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.     

Light-microscopic distribution and parasagittal organisation of muscarinic receptors in rabbit cerebellar cortex

Recent studies on the effects of intrafloccular injections of muscarinic agonists and antagonists on compensatory eye movements in rabbit, indicate that muscarinic receptors may play a modulatory role in the rabbit cerebellar circuitry. It was previously demonstrated by Neustadt et al. (1988), that muscarinic receptors in rabbit cerebellar cortex are distributed into alternating longitudinal zones of very high and very low receptor density. In the present study, the zonal and cellular distribution of muscarinic receptors in the rabbit cerebellar cortex is investigated in detail using in vitro ligand autoradiography with the non-selective high-affinity antagonist [³H]quinuclidinyl benzilate (QNB), and the M2-specific antagonist [³H]AF-DX384, and immunocytochemistry with a monoclonal antibody specific for the cloned m2 muscarinic receptor protein. [³H]QNB and [³H]AF-DX384 binding sites and m2-immunoreactivity had similar overall distributions: dense labeling occurred in the dendritec arbors of a subset of Purkinje cells that are organized into parasagittal bands. A high level of muscarinic receptor labeling was also observed in a thin substratum of the molecular layer immediately above the Purkinje cell layer of the vestibulo-cerebellar lobules, i.e. the nodulus, the ventral uvula and the flocculus. Labeling in this stratum was associated with densely packed fibres, which were putatively identified as parallel fibres. Also Golgi cells, which were localized in part in the molecular layer, and a subset of mossy fibre rosettes, primarily concentrated in lobule VI, were immunoreactive for the m2 receptor. The parasagittal bands of labeled Purkinje cell dendrites were most prominent in the anterior lobe (lobules I–V), in crus 1 and 2, in the flocculus, the ventral paraflocculus and the rostral folium of the nodulus. In other lobules, only infrequent Purkinje cells contained muscarinic receptors. The parasagittal organisation of muscarinic receptors differed from that of zebrin I, a Purkinje cell-specific protein which is often used as a marker of parasagittal parcelation of the cerebellar cortex. In the anterior lobe, however, there was a partial correspondence between muscarinic receptor and zebrin I bands. In the flocculus the distribution of muscarinic-receptor-positive Purkinje cells was related to the distinct white matter compartments as revealed with acetylcholinesterase (AChE) histochemistry. Muscarinic receptor-containing Purkinje cells were located primarily in the floccular zone 1, which is implicated in the control of eye movements about a horizontal axis. In order to relate the distribution of muscarinic receptor labeling to that of cholinergic nerve terminals, [³H]QNB binding sites and sodium-dependent [³H]hemicholinium-3 binding were compared. Sodium-dependent [³H]hemicholinium-3 binding sites mainly occurred in the granule cell layer of the vestibulo-cerebellum, which corresponds well with the distribution of the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT). However, sodium-dependent [³H]hemicholinium binding complemented, rather than co-localized with, muscarinic receptors which were primarily distributed in the molecular layer of the lobules of the vestibulo-cerebellar lobules. Their functional significance is puzzling, since their distribution does not correspond to that of markers of cholinergic innervation.     

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 nicotinic [H]acetylcholine binding sites in rat brain

Quantitative autoradiography was used to localize nicotinic [³H]acetylcholine (ACh) binding sites in rat brain. High concentrations of nicotinic [³H]ACh binding sites were observed in the anterior and medial nuclei of the thalamus, the medial habenula and the superficial layer of the superior colliculus. Moderate levels of binding sites were observed in a variety of brain regions such as the frontoparietal cortex and the hippocampus. Low levels of nicotinic ACh sites occurred throughout the hypothalamus and the primary olfactory cortex.     

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.     

Localization of the dopamine uptake complex using [3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP) in rat brain

[³H]N-[1-(2-Benzo(b)thiophenyl)cyclohexyl]piperidine ([³H]BTCP) is a novel phencyclidine derivative with considerable selectivity for dopamine uptake sites. [³H]BTCP was used to label dopamine uptake sites in vitro, in rat brain, and the regions containing these sites were visualized with an autoradiographic technique. The binding was found to be highest in the striatum, where > 90% of binding was specific. Furthermore, 6-hydroxydopamine lesions of the nigrostriatal pathway obliterated striatal [³H]BTCP binding ipsilaterally, whereas ibotenic acid injection into the caudate-putamen failed to significantly reduce [³H]BTCP binding in that structure. These results indicate that [³H]BTCP labels dopamine uptake sites in mammalian brain and that it can be employed for autoradiographic studies of this transport complex.     

Dopaminergic innervation and binding in the rat cerebellum

In the present study, we used an antiserum against dopamine (DA), and specific [³H]ligands in order to shed more light on the dopaminergic system of the rat cerebellum. The immunocytochemical approach showed that the entire rat cerebellum is innervated by DA fibers. All cerebellar layers were found to receive a considerable amount of DA afferents but the molecular layer was the most heavily innervated. The analysis of [³H]DA and [³H]spiperone binding showed that in the rat cerebellum there exists DAergic binding with kinetic parameters similar to those reported for the mouse cerebellum. The results of the present study support the existence of a DA system in the rat cerebellum.     

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     

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.     

35S]tert.-butylbicyclophosphorothionate and avermectin bind to different sites associated with the gamma- aminobutyric acid-benzodiazepine receptor complex

Low concentrations of avermectin B₁a (AVM) stimulated the specific high affinity binding of [³⁵S]tert.-butylbicyclophosphorothionate ([³⁵S]TBPT) to membranes from rat cerebral cortex in the absence or presence of chloride or bromide ions. In contrast, TBPT either weakly stimulates or does not significantly influence the specific high affinity binding of [³H]AVM to the same membranes in the absence or presence of chloride ions, respectively. These results indicate that [³H]AVM and [³⁵S]TBPT bind to different but closely associated binding sites.     

Cerebellar excitatory amino acid binding sites in normal, granuloprival, and Purkinje cell-deficient mice.

Using quantitative autoradiography, the cellular localization and characterization of cerebellar excitatory amino acid binding sites in normal, Purkinje cell-deficient and granuloprival (granule cell-deficient) mouse cerebella were investigated. In the molecular layer of normal mouse cerebellum, the quisqualate subtype of excitatory amino acid receptor (assayed by [3H](RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate, quisqualate-sensitive L-[3H]glutamate, and [3H]6-cyano-7-nitroquinoxaline-2,3-dione binding) predominated. In the granule cell layer of the cerebellum, N-methyl-D-aspartate-sensitive L-[3H]glutamate and [3H]glycine binding sites were predominant. In the molecular layer of Purkinje cell-deficient mutant mice, [3H](RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate binding sites and [3H]6-cyano-7-nitro-quinoxaline-2,3-dione binding were reduced to 24% (P less than 0.01) and 36% (P less than 0.001) of control, respectively, while quisqualate-sensitive [3H]glutamate binding sites were reduced to 54% of control (P less than 0.01). N-Methyl-D-aspartate-sensitive [3H]glutamate and [3H]glycine binding were unchanged. In the granule cell layer of these mouse cerebella, there was no change in excitatory amino acid receptor binding. In the molecular layer of granuloprival mouse cerebella, [3H](RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate binding was increased to 205% of control (P less than 0.01), [3H]6-cyano-7-nitro-quinoxaline-2,3-dione binding was increased to 136% of control (P less than 0.02), and quisqualate-sensitive [3H]glutamate binding was increased to 152% of control (P less than 0.01). N-Methyl-D-aspartate-sensitive [3H]glutamate and [3H]glycine binding were unchanged. In areas of granule cell depletion N-methyl-D-aspartate-sensitive [3H]glutamate and [3H]glycine binding were reduced to 68% (P less than 0.01) and 59% (P less than 0.01) of control, respectively. In the granule cell layer, binding to quisqualate receptors was not significantly different from binding in controls with any of the ligands tested. These results suggest that three different receptor assays: [3H](RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate, quisqualate-sensitive L-[3H]glutamate, and [3H]6-cyano-7-nitro-quinoxaline-2,3-dione binding can be used to demonstrate that quisqualate receptor specific binding sites are located on Purkinje cell dendrites in the molecular layer of cerebellum, and that these binding sites apparently up-regulate in response to granule cell ablation and Purkinje cell deafferentation.     

Cerebellar benzodiazepine receptor distribution: an autoradiographic study of the normal C57BL/6J and Purkinje cell degeneration mutant mouse

The distribution of [3H]flunitrazepam binding sites in the cerebella of normal mice and Purkinje cell degeneration mutant mice was studied by light microscopic autoradiography. In the cerebellar cortex of normal mice, a high density of [3H]flunitrazepam binding was observed over the molecular layer, an intermediate density over the Purkinje cell layer and a low density over the granule cell layer; the white matter was devoid of labeling. The deep cerebellar nuclei were labeled to an intermediate density. In the 54-day-old Purkinje cell degeneration mutant cerebellum, which is depleted of Purkinje cells, a 36% reduction in labeling density of the cerebellar cortex was observed. The density was reduced by approximately equal amounts in both the molecular and granule cell layers; labeling in the deep cerebellar nuclei was, however, substantially increased.     

Muscarinic cholinergic receptors in the rat deep cerebellar nuclei: A quantitative autoradiographic study

The distribution of muscarinic cholinergic receptors within the rat deep cerebellar nuclei was analyzed using in vitro receptor binding of [³H]quinuclidinylbenzilate (QNB) in conjunction with autoradiography. The highest density of QNB binding sites occurred in the lateral cerebellar (dentate) nucleus. Interpositus nuclei displayed an intermediate density of muscarinic cholinergic binding sites with the posterior interpositus nucleus demonstrating higher binding than the anterior nucleus. The fastigial (medial) cerebellar nucleus exhibited the lowest levels of QNB binding among the four cerebellar nuclei. These results indicate that muscarinic cholinergic receptors are present in the deep cerebellar nuclei and that differences in receptor density occur among the four nuclear groups.     

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.     

Age-related decrease in GABAB receptor binding in the Fischer 344 rat i inferior colliculus

Quantitative receptor autoradiography was used to asses GABA_B receptor binding in three primary subdivisions of the inferior colliculus (IC): dorsal cortex (DCIC), external cortex (ECIC), and the central nucleus (CIC) of 3-, 18–20- and 26-month-old Fischer 344 rats. GABA_B binding sites were localized using [³H]GABA in the presence of a saturating concentration of isoguvacine, a selective GABA_A receptor agonist, to displace [³H]GABA bound to GABA_A receptor sites. In the three IC subdivisions examined, GABA_B receptor binding was significantly reduced in 26-month-old rats when compared to 3-month-old rats (DCIC, −44%; ECIC, −36%; CIC, −32%; p .05 For comparison, GABA_B binding was determined in the portion of cerebellum located in the recess of the IC. In the molecular layer of this region, there were no statistically significant differences in receptor binding between 3, 18–20- and 26-month-old rats. In addition, there was not a significant age-related change in the cross-sectional area of the IC. These findings provide additional evidence to support the existence of selective age-related changes in GABA neurotransmitter function in the rat IC.     

Daily variations in GABA receptor function in Syrian hamster cerebral cortex

The existence of diurnal changes in postsynaptic expression of γ-aminobutyric acid (GABA) type A receptors was assessed in cerebral cortex of Syrian hamsters by measuring [³H]GABA binding and the influx of ³⁶Cl⁻ in synaptoneurosomes. A diurnal variation in dissociation constant of [³H]GABA binding to cerebral cortex membranes, and the absence of diurnal differences in maximal number of sites, were found. When the nycthemeral changes in muscimol-stimulated ³⁶Cl⁻ uptake by cortical synaptoneurosomes were assessed, a maximum occurred late at night (i.e. 0400 h). At 1600 h, micromolar concentrations of flunitrazepam potentiated significantly the influx of chloride induced by muscimol, while at 0400 h flunitrazepam did not exert any significant effect on ³⁶Cl⁻ uptake. The results indicate that postsynaptic type A GABAergic activity peaked at nocturnal hours in the cerebral cortex of Syrian hamsters.     

Autoradiographic localization of binding sites for vasotocin in the brain and pituitary of the sea bass (Dicentrarchus labrax)

Specific binding sites for vasotocin (VT) were detected in brain and pituitary of a teleost fish, the sea bass, after in vitro incubation of tissue sections with [³H]arginine-vasopressin (AVP) and light microscopic autoradiography. Conditions for the binding assay were optimized and as a result the binding was saturable and specific. In the brain [³H]AVP binding was found to occur in the pars lateralis and the pars ventralis of the ventral telencephalon, in the pars centralis of the dorsal telencephalon, in the hypothalamic region (especially in the nucleus preopticus, in the tuberal hypothalamus and around the posterior recess), in the tectum opticum and in the noncellular layer of the corpus cerebelli. In the pituitary a high density of [³H]AVP binding was observed in the areas of the pars distalis (PD) occupied by ACTH-, TSH- and GH-cells and also in the pars intermedia (PI). The present study presents the first anatomical evidence for the presence of VT specific binding sites in teleost brain and pituitary.     

Spinal nerve ligation does not alter the expression or function of GABA(B) receptors in spinal cord and dorsal root ganglia of the rat

Several postmortem and neuroimaging studies suggest that central nicotinic and muscarinic acetylcholine receptors are important in both the pathophysiology and pharmacotherapy of schizophrenia. However, while antipsychotic drugs are routinely used in the therapeutics of schizophrenia, little is known about their effects on the densities of these receptors when they are administered for extended periods of time (a common practice in the clinical setting). In the present study in rats, the residual effects of prior chronic exposure to representative first generation antipsychotics and second generation antipsychotics on the densities of high affinity nicotinic acetylcholine receptors and muscarinic acetylcholine receptor in the brain were investigated. Test subjects were treated with the first generation antipsychotics, haloperidol (2.0 mg/kg/day) or chlorpromazine (10.0 mg/kg/day) or the second generation antipsychotics, risperidone (2.5 mg/kg/day) or olanzapine (10.0 mg/kg/day) in drinking water for periods of 90 or 180 days, given a drug-free washout period (i.e. returned to normal drinking water) for two weeks and then killed. Quantitative receptor autoradiography was subsequently performed using 16 μm sagittal slices of whole brain incubated with [³H]-epibatidine, [³H]-pirenzepine or [³H]-AFDX-384 to measure high affinity nicotinic acetylcholine receptors, M₁ and M₂ muscarinic acetylcholine receptors, respectively. The most notable experimental result was a moderate, but significant (P<0.01) increase in [³H]-AFDX-384 binding sites in a number of brain regions (including cortex, hippocampus, subiculum, substantia innominata, and thalamus) associated with prior exposure to olanzapine for 90, but not 180 days. Olanzapine was also associated with a significantly higher density of [³H]-pirenzepine binding sites in cortex lamina I after 90 days of prior drug exposure. These data indicate that chronic treatment with a commonly used second generation antipsychotic, olanzapine is associated with modest increases in M₂ muscarinic acetylcholine receptors in memory-related brain regions that may eventually abate with longer periods of chronic drug exposure.     

Localisation of dopamine D3 receptor in the rat cerebellar cortex: a light microscope autoradiographic study

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.     

Developmentally regulated changes of glutamate binding sites in mouse deep cerebellar nuclei

The expression of L-[³H]glutamate binding sites of different ionic and pharmacological sensitivities was studied in mouse deep cerebellar nuclei during early postnatal development by means of in vitro autoradiography. Ca²⁺/Cl⁻-dependent, quisqualate/AMPA/ibotenate-sensitive, and APB-insensitive binding sites are present at high density in the deep cerebellar nuclei of young animals, but greatly decrease between the 10th and 25th postnatal day and remain low in the adult. The density of Ca²⁺/Cl⁻-independent binding sites remains low and constant during the whole of postnatal development. The possible involvement of the Ca²⁺/Cl⁻-dependent binding sites in brain development is discussed.