Localization of NADPH-diaphorase activity in the salt gland of the saltwater-acclimated Pekin duck

The pharmacological properties and the anatomical localisation of dopamine D₃ receptor were assessed in the rat cerebellar cortex using radioligand binding techniques associated with light microscope autoradiography and 7-[³H]hydroxy-N,N-di-n-propyl-2-aminotetralin (7-[³H]OH-DPAT) as a ligand. 7-[³H]OH-DPAT was specifically bound to sections of rat cerebellar cortex with a dissociation constant (K_d) of 0.5 nM and a maximum density of binding sites (B_max) of 97 ± 4 fmol/mg tissue. The rank order of potency of competitors of 7-[³H]OH-DPAT binding and the observation that guanosine triphosphate did not affect radioligand binding suggest the labelling of a dopamine D₃ receptor. 7-[³H]OH-DPAT binding sites are located mainly in the molecular layer and in lesser amounts in the Purkinje neuron layer, primarily within the cell body of Purkinje neurons. No specific accumulation of silver grains was observed in the granule neuron layer or in the white matter of the cerebellar cortex. The localisation of a putative dopamine D₃ receptor within Purkinje neurons suggests that this site may have functional relevance in the cerebellar cortex.     

Retinal [125I]iodomelatonin binding sites in the tree shrew (Tupaiidae).

The characteristics of melatonin-binding sites labelled by [¹²⁵I]iodomelatonin in membrane preparations from the tree shrew retina were determined. Specific binding of [¹²⁵I]iodomelatonin to the membrane preparations of tree shrew retina was rapid, stable, saturable, and reversible. Among the indoles tested only 6-chloromelatonin, melatonin and N-acetylserotonin had significant affinities to the [¹²⁵I]iodomelatonin binding site. Scatchard analysis of the membrane preparations revealed a dissociation constant (K_d) of 51.0 ± 16 pM and total number of binding sites (B_max) of 1.97 ± 0.6 fmol/mg protein.     

Decreased density of beta-adrenergic and muscarinic cholinergic receptor sites in the vasa nervorum of aged rats

The pharmacological profile and the anatomical localization of beta-adrenergic and muscarinic cholinergic receptors of the vasa nervorum were studied in sections of sciatic nerve using radioreceptor binding and light microscope autoradiography techniques. Sprague—Dawley rats of 4 and 24 months of age were used. [³H]Dihydroalprenolol (DHA) and [³H]quinuclidinyl benzilate (QNB) were used to label beta-adrenergic and muscarinic cholinergic receptors, respectively. The ligands were bound to sections of rat sciatic nerve in a manner consistent with the labelling of beta-adrenergic or muscarinic cholinergic receptors in the 2 age groups investigated. The dissociation constant (K_d) values (about 1.37 nM for [³H]DHA and 0.75 nM for [³H]QNB) did not significantly change between 4- and 24-month-old rats. The maximum concentration of binding sites (B_max) for [³H]DHA was decreased by about 35% in 24 in comparison with 4-month-old rats. The B_max value autoradiogaphy revealed the development of specific silver grains in the medial layer of epineurial and perineurial arteries in sections of sciatic nerve exposed either to [³H]DHA or [³H]QNB. The number of silver grains developed in epineurial and perineurial arteries of rats of 24 months is significantly lower than in animals of 4 months. The above results suggest the occurrence of an age-dependent loss in the density of beta-adrenergic and muscarinic cholinergic receptors of vasa nervorum.     

Binding characteristics and regional distribution of [I]iodomelatonin binding sites in the brain of the human fetus

The binding and pharmacological characteristics of [¹²⁵I]iodomelatonin binding sites in human fetal brain membrane preparations were determined. Membrane preparations of the whole brain revealed a equilibrium binding constant (K_d) of 17.5 pmol/l with a total number of binding sites (B_max) at 0.8 fmol/mg protein. Among the various brain regions studied, [¹²⁵I]iodomelatonin binding was highest in the hypothalamus, and lowest in the mid-brain, pons-medulla, and cerebral cortex. The K_d of the hypothalamus was calculated to be 26.1 pmol/l and the B_max 5.4 fmol/mg protein. Only 6-chloromelatonin, melatonin and N-acetylserotonin had significant inhibition in the binding. Our results suggest that melatonin receptors are present in the human brain and that melatonin may exert a central action.     

Oocytes from Xenopus laevis contain an intrinsic σ2-like binding site

In preparation for expression studies for rat brain σ-binding sites, Xenopus oocytes were tested for the presence of [³H]di-o-tolylguanidine (DTG)-binding sites. Native oocytes were found to contain two intrinsic [³H]DTG-binding sites, a high-affinity site (K_d = 32 ± 6 nM, B_max of 45.7 ± 19 pmol/mg protein) and a low-affinity binding site (K_d = 1.3 ± 0.7 μM, B_max of 3.2 ± 0.7 nmol/mg protein). In a series of radioligand-binding-displacement studies, the high-affinity binding sites were found to have a binding profile which has a similar K_d to that of the mammalian σ₂-binding site (32 vs. 38 nM). Comparison of the IC₅₀ values for inhibition of [³H]DTG binding in rat liver and oocytes for DTG, haloperidol (HAL), (−)-pentazocine, (+)-3-(3-hydroxyphenyl)-N-propylpiperidine hydrochloride ((+)-3-PPP), (+(-pentazocine and Zn²⁺, showed similarity in rank (r² = 0.913) but a 7-fold lower potency in oocytes. These results suggest that the high-affinity [³H]DTG-binding site in oocytes represents a σ₂-like binding site.     

Age-correlated loss of dopamine uptake sites labeled with [H]GBR-12935 in human putamen

The effects of age (19–100 years) upon dopamine uptake sites labeled with [³H]GBR-12935 in human postmortem putamen from 20 individuals were studied. There was a 70% decrease in binding density (B_max) over the adult age range. No significant changes in binding affinity (K_d) were detected, the mean K_d being 1.0 ± 0.2 NM (mean ± S.E.M.). Nor were there any changes in binding related to the postmortem delay. Based on the findings that [³H]GBR-12935 labels the uptake site for dopamine, it is suggested that the age-related loss of [³H]GBR-12935 binding in human putamen reflects a degeneration of dopamine neurites.     

Adenosine A1 receptors in human hippocampus: inhibition of [H]8-cyclopentyl-1,3-dipropylxanthine binding by antagonist drugs

Adenosine A₁ receptors were visualized in human hippocampus using [³H]8-cyclopentyl-1,3-dipropylxanthine (DPCPX) as a radioactive ligand probe. The receptor antagonists caffeine, the xanthine derivative KFM 19 and the carbamazepine analogue oxcarbazepine displaced [³H]DPCPX binding homogeneously without any marked difference between the individual layers in the investigated hippocampal subregions (n = 4). K_i's in the individual layers were in a range between 8.5 ± 6.5 μM and 18.9 ± 16.0 μM for caffeine and 11.5 ± 2.8 nM and 18.1 ± 14.1 nM for KFM 19.K_i's could not be calculated for oxcarbazepine as the IC₅₀'s were greater than 100 μM with estimated IC₂₅'s varying between 51.2 ± 53.3 μM and 179.9 ± 89.9 μM. Antagonism of endogenous adenosine at A₁ receptors may thus explain part of the clinical effects of caffeine in humans and possibly exclusively the behavioral effects of KFM 19 in non-human primates.     

Influence of age on L-type Ca2+ channels in the pulmonary artery and vein of spontaneously hypertensive rats

The influence of age on the density and localization of L-type Ca²⁺ channels was studied during development of hypertension in the pulmonary artery and vein of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar–Kyoto (WKY) rats by radioligand binding assay and light microscope autoradiography. SHR were examined at 6 weeks (juvenile, pre-hypertensive stage), 12 weeks (young, developing hypertension) and 24 weeks (mature, established hypertension). The dihydropyridine-type Ca²⁺ antagonist [³H]nicardipine was used as a radioligand. It was bound specifically to sections of rat pulmonary artery and vein. Dissociation constant (K_d) values were similar in WKY rats and SHR, whereas maximum density of binding sites (B_max) values increased in SHR in comparison with WKY rats. This increase was noticeable from the pre-hypertensive phase. The pharmacological profile of [³H]nicardipine binding was similar in different age groups of either normotensive and hypertensive rats. Quantitative analysis of autoradiographs from SHR revealed a progressive increase of silver grains in smooth muscle of tunica media and to a lesser extent in the adventitia of pulmonary artery but not of pulmonary vein from pre-hypertensive stage to developing hypertension. No further changes were observed in established hypertension. The above data indicate that the density of L-type Ca²⁺ channels of pulmonary arteries is increased in SHR. This augmentation after the pre-hypertensive phase suggests the occurrence of dysregulation of Ca²⁺ handling in the pulmonary vasculature of developing SHR.     

Slow isomerization step in the interaction between mouse dopamine transporter and dopamine re-uptake inhibitor N-(3-iodoprop-2E-enyl)-2beta-carbo-[3H]methoxy-3beta-(4'-methylphenyl)nortropane

The kinetics of the association and dissociation of the tritium-labeled selective and potent dopamine transporter inhibitor N-(3-iodoprop-2E-enyl)-2β-carbo-[³H]methoxy-3β-(4′-methylphenyl)nortropane ([³H]PE2I) with the transporter of mouse striatal membranes was studied. The analysis revealed that the specific binding of [³H]PE2I occurs within a homogeneous population of binding sites in these membranes. The relatively slow binding process was characterized by the pseudo-first-order rate constant k_obs. The plot of these rate constants versus free radioligand concentration was hyperbolic, demonstrating that at least two kinetically distinguishable steps can be identified in the interaction of dopamine transporter with this inhibitor. The fast and reversible binding step, characterized by dissociation constant K_A = 51 ± 23 nM, is followed by a slow but also reversible isomerization step of the complex, characterized by the isomerization rate constant k_i = (7 ± 2)10⁻² s⁻¹ and by the rate constant k_−i = (3.9 ± 0.5)10⁻³ s⁻¹ for the reverse process. This isomerization step increases the apparent affinity of the ligand and probably consists of a conformational transition of the transporter protein, induced by the inhibitor molecule.     

Distribution of dopaminergic receptors in the primate cerebral cortex: Quantitative autoradiographic analysis using [H]raclopride, [H]spiperone and [H]SCH23390

A widespread distribution of dopamine D₁ receptors in the neocortex is well recognized. However, the presence of dopamine D₂ receptors in this structure has only recently been established [Martres et al. (1985) Eur. J. Pharmac.118, 211–219; Lidow et al. (1989) Proc. natn. Acad. Sci. U.S.A.86, 6412–6416]. In the present paper, a highly specific antagonist, [³H]raclopride, was used for autoradiographic determination of the distribution of D₂ receptors in 12 cytoarchitectonic areas of the frontal, parietal, and occipital lobes of the rhesus monkey. A low density of D₂-specific [³H]raclopride binding (1.5–4.0 fmol/mg tissue) was detected in all layers of all cortical areas studied. Throughout the entire cortex, the highest density of binding was consistently found in layer V. This is a unique distribution not observed so far for any other neurotransmitter receptor subtype in monkey cerebral cortex, including D₁ receptor. In addition, a comparison was made of the distribution of [³H]raclopride and [³H]spiperone, which has been commonly used in previous attempts to label cortical D₂ receptors. We found marked differences in the distribution of these two radioligands. In the prefrontal cortex, the pattern of [³H]spiperone binding in the presence of ketanserin resembled the combined distribution of 5-HT_ic serotoninergic and ₂-adrenergic sites as well as D₂ receptors. Thus, [³H]raclopride provides a better estimation of the D₂ receptor distribution than does [³H]spiperone. The distribution of D₂-specific binding of [³H]raclopride was also compared with the D₁-specific binding of [³H]SCH23390 in the presence of mianserin to block labeling to 5-HT₂ and 5-HT_IC sites. The density of D₁-specific [³H]SCH23390 binding was 10–20 times higher than that of D₂-speciflc [³H]raclopride binding throughout the cortex. The densities of both [³H]raclopride and [³H]SCH23390 binding sites display a rostral-caudal gradient with the highest concentrations in prefrontal and the lowest concentrations in the occipital cortex. However, the binding sites of these two ligands had different laminar distributions in all areas examined. In contrast to preferential [³H]raclopride binding in layer V, a bilaminar pattern of [³H]SCH23390 labeling was observed in most cytoarchitectonic areas, with the highest concentrations in supragranular layers I, II and IIIa and infragranular layers V and VI. Whereas [³H]raclopride binding was similar in all cytoarchitectonic areas, [³H]SCH23390 exhibited some region-specific variations in the primary visual and motor cortex.

The different regional and laminar distributions of D₁ and D₂ dopaminergic receptors indicates that they may subserve different aspects of dopamine function in the cerebral cortex.     

Quantitative autoradiography of [H]prazosin binding sites in rat forebrain

We have used the LKB Ultrofilm method of autoradiography to localize and quantify in rat forebrain the binding sites for [³H]prazosin, a highly-selective antagonist for the ₁ adrenoreceptor subtype. Frozen 32 μm thick brain sections were labeled in vitro with 1 nM [³H]prazosin and applied against LKB Ultrofilm for 60 days to generate autoradiograms. Non-specific binding was defined as the labeling in the presence of 10 μM phentolamine. The highest levels of prazosin binding were found in layer V of the motor portion of the frontoparietal cortex and in all nuclei of the thalamus. Moderate levels of ₁ receptors were observed in the remaining layers of the cerebral cortex and in most regions of the limbic system. Low levels of prazosin binding occurred in the caudate-putamen and the accumbens nucleus. Our results indicate that ₁ adrenoreceptors are distributed heterogenously throughout the rat forebrain.     

Distribution and postnatal ontogeny of adenosine A2A receptors in rat brain: comparison with dopamine receptors

In adult rat brain, adenosine A_2A receptors and dopamine D₂ receptors are known to be located on the same cells where they interact in an antagonistic manner. In the present study we wanted to examine when this situation develops and compared the postnatal ontogeny of the binding of the adenosine A_2A receptor agonist [³H]CGS 21680, the binding of the dopamine D₁ receptor antagonist [³H]SCH 23390 and the dopamine D₂ receptor antagonist [³H]raclopride.

All three radioligands bound to the striatum at birth and this binding increased several-fold during the postnatal period. [³H]SCH 23390 binding developed first (mostly during the first week), followed by [³H]raclopride binding (first to third week) and [³H]CGS 21680 binding (only during second and third week). For all three radioligands the binding tended to decrease between 21 days and adulthood. This occurred earlier and was more pronounced in the globus pallidus than in the other examined structures. The increase in [³H]CGS 21680 binding from newborn to adult was mainly due to four-fold increase in the number of binding sites. The pharmacology of [³H]CGS 21680 binding to caudate–putamen was similar in newborn, one-week-old and adult animals, and was indicative of A_2A receptors. The binding was inhibited by guanylyl imidodiphosphate at all ages, indicating that A_2A receptors are G-protein-coupled already at birth. In contrast to the large increase in [³H]CGS 21680 binding, there was a decrease in the levels of A_2A messenger RNA during the postnatal period in the caudate–putamen. In cerebral cortex [³H]CGS 21680 bound to a different site than the A_2A receptor. From birth to adulthood cortical binding of [³H]CGS 21680 increased four-fold and that of the adenosine A₁ agonist [³H]cyclohexyladenosine 19-fold. During early postnatal development [³H]SCH 23390 binding was higher in deep than in superficial cortical layers, but this difference disappeared in adult animals. There was binding of both [³H]CGS 21680 and [³H]cyclohexyladenosine to the olfactory bulb, suggesting a role of the two adenosine receptors in processing of olfactory information. [³H]CGS 21680 binding was present in the external plexiform layer and glomerular layer, and increased during development, but the density of binding sites was about one tenth of that seen in caudate–putamen. [³H]cyclohexyladenosine showed a very different labelling pattern, resembling that observed with [³H]SCH 23390.

Postnatal changes in adenosine receptors may explain age-dependent differences in stimulatory caffeine effects and endogenous protection against seizures. Since A_2A receptors show a co-distribution with D₂ receptors throughout development, caffeine may partly exert such actions by regulating the activity of D₂ receptor-containing striatopallidal neurons     

Acquisition of lipoproteins in the procyclic form of Trypanosoma brucei

The procyclic form of Trypanosoma brucei binds and internalizes bovine high density lipoprotein (HDL) particles in a saturable process; the binding and uptake of ¹²⁵I-labeled HDL are inhibited by excess unlabeled HDL. We calculated that each procyclic trypanosome exposes ≈1.0×10⁶ binding sites for bovine HDL, with an equilibrium dissociation constant (K_d) of ≈1.26×10⁻⁷ M. Uptake of HDL particles does not occur at 4°C. At 28°C, a significant amount of the internalized HDL particles were efficiently degraded through a process that is sensitive to the presence of 50 μM chloroquine. These results suggested that the uptake of HDL particles in procyclic T. brucei may occur via receptor mediated endocytosis, leading to proteolytic degradation of the particles in an acidic and endocytic compartment.     

Carotid body amine levels in goats exposed to hypoxia or hypercapnia

The μ-opioid receptor agonist stimulation of low-K_m GTPase in rat striatal membranes was abolished by islet-activating protein (IAP) treatment, and recovered by Gi reconstitution. When the IAP-treated membranes were phosphorylated with a cAMP-dependent protein kinase, there was no such recovery by Gi. The agonist binding was not affected with respect to K_d, B_max and sensitivity to guanine nucleotides in the phosphorylated membranes. These findings suggest that phosphorylation of μ-opioid receptors dissociates the agonist change in G-protein activity from the guanine nucleotide-sensitive agonist binding.     

Binding of platelet-activating factor to platelets of Alzheimer''s disease and multiinfarct Dementia patients

The binding of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor, PAF) to platelets was studied in 22 patients with probable Alzheimer's disease (AD), 11 with multi-infarct dementia (MID), 22 age-matched normal old controls, and 20 young subjects. The results showed a significantly lower degree of PAF binding to platelets of AD and MID patients than in those of the old controls and young subjects (133.3 ± 8.5, and 123.4 ± 16.5 vs. 202.3 ± 11.6 and 206.7 ± 17.3 receptors/cell, respectively; p < 0.01). These differences were due to reduced B_max, while K_d remained unchanged. No significant difference was observed between the PAF binding to platelets of AD and MID patients nor between that of old and young controls. No correlation was found between age and binding in the various elderly groups. However, a significant correlation was found between PAF binding and degree of cognitive impairment in the AD patients. This is the first evidence to support a possible involvement of PAF in dementing disorders.     

GABA enhances acetylcholine release from hippocampal nerve endings through a mechanism blocked by a GABA uptake inhibitor

The effect of γ-aminobutyric acid (GABA) on the release of [³H]acetylcholine ([³H]ACh) was investigated using superfused rat hippocampal synaptosomes. GABA enhanced the basal efflux of [³H]ACh. The effect of GABA was bicuculline-insensitive. Muscimol, (±)-baclofen or (−)-baclofen did not increase [³H]ACh release. The effect of GABA was counteracted by SK&F 89976 A (N-(4,4-diphenyl-3-butenyl)-nipecotic acid), a GABA uptake inhibitor. One possible interpretation of the results is that a GABA transport system is present on cholinergic terminals, suggesting that GABA and ACh may coexist in some rat hippocampus nerve endings. Another possibility is that the effect of GABA is mediated by a novel subtype of GABA receptor sensitive to SK&F 89976 A.     

Acetylcholinesterase activity of Xenopus laevis oocytes

The cholinesterase activity of Xenopus laevis oocytes was assessed using [³H]acetylcholine in a simple radiometric procedure. The cholinesterase activity of mature (stage V–VI) oocytes was very sensitive to inhibition by the specific acetylcholinesterase inhibitor, BW284-C51, and relatively insensitive to an inhibitor of non-specific, or butyrylcholinesterase. The K_m and v_max of the acetylcholinesterase measured in homogenates of oocytes were 312 μM and 4.6 nmol-oocyte⁻¹-h⁻¹, respectively. Triton X-100 increased the enzyme activity of homogenates four- to five-fold while collagenase treatment displaced into the medium none of the acetylcholinesterase activity from either homogenates or intact oocytes. Cations were found generally to diminish the acetylcholinesterase activity of oocyte homogenates, and lanthanum ions inhibited acetylcholine hydrolysis with an IC₅₀ of 0.63 mM. Subcellular fractionation of oocytes revealed that the bulk of enzyme activity was associated with particulate fractions. Acetylcholinesterase activity was also detected on the surface, and in homogenates, of immature oocytes. Peak enzyme activity resided in stage IV oocytes. Eggs obtained from females induced to spawn were found to have acetylcholinesterase activity in homogenates but little or no hydrolytic activity was detected on the egg surface. These results provide a point of departure for further investigations of the functional significance of this enzyme in Xenopus oocytes.     

Quantitative autoradiography of dopamine D2 sites in rat caudate-putamen: Localization to intrinsic neurons and not to neocortical afferents

Dopamine D₂ receptors, labeled with [³H]spiroperidol or [³H]sulpiride, show a lateral-to-medial gradient in the caudate-putamen, with a more than two-fold greater density laterally than medially. It has been thought that D₂ receptors are located on at least two neuronal elements of the caudate-putamen, neurons intrinsic to this structure and axons whose cell bodies reside in the cortex. As a first step in establishing what neuronal elements underlie this heterogeneous organization of D₂ receptors, we took advantage of quantitative autoradiography to examine the association of these receptors with those elements. The present findings show that the D₂ sites are almost exclusively located on neurons whose somata reside in the caudate-putamen and are not located on terminals of corticostriatal axons. A detailed comparison of the distribution of histochemically identified acetylcholinesterase neurons with that of D₂ receptors in serially adjoining sections suggests a common organizational pattern.

The density of [³H]spiroperidol sites in rat caudate-putamen was determined after unilateral injection of the neurotoxin quinolinic acid into this structure or after ablation of neocortical regions. Quantification of the tissue damage was achieved by acetylcholinesterase histochemistry (following diisopropylfluoro-phosphate treatment), as well as by thionin and luxol fast staining of sections adjacent to those used for [³H]spiroperidol autoradiography. In identically treated animals, biochemical determination of the extent of tissue damage was made utilizing assays for high-affinity [³H]choline and [³H]glutamate uptake in the caudate-putamen. In quinolinic acid-injected rats, the density of D₂ sites was decreased by 90–95% at the site of complete loss of large acetylcholinesterase-positive neurons. Other animals, given ablations of specific neocortical fields (medial prefrontal, motor, somatosensory) or of the entire parietal-frontal cortex of one hemisphere, showed no loss of caudate-putamen D₂ sites unless the cortical ablation caused accompanying damage of the caudate-putamen. In the caudate-putamen of all animals there was a close correspondence between the D₂ sites and the striatal neurons (and processes) that show strong acetylcholinesterase reactivity.

We suggest that the caudate-putamen topography of D₂ sites is based largely on the internal organization of this structure and may preferentially involve acetylcholine-containing intrinsic neurons.     

Binding of thyroid hormones by nuclei of target tissues during the chick embryo development

In the present studies we have compared the ontogeny of the binding of thyroxine (T4) and triiodothyronine (T3) to isolated nuclei from various target tissues of chick embryo. We observed a marked difference between the patterns of Satchard plots, maximal binding capacities (MBC) and association constants (K_a) of T4 and those of T3. Scatchard plots revealed that T4 and T3 had different binding sites. In liver, brain and lung MBCs and K_as of T3 and T4 were rather similar at day 9, but during the following days (12–19) T3 MBCs and K_as showed small changes, whereas T4 MBC markedly increased (4–5-fold) and T4 K_a significantly declined. In liver, for instance, T3 MBC = 395 ± 19 (day 9) and 489 ± 66 fmol/mg protein (day 19); T4 MBC = 631 ± 6.5 (day 9) and 2201 ± 516 fmol/mg protein (day 19); T4 K_a = 1.92 ± 0.01 (day 9) and 0.56 ± 0.21 X 10⁸ M⁻¹ (day 19). These data indicate that, during chick embryogenesis, nuclei of target tissues contain multiple T4 binding proteins, but only a single T3 binding site.     

Distribution of [H]kainic acid and binding sites in the rat brain: in vivo and in vitro receptor autoradiography

Brain sections incubated in vitro with a-[³H]kainic acid (KA; spec. act. 62.5 Ci/mmol), reveal a heterogenous distribution of low and high affinity KA binding sites in the brain. The highest density of KA binding sites was localised to the hippocampus CA₃ region and to superficial layers of the entorhinal cortex (3.8 6.0 μCi/g tissue). Intravenous injection of [³H]KA (1 μCi/g) reveals limited overall penetration of [³H]KA across the blood-brain barrier. However, a dense labelling of the hippocampus, entorhinal cortex and lateral septal regions (2.5–3.8 μCi/g tissue) was observed. Behaviourally, these rats exhibited mild limbic seizure activity possibly as a result of a direct action of KA in the hippocampus or entorhinal cortex.