Giant interneurons mediating equilibrium reception in an insect.

In the burrowing cockroach Arenivaga, two giant interneurons in each connective of the ventral nerve cord provide gravity orientation information. The interneurons receive input from plumb bob-like equilibrium receptors on the ventral surface of the cerci. Ouir results support the theory that the cerci of cockroaches are specialized equilibrium organs.

Benzisoxazole- and benzisothiazole-3-carboxamides as potential atypical antipsychotic agents.

A series of benzisoxazole- and benzisothiazole-3-carboxamides has been prepared and tested for potential antipsychotic activity. In general, the compounds showed an affinity for dopamine D2 and serotonin 5HT2A and 5HT1A receptors. Several members of this series have demonstrated activity in animal models predictive of potential antipsychotic activity. In addition, compounds 18, 19, 22, 27, 28, 43, and 44 have also shown a potential for reduced EPS liability as suggested by the ratio of activity seen in mesolimbic-mediated vs nigrostriatal-mediated behavioral assays.

3-[[(Aryloxy)alkyl]piperidinyl]-1,2-benzisoxazoles as D2/5-HT2 antagonists with potential atypical antipsychotic activity: antipsychotic profile of iloperidone (HP 873).

A series of 3-[[(aryloxy)alkyl]piperidinyl]-1,2-benzisoxazoles was synthesized and evaluated as potential antipsychotic D2/5-HT2 antagonists. Most of these compounds showed potent antipsychotic-like activity in an apomorphine-induced climbing mouse paradigm, with many also showing preferential mesolimbic activity, as indicated by their weaker effects in an apomorphine-induced stereotypy model. In receptor binding assays, many displayed a moderate affinity for the D2 receptor coupled with a significantly greater affinity for the 5-HT2 receptor: a property that has been suggested as necessary for atypicality. From this series, compound 45, 1-[4-[3-[4-(6-fluoro-1,2-benzisoxazol-3-yl)-1- piperidinyl]propoxy]-3-methoxyphenyl]ethanone (iloperidone, HP 873), was further evaluated in a battery of in vivo and in vitro assays. This compound showed a 300-fold greater potency in inhibition of climbing than in inhibition of stereotypy or induction of catalepsy, and when evaluated chronically in an electrophysiological model, 45 caused a depolarization blockade of dopamine neurons in the A10 area of the rat brain but not in the A9 area. Additionally, it showed positive activity in a social interaction paradigm, suggesting potential efficacy against asociality, a component of the negative symptoms of schizophrenia. In chronic ex vivo studies, 45, similar to clozapine, caused a down regulation of 5-HT2 receptors but had no effect on the number of D2 receptors. Compound 45 is currently undergoing clinical evaluation.

Structure-activity relationships of a series of novel (piperazinylbutyl)thiazolidinone antipsychotic agents related to 3-[4-[4-(6-fluorobenzo[b]thien-3-yl)-1-piperazinyl]butyl]-2,5,5- trimethyl-4-thiazolidinone maleate.

HP-236 (3-[4-[4-(6-Fluorobenzo[b]thien-3-yl)-1-piperazinyl]butyl]-2,5,5- trimethyl-4-thiazolidinone maleate; P-9236) (54) displayed a pharmacological profile indicative of potential atypical antipsychotic activity. A series of piperazinyl butyl thiazolidinones structurally related to this compound were prepared and evaluated in vitro for dopamine D2 and serotonin 5HT2 and 5HT1A receptor affinity. The compounds were examined in vivo in animal models of potential antipsychotic activity and screened in models predictive of extrapyramidal side effect (EPS) liability. The synthesis of these compounds, details of their structure-activity relationships, and discovery of a new lead, compound 50, as well as further development of the profiles of compounds 50 and 54 are described.

Iloperidone binding to human and rat dopamine and 5-HT receptors.

Iloperidone (HP 873; 1-[4-[3-[4-(6-fluoro-1,2-benzisoxazol-3-yl)-1-piperidinyl]propoxy] -3- methoxyphenyl]ethanone) is a compound currently in clinical trials for the treatment of schizophrenia. Iloperidone displays affinity for dopamine D2 receptors and for 5-HT2A receptors and has a variety of in vivo activities suggestive of an atypical antipsychotic. Here we present an examination of the affinity of iloperidone to a variety of human and rat homologs of dopamine and 5-HT receptor subtypes. We employed receptor binding assays using membranes from cells stably expressing human dopamine D1, D2S, D2L, D3, D4 and D5 and 5-HT2A and 5-HT2C receptors and rat 5-HT6 and 5-HT7 receptors. Iloperidone displayed higher affinity for the dopamine D3 receptor (Ki = 7.1 nM) than for the dopamine D4 receptor (Ki = 25 nM). Iloperidone displayed high affinity for the 5-HT6 and 5-HT7 receptors (Ki = 42.7 and 21.6 nM, respectively), and was found to have higher affinity for the 5-HT2A (Ki = 5.6 nM) than for the 5-HT2C receptor (Ki = 42.8 nM). The potential implications of this receptor binding profile are discussed in comparison with data for other antipsychotic compounds.

Regeneration and molting effects on a proprioceptor organ in the Dungeness crab, Cancer magister.

Decapoda Crustacea molt in order to grow; some species, such as the Dungeness crab Cancer magister, achieve a very large size. Does sensory neuron hyperplasia in internal proprioceptors accompany this growth? To determine this, neurons in propodite-dactylopodite (PD) chordotonal organs were counted in first walking legs of juvenile (5th through 9th instar) and adult (10th through 13th instar) C. magister. We found that the PD organs of J5 crabs have about 56 neurons; the number increases to about 61 neurons in J6 crabs. Significant hyperplasia now occurs because an average of 79 neurons are found in the PD organs of J7 crabs. Little to no hyperplasia accompanies the several succeeding juvenile and adult molts (ca. 82-86 neurons are present). Because autotomized limbs are regenerated upon molting, we also examined how the number of PD organ neurons in regenerated legs compares with those of pristine legs. Newly regenerated legs (termed 1st stage regenerates) have fewer sensory neurons than do their contralateral pristine partners (65 vs 81); larger regenerated legs which have attained nearly normal size as a result of additional molts (2nd stage regenerates) still have fewer neurons than their pristine partners (69 vs 81). Additionally, in contrast to those of pristine walking legs, the elastic strand of PD organs from 1st stage regenerates in a misshapen sheet containing a cluster of small neurons with no obvious functional organization. Nonetheless, neurophysiological recordings indicate that all the receptor types typical for pristine legs (movement and position cells) are represented. The PD organs of 2nd stage regenerates differentiate to the shape and neuronal organization of pristine legs.

Dynamic responses of series force receptors innervating the opener muscle apodeme in the blue crab, Callinectes sapidus.

Receptors monitoring muscle force innervate the opener muscle apodeme in the walking legs of the blue crab, Callinectes sapidus. Biocytin backfills reveal 9-15 bipolar neurons with somata as large as 60 micrometer m positioned at the distal end of the apodeme. Sensory endings insert into the apodeme and are in series with the opener muscle. The axons of these neurons form the opener apodeme sensory nerve that merges with the most distal branch of the opener motor nerve. Recordings reveal that the receptors are not spontaneously active nor do they respond to passive muscle stretch. Isometric muscle contraction evoked by stimulating the opener excitor motor neuron is the adequate stimulus for receptor firing. Most significant is the finding that during contraction, over a wide range of forces, the firing rate of individual receptors closely parallels the rate of change of isometric force. The peak instantaneous frequency typically occurs at the force derivative maximum, but not at maximum force development. Thus, receptors of the opener apodeme sensory nerve more closely monitor changes in isometric force rather than the total force achieved.

Quantification of responses from proprioceptive neurons in the limbs of the crab, Cancer magister.

In the limbs of crustaceans, proprioception is monitored by chordotonal organs. One in particular, MC1, is arranged in a manner that is accessible for single unit recording of primary sensory neurons while simulating joint movement. The movement-sensitive cells are of two types, those sensitive to relaxation or to elongation of the chordotonal strand which corresponds to flexion or extension of the meropodite-carpopodite joint, respectively. A statistical method for the quantification of these movement-sensitive proprioceptive neuronal responses was implemented. This statistical index, eta(2), should allow neuronal responses recorded in different laboratories to be easily and quantitatively compared. In addition, an eta(2) value can be assigned to individual cells which represents a cell's consistency and degree to which the response is related to the stimulus. We found some cells to have a high eta(2) and to be consistent in their activity while other cells had a high degree of variability with low eta(2) values. J. Exp. Zool. 284:629-636, 1999.

Cardiovascular effects of chloroethylclonidine, an irreversible alpha 1B-adrenoceptor antagonist, in the unanesthetized rat: a pharmacological analysis in vivo and in vitro.

The role of vascular alpha 1B-adrenergic receptors in the regulation of arterial pressure (MAP) and heart rate (HR) was examined by assessing the effect of i.v. chloroethylclonidine (CEC; irreversible alpha 1B antagonist) in unanesthetized, normotensive Long-Evans rats. MAP, HR and the pressor response to i.v. phenylephrine (PE) were monitored for 24 hr after saline or CEC (15 mg/kg and 25 mg/kg) injection. Neither i.v. saline nor CEC affected MAP or HR throughout the course of the study, yet the PE response was maximally inhibited (> 75% at 15 min) by both doses of CEC. The PE response recovered by 2 hr at the 15-mg/kg dose but remained inhibited up to 4 hr at 25 mg/kg. At 24 hr, all cardiovascular parameters returned to control levels. CEC (100 microM, 30 min) produced irreversible blockade of norepinephrine-induced contractions in rat aortic rings; prazosin (10 nM) and sodium thiosulphate (1 mM, a reagent that inactivates aziridinium ions) reversed CEC's inhibitory effect. Precyclized CEC and its hydrolysis product beta-hydroxyethylclonidine (beta-HEC) poorly antagonized aortic alpha 1B-receptors. Ex vivo analysis of aortic rings from saline and CEC-treated rats showed that PE-induced contractions were shifted to the right and maximally depressed in a dose-dependent manner after 24 hr. These results suggest that 1) CEC produces long lasting blockade of alpha 1B-adrenoceptors in vitro and in vivo via formation of an aziridinium ion intermediate and 2) vascular alpha 1B-adrenoceptors are not coupled to the tonic physiological regulation of MAP in the rat.

Cardiac adenylate cyclase activity, positive chronotropic and inotropic effects of forskolin analogs with either low, medium or high binding site affinity.

A series of in vitro studies were conducted examining the adenylate cyclase stimulation, positive chronotropic and inotropic effects of forskolin and nine analogs which exhibited a range of [3H]forskolin binding site affinities (K1) from 0.020 to 3.174 microM. A significant (P less than .001) linear correlation (r = 0.94) was found between binding site affinity and adenylate cyclase stimulation (EC50) for forskolin and the nine structural analogs. Adenylate cyclase activity was also significantly correlated with the positive chronotropic and inotropic effects of these substances on isolated guinea pig atria. Compounds with K1 values between 0.020 and 1.136 microM produced concentration-dependent increases in heart rate and contractile force in isolated spontaneous and electrically paced guinea pig atria, respectively. In contrast, an analog with a K1 of 3.174 microM caused significant (P less than .05) negative chronotropic and inotropic effects at concentrations above 10 microM. The optimal separation between positive inotropic and chronotropic activity was found with compounds displaying potent [3H]forskolin binding site affinity but moderate adenylate cyclase stimulation, i.e., K1 and EC50 values of approximately 0.05 to 0.10 and 3 microM, respectively. The results of this study show that the forskolin analog, P87-7692 [7-desacetyl-7-(O-propionyl)-hydroxyl amino-carbonyl-forskolin], has marked activity with a wide separation between positive inotropic (248 +/- 41%) and chronotropic effects (43 +/- 13%) at 6.2 microM and may serve as a prototype for a forskolin-based cardiotonic.

Pharmacological activity and safety profile of P10358, a novel, orally active acetylcholinesterase inhibitor for Alzheimer's disease.

1-[(3-Fluoro-4-pyridinyl)amino]-3-methyl-1(H)-indol-5-yl methyl carbamate (P10358) is a potent, reversible acetylcholinesterase inhibitor that produces central cholinergic stimulation after oral and parental administration in rats and mice. P10358 is a 2.5 times more potent acetylcholinesterase inhibitor than THA in vitro (IC50 = 0.10 +/- 0.02 microM vs. IC50 = 0.25 +/- 0.03 microM). It also inhibits butyrylcholinesterase activity as potently as THA (IC50 = 0.08 +/- 0.05 microM vs. IC50 = 0.07 +/- 0.01 microM). Ex vivo, P10358 (0.2 - 20 mg/kg, p.o.) produced dose-dependent inhibition of brain acetylcholinesterase activity. At 10 and 20 mg/ kg, it produced profound and long-lasting hypothermia in mice. P10358 enhanced performance in rats in a step-down passive avoidance task (0.62 and 1.25 mg/kg) and in a social recognition paradigm (0.32, 0.64 and 1.25 mg/kg) in mice. It reversed scopolamine-induced deficits in the Morris Water maze in rats (1.25 and 2.5 mg/kg) and a higher dose elevated striatal homovanillic acid levels. These behavioral and biochemical effects are consistent with central cholinergic stimulation. Hemodynamic studies in the rat demonstrated a 16-fold separation between behaviorally active doses (1.25 mg/kg) and those that elevated arterial pressure (20 mg/kg). Lethality in rats occurred at an oral dose of 80 mg/kg, but not at lower doses. Chemically, P10358 is an N-aminoindole and may not have the hepatotoxic liability associated with aminoacridine structure of tacrine. P10358 had weak affinity (>10 microM) at a variety of aminergic and peptidergic receptors and uptake carriers. These properties suggest that P10358 may be a safe and promising symptomatic treatment for Alzheimer's disease.