2-Phenyl-2-(1-hydroxycycloalkyl)ethylamine derivatives: synthesis and antidepressant activity.

A series of 2-phenyl-2-(1-hydroxycycloalkyl)ethylamine derivatives was examined for the ability to inhibit both rat brain imipramine receptor binding and the synaptosomal uptake of norepinephrine (NE) and serotonin (5-HT). Neurotransmitter uptake inhibition was highest for a subset of 2-phenyl-2-(1-hydroxycyclohexyl)dimethylethylamines in which the aryl ring has a halogen or methoxy substituent at the 3- and/or 4-positions. Potential antidepressant activity in this subset was assayed in three rodent models--the antagonism of reserpine-induced hypothermia, the antagonism of histamine-induced ACTH release, and the ability to reduce noradrenergic responsiveness in the rat pineal gland. An acute effect seen in the rat pineal gland with several analogues, including 1-[1-(3,4-dichlorophenyl)-2-(dimethylamino)ethyl]cyclohexanol (23) and 1-[2-(dimethylamino)-1)-(4-methoxyphenyl)ethyl]cyclohexanol (4), was taken as a possible correlate of a rapid onset of antidepressant activity. Compound 4 (venlafaxine) is presently undergoing clinical evaluation.

Polycyclic aryl- and heteroarylpiperazinyl imides as 5-HT1A receptor ligands and potential anxiolytic agents: synthesis and structure-activity relationship studies.

A series of polycyclic aryl- and heteroarylpiperazinyl imides were prepared and tested in various receptor-binding and behavioral tests. Parameters measured included in vitro inhibition of D2 and 5-HT1A receptor binding, inhibition of apomorphine (APO) induced stereotyped and climbing behavior, and activity in blocking conditioned avoidance responding (CAR). Several compounds demonstrated moderate to high affinity for the 5-HT1A receptor binding site; compounds 27 and 36 containing the serotonin mimetic (o-methoxyphenyl)piperazinyl moiety and compounds 42 and 50 containing the 2-pyrimidinylpiperazinyl moiety displayed the highest affinity, being equal to that of the 5-HT1A agonist 8-OH-DPAT (Ki = 1-1.3 nM). In addition to affinity at 5-HT1A binding sites, many compounds were active in blocking CAR. Compound 34, 2-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl]hexahydro-4,7-etheno-1H- cyclobut[f]isoindole-1,3(2H)-dione, demonstrated 3 times the activity of buspirone, blocking CAR in rats with an AB50 of 13 mg/kg. It also displayed high affinity for the 5-HT1A receptor (Ki = 16 nM), which is at least 20 times higher than its affinity for D2 (Ki = 345 nM) and 5-HT2 (Ki = 458 nM) receptors. Compound 34 was selected for further preclinical and pharmacokinetic evaluations for possible development as an anxiolytic agent. Structure-activity relationships within this series are discussed.

Antipsychotic activity of substituted gamma-carbolines.

Several novel substituted gamma-carbolines were synthesized and examined in a series of in vitro and in vivo pharmacological tests to determine potential antipsychotic activity. Most compounds were orally active in blocking the conditioned avoidance response (CAR) in rats but did not antagonize apomorphine-induced stereotyped behavior. Compound 17 (Wy-47,384), a gamma-carboline with a 3-(3-pyridinyl)propyl side chain, was selected for development as an atypical antipsychotic agent because of its potent and selective profile in preclinical psychopharmacological tests. It blocked CAR in rats with an AB50 of 14 mg/kg po, showed weak affinity for the D2 receptor site (Ki = 104 nM), and showed differential potency in antagonizing apomorphine-induced stereotyped behavior (ED50 = 11 mg/kg ip) and climbing behavior (ED50 = 4 mg/kg ip). Such activities are suggestive of antipsychotic efficacy combined with a low potential for extrapyramidal side effect (EPS) liability.

Biochemical and electrophysiological studies of the psychotropic compound, amperozide.

Amperozide (AB Ferrosan, FG 5606), a new antiaggressive agent which exhibits a diverse preclinical profile of in vivo and in vitro activities, was examined to determine its acute effects on noradrenergic neurons of the locus coeruleus. The firing rates of all locus coeruleus neurons tested were increased by IV administration of amperozide. The amperozide-induced increase in locus coeruleus firing rate was similar in magnitude to that of an alpha-2 antagonist; however, amperozide was weaker than the alpha-2 antagonist yohimbine in reversing clonidine-induced inhibition of locus coeruleus neuronal activity and had weak affinity at the alpha-2 receptor (Ki = 3.5 microM). Biochemically, amperozide displayed the most significant in vitro affinity at serotonin-2 receptors (Ki = 26 nM) and had low affinities at all other receptors examined. These properties are discussed in the context of amperozide's activation of the locus coeruleus as a part of its hypothetical mechanism of antiaggressive action.

Psychotropic agents: synthesis and antipsychotic activity of substituted beta-carbolines.

A series of novel substituted beta-carbolines was synthesized and tested for potential antipsychotic activity. Several compounds displayed moderate antipsychotic activity in vitro and in vivo as determined by relevant receptor binding assays and behavioral tests. The effect of substituents on antipsychotic activity was examined. The beta-carbolines 10 and 19 containing 2-(2-pyridinyl)ethyl and 2-(2-quinolinyl)ethyl side chains were the most potent analogues, blocking discrete trial conditioned avoidance responding in rats with AB50's of 23 and 10 mg/kg, respectively. Both showed moderate activity at the D2 receptor sites, but they lacked oral activity. In contrast, the beta-carboline 13 containing the 4-(4-pyridinyl)butyl side chain exhibited oral activity in the discrete trial conditioned avoidance screen with an AB50 of 31 mg/kg. Most compounds did not antagonize apomorphine-induced stereotyped behavior, which is indicative of low potential for extrapyramidal side effect (EPS) liability.

Antidepressant biochemical profile of the novel bicyclic compound Wy-45,030, an ethyl cyclohexanol derivative.

The novel bicyclic compound Wy-45,030 [1-2-(dimethylamino)-1-(4-methoxyphenyl)ethyl cyclohexanol, hydrochloride] exhibited a neurochemical profile predictive of antidepressant activity. Like the tricyclic antidepressants, it inhibited rat brain imipramine receptor binding and synaptosomal monoamine uptake (dopamine as well as norepinephrine and serotonin). It did not inhibit monoamine oxidase. Unlike the tricyclic antidepressants, it was not antimuscarinic in the guinea pig ileum, nor did it have any appreciable affinity for brain alpha-1 adrenergic or histamine-1 binding sites. Wy-45,030 was also without affinity for alpha-2 or beta adrenergic, benzodiazepine, serotonin-1, serotonin-2, dopamine-2, and opiate receptors. Such a profile is predictive of antidepressant activity devoid of the side-effects common to tricyclic therapy.

DMI, Wy-45,030, Wy-45,881 and ciramadol inhibit locus coeruleus neuronal activity.

Wy-45,030 and Wy-45,881 block the uptake of norepinephrine and serotonin in rat brain synaptosomal preparations and share several in vivo and in vitro effects with known tricyclic antidepressants. To further characterize their activity, these compounds were compared to desipramine and ciramadol in electrophysiological studies of their acute effects on noradrenergic neuronal activity. All four compounds inhibited locus coeruleus neuronal activity with a rank order of potency of desipramine greater than Wy-45,881 greater than Wy-45,030 greater than ciramadol. Administration of the alpha-adrenergic blocking drug, piperoxane, increased locus coeruleus firing rate after desipramine, Wy-45,030 and Wy-45-881. Pretreatment with naloxone prevented the reduction in locus coeruleus impulse flow observed after ciramadol administration but had no effect on the inhibition produced by Wy-45,030. Wy-45,030 and Wy-45,881, like classical antidepressants, appear to inhibit locus coeruleus neuronal firing by potentiating neuroinhibitory transmission of locus coeruleus neurons by blocking the uptake of norepinephrine into presynaptic terminals.

Regional distribution of calmodulin activity in rat brain.

Calmodulin activity in 68 discrete areas of rat brain, obtained by micropunch technique, was assessed by its capacity to activate a calmodulin-sensitive form of phosphodiesterase. In general, the activity of calmodulin was higher in the telencephalon, limbic system, and hypothalamus than in the mesencephalon, pons, cerebellum, and medulla. However, there were substantial differences in calmodulin activity in discrete nuclei of each region. The regional distribution of calmodulin activity in rat brain does not appear to correlate with that of any of the known putative neurotransmitters or peptides.

Evidence that noradrenaline modulates the increase in striatal dopamine metabolism induced by muscarinic receptor stimulation.

The effect of oxotremorine was studied on the concentration of homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylethylglycol (MHPG) in the corpus striatum of rats. At a dose of 1 mg/kg oxotremorine increased HVA levels by 68% and MHPG, by 51%. MHPG was also increased in the nucl. accumbens (58%) and neocortex (42%). Pretreatment with clonidine, 0.1 mg/kg abolished the increase in MHPG in the striatum and significantly inhibited the rise in HVA. 1-Propranolol 2.5 mg/kg, but not d-propranolol, had an effect similar to that of clonidine. A lower dose of oxotremorine (0.5 mg/kg) increased striatal HVA by 36% but did not alter MHPG levels. This increase in HVA was not reduced by 1-propranolol. Eight days after bilateral lesions of the locus coeruleus, there was a reduction in the basal concentrations of noradrenaline (41%) and MHPG (57%) in the striatum. The data suggest that at higher doses of oxotremorine (1 mg/kg), but not a lower dose (0.5 mg/kg), a noradrenergic pathway is stimulated to increase the rate of metabolism of noradrenaline in the striatum. Oxotremorine also appears to increase dopamine metabolism in the striatum by at least two separate mechanisms, one of which involves the mediation of noradrenaline.

Changes in central cholinergic neurons in the spontaneously hypertensive rat.

The activity of choline acetyltransferase (ChAT) was measured in discrete areas of the brain in 4-, 8- and 12-week-old spontaneously hypertensive rats (SH rats) and age matched Wistar Kyoto (WKY rats) controls. The concentration of acetylcholine (ACh) was also measured in certain hindbrain nuclei of 12 week SH and WKY rats. An increase in the ChAT activity and ACh concentration in the locus coeruleus was detected in 12-week-old SH rats. Decreases in the ChAT activity were found in several hypothalamic nuclei of SH rats, specifically in the paraventricular nucleus of 4-week-old rats, in the dorsomedial nucleus at 8 and 12 weeks and in the posterior hypothalamic nucleus at 12 weeks. Changes in ChAT activity were also detected in 4- and 8-week-old SH rats in the anterior ventral thalamus and in the nucleus gigantocellularis. These results suggest that cholinergic nerve activity in certain rat brain areas, several of which play a role in cardiovascular control, is altered in spontaneously hypertensive rats.

Effects of ovarian hormones on levels of luteinizing hormone in plasma and on serotonin concentrations in discrete brain nuclei.

Levels of serotonin were measureed in microdissected, individual brain nuclei in ovariectomized rats after treatment with ovarian hormones. Regions sampled included nuclei in the forebrain, rostral and medial hypothalamus, and midbrain tegmentum. Estradiol benzoate decreased levels of luteinizing hormone in plasma but did not affect serotonin levels in any region. Progesterone alone elevated serotonin content in the nucleus tractus diagonalis and ventral tegmental area. The combined estrogen plus progesterone regime produced a surge in plasma luteinizing hormone and also markedly elevated serotonin in the median eminence. These results may be of significance for ovarian hormonal regulation of gonadotropin secretion and reproductive behavior.

A mapping of the distribution of acetycholine, choline acetyltransferase and acetylcholinesterase in discrete areas of rat brain.

Acetylcholine (ACh) concentration, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were measured in 60 discrete areas dissected from the rat forebrain. All 3 substances were detectable in every region examined. The range for ACh levels was approximately 9-fold, with highest levels in the striatal and mesolimbic areas. Wider ranges were found for ChAT and AChE. In addition to not having a uniform distribution ACh, ChAT and AChE did not always show proportional variations. ACh levels did not appear to relate to the activity of either enzyme in a simple manner. There was a better correlation (r = 0.902) between the activities of ChAT and AChE, with AChE activities always being higher. In some regions, AChE was disproportionately low or high relative to ChAT. In general, the biochemical results presented here are compatible with histochemical studies of AChE. Such measurements in small brain regions should prove valuable in future experiments designed to determine cholinergic function and localize cholinergic pathways.

A method for sectioning microwave-fixed brain prior to microdissection and acetylcholine analysis.

Before proceeding with a detailed study of acetylcholine (ACh) distribution in the rat brain, a method was needed to make 300 microm brain sections for microdissection. We found cryostat sections of microwave-irradiated brains to be of poor quality, with rough surfaces and cracks. The use of a vibratome resulted in smooth, intact sections. This technique requires that unfrozen tissue be immersed in liquid during sectioning. Krebs-Ringer buffer or an inert fluorocarbon liquid (FC-47) were used for such sectioning. ACh was measured in forebrain regions from cryostat sections and vibratome sections cut in buffer or FC-47. Diffusion of ACh was apparent after sectioning in buffer, but not in FC-47. Vibratome sectioning in FC-47 should facilitate study of the distribution of ACh and other labile substances in rat brain.

The effect of two anesthetic agents on norepinephrine and dopamine in discrete brain nuclei, fiber tracts, and terminal regions of the rat.

Catecholaminergic neurons have been implicated in the mechanism of general anesthesia, but previous attempts at measuring changes in adrenergic neuron function during anesthesia have been limited by techniques to whole brain. Microdissection techniques and sensitive radioisotopic-enzymatic assays were used to measure levels of catecholamines in 20 different nuclei, fiber tracts or nerve terminal regions in brains of rats anesthetized for 90-105 min with 1% halothane or 18% cyclopropane. These two anesthetics were chosen because of their diverse effects on the electroencephalogram and on the cardiovascular and respiratory systems. Of the areas examined, significant increases in norepinephrine content with both anesthetic agents were found only in the nucleus accumbens, locus coeruleus and central gray catecholamine areas. Only in the nucleus accumbens was the dopamine level increased by both anesthetics; cyclopropane, but not halothane anesthesia, also increased the dopamine content of the caudate nucleus, while halothane, but not cyclopropane anesthesia, significantly decreased the dopamine level of the ventral nucleus of the thalamus. Changes in levels of transmitters do not distinguish cause from effect of anesthesia, and further experiments are needed to delineate what role, if any, the specific areas play in muscle relaxation, analgesia, sleep or anesthesia. This study shows that a drug can affect one nucleus or region without significantly affecting other regions that contain the same transmitter substance, and that changes in transmitter levels can occur selectively in different regions of brain even if the nerve endings are derived from contiguous cell bodies.