Kathleen Hauser

Alteration of central alpha2- and beta-adrenergic receptors in the rat after DSP-4, a selective noradrenergic neurotoxin

A peripheral injection of DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] produced a marked, selective, and lasting depletion of norepinephrine in certain regions of the rat central nervous system. This depletion at 10 days after injection was associated with regional alterations in some, but not all, adrenergic binding sites (receptors) as determined by in vitro [3H]prazosin (alpha 1), [3H]p-aminoclonidine (alpha 2), and [3H]dihydroalprenolol (beta) binding. The neocortical alpha 1-receptor was not changed. The alpha 2-receptor in several regions was altered as indicated by an increase in ligand affinity; additionally, the density of this receptor was slightly decreased in some regions. Depending on the region, the beta-receptor either increased in density or was unchanged. The increased density of this receptor in neocortex corresponded to an increased activity of isoproterenol-sensitive adenylate cyclase. These two changes were not affected by subchronic treatment with desipramine, a norepinephrine uptake inhibitor. The changes were, however, partially or completely reversed by subchronic administration of clenbuterol, a centrally-acting beta-receptor agonist. The dopaminergic receptor in various regions was unaltered as assessed by in vivo and/or in vitro binding of [3H]spiperone. The in vivo binding of this ligand also indicated that the serotoninergic receptor in frontal neocortex was unchanged. Assessment of adrenergic receptors in neocortex at 50 days after injection indicated only the above affinity change of the (presumably postsynaptic) alpha 2-receptor. The alpha 1-receptor remained unaltered. The density of the beta-receptor had normalized, as had the activity of isoproterenol-sensitive adenylate cyclase. Implicit in these findings is the following rank order of receptor sensitivity to chronic norepinephrine depletion: alpha 2 greater than beta greater than alpha 1. The use of DSP-4 has clear advantages over other methods of depleting central norepinephrine. This neurotoxin can be administered by intraperitoneal injection, the depletion of norepinephrine can be readily checked by absence of the post-decapitation reflex, and the changes in other neurotransmitter concentrations are relatively minor or nonexistent. The alteration of alpha 2- and beta-receptors, as a consequence of DSP-4 treatment, may form the basis of a new animal model of adrenergic receptor supersensitivity. Such a model may clarify the importance of these central receptors to physiological and behavioral processes.

Topography of substantia nigra innervation by D1 receptor-containing striatal neurons.

Iodinated SCH 23390, [125I]SCH 23982, saturably binds in brain to D1 receptors that mostly reside on striatal and striatonigral neurons. [125I]SCH 23982 autoradiography was used to determine the topography of D1 receptor-containing striatal inputs to subregions of the substantia nigra. The concentration of D1 sites was greatest in the pars reticulata of the substantia nigra and exceeded by over 50% the equal concentrations of D1 sites in the lateral substantia nigra, caudate-putamen, nucleus accumbens, and olfactory tubercle. D1 receptors were uniformly concentrated throughout the caudate-putamen and were absent in the pars compacta of the substantia nigra and ventral tegmental area. Injections into the rostral striatum of the axon-sparing neurotoxin, quinolinic acid, depleted the concentration of D1 sites in the rostral caudate-putamen by 98% and the concentration of D1 sites in the medial substantia nigra by up to 74%. Quinolinic acid-induced losses of the D1 sites in the central striatum of up to 85% were associated with 87% losses of D1 sites in the central nigra. D1 losses of 91% in the caudal striatum were associated with D1 losses of 85% in the lateral nigra. Thus, most D1 sites in the striatum reside on neurons that are intrinsic to that brain region, and the vast majority of D1 sites in the substantia nigra are on the terminals of striatonigral neurons. These D1 receptor-containing striatonigral neurons have a rostral, central, or caudal origin in the striatum and a corresponding medial, central, or lateral termination in the nigra. This topographical organization of striatal inputs to the substantia nigra indicates that substance P or dynorphin B-containing striatonigral neurons may have D1 receptors on their terminals.

Oxaprotiline, a noradrenaline uptake inhibitor with an active and an inactive enantiomer

Abstract The new antidepressant drug, oxaprotiline, and its two enantiomers were investigated with respect to their effects on noradrenaline (NA) and serotonin (5-HT) uptake in vitro and in vivo after acute and repeated treatment. Moreover, the alpha-adrenolytic effects in vitro were also studied. Oxaprotiline proved to be a highly potent and selective inhibitor of NA uptake in rat synaptosomal preparations in vitro and in the rat heart and brain in vivo The NA uptake-inhibiting properties were found to be confined entirely to the (+)- or S-enantiomer: (−)- or R-oxaprotiline, the absolute configuration of which corresponds to that of the naturally occurring (−)-NA, was about 1000 times less potent than the (+)-form in vitro , and was inactive in vivo at doses exceeding the ED 50 of the latter 100-fold. The selectivity of oxaprotiline with respect to NA uptake inhibition was retained after 10 daily administrations. No sign of cumulation or attenuation of the effect was evident. No uptake-inhibiting effect of (−)-oxaprotiline appeared after 10 daily administrations of high doses, indicating that no racemization occurred in the organism. The α 1 -adrenoceptor antagonistic effect of oxaprotiline, as determined by the ability to displace [ 3 H]prazosin, was in the range of that of imipramine, the (−)-enantiomer being somewhat more potent than the (+)-form. In contrast to imipramine, oxaprotiline was devoid of α 2 -adrenoceptor antagonistic effects, as judged by the ability to affect the impulse-related release of [ 3 H]NA from rat cortical slices. Since oxaprotiline proved to be an effective antidepressant, clinical testing of its two enantiomers might be helpful with respect to the validation of the catecholamine hypothesis of depression. Moreover, in animal studies, they might help to determine which effects of antidepressants are related to NA uptake inhibition and which are not.

NKP608: a selective NK-1 receptor antagonist with anxiolytic-like effects in the social interaction and social exploration test in rats.

NKP608 is a non-peptidic derivative of 4-aminopiperidine which acts as a selective, specific and potent antagonist at the neurokinin-1 (NK-1) receptor both in vitro and in vivo. In vitro, the binding of NKP608 to bovine retina was characterized by an IC50 of 2.6+/-0.4 nM, whereas the compounds affinity to other receptor binding sites, including NK-2 and NK-3, was much lower. Species differences in IC(50) values with NKP608 were less pronounced than with previously described NK-1 receptor antagonists, being 13+/-2 and 27+/-2 nM in gerbil midbrain and rat striatum, respectively. In vivo, using the hind foot thumping model in gerbils, NKP608 exhibited a potent NK-1 antagonistic activity following oral administration (ID(50)=0.23 mg/kg; 2 h pretreatment), supporting a central activity of NKP608. The compound had a long duration of action with an ID(50) value of 0. 15 mg/kg p.o. and 0.38 mg/kg p.o. following a pretreatment of 5 and 24 h, respectively. Following a subchronic administration for 7 consecutive days (once daily) there was no evidence for the development of tolerance or accumulation. In the social interaction test performed in a highly illuminated, unfamiliar test arena, NKP608 specifically increased the time the two rats spent in social contact, and there was no concomitant increase in parameters reflecting general activity, i.e. ambulation (number of square entries) or the number of rearings. Active social time was maximally increased at a dose range of 0.01-1 mg/kg p.o. NKP608, the effect being weaker or absent at both lower (0.001 mg/kg p.o.) and higher (10 mg/kg p.o.) doses. A comparable bell-shaped dose-response relation was seen in the social exploration test in rats. In this modified resident/intruder paradigm, maximal increase in social contact of the intruder rat directed towards the resident rat was seen at a similar dose range (0.03-3 mg/kg p.o.) The effects observed following an acute oral administration of NKP608 were comparable to those seen following a treatment with the well-known benzodiazepine, chlordiazepoxide, in both these tests. These findings indicate that NKP608 exhibits an anxiolytic-like effect and that this effect, as concluded from the observed antagonism of the hind foot thumping induced by i.c.v. administration of the NK-1 receptor agonist SPOMe, is centrally mediated. This makes this compound a potentially promising candidate for treating anxiety-related disorders in humans.

SAR of 2-benzyl-4-aminopiperidines: CGP 49823, an orally and centrally active non-peptide NK1 antagonist

Abstract Novel 2-benzyl-4-aminopiperidines have been shown to be potent and selective antagonists at the NK 1 receptor. Some compounds of this series, e.g. CGP 49823 ( 2 ), show CNS activity after oral administration.

Development of GABA neurons in dissociated cell culture of rat cerebral cortex

Abstract Cortical neurons dissociated from newborn rat brain were maintained on supporting glial monolayers in the presence of the mitotic inhibitor, FUdR. The ability of this type of primary culture (NG) to synthesize, store, metabolize, accumulate and release GABA was compared to that of neuron-free glial monolayers (G) cultured under the same conditions. While NG cultures synthesized and stored GABA, there was little GABA, or GABA-synthesizing activity (GAD) in G cultures. In contrast, appreciable activities of the GABA catabolizing enzyme, GABA-T, were present in both cultures. Furthermore, accumulation of GABA by high affinity uptake and K + -stimulated release of GABA were associated exclusively with the neurons. Morphological differentiation, GABA metabolism, uptake and release increased with increasing time in culture. The present evidence suggests that the NG preparation may represent a good model system to study GABA-mediated transmission in culture.

Subchronic infusion of clenbuterol, a beta-adrenergic agonist, decreases the cerebellar beta receptor

Subchronic, peripheral infusion of clenbuterol, a beta-adrenergic agonist, markedly reduced beta receptor density and isoproterenol-sensitive adenylate cyclase activity in the cerebellum of the rat. In contrast, infusion of salbutamol, isoproterenol or desipramine did not alter the beta receptor. The result of clenbuterol administration demonstrates, for the first time, a significant alteration of the cerebellar beta 2 receptor to a pharmacologic manipulation. This alteration may influence physiological and behavioral processes regulated by the cerebellum.

Differential decrease of the central beta-adrenergic receptor in the rat after subchronic infusion of desipramine and clenbuterol.

The effect of subchronic infusion of desipramine, a norepinephrine uptake inhibitor, and clenbuterol, a beta-adrenergic agonist, on the central beta receptor of the rat was determined using in vitro [(3)H]dihydroalprenolol binding. Desipramine produced significant decreases of the receptor in neocortex and hippocampal formation, and clenbuterol effected such decreases in corpus striatum and cerebellum. Both drugs caused a marked decrease in the activity of isoproterenol-sensitive adenylate cyclase in neocortex. The alpha(2) receptor of neocortex and cerebellum was unchanged by either drug as assessed by in vitro[ (3)H ]p- aminoclonidine binding. The results are discussed in terms of the different mechanisms of action of desipramine and clenbuterol, and the efficacy of these two drugs in the treatment of depression.

N-[(R,R)-(E)-1-(4-chloro-benzyl)-3-(2-oxo-azepan-3-ylcarbamoyl)-allyl]-N-methyl-3,5-bis-trifluoromethyl-benzamide: an orally active neurokinin NK1/NK2 antagonist.

The stereoselective synthesis of N-[(R,R)-(E)-1-(4-chloro-benzyl)-3-(2-oxo-azepan-3-ylcarbamoyl+ ++)-allyl]-N-methyl-3,5-bis-trifluoromethyl-benzamide (4) and its NK1 and NK2 receptor binding properties are reported. In addition the potent inhibitory effects in vivo on sar9-SP- and beta-Ala-NKA-induced airway bronchoconstriction in guinea pigs are demonstrated.

Studies on the active conformation of the NK1 antagonist CGP 49823. Part 21. Fluoro-olefin analogs of tertiary amide rotamers.

Abstract Four fluoro-olefin analogs of CGP 49823 have been synthesized. Comparison of their binding affinities for the NK1 receptor suggests an active conformation of CGP 49823, where the aromatic ring of the benzamide has a syn orientation towards the 2-benzyl substituent.