. These effects still persisted after 60 days, with a further reduction in striatal muscarinic density to 74% of control values. Data are interpreted with respect to the proposed model for cholinergic modulation of central catecholamine release and cholinergic-catecholaminergic interactions in the striatum.     

Effects of haloperidol on rat behavior and density of dopaminergic D2-like receptors

The present work shows the effects of a typical neuroleptic drug (haloperidol, HAL) on rat behavior (catalepsy and locomotor activity) and dopaminergic D2-like receptor densities in the hippocampus and striatum. Male Wistar rats (2-3 months old) were treated daily for 30 days with HAL (0.2 or 1mg/kg, intraperitoneally (i.p.)). At the end of treatment and 1h or 1, 3, 7 and 15 days after drug withdrawal, animals were subjected to behavioral tests and sacrificed afterwards for binding assays. The results showed that behavioral effects with both doses were significant only 1h and 1 day after withdrawal, and similar to controls at the third day. An up-regulation of D2 receptors was observed in the striatum (28% increase) but not in the hippocampus after 24h HAL (1mg/kg) withdrawal. However, an up-regulation was seen in both areas (1mg/kg) 3 days after drug withdrawal (58 and 42% increases in the hippocampus and striatum, respectively), and continued after 7 days of withdrawal only in the striatum (43 and 49% for the doses of 0.2 and 1mg/kg, respectively), suggesting the influence of dose, age, and time of drug withdrawal on these parameters. The up-regulation disappeared after 15 days of haloperidol withdrawal. Increases (72 and 140%) in constant dissociation values (K(d)) values were also observed 7 days after withdrawal. Results show differences on a time-basis between behavioral alterations and dopaminergic D2 receptors up-regulation.     

Alterations in central neurotransmitter receptor binding sites following estradiol implantation in female rats

The subcutaneous implantation of an estradiol pellet (10 mg) into female rats induced a hypophyseal hyperplasia with hyperprolactinaemia. Examination of neurotransmitter receptors in the hippocampus, striatum and cerebral cortex one month after the implantation revealed that estrogenization was associated with: an increased density of ³H-domperidone binding sites (D₂ receptors) in the striatum and reduced numbers of ³H-serotonin high affinity sites (5-HT₁ receptors) in the hippocampus and of ³H-muscimol binding sites (GABA receptors) in the hippocampus, striatum and cerebral cortex. In contrast, the characteristics of ³H-spiperone binding to 5-HT₂ receptors (in the cerebral cortex) and those of ³H-flunitrazepam binding to benzodiazepine sites (in the three brain regions examined) were not significantly different in estrogenized and in control female rats. However, the enhancing effect of GABA on ³H-flunitrazepam binding was markedly reduced in brain membranes from estrogenized animals. The respective roles of estradiol and prolactin in mediating these changes in neurotransmitter receptors are discussed notably with regard to the regional heterogeneity of estradiol binding capacity in the rat brain.     

Effects of Repeated Low-dose Soman Exposure on Monoamine Levels in Different Brain Structures in Mice

In order to better understand the effects of repeated low-dose exposure to organophosphorus (OPs) on physiological and behavioural functions, we analysed the levels of endogenous monoamines (serotonin and dopamine) in different brain areas after repeated exposure of mice to sublethal dose of soman. Animals were injected once a day for 3 days with 0.12 LD50 of soman (47 μg/kg, i.p.). They did not show either severe signs of cholinergic toxicity or pathological changes in brain tissue. 24 h after the last injection of soman, inhibition of cholinesterase was similar in plasma and brain (32% and 37% of inhibition respectively). Afterwards, recovery of cholinesterase activity was faster in the plasma than in the brain. Dopamine levels were not significantly modified. On the other hand, we observed a significant modification of the serotoninergic system. An increase of the 5-HIAA/5-HT ratio was maintained for 2 and 4 weeks after exposure in the hippocampus and the striatum respectively. This study provides the first evidence of a modification of the 5-HT turnover in the hippocampus and the striatum after repeated low-dose intoxication with a nerve agent. Further experiments are necessary to evaluate the relationship between these modifications and the unexpected neuropsychological disorders usually reported after chronic exposure of organophosphorus.     

CNS Adenosine A1 Receptors Are Altered After the Administration of Convulsant 3-Mercaptopropionic Acid and Cyclopentyladenosine: An Autoradiographic Study

Rat CNS adenosine A₁ receptors were studied by quantitative autoradiography after the administration of convulsant 3-mercaptopropionic acid (MP) and an adenosine analogue cyclopentyladenosine (CPA), using 2-chloro-N⁶-[cyclopentyl-2,3,4,5-³H adenosine]-([³H]CCPA) as radioactive ligand. Specific binding was quantified in hippocampus, cerebellum, cerebral cortex, thalamic nuclei, superior colliculus and striatum, and the highest densities were found in CA1, CA2, and CA3 hippocampus subareas and the lowest levels in superior colliculus and striatum. MP administration (150 mg/kg, i.p.) produced significant increases in [³H]CCPA binding in CA1 subarea at seizure (15%) and postseizure (21%) and in CA2 at seizure (15%) but a tendency to decrease in dentate gyrus. There was an increase in cerebellum at seizure (18%) but no significant changes in the other studied regions. CPA injection (2 mg/kg, i.p.) enhanced [³H]CCPA binding in CA1 and CA2 areas (17–18%) but not in CA3 area of the hippocampus. When CPA was administered before MP, which delayed seizure onset, an increase in [³H]CCPA binding in CA1 hippocampus subarea (19%) and cerebellum (28%) was also observed. Results showed that the administration of convulsant MP and adenosine analogue CPA exerts differential effects on adenosine A₁ receptors in CNS areas; hippocampus is the most affected area with all treatments, specially CA1 subarea, supporting an essential role in convulsant activity as well as in seizure prevention.     

Differential responsiveness of metabotropic glutamate receptors coupled to phosphoinositide hydrolysis to agonists in various brain areas of the adult rat

The effects of metabotropic glutamate receptor (mGluR) agonists on inositol phosphates (IP) accumulation were investigated in slices of the cerebral cortex, hippocampus, striatum and cerebellum of adult Sprague-Dawley rats. EC₅₀ values for 1S, 3R-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) did not differ significantly between various brain areas (range 10⁻⁵ M), quisqualate was the most potent in all the brain areas (range 10⁻⁷−10⁻⁶ M), except the cerebellum (10⁻⁵ M), ibotenate was the most potent in the striatum (range 10⁻⁶ M) and the least potent in the cerebral cortex and hippocampus (range 10⁻⁴ M). The efficacy in the four brain areas showed the following trend of ranking order for ACPD and quisqualate: hippocampus > striatum > cerebral cortex > cerebellum, and for ibotenate: hippocampus > cerebral cortex > striatum > cerebellum, although the observed differences reached the level of statistical significance only in the case of ACPD (hippocampus and striatum vs cerebellum) and ibotenate (hippocampus vs cerebellum). Co-incubation of the agonists at maximally effective concentrations in any pairwise combination resulted in no substantial additivity of IP accumulation. D,L-1-amino-3-phosphonopropionic acid (AP3) and D,L-2-amino-4-phosphonobutyric acid (AP4) at 0.5 mM concentration antagonized ACPD-induced IP accumulation by about 70 and 45%, respectively, without differences between brain areas. On the other hand, the antagonistic effects ofl-serine-o-phosphate (SOP) at 1 mM concentration were the highest in the hippocampus (75%) and the lowest in the cerebellum (25%). The comparative data indicate considerable regional receptor heterogeneity, in terms of different ratios of response to the agonists (but not antagonists, except SOP). There is a robust responsiveness of mGluRs not only in the hippocampus and cerebral cortex, but also in the striatum which exhibits the highest affinity to both quisqualate and ibotenate.     

Persistent alterations in biomarkers of oxidative stress resulting from combined in Utero and neonatal manganese inhalation

Neonatal female and male rats were exposed to airborne manganese sulfate (MnSO₄) during gestation and postnatal d 1–18. Three weeks post-exposure, rats were killed and we assessed biochemical end points indicative of oxidative stress in five brain regions: cerebellum, hippocampus, hypothalamus, olfactory bulb, and striatum. Glutamine synthetase (GS) protein levels, metallothionein (MT) and GS mRNA levels, and total glutathione (GSH) levels were determined for all five regions. Overall, there was a statistically significant effect of manganese exposure on decreasing brain GS protein levels (p=0.0061), although only the highest dose of manganese (1 mg Mn/m³) caused a significant increase in GS messenger RNA (mRNA) in both the hypothalamus and olfactory bulb of male rats and a significant decrease in GS mRNA in the striatum of female rats. This highest dose of manganese had no effect on MT mRNA in either males or females; however, the lowest dose (0.05 mg Mn/m³) decreased MT mRNA in the hippocampus, hypothalamus, and striatum in males. The median dose (0.5 mg Mn/m³) led to decreased MT mRNA in the hippocampus and hypothalamus of the males and olfactory bulb of the females. Overall, manganese exposure did not affect total GSH levels, a finding that is contrary to those in our previous studies. Only the cerebellum of manganese-exposed young male rats showed a significant reduction (p<0.05) in total GSH levels compared to control levels. These data reveal that alterations in biomarkers of oxidative stress resulting from in utero and neonatal exposures of airborne managanese remain despite 3 wk of recovery; however, it is important to note that the doses of manganese utilized represent levels that are 100-fold to a 1000-fold higher than the inhalation reference concentration set by the US Environmental Protection Agency.     

HU210-Induced Downregulation in Cannabinoid CB1 Receptor Binding Strongly Correlates with Body Weight Loss in the Adult Rat

In vitro autoradiography was used to examine changes in cannabinoid CB1 receptors (targeted with [³H] CP55,940) in rats treated with the potent cannabinoid agonist HU210. Animals were administered with HU210 (25, 50, 100 μg/kg) for 4 or 14 days or received a single 100 μg/kg injection of HU210 and sacrificed 24 h later. The acute dose resulted in a decrease in binding in the caudate putamen and hippocampus. A dose dependent, region-specific reduction (P < 0.0001) in [³H] CP55,940 binding was seen in all brain regions examined after 4 and 14 days treatment. A decrease in body weight was recorded during the first 4 days of treatment but after this animals began to gain weight. Correlations (0.865 < r < 0.659, P < 0.0001) between body weight on day four and CB1 receptor binding were found in all brain regions examined suggesting that downregulation of CB1 receptors may contribute to the induction of tolerance to body weight loss induced by HU210.     

Distribution and characteristics of nerve growth factor binding on cholinergic neurons of rat and monkey forebrain

In sections of rat forebrain, perikarya labeled radioautographically with¹²⁵I-NGF resembled cholinesterase-positive neurons in their distribution within striatum and basal forebrain. Neurons with NGF receptors were also visualized in radioautographs prepared from the basal forebrain of a cerebrus monkey. Present techniques fail to detect axons projecting from basal forebrain to hippocampus or cortex which have been shown to take up NGF selectively in retrograde transport studies. In studies with membrane-enriched preparations from rat, high-affinity binding of¹²⁵I-NGF (half maximal saturation in the 15–30 pM range) was detected in basal forebrain and striatum; lower levels of high-affinity binding were seen in hippocampus and neocortex. The binding and molecular properties of these receptors are similar to those described in other NGF-responsive tissues. These observations are further evidence supporting a biological role for NGF on some forebrain cholinergic neurons in adult rat.Special issue dedicated to Dr. E. M. Shooter and Dr. S. Varon.     

EFFECTS OF LITHIUM TREATMENT IN VITRO AND IN VIVO ON ACETYLCHOLINE METABOLISM IN RAT BRAIN

Abstract— The effects of LiCl on cholinergic function in rat brain in vitro and in vivo have been investigated. The high affinity transport of choline and the synthesis of acetylcholine in synaptosomes were reduced when part (25-75%) of the NaCl in the buffer was replaced with LiCl or sucrose. This appeared to be due to lack of Na⁺ rather than to Li⁺, as addition of LiCl to normal buffer had little effect. Following an injection of LiCl (10mmol/kg, i.p.) into rats the concentration of a pulsed dose of [²H₄]choline (20 μmol/kg, i.v., 1 min) and its conversion to [²H₄]acetylcholine, and the concentrations of [²H₂]acetylcholine and [²H₀]choline were measured in the striatum, cortex, hippocampus and cerebellum. The [²H₄]choline and [²H₄]acetylcholine were initially (15 min after LiCl) reduced (to ?30% in the cortex) and later (24 h after LiCl) increased (to + 50% in the striatum). There was a corresponding initial increase (to +50% in the cerebellum) and later decrease (to ?30% in the hippocampus) of the endogenous acetylcholine and choline. These results indicate an initial decrease and later increase in the utilization of acetylcholine after acute treatment with LiCl. Following 10 days of treatment with LiCl there was an increased rate of synthesis of [²H₄]acetylcholine from pulsed [²H₄]choline in the striatum, hippocampus and cortex (P < 0.05). The high affinity transport of [²H₄]choline and its conversion to [²H₄]acetylcholine was activated (131% of control; P < 0.01) in synaptosomes isolated from brains of 10-day treated rats. Investigation of synaptosomes isolated from striatum, hippocampus and cortex revealed that only striatal [²H₄]acetylcholine synthesis was significantly stimulated. Kinetic analysis demonstrated that the apparent K_T for choline was decreased by 30% in striatal synaptosomes isolated from rats treated for 10 days with LiCl. Striatal synaptosomes from 10-day treated rats compared to striatal synaptosomes from untreated rats also released acetylcholine at a stimulated rate in a medium containing 35 mM-KCl. These results indicate that LiCl treatment stimulates cholinergic activity in certain brain regions and this may play a significant role in the therapeutic effect of LiCl in neuropsychiatric disorders.     

NMDA receptor function is enhanced in the hippocampus of aged rats

The density and functional activity of theN-methyl-D-aspartate (NMDA)-sensitive glutamate receptor was examined in various brain areas of 3-, 18- and 24-month-old rats. The total numbers of binding sites for the NMDA receptor antagonists [³H]CGP 39653 and [³H]MK 801 binding sites were decreased in the hippocampus, cerebral cortex and striatum of 18- and 24-month-old rats, relative to 3-month-old animals. In the hippocampus of 18-month-old rats, the reduced number of NMDA receptors was associated with an increased sensitivity of [³H]MK 801 binding to the stimulatory action of glycine and glutamate. Thus, 10 M glycine and 10 M glutamate increased [³H]MK 801 binding in the hippocampus of 18-month-old rats by 75 and 160%, respectively; in 3-month-old animals, the same concentration of these amino acids increased binding by 37 and 95%, respectively. The sensitivity of [³H]MK 801 binding to glycine and glutamate was not increased in the cerebral cortex and striatum of aged rats. Moreover, an increased efficacy of glycine and glutamate in stimulating the binding of [³H]MK 801 in the hippocampus was no longer apparent in the 24-month-old rats. The increased sensitivity of [³H]MK 801 binding to glycine and glutamate in the hippocampus of 18-month-old rats may reflect an increase in NMDA receptor activity to compensate for the decrease in receptor number.     

CHOLINE: SELECTIVE ACCUMULATION BY CENTRAL CHOLINERGIC NEURONS

Abstract— Most of the cholinergic input to the hippocampus was destroyed by placement of lesions in the medial septal area. In animals with such lesions we found that hippocampal ChAc activity was reduced by 85–90% and endogenous acetylcholine levels were reduced by more than 80 %. When hippocampal synaptosomes from animals with lesions were incubated with [³H]choline at concentrations of 7.5 nm, 1 μm and 10 μm there was approximately a 60 % reduction in the uptake of [³H]choline, suggesting that cholinergic nerve endings were mainly responsible for [³H]choline uptake. At 0.1 mm concentrations of [³H]choline, there was only a 25 % reduction of choline uptake, suggesting that at higher concentrations of choline there was more nonspecific uptake. The uptake of radiolabelled tryptophan, glutamate and GABA were only slightly or not at all affected by the lesions. There was a significant reduction of uptake of radiolabelled serotonin and norepinephrine, since known monoaminergic tracts were disrupted. Choline uptake was reduced only in brain regions in which cholinergic input was interrupted (i.e. the cerebral cortex and hippocampus) and remained unchanged in other regions (i.e. the cerebellum and striatum). The time course of the reduction in choline uptake was similar to that of the reductions in ChAc activity and endogenous ACh levels; there was no decrease at 1 day, a significant decrease at 2 days, and the maximal decrease at 4 days postlesion. There was a close correlation among choline uptake, ChAc activity and ACh levels in the four brain regions examined (i.e. the striatum, cerebral cortex, hippocampus and cerebellum). Our results suggest that when hippocampal synaptosomes (and perhaps synaptosomes from other brain areas as well) are incubated in the presence of choline, at concentrations of 10 μm m or lower, then cholinergic nerve endings are responsible for the bulk of the choline accumulated by the tissue.     

Accumulation,elimination, release and metabolism of pipecolic acid in the mouse brain following intraventricular injection

Following i.c.v. (intracerebral ventricular) injections ofd,l-[³H]pipecolic acid (PA), it is reabsorbed from the ventricles and redistributed to various brain regions. The highest accumulation is found in three brain regions ipsilateral to the injection site, hippocampus, neocortex, striatum, and in the diencephalon. Following preloading in vivo, the radioactivity is released from hippocampus slices in the perfusion medium after depolarization induced by high K⁺. During perfusion with a Ca⁺⁺ free medium containing EGTA, a significant reduction of release is observed.The radioactivity ofd,l-[³H]PA in the brain shows a more rapid phase of decrease from 0 to 2 hours and a slower phase from 2 to 5 hours. At 5 hours, only 28% radioactivity, represented mainly by PA, is left in the brain. Kidney secretion represents the major route of elimination of the injected PA. The presence of -aminoadipic acid both in brain and urine was observed. Probenecid (200 mg/kg) significantly increases the accumulation of i.c.v. injectedd,l-[³H]PA in brain and kidney. The presence of a regional accumulation of PA in certain brain regions, its metabolism in brain, its enhanced retention following probenecid administration and its Ca⁺⁺ dependent release following high K⁺ stimulation, all constitute indirect evidence for a neuronal localization of this brain endogenous iminoacid.     

Selective Lesions by Manganese and Extensive Damage by Iron After Injection into Rat Striatum or Hippocampus

Abstract: Regional ⁴⁵Ca²⁺ accumulation and analysis of monoamines and metabolites in dissected tissues were used to localize, quantify, and characterize brain damage after intracerebral injections of Mn²⁺ into striatum and hippocampus. The specificity of Mn²⁺-induced lesions is described in relation to brain damage produced by local Fe²⁺or 6-hydroxydopamine (6-OHDA) injections. In striatum, Fe²⁺ and Mn²⁺ produced dose-dependent (0.05-0.8 μmol) dopamine (DA) depletion, with Fe²⁺ being 3.4 times more potent than Mn²⁺. Studies examining the time course of changes in monoamine levels in striatum following local application of 0.4 μmol of Mn²⁺ revealed maximal depletion of all substances investigated (except 5-hydroxyin-doleacetic acid) after 3 days. The effects on DA (87% depletion at day 3) and its major metabolites were most pronounced and lasted until at least 90 days (40% depletion), whereas serotonin and noradrenaline levels recovered within 21 and 42 days, respectively. In addition, levels of 3-methoxytyramine, which is used as an index of DA release, also recovered within 42 days, indicating a functional restoration of DA neurotransmission despite substantial loss of DA content. Intrastriatal Mn²⁺ (0.4 μmol) produced time-dependent ⁴⁵Ca²⁺ accumulation in striatum, globus pallidus, entopeduncular nucleus, several thalamic nuclei, and substantia nigra pars reticulata ipsilateral to the injection site. In contrast, 6-OHDA injected at a dose equipotent in depleting DA produced significantly less ⁴⁵Ca²⁺ accumulation in striatum and globus pallidus and no labeling of other brain areas, whereas Fe²⁺ (0.4 μmol) produced extensive ⁴⁵Ca²⁺ accumulation throughout basal ganglia, accumbens, and cerebral cortex. In hippocampus, high Mn²⁺ (0.4 μmol) produced limited ⁴⁵Ca²⁺ accumulation in subiculum and dentate gyrus, whereas low Fe²⁺ (0.1 μmol) produced widespread ⁴⁵Ca²⁺ accumulation throughout hippocampus, thalamus, and cerebral cortex. It is concluded that (a) Mn²⁺ is selectively neurotoxic to pathways intrinsic to the basal ganglia, (b) intrastriatal injections can be used as a model for systemic Mn²⁺ intoxications, and (c) high endogenous Fe³⁺ and/or catecholamine levels potentiate the neurotoxicity of Mn²⁺.