Opposite presynaptic regulations by glutamate through NMDA receptors of dopamine synthesis and release in rat striatal synaptosomes

Purified striatal synaptosomes were superfused continuously with L-[3,5-³H]tyrosine to measure simultaneously the synthesis ([³H]water formed during the conversion of [³H]tyrosine into [³H]DOPA) and the release of [³H]dopamine ([³H]DA). Glutamate (10⁻³ M) and NMDA (10⁻³ M, in the absence of Mg²⁺) stimulated the release of [³H]DA, but they reduced the efflux of [³H]water. This reduction of [³H]DA synthesis was blocked by 2-amino-5-phosphonovalerate indicating the involvement of NMDA receptors. Although D,L--amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA) and kainate stimulated the release of [³H]DA, they did not affect its synthesis. The glutamate-evoked inhibition of [³H]DA synthesis was prevented when synaptosomes were superfused continuously with adenosine adenosine deaminase plus quinpirole, a treatment which markedly reduces the phosphorylation of tyrosine hydroxylase by cAMP dependent protein kinase. The opposite effects of glutamate on [³H]DA synthesis and release were mimicked by ionomycin (10⁻⁶ M). It is proposed that both an activation of a cyclic nucleotide phosphodiesterase and a dephosphorylation of tyrosine hydroxylase linked to the influx of calcium through NMDA receptors is responsible for the inhibition of dopamine synthesis by glutamate and that calcineurin could play a critical role in these processes.     

Regional distribution of [H]imipramine binding in rat brain

[³H]imipramine binding was measured in 23 microdissected areas of the rat brain and compared to published values for the endogenous levels of serotonin, noradrenaline and dopamine in the same areas.

The density of [³H]imipramine binding sites appears to be highly correlated with the distribution of endogenous serotonin especially where the serotonin is located mainly in nerve terminals. A weak but still significant correlation also exists with the distribution of endogenous noradrenaline whereas no such correlation could be detected for endogenous dopamine.     

Evidence for defective incorporation of proteins in myelin of the quaking mutant mouse

The defect in myelinogenesis present in the Quaking mutant mouse was investigated using a double radioisotope technique for comparing the incorporation of amino acid into myelin proteins of normal and mutant mice. Quaking mice and littermate controls recieved intracranial injections of 150 μCi [³H]glycine and 25 μCi of [¹⁴C]glycine respectively. After 2 h their brains were combined and jointly processed to obtain subcellular fractions. The ³H/¹⁴C ratio for the myelin subfraction was 1.88 as compared to a ³H/¹⁴C ratio of 3.0 for the other subfractions, indicating a 40% decrease in glycine incorporation into myelin of Quaking mice. Myelin proteins were separated by discontinuous gel electrophoresis in the presence of sodium dodecyl sulfate (SDS) and the ³H/¹⁴C ratios determined in each gel slice. In contrast to the microsomal subfractions which gave a ³H/¹⁴C ratio of 2.6 across the gel, the ³H/¹⁴C ratio of myelin showed large variations with values ranging from 0.54 for proteolipid protein to 2.0 for some of the high molecular weight proteins. During development, the Quaking mutant exhibited a preferential depression in glycine incorporation into proteolipid protein in 18-day-old mice, while in older animals (32–54 days) the fast migrating basic protein, as well as the proteolipid protein, was labeled to a significantly lesser extent.     

Homovanillic acid: Entry rate kinetics for transfer from plasma to cerebrospinal fluid

Because some studies have indicated that 3-methoxy-4-hydroxyphenylacetic acid (homovanillic acid [HVA]) does not cross the blood-CSF barrier, it is assumed by some that CSF HVA levels, after L-DOPA administration, validly reflect central nervous system (CNS) metabolism of dopamine. These experiments were designed to test the validity of this assumption. First, it was established that DOPA, administered i.v. to dogs, causes elevations of blood HVA, indicating systemic metabolism of DOPA to the end-product of its metabolic cycle, i.e., HVA. Then, a loading dose and i.v. infusion of HVA were administered to anesthetized dogs to produce a constant blood level for 2–3 h. Serial blood and CSF samples were analyzed fluorometrically for HVA. CSF samples were withdrawn via an indwelling cisternal needle. Entry rates (%/min) were calculated according to Davson⁸. In 5 animals, the values were 0.44 ± 0.16 (S.D.). In 2 of these animals, [¹⁴C]mannitol was administered simultaneously with the HVA. Entry rate for mannitol was calculated in 5 animals and was 0.07 ± 0.04 (S.D.). The diffusion coefficients for HVA and [¹⁴C]mannitol in agar gel were determined. Values were similar, i.e., 0.76 and 0.41 (× 10⁻⁵) respectively. The data indicate that a significant amount enters CSF at a rate faster than that which would be expected by simple diffusion alone. Therefore, canine CSF HVA levels do not indicate CNS DOPA metabolism alone after systemic DOPA administration. Consequently, CSF HVA levels may not indicate human CNS DOPA metabolism after therapeutic administration.     

Vascular lipoxygenase activity: synthesis of 15-hydroxyeicosatetraenoic acid from arachidonic acid by blood vessels and cultured vascular endothelial cells

Although indirect pharmacologic evidence has suggested the presence of a lipoxygenase pathway of arachidonic acid (AA) metabolism in blood vessels, direct biochemical evidence has been difficult to demonstrate. We have investigated lipoxygenase metabolism in both fresh vessel preparations and cultured vascular cells from various sources and species. Lipoxygenase-derived [³H]HETE (composed of 12-HETE, 15-HETE and 5-HETE), which was abolished by ETYA but not by aspirin, was formed when [³H]AA was incubated with fresh sections of rat aorta. Lipoxygenase activity was lost following deendothelialization. A single peak of [³H]15-HETE was produced by cultured bovine aortic and human umbilical vein endothelial cells (EC) in response to exogenous [³H]AA or from [³H]AA released by ionophore A23187 from endogenous EC membrane phospholipid pools. Cultured bovine, rabbit or rat aorta smooth muscle cells had no detectable 15-lipoxygenase activity. ¹⁴C]Linoleic acid was converted by EC to its 15-lipoxygenase metabolite, [¹⁴C]13-hydroxyoctadecadienoic acid. These results indicate that blood vessels from different sources and species have a 15-lipoxygenase system, and this activity resides predominantly in the endothelial cells.     

Transport, uptake, and metabolism of blood-borne vasopressin by the blood-brain barrier

Transport, binding, and metabolism of [phenylalanyl-3,4,5-³H(N)]arginine vasopressin (AVP) by the blood-brain barrier (BBB) was studied in adult guinea-pigs by means of a novel vascular brain perfusion (VBP)/capillary depletion technique and HPLC. A time-dependent, progressive brain uptake of ³H-radioactivity was measured over the 10 min period of VBP both in brain homogenates and in brain tissue depleted of cerebral microvessels. The unidirectional blood-to-brain transport constant, K_IN, estimated by multiple-time tissue uptake analysis of the homogenate and postcapillary supernatant, indicated that the BBB transfer rat ffor [³H]AVP (K_IN = 2.37±0.25 μl min⁻¹ per gram brain homogenate) was almost 10 times higher than for simultaneously perfused [¹⁴C]sucrose, a cerebrosvascular space marker. In contrast to homogenate and postcapillary supernatant, the [³H]radioactivity determined in the vascular pellet after dextran density centrifugation of the brain homogenate was very low and only somewhat higher than for [¹⁴C]sucrose. HPLC analysis of the perfused brain tissue revealed time-dependent degradation of the blood-borne neuropeptide. The percentage of intact [³H]AVP as determined in the postcapillary supernatant progressively declined during brain perfusion, from 49% at 1 min to 11.9% at 10 min. The major detectable labeled metabolite was [³H]phenylalanine, the labeled amino acid residue of [³H]AVP. The aminopeptidase inhibitor bestatin (0.5 mM), perfused simultaneously with [³H]AVP by the VBP technique, did not alter tissue uptake of [³H]AVP, indicating that there was no significant hydrolysis of peptide by the luminal BBB surface. The results suggest that rapid in vivo metabolism of AVP occurs after BBB transport in the brain parenchyma with no evidence of significant capillary sequestration, or degradation of AVP by the BBB.     

The differentiation of synthesis from incorporation of basic protein in quaking mutant mouse myelin

The incorporation of radioactive label into the myelin basic protein isolated from whole brain and from purified myelin of Quaking mice and normal littermates was compared. Four Quaking mice (32 days) and 4 littermate controls were injected intracranially with 150 μCi [2-²H]glycine and 25 μCi of [2-¹⁴C]glycine, respectively. One hour later, the 8 mice were sacrificed and their brains combined for common homogenization. The ³H/¹⁴C ratios of the small and large basic proteins in whole brain were 3.44 and 2.48 respectively, while the ³H/¹⁴C ratios for these proteins in myelin were 0.79 and 1.00, respectively. In the same experiment, the microsomal fraction had a ³H/¹⁴C ratio of 2.98 which is the expected ratio for normal incorporation. The results indicate that the synthesis of basic protein in whole brain of Quaking mouse proceeds at a normal rate, but specifically, the incorporation of basic protein into myelin is depressed suggesting a defect at the step of assembly of myelin components into a final membrane product.     

Quantitative autoradiography of the dopamine uptake complex in rat brain using [H]GBR 12935: binding characteristics

The dopamine uptake complex was examined in the rat central nervous system using [³H]GBR 12935 and in vitro quantitative autoradiography to determine all binding data. [³H]GBR 12935 labels two unique binding sites, the dopamine uptake complex and a piperazine acceptor site. These two sites differ in their pharmacologic properties, anatomical distributions, densities, and response to lesions. Using appropriate binding conditions, [³H]GBR 12935 can be used to specifically label the dopamine uptake complex. [³H]GBR 12935 labeled a single binding site with characteristics of the dopamine uptake complex when mazindol (25 μM) was used as a blank. The specific binding and autoradiographic appearance of [³H]GBR 12935 to the dopamine uptake complex was improved by including trans-flupentixol (0.75 μM) to displace binding to a previously desrribed piperazine acceptor site, recently determined to be a site on cytochrome P450IID1. Binding was saturable and reversible to the dopamine uptake complex. The equilibrium dissociation constant (1.4 ± 0.7nM), maximal number of binding sites (6.0 ± 1.3pmol/mg protein), and Hill coefficient (1.1 ± 0.1) of [³H]GBR 12935 in rat striatum using mazindol to define non-specific binding was not significantly altered by the inclusion of trans-flupentixol (0.75 μM). Using GBR 12909 as a blank produced a greater maximal number of binding sites (8.4 ± 2.3pmol/mg protein), but no significant difference in the equilibrium dissociation constant (1.6 ± 0.3nM) or Hill coefficient (1.1 ± 0.1). A series of drugs that bind to the dopamine uptake complex displaced [³H]GBR 12935 in a rank order consistent with other binding and behavioral studies of this complex. The rank order of these drugs was GBR 12909 > mazindol > nomifensine > benztropine > desipramine > amphetamine > dopamine; all these drugs displayed a Hill coefficient near one and were best modeled as a single site. Cocaine and WIN 35, 428 (a cocaine congener) were unique in their competition for [³H]GBR 12935 binding, displaying biphasic curves, low Hill coefficients, and were best modeled as two site fits. Lesioning of the dopaminergic median forebrain bundle resulted in a dramatic loss of the dopamine uptake complex in the striatum, nucleus accumbens, olfactory tubercle, and substantia nigra. Other dopaminergic projection areas were decreased to a lesser extent. Striatal ibotenate lesions did not decrease the density of the dopamine uptake complex, despite a large decrease in the dopamine D₁ receptor. [³H]GBR 12935 can be used as an effective ligand to label the dopamine uptake complex for quantitative autoradiographic studies. It offers a number of advantages over previous autoradiographic assays for this complex including high specificity (> 95% specific binding in rat striatum), high sensitivity (detection of mazindol displaceable sites in the cerebral cortex), low background (comparable to film background), and low cost. This assay also supports the existence of two binding sites for cocaine on the dopamine uptake complex. The exact nature and differences between these two cocaine sites remains to be determined.     

Alterations in neurotransmitter receptors and glucose use after unilateral orbital enucleation

Serotonin (5-hydroxytryptamine; 5-HT), acetylcholine and γ-aminobutyric acid (GABA) are neurotransmitters in the rat visual system. Using quantitative autoradiography, the effect of unilateral orbitral enucleationon [^3H]5-HT, [³H]ketanserin, [³H]quinuclidinyl benilate (QNB) and [³H]muscimol binding to 5-HT₁, 5-HT₂, muscarinic and GABA_A receptors has been examined within anatomical components of the visual pathway at 4 time points up to 20 days after the lesion. The functional deficit was assessed in the same animals using quantitative [¹⁴C]2-deoxyglucose autoradiography. At 1 day after unilateral orbital enucleation, there were no significant alterations in ligand binding although local cerebral glucose use was reduced in primary visual structures in the visually deprived hemisphere. At 5 days post-enucleation, however, [³H]5-HT binding was significantly reduced in both the visually deprived superior colliculus (by 17%) and dorsal lateral geniculate body (DLG) (by 33%). There were similar alterations in the binding of this ligand in these primary retinal projections areas at 10 and 20 days after orbital enucleation, but there were no changes in secondary areas (e.g. visual cortex) at any time point. [³H]Muscimol binding was significantly reduced in the visually deprived DLG (30%) and visual cortex (21%) only at 20 days post-lesion, whilst [³H]ketanserin and [³H]QNB were not altered in any region in the visually deprived hemisphere at any time point post-enucleation. At 10 and 20 days post-enucleation, the degree of [³H]5-HT, and [³H]muscimol binding deficits in visually deprived structures correlated significantly with the level of reduced metabolic activity in these areas (r = 0.700andr = 0.543respectively). The specificity and regional and temporal heterogeneity of neurotransmitter receptor binding alterations provides evidence of selective adjustments within visual system component6s in response to orbital enucleation.     

Downregulation of muscarinic receptors in the rat caudate-putamen after lesioning of the ipsilateral nigrostriatal dopamine pathway with 6-hydroxydopamine (6-OHDA): normalization by fetal mesencephalic transplants

The autoradiographic distribution and density of muscarinic receptors was studied in the neostriatum of rats with long-term unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal dopaminergic pathway and in lesioned rats who had additionally received embryonic substantia nigra grafts in the dopamine denervated striatum. Muscarinic receptors were labeled with [³H]quinuclidinyl benzilate (QNB), M₁ receptors were directly labeled with [³H]pirenzepine (PZ) and non-M₁ receptors were labeled by the competition of 100 nM PZ with [³H]QNB. The density and distribution of muscarinic receptors were directly compared to the sodium-dependent, high-affinity, choline uptake sites as labeled with [³H]hemicholinium-3 (HC-3). In the 6-OHDA-lesioned animals, there was a 25% reduction in muscarinic receptors labeled with [³H]QNB. Subtype analysis showed that there was a reduction of both M₁ (−26%) and non-M₁ (−33%) receptors. A normal density of both muscarinic receptor populations was found in animals with successful transplants. Saturation analysis demonstrated that the changes, in muscarinic receptor density, were due to a change in receptor number (B_max) and not affinity (K_d). There was no significant change in [³H]HC-3 binding in the 6-OHDA-lesioned or transplanted animals, indicating that alterations in muscarinic receptors were not due to transynaptic degeneration of striatal cholinergic interneurons. The findings of downregulation of muscarinic receptors following long-term dopamine denervation and the subsequent normalization of muscarinic receptor density after fetal mesencephalic transplantation suggests that transplanted substantia nigra cells are able to restore inhibitory control on striatal cholinergic interneurons.     

Localization and quantification of the dopamine transporter: comparison of [H]WIN 35,428 and [I]RTI-55

Transport into the presynaptic terminal by the dopamine transporter is the primary mechanism for removing dopamine from the synaptic cleft. This transporter is a specific marker for dopamine terminals and is a primary site for CNS actions of cocaine. Several radioligands have been developed for analysis of the dopamine transporter. The ligands vary in affinity and specificity, leading to differences in reported transporter density in brain regions. We compared two of the most commonly used ligands, [³H]WIN 35,428 and [¹²⁵I]RTI-55, analyzing the localization and density of sites in the rat brain using serial sections and quantitative autoradiography. Citalopram at 50 nmol/1 was used to block [¹²⁵I]RTI-55 binding to serotonin transport sites. Transporter density was highest in the striatum and both ligands labeled equivalent numbers of sites, with lateral to medial and anterior to posterior gradients. In most areas the density of sites measured with the two ligands was similar. However, [¹²⁵I]RTI-55 binding was significantly higher than [³H]WIN 35,428 binding in the substantia nigra zona compacta, ventral tegmental area, subthalamic nucleus and a number of other subcortical nuclear groups while [³H]WIN 35,428 binding was higher in lateral striatum and in olfactory tubercle. These differences could reflect different forms of the transporter, perhaps due to post-translational modifications, and they may provide a basis for differential pharmacological regulation of transporter function in discrete brain regions and disease states.     

Selective alterations in glutamate receptor subtypes after unilateral orbital enucleation

Glutamate is the major excitatory neurotransmitter in the rat visual system. Using quantitative autoradiography the effect of unilateral orbital enucleation on [³H]kainate, [³H]-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid ([³H]AMPA) and [³H]glutamate binding to kainate, quisqualate and NMDA receptors respectively has been examined within anatomical components of the visual pathway at 4 time points up to 20 days post-lesion. The time course for the degeneration of retinal projection fibres was assessed in a separate group of animals by quantifying [³H]cyclohexyladenosine ([³H]CHA) binding to presynaptic adenosine A₁ receptors. Over the first 5 days after orbital enucleation, there were no significant alterations in glutamate or adenosine A₁ receptor binding in visual structures of the visually deprived hemisphere. However, at 10 days post-lesion [³H]AMPA binding was significantly reduced (30%) in the visually deprived superior colliculus but unaltered in other visual structures. At this time point there was also a significant reduction (50%) in [³H]CHA binding in the visually deprived superior colliculus but not in other retino-recipient nuclei. There were similar changes in [³H]AMPA and [³H]CHA binding at 20 days post-enucleation. [³H]Kainate binding was significantly increased in the visually deprived superior colliculus only at 20 days post-enucleation. Saturation analysis of [³H]kainate and [³H]AMPA binding at this time point indicated a selective increase in the b_max value for the high affinity [³H]kainate binding site and a concomitant decrease in the b_max value for the high affinity [³H]AMPA binding site in the visually deprived superior colliculus. There were, however, no significant alterations in [³H]AMPA or [³H]kainate binding in other primary projection areas or in secondary visual areas (e.g. visual cortex) at any time point. NMDA sensitive [³H]glutamate binding was unaltered in the visually deprived hemisphere up to 20 days post-enucleation. These results suggest an upregulation of kainate receptors in the visually deprived superior colliculus after orbital enucleation and a loss of presynaptic quisqualate receptors on degenerating retinal fibres. The plastic alterations in kainate receptors in the superior colliculus are supportive of electrophysiological data suggesting a physiological role for these sites in mediating excitatory postsynaptic potentials in tectal neurons.     

Regional [H]acetylcholine and [H]nicotine binding in developing mouse brain

The postnatal development of nicotine-like binding sites in the cortex, hippocampus, midbrain and cerebellum of 3-, 7-, 12-, 17- and 30-day-old mice was studied. Two different nicotinic cholinergic ligands, namely [³H]acetylcholine ([³H]ACh) and [³H]nicotine ([³H]NIC) were used to detect the nicotine-like binding sites in in vitro binding assays. The postnatal development of the binding sites of [³H]NIC increased gradually with age in all brain regions studied. The [³H]ACh binding, on the other hand, showed a marked peak on day 12 in the cerebellum and midbrain but did not change notably with age in the hippocampus and cortex, except for a slight temporary increase in the cortex on day 7. The time-course for the appearance of nicotinic binding sites as observed with [³H]ACh was found to be rather similar to that earlier described for [³H]alpha-bungarotoxin binding sites, whereas that for [³H]NIC differed from that described for other nicotinic ligands.     

Consequences of decreased brain serotonin in the pyridoxine-deficient young rat

1. 1. The concentrations of serotonin in various brain areas were significantly decreased in the pyridoxine-deficient young rat.

2. 2. There was no change in the concentration of dopamine.

3. 3. Both Bmax and Kd of [³H] serotonin binding to membrane preparations from cerebral cortex were increased in deficiency and were restored to normal upon pyridoxine supplementation.

4. 4. There was no change in [³H] spiroperidol binding to corpus striatal membrane preparations in pyridoxine-deficient rats.

Regulation of peripheral-type benzodiazepine receptors in cultured astrocytes by monoamine and amino acid neurotransmitters

Exposure of primary cultured astrocytes for 3 days to 1 μM of either dopamine, serotonin or norepinephrine resulted in upregulation (25–34% increase in B_max) of the peripheral-type benzodiazepine receptors (PBRs) labeled with [³H]Ro5-4864. A similar treatment with γ-aminobutyric acid [GABA] caused a 2-fold increase in the affinity (K_d) of [³H]Ro5-4864. The monoamines tested and GABA had no effect on the binding parameters of [³H]PK 11195, another selective PBR ligand. The present study indicates that Ro5-4864 binding sites are susceptible to regulation by specific neurotransmitters and provides further evidence for the distinction between Ro5-4864 and PK 11195 binding sites of the PBRs in cultured astrocytes.     

The noradrenergic system in cultured aggregates of fetal rat brain cells: Morphology of the aggregates and pharmacological indices of noradrenergic neurons

Spherical aggregates formed rapidly in culture by re-aggregation of trypsin-dissociated brain cells from the 17-day-old fetal rat. Over days 10 days an initially random distribution of cells evolved into a 30layered arrangement; cells with characteristics of neurons were found largely in the intermediate layer. The survival of neuronal and glial cell types was evaluated histologically and verified by electron microscopy, which revealed synaptic and myelin structures that rapidly increased in number after 18 days in culture. Levels of norepinephrine (NE) and dopamine (DA) reached peaks of 9.5 and 4.4 ng/mg protein, respectively, at culture day 21. Uptake of [³H]NE paralleled these amine levels and was blocked by desipramine or pretreatment with either reserpine or 6-OH-DA. Autoradiographs of aggregates labeled with [³H]NE showed a high density of silver grains over cells, apparently neurons, with branching processes traced for 120 μm. Previously accumulated [³H]NE was released under depolarizing conditions (high [K⁺] or vertridine) only in the presence of Ca²⁺. Release was induced to a lesser extent by kainic > glutamic acid. Thus, such aggregates appear to contain catecholaminergic neurons capable of synthesis, uptake and release of NE. The time course of development of these functions supports suggestions that aggregate preparations might be useful in studying neurochemical or morphological aspects of brain development and function in vitro.     

Comparison of two different benzodiazepine binding proteins by peptide mapping after limited proteolysis

Proteins P₅₁ and P₅₅ were photolabeled by [³H]flunitrazepam, [³H]clonazepam or ³H-Ro 15–4513 and then compared by peptide mapping after limited digestion with various proteases. Results indicated that [³H]flunitrazepam or [³H]clonazepam irreversibly bind to the same and [³H]Ro 15–4513 to a different part of these proteins. The different radiolabeled peptide patterns obtained from P₅₁ or P₅₅ irrespective of the photolabel used, suggest a difference in the molecular structure of these proteins.     

Transport of [H]mazindol binding sites in mesostriatal dopamine axons

6-Hydroxydopamine injections along mesostriatal dopaminergic axons can be used to interrupt axonal transport from cell bodies in the substantia nigra pars compacta to terminal fields in the striatum. Such lesions produce accumulations of high-affinity dopamine uptake sites (as measured by [³H]mazindol binding) and acetylcholinesterase proximal to the injection, suggesting that at least a portion of the [³H]mazindol binding and acetylcholinesterase activity seen in the striatum is located presynaptically on the mesostriatal dopaminergic fibers.     

Functional damage of dopamine nerve terminals following intrastriatal kainic acid injection

The release of [³H] dopamine ([³H]DA) previously taken up into rat striatal slices was studied one week after a monolateral intrastriatal injectuion of kainic acid (KA). Different releasing stimuli (electrical pulses, veratrine, high-K⁺) were applied. The electrically evoked release in the KA-lesioned striata was drastically reduced with respect to the unlesioned contralateral striata. In contrast, KA had no effect on the release of [³H]DA evoked by veratrine or high-K⁺. In unlesioned striatal slices, depolarized with 15 mM KCl, apomorphine reduced and (−)sulpiride increased the release of [³H]DA. The effect of apomorphine was antagonized by (−)sulpiride indicating the presence of an autoreceptor system similar to that seen in unlesioned striata stimulated electrically. However, the effects of apomorphine and of (−)sulpiride were dramatically reduced in K⁺-depolarized slices prepared from KA-lesioned striata. The results suggest that the axon terminals in KA-treated areas remain intact in several of their properties but may be damaged in some critical processes.     

Genotypic influences on striatal dopaminergic regulation in mice

Genotypic influences on dopaminergic-induced behaviors and striatal dopaminergic receptors were evaluated in CBA/J, C57BL/6J and BALB/cJ male mice. CBA/J mice were less behaviorally sensitive to apomorphine (stereotypic behavior), but more sensitive to haloperidol (catalepsy) than C57BL/6J and BALB/cJ mice. Striatal dopaminergic receptors, assayed by binding of [³H]spiroperidol (antagonist) and [³H]ADTN (agonist), were 50% fewer in CBA/J compared to BALB/cJ mice; C57BL/6J mice had low to intermediate numbers of receptors.

Striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations were similar in all strains. However, a 20% higher DOPAC/dopamine ratio in CBA/J mice suggests greater dopamine turnover. Median eminence dopamine was similar in all strains, but norepinephrine was 30% higher in BALB/cJ mice.

CBA/J mice failed to show antagonist-induced supersensitivity-type responses to chronic haloperidol treatment: enhanced stereotypic response to apomorphine and a 30% increase of dopaminergic receptors occurred in C57BL/6J and BALB/cJ mice, but not in CBA/J mice. These data suggest that CBA/J mice either cannot respond to chronic haloperidol treatment or have an elevated threshold for induction of supersensitivity response.

Chronic treatment with the dopamine agonist bromocriptine (7d) depressed apomorphine-induced stereotypic behavior in C57BL/6J mice and eliminated stereotypy in BALB/cJ mice, but caused no change in stereotypic behavior in CBA/J mice. Dopaminergic receptors were 15% lower after bromocriptine treatment in all strains.

These results suggest that some striatal dopaminergic functions are impaired in CBA/J mice relative to BALB/cJ and C57BL/6J mice. The impaired haloperidol-induced supersensitivity responses in the CBA/J mouse may be a useful model for analyzing similar impairments of supersensitivity responses in old rodents.