Postischemic changes of [3H]nimodipine and [3H]ryanodine binding in the gerbil striatum and hippocampus

Sequential alterations of [³H]nimodipine and [³H]ryanodine binding in gerbils were investigated in selectively vulnerable regions, such as the striatum and hippocampus, 1 h to 7 days after 10 min of transient cerebral ischemia. [³H]Nimodipine binding showed no significant changes in the striatum and hippocampus up to 48 h after ischemia. Seven days after ischemia, however, a severe reduction in [³H]nimodipine binding was observed in the dorsolateral striatum, hippocampal CA1 (stratum oriens, stratum pyramidale and stratum radiatum) and hippocampal CA3 sector. On the other hand, [³H]ryanodine binding showed a significant increase in the hippocampus 1 h after ischemia. Five hours after ischemia, a significant reduction in [³H]ryanodine binding was observed only in the hippocampal CA1 sector. Thereafter, the striatum and hippocampus showed no significant alterations in [³H]ryanodine binding up to 48 h after ischemia. After 7 days, a marked reduction in [³H]ryanodine binding was observed in the striatum and hippocampus which were particularly vulnerable to ischemia. These results demonstrate that postischemic alteration in [³H]nimodipine and [³H]ryanodine binding is produced with different processes in the hippocampus. They also suggest that the mechanism for striatal cell damage caused by transient cerebral ischemia may, at least in part, differ from that for hippocampal neuronal damage. Furthermore, our findings suggest that abnormal calcium release from intracellular stores may play a pivotal role in the development of hippocampal neuronal damage.     

HIV-1 Envelope Protein gp120 Potentiates NMDA-evoked Noradrenaline Release by a Direct Action at Rat Hippocampal and Cortical Noradrenergic Nerve Endings

Exposure of rat or human neocortical or hippocampal tissue to glutamate receptor agonists elicits a Ca²⁺-dependent, exocytotic-like release of previously accumulated [³H]noradrenaline through activation of both N -methyl- d -aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors colocalized on the noradrenergic axon terminals. Here we show that the NMDA (100 μM)-evoked release of [³H]noradrenaline from superfused thin layers of isolated rat hippocampal or cortical nerve endings was potentiated when the human immunodeficiency virus type 1 coat protein gp120 was added to the superfusion medium concomitantly with NMDA. The effect of gp120 (10 pM to 3 nM) on the 100 μM NMDA-evoked release of [³H]noradrenaline was concentration-dependent; the maximal effect (-140% potentiation) was reached at 100 pM of gp120. The protein was inactive on its own. The [³H]noradrenaline release evoked by NMDA (100 μM) + gp120 (100 μM) was prevented by classical NMDA receptor antagonists, as well as by 10 μM memantine. Neither the release evoked by NMDA nor that elicited by NMDA + gp120 was sensitive to the nitric oxide synthase inhibitor N ^G -nitro- l -arginine, suggesting no involvement of nitric oxide. The [³H]noradrenaline release elicited by 100 nM AMPA was unaffected by gp120. The protein potentiated the release evoked by 100 nM glutamate; the effect of 100 pM gp120 was quantitatively identical to that of 1 μM glycine, with no apparent additivity between gp120 and glycine. The antagonism by 1 μM 7-chloro-kynurenic acid of the NMDA-induced [³H]noradrenaline release was reversed by glycine or gp120. The data are compatible with gp120 acting directly as a powerful positive allosteric modulator at a neuronal NMDA receptor.     

Glutamate-induced Release of the Nitric Oxide Precursor, Arginine, From Glial Cells

Arginine, the nitric oxide precursor, is predominantly localized in glial cells, whereas the constitutive nitric oxide synthase is mainly found in neurons. Therefore, a transfer of arginine from glial cells to neurons is needed to replenish the neuronal precursor pool. This is further supported by the finding that arginine is released upon selective pathway stimulation both in vitro and in vivo . We investigated the mechanism underlying this glial-neuronal interaction by analysing the effect of glutamate receptor agonists on the extracellular [³H]arginine level in cerebellar and cortical slices and in cultures of either cortical astroglial cells or neurons. We present data indicating that arginine is released from cerebellar and cortical slices and astroglial cell cultures upon activation of ionotropic non-NMDA glutamate receptors. Glutamate had no effect on the extracellular [³H]arginine level in neuronal cultures. Moreover, the effect of glutamate in cerebellar slices was tetrodotoxin-insensitive, and the calcium ionophore A23187 evoked the release of [³H]arginine from astroglial cell cultures. Thus, nitric oxide synthesis and nitric oxide transmission may be based on the glial-neuronal transfer of arginine which is induced by activation of excitatory amino acid receptors on glial cells.     

Effects of the Anticonvulsant Losigamone and Its Isomers on the GABAA Receptor System

Summary: We conducted in vitro studies to clarify the possible involvement of GABA, receptor-mediated processes in the anticonvulsant effects of losigamone and its optical isomers AO-242 (+losigamone) and AO-294 (-losigamone). In binding experiments with cortical and cerebellar membrane preparations of rat brain, ≤100 μM losigamone did not affect the specific binding of [³H]GABA, [³H]flunitrazepam, or [³⁵S]t-butyl-bicyclo-phosphorothionate (TBPS) to their receptors. Losigamone, however, in concentrations of 10-8-10-5 M, stimulated ³⁶Cl influx into spinal cord neurons in the absence of exogenous GABA. This effect was inhibited by the GABA antagonists bicuculline (BIC) and picrotoxin (PIC). Losigamone 10^-5 M potentiated the effect of a suboptimal concentration of exogenous GABA M on 3³⁶Cl influx. Both isomers of losigamone likewise stimulated 36Cl influx into spinal cord neurons, and these effects were similarly antagonized by BIC and PIC. Losigamone and its optical isomers AO-294 and AO-242 antagonized potassium-induced hyperexcitability in rat hippocampal slices concentration dependently. There were no clear differences in the potencies of losigamone, AO-242, or AO-294. However, AO-294 and AO-242 differed significantly in their ability to suppress TBPS- induced hyperexcitability of hippocampal slices. Such observations demonstrate that although losigamone does not bind to GABA, benzodiazepine (BZD) or PIC binding sites of the neuronal chloride channel, it is capable of stimulating ³⁶Cl influx in the spinal cord neurons by a GABA-sensitive mechanism and at a side distant from the GABA channel.     

In Vivo Modulation of Sigma Receptor Sites by Calcitonin Gene-related Peptide in the Mouse and Rat Hippocampal Formation: Radioligand Binding and Electrophysiological Studies

Possible interactions between sigma (σ) receptor sites and calcitonin gene-related peptides (CGRP) were investigated using receptor subtype-related analogues and fragments in in vivo [³H](+)SKF 10 047/σ binding in the hippocampus, and electrophysiological recording of the N -methyl-D-aspartate (NMDA)-induced activation of CA3 pyramidal neurons, two well-established σ assays. In both paradigms, CGRP and the agonist [Cys(ACM)^2,7]hCGRPα modulated σ systems. In vivo binding experiments demonstrated that CGRP and [Cys(ACM)^2,7]hCGRPα inhibited 25–40% of specific [³H](+)SKF 10 047 labelling in the mouse hippocampal formation while the purported antagonist hCGRP_8–37 was inactive. The specificity of this modulation was demonstrated further by the lack of effect of other vasoactive peptides, including the atrial natriuretic peptide, substance P, and its N-terminal fragment, substance P_1–7. In the CA3 subfield of the rat dorsal hippocampus, hCGRPα decreased (up to 61%) the NMDA-induced activation of the pyramidal neurons. Conversely, the linear analogue [Cys(ACM)^2,7]hCGRPα enhanced (by 85%) the NMDA-induced activation of CA3 pyramidal neurons, while the antagonistic fragment hCGRP_8–37 had no effect. Haloperidol, a high-affinity σ receptor ligand, inhibited by 90% the in vivo [3H](+)SKF 10 047 labelling, and prevented the modulation of the NMDA-induced activation by hCGRPα and [Cys(ACM)^2,7]hCGRPα. It thus appears that CGRP can modulate σ-related systems in the hippocampal formation.     

Carbamazepine-Induced Release of Serotonin from Rat Hippocampus In Vitro

Summary: Purpose: Carbamazepine is one of several antiepileptic drugs (AEDs) that release the inhibitory neurotransmitter serotonin as part of their pharmacodynamic action on brain neurons. We undertook this study to investigate the cellular processes by which carbamazepine (CBZ) releases serotonin from brain tissue.
Methods: Tissue slices were prepared from hippocampi of Sprague-Dawley rats. These hippocampal slices were preincubated in vitro in a buffer so that neurons within the slice would take up tritium-labeled serotonin. Subsequently the slices were superfused with buffer containing CBZ or other chemicals (or both) that increase the overflow of serotonin radioactivity.
Results: Carbamazepine produced a concentration-dependent (50, 125, 250, or 500 μM) increase in basal overflow of serotonin radioactivity from superfused rat hippocampal slices in vitro. In contrast, these concentrations did not alter potassium-stimulated release, suggesting that the CBZ-induced release does not depend on depolarization or exocytosis. Blockade of the neuronal membrane serotonin transporter by fluoxetine (1 μM) or citaloprarn (2 μM) did not alter overflow of serotonin radioactivity produced by 250 μM CBZ. p -chloramphetamine (10 μM) produced a substantial increase in overflow of serotonin radioactivity, and this effect appears to be antagonized by 250 μM CBZ. Uptake of [³H]-labeled serotonin into hippocampal synaptosomes was inhibited by CBZ with a median inhibitory concentration (IC₅₀) of 511 ± 33 μM and a Hill coefficient of 0.87 ± 0.11, suggesting competitive inhibition of uptake by CBZ.
Conclusions: We conclude that CBZ (a) releases serotonin from hippocampal slices independent of exocytosis and by a mechanism not involving the neuronal membrane serotonin transporter, and (b) at high enough concentration, blocks the neuronal serotonin transporter.     

Visual Activation in α-Chloralose-anaesthetized Cats Does Not Cause Lactate Accumulation in the Visual Cortex as Detected by [1HINMR Difference Spectroscopy

The hypothesis that neuronal activation results in lactate accumulation due to mismatch between glucose and oxygen consumption was tested in the cat model of visual activation by monitoring cerebral metabolism with localized ¹H nuclear magnetic resonance spectroscopy (MRS). Adult cats were anaesthetized with α-chloralose, paralysed and mechanically ventilated. Visual evoked potentials measured over the occipital cortex showed maximal amplitude at 2 Hz stimulation, but the latencies of the early cortical potentials, N1 and P1, were independent of stimulation frequency. High signal-to-noise ratio, short echo time volume-selected [¹H]MRS was used to monitor cerebral lactate with a temporal resolution of 70 s. Difference proton spectroscopy unambiguously showed no lactate peak in the visual cortex during visual activation at stimulation frequencies ranging from 1 to 16 Hz. Absence of change in lactate concentration during visual stimulation was confirmed by averaging all the spectra acquired during activation and subtracting them from reference spectra collected in darkness, a procedure that had a calculated lactate detection limit of 0.17 mM. We also reduced the O₂ in the inspired air to 13%, which decreased pO₂ from 94.5 ± 8.9 to 47.0 ± 6.8 mmHg, during visual stimulation at 2 or 4 Hz. At this low pO₂ level, visual stimulation did not cause lactate accumulation in the visual cortex, however. The present data show that neuronal activation to this degree in the cat brain is not associated with aerobic lactate production to an extent that can be detected with ¹H MRS.     

Changes in Cholinergic Markers Following Kainic Acid Lesion of the Ventral Globus Pallidus in Rat

Abstract: Choline acetyltransferase (CAT) and glutamate decarboxylase (GAD) activities and [³H] quinuclidinyl benzilate ([³H]QNB) binding were determined in the rat frontal cortex following damage to the basal forebrain cholinergic system. Pre- and postsynaptic changes in the cholinergic system with the passage of time werealso studied. After a unilateral injection of kainic acid into the right ventral globus pallidus, the GAD levels remained unaffected, but the CAT levels decreased to 63.4% after 7 days. After 12 weeks, the CAT levels had returned to 87% of the control value. The Umaxof [³H]QNB binding for the muscarinic receptor was higher in the ipsilateral cortex up to 4 weeks. On the other hand, the K_D value at 12 weeks was higher without a change in the Bmax of the [³H]QNB binding.
These findings might indicate an ongoing compensatory receptor mechanism of denervation supersensitivity as a response to early changes in presynaptic cholinergic activity and the production of postsynaptic effect with presynaptic cholinergic damage over a long period of time.     

[3H]Nitrendipine Binding to Rabbit Colonic Smooth Muscle

We used [³H] nitrendipine binding to isolated smooth muscle cells and isometric tension studies of muscle strips to characterize the calcium channels from rabbit proximal and distal colon. At 25°C [³H] nitrendipine binding was rapid, saturable, reversible, specific, and linearly proportional to cell number. The affinity of the ligand for its receptor was similar in proximal and distal colon (K_D 129 ± 21 pM and 124 ± 17 pM, respectively). In the proximal colon there were 68,000 receptors per cell, compared to 58,000 receptors per cell in the distal colon (p > .1). The Hill coefficient for nitrendipine was close to unity, suggesting binding to a single receptor. Although nitrendipine and nifedipine competitively inhibited [³H]nitrendipine binding, verapamil did not alter [³H] nitrendipine binding, suggesting the presence of at least two discrete, noninteracting sites for the binding of drugs that block calcium channels. In studies with muscle strips nitrendipine competitively inhibited isometric tension stimulated by both bethanechol and high extracellular potassium concentration. There were no significant differences in response from proximal and distal colon. These results suggest that calcium antagonist binding characteristics to calcium channels are similar in proximal and distal colon, and do not explain previously observed differences in the function of muscle in these tissues.     

Effect of Chronic Administration of Haloperidol (Intermittently) and Haloperidol-Decanoate (Continuously) on D2 Dopamine and Muscarinic Cholinergic Receptors and on Carbachol-Stimulated Phosphoinositide Hydrolysis in the Rat Striatum

Abstract: It has been reported that apomorphine-induced stereotypy is sensitized after a chronic intermittent administration of haloperidol (HPD), but not after a chronic continuous exposure to haloperidol-decanoate (HPD-D). The present study was undertaken to investigate changes in the D₂ dopamine and muscarinic receptors in the ratstriatum after the administration of HPD intermittently and HPD-D continuously. The number of striatal [³H] spiperone binding sites increased significantly after HPD-D, but did not change after HPD. Neither the number of [³H](–)QNB binding sites nor carbachol-stimulated phosphoinositide hydrolysis changed after either HPD or HPD-D. These results indicate that the increase in striatal D₂ receptors in rats administered HPD-D represents behavioral and biochemical tolerance, and that neither the D₂ dopamine receptor supersensitivity nor muscarinic receptor hyposensitivity underlies sensitization of apomorphine-induced stereotypy.     

Evidence For Two Neurochemical Divisions in the Human Nucleus Accumbens

The neurochemical anatomy of the human nucleus accumbens was studied by comparing the distributional patterns of [³H]DAMGE (μ opioid receptor), [³H]bremazocine (κ opioid receptor), [³H]SCH-23390 (D₁-like dopamine receptor), [³H]7-OH-DPAT (D₃ dopamine receptor) binding, preproenkephalin mRNA and acetylcholinesterase activity in sections of post mortem human striatum. Our results demonstrate the presence of at least two neurochemically distinct divisions within the human nucleus accumbens, which may be homologous to the 'shell'and'core'divisions of the nucleus as found in the rat.     

Time Course of Dopamine-D2 and Serotonin-5-HT2 Receptor Occupancy Rates by Haloperidol and Clozapine In Vivo

Abstract: In vivo occupancy of dopamine-D₁, D₂ and serotonin-5-HT₂ receptors by haloperidol 10 mg/kg and clozapine 20 mg/kg were studied. Rats were injected intravenously with [³H]-YM-09151-2, [³H]-SCH23390, or [³H]-ketanserin 10 min after the administration of the tested drugs. Fifteen to 240 min after the ligand injection, the receptor occupancy rates of the drugs in the striatum and frontal cortex were calculated. Clozapine demonstrated the higher 5-HT₂ and lower D₂ occupancies in the respective regions. A dose-response analysis of D₂ and 5-HT₂, receptor occupancy by the drugs consolidated the higher 5-HT₂ binding affinity of clozapine in comparison with haloperidol. The present methodology may serve as an accurate tool to evaluate the peculiarity of various antipsychotics.     

Competitive inhibition of phosphoinositide hydrolysis by the muscarinic receptor antagonist AF-DX 116 is of low affinity in mouse cerebral cortex

Carbamylcholine stimulated [³H]inositol phosphate accumulation in mouse cerebral cortical slices with an ED₅₀ value of approximately 70 μM. Increasing concentrations of the M₂ selective muscarinic cholinergic receptor antagonist, AF-DX 116 (0.3–3.0 μM), produced parallel shifts to the right for concentration-response curves to carbamylcholine. A pA₂ value for AF-DX 116 of 6.5 (low affinity) was obtained frommSchild plot analysis. It is concluded that the M₂ muscarinic receptor subtype, as defined by high affinity [³H]AF-DX 116 radioligand binding, is not appreciably coupled to polyphosphoinositide hydrolysis in the mouse cerebral cortex.     

Pentylenetetrazol-Induced Seizures Decrease γ-Aminobutyric Acid-Mediated Recurrent Inhibition and Enhance Adenosine-Mediated Depression

Summary: To elucidate the consequences of convulsions, we examined biochemically and electrophysiologically the brains of mice that had sustained two complete tonicclonic convulsions after administration of pentylenetetrazol (PTZ 50 mg/kg intraperitoneally, i.p.), 48 and 24 h before decapitation. Control mice were injected with saline. Input/output curves of the extracellular synaptic responses in the CAI area of hippocampal slices showed that PTZ-induced seizures do not establish the persistent change in hippocampal excitability itself that can be detected in vitro. However, use of the paired-pulse stimulation paradigm showed that γ-aminobutyric acid, (GABA)-mediated recurrent inhibition was significantly weaker (by 19–25%) in the CA1 area of slices from PTZtreated mice (PTZ slices) as compared with slices from control mice (control slices). The density of GABA, receptors (high-affinity component) was also lower in hippocampus (by 19%) and cortex (by 14%) of PTZ-treated mice. A GABA-related disinhibitory mechanism underlying PTZ seizures may thus persist for 1 day after the seizure, predisposing the brain to subsequent seizures. On the other hand, the depressant effect of a single dose of adenosine 10 μ M on the CA1 synaptic response was stronger (by 35% on population spikes) and longer lasting in PTZ slices as compared with controls. This could be attributed to significantly higher adenosine A₁ receptor density in hippocampus ( B _max of [³H]CHA was higher by 34%) as well as cortex and cerebellum of these animals. The phenomenon may reflect an adenosine A₁-mediated adaptive mechanism that offers protection from subsequent seizures.     

Muscarinic Cholinergic Receptors of the Convulsive Strain (E1) Mouse

Abstract: The biochemical characteristics of the muscarinic acetylcholine receptors were studied on the El strain mouse brain by the binding assay using [³H]l-quinuclydinyl benzylate. Scatchard analyses showed that the receptor density (B_max) of the hippocampus significantly decreased by 26.4% and the affinity (K_d) increased by 18.8% in El(+) compared to dd-Y. It is suggested that this hippocampal subsensitivity found in El(+) mouse might be strain-specific, because repeated megimide convulsions failed to produce the same down regulation.     

Reserpine Affects Differentially the Density of the Vesicular Monoamine Transporter and Dihydrotetrabenazine Binding Sites

We have studied the effect of a single injection of reserpine (5 mg/kg, s.c.) on the synaptic vesicle monoamine transporter (VMAT) density in the rat striatum, using two labelling procedures: radioimmunolabelling with an antibody against VMAT, and binding of the specific ligand [³H]dihydrotetrabenazine ([³H]TBZOH). In the rostral and medial striatum, the distribution of VMAT immunoreactivity displayed the highest density in the lateral subregions. In the caudal part of the striatum, VMAT immunoreactivity showed increasing density from dorsal to ventral subregions. The VMAT immunoreactivity was not altered 2 and 30 days after the reserpine injection, whereas [³H]TBZOH binding site density, measured on adjacent slices, showed a dramatic decrease at day 2 and a moderate recovery at day 30, suggesting that despite a persistent blockade of [³H]TBZOH binding sites, VMAT protein density was unchanged.     

A Comparative Study of α2- and β-Adrenoceptor Distribution in Pigeon and Chick Brain

The pharmacological properties and anatomical distribution of α₂, β₁ and β₂-adrenoceptors in pigeon and chick brains were studied by both homogenate binding and tissue section autoradiography. [³H]Bromoxidine (α₂-adrenoceptor-), [³H]CGP 12177 (β-adrenoceptor) and [¹²⁵1]cyanopindolol (β-adrenoceptor) were used as radioligands. In both species, [³H]bromoxidine binding to avian brain tissue showed a pharmacological profile similar to that previously reported for α₂-adrenoceptors in mammals. Regarding the anatomical distribution, the areas with the highest densities of α₂-adrenoceptors in the pigeon brain included the hyperstriatum, nuclei septalis, tectum opticum and some brainstem nuclei. Most β-adrenoceptors found in tissue membranes and sections from chick and pigeon brain were of the β₂ subtype, in contrast to what has been reported in the mammalian brain, where the β₁ subtype is predominant. A striking difference was found between the two species regarding the densities of these receptors: while pigeon brain was extremely rich in [¹²⁵1]cyanopindolol binding throughout the brain (mainly cerebellum) in the pigeon, the levels of labelling in the chick brain were much lower; the exception was the cerebellum, which displayed a higher density than other parts of the brain in both species. Overall, our results support the proposed anatomical equivalences between a number of structures in the avian and mammalian encephalon.     

Presynaptic Modulation of Glutamate Release Targets Different Calcium Channels in Rat Cerebrocortical Nerve Terminals

We have studied which type/s of Ca²⁺ -channel/s support glutamate exocytosis and its modulation by presynaptic receptors in cerebrocortical nerve terminals. Depolarization of nerve terminals with 30 mM KCI induced a Ca²⁺ -dependent release of 3.64 ± 0.25 nmol/mg of protein. The addition of either 2 μM ω-conotoxin-GVIA or 200 nM ω-agatoxin-IVA reduced the KCI-evoked release by 47.7 ± 3.5% and 70.4 ± 8.9% respectively, and by 85.7 ± 4.1% when both toxins were co-applied. The activation of adenosine A₁ receptors with N ⁶-cyclohexyladenosine or the activation of rnetabotropìc glutamate receptors with L(+)-2-amino-4-phosphonobutyrate inhibited the KCI-evoked release by 41.0 ± 5.9 and 54.3 ± 10% respectively. The extent of these inhibitions was not altered by the prior addition of 2 μM ω-conotoxin-GVIA but they were significantly enhanced when ω-agatoxin-IVA was added together with the adenosine A₁ receptor agonist or the metabotropic glutamate receptor agonist, suggesting that ω-conotoxin-GVIA-sensitive and not ω-agatoxin-IVA-sensitive Ca²⁺-channels are ínvolved in the action of these inhibitory receptors. By contrast, the facilitation of glutamate release that follows the activation of the protein kinase C, either with phorbol esters or with the stimulation of phospholipase C-linked metabotropic receptors, was expressed by both ω-conotoxin-GVIA-sensitive and ω-agatoxin-sensitive Ca²⁺-channels. It is concluded that different Ca²⁺-channels support the modulation of glutamate release by presynaptic receptors.     

Consequences of Transient Focal Cerebral Ischaemia for Second Messenger and Neurotransmitter Binding in the Rat: Quantitative Autoradiographic Analysis of Forskolin, Dopamine D1 Receptor Binding and Cerebral Blood Flow Changes

In order to study the consequences of reperfusion for ischaemic brain injury, quantitative ligand binding autoradiography was carried out in a model of reversible focal cerebral ischaemia. Endothelin-1 applied to the abluminal surface of the middle cerebral artery in anaesthetized Sprague-Dawley rats induced severe focal ischaemia and subsequent reperfusion (assessed by blood flow tracers [^99mTc]HMPAO and [¹⁴C]iodoantipyrine respectively) by 2 h after insult. Ligand binding autoradiography on consecutive sections demonstrated these blood flow changes to be associated with a significant reduction in forskolin binding throughout the middle cerebral artery territory (e.g. 25% in parietal cortex, 11% in dorsolateral caudate nucleus). The most marked losses in forskolin binding were in areas where ischaemia was severe and reperfusion was poor. However, the same changes in cerebral blood flow had no significant effect on D₁ dopamine receptor binding (e.g. >2% reduction in the caudate nucleus). These data demonstrate that ligand binding characteristics are significantly affected as early as 2 h after insult, with evidence of differential sensitivity for forskolin and D₁ dopamine binding. With regard to the consequences of reperfusion, comparison with our previous study of 2 h maintained ischaemia demonstrates reperfusion-related salvage of dopamine and forskolin binding in the caudate nucleus but possible exacerbation of forskolin binding loss in the cortex.