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Escape behavior is a set of locomotor actions that move an animal away from threat. While these actions can be stereotyped, it is advantageous for survival that they are flexible. 1 , 2 , 3 For example, escape probability depends on predation risk and competing motivations, 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 and flight to safety requires continuous adjustments of trajectory and must terminate at the appropriate place and time. 12 , 13 , 14 , 15 , 16 This degree of flexibility suggests that modulatory components, like inhibitory networks, act on the neural circuits controlling instinctive escape. 17 , 18 , 19 , 20 , 21 , 22 In mice, the decision to escape from imminent threats is implemented by a feedforward circuit in the midbrain, where excitatory vesicular glutamate transporter 2-positive (VGluT2 + ) neurons in the dorsal periaqueductal gray (dPAG) compute escape initiation and escape vigor. 23 , 24 , 25 Here we tested the hypothesis that local GABAergic neurons within the dPAG control escape behavior by setting the excitability of the dPAG escape network. Using in vitro patch-clamp and in vivo neural activity recordings, we found that vesicular GABA transporter-positive (VGAT + ) dPAG neurons fire action potentials tonically in the absence of synaptic inputs and are a major source of inhibition to VGluT2 + dPAG neurons. Activity in VGAT + dPAG cells transiently decreases at escape onset and increases during escape, peaking at escape termination. Optogenetically increasing or decreasing VGAT + dPAG activity changes the probability of escape when the stimulation is delivered at threat onset and the duration of escape when delivered after escape initiation. We conclude that the activity of tonically firing VGAT + dPAG neurons sets a threshold for escape initiation and controls the execution of the flight action., Competing Interests: Declaration of interests The authors declare there are no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

When faced with predatory threats, escape towards shelter is an adaptive action that offers long-term protection against the attacker. Animals rely on knowledge of safe locations in the environment to instinctively execute rapid shelter-directed escape actions 1,2 . Although previous work has identified neural mechanisms of escape initiation 3,4 , it is not known how the escape circuit incorporates spatial information to execute rapid flights along the most efficient route to shelter. Here we show that the mouse retrosplenial cortex (RSP) and superior colliculus (SC) form a circuit that encodes the shelter-direction vector and is specifically required for accurately orienting to shelter during escape. Shelter direction is encoded in RSP and SC neurons in egocentric coordinates and SC shelter-direction tuning depends on RSP activity. Inactivation of the RSP-SC pathway disrupts the orientation to shelter and causes escapes away from the optimal shelter-directed route, but does not lead to generic deficits in orientation or spatial navigation. We find that the RSP and SC are monosynaptically connected and form a feedforward lateral inhibition microcircuit that strongly drives the inhibitory collicular network because of higher RSP input convergence and synaptic integration efficiency in inhibitory SC neurons. This results in broad shelter-direction tuning in inhibitory SC neurons and sharply tuned excitatory SC neurons. These findings are recapitulated by a biologically constrained spiking network model in which RSP input to the local SC recurrent ring architecture generates a circular shelter-direction map. We propose that this RSP-SC circuit might be specialized for generating collicular representations of memorized spatial goals that are readily accessible to the motor system during escape, or more broadly, during navigation when the goal must be reached as fast as possible., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Neural computations can be framed as dynamical processes, whereby the structure of the dynamics within a neural network is a direct reflection of the computations that the network performs. A key step in generating mechanistic interpretations within this computation through dynamics framework is to establish the link among network connectivity, dynamics, and computation. This link is only partly understood. Recent work has focused on producing algorithms for engineering artificial recurrent neural networks (RNN) with dynamics targeted to a specific goal manifold. Some of these algorithms require only a set of vectors tangent to the target manifold to be computed and thus provide a general method that can be applied to a diverse set of problems. Nevertheless, computing such vectors for an arbitrary manifold in a high-dimensional state space remains highly challenging, which in practice limits the applicability of this approach. Here we demonstrate how topology and differential geometry can be leveraged to simplify this task by first computing tangent vectors on a low-dimensional topological manifold and then embedding these in state space. The simplicity of this procedure greatly facilitates the creation of manifold-targeted RNNs, as well as the process of designing task-solving, on-manifold dynamics. This new method should enable the application of network engineering-based approaches to a wide set of problems in neuroscience and machine learning. Our description of how fundamental concepts from differential geometry can be mapped onto different aspects of neural dynamics is a further demonstration of how the language of differential geometry can enrich the conceptual framework for describing neural dynamics and computation., (© 2022 Massachusetts Institute of Technology.)

When faced with imminent danger, animals must rapidly take defensive actions to reach safety. Mice can react to threatening stimuli in ∼250 milliseconds 1 and, in simple environments, use spatial memory to quickly escape to shelter. 2 , 3 Natural habitats, however, often offer multiple routes to safety that animals must identify and choose from. 4 This is challenging because although rodents can learn to navigate complex mazes, 5 , 6 learning the value of different routes through trial and error during escape could be deadly. Here, we investigated how mice learn to choose between different escape routes. Using environments with paths to shelter of varying length and geometry, we find that mice prefer options that minimize path distance and angle relative to the shelter. This strategy is already present during the first threat encounter and after only ∼10 minutes of exploration in a novel environment, indicating that route selection does not require experience of escaping. Instead, an innate heuristic assigns survival value to each path after rapidly learning the spatial environment. This route selection process is flexible and allows quick adaptation to arenas with dynamic geometries. Computational modeling shows that model-based reinforcement learning agents replicate the observed behavior in environments where the shelter location is rewarding during exploration. These results show that mice combine fast spatial learning with innate heuristics to choose escape routes with the highest survival value. The results further suggest that integrating prior knowledge acquired through evolution with knowledge learned from experience supports adaptation to changing environments and minimizes the need for trial and error when the errors are costly., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

High-resolution whole-brain microscopy provides a means for post hoc determination of the location of implanted devices and labelled cell populations that are necessary to interpret in vivo experiments designed to understand brain function. Here we have developed two plugins (brainreg and brainreg-segment) for the Python-based image viewer napari, to accurately map any object in a common coordinate space. We analysed the position of dye-labelled electrode tracks and two-photon imaged cell populations expressing fluorescent proteins. The precise location of probes and cells were physiologically interrogated and revealed accurate segmentation with near-cellular resolution., (© 2022. The Author(s).)

Executing learned motor behaviors often requires the transformation of sensory cues into patterns of motor commands that generate appropriately timed actions. The cerebellum and thalamus are two key areas involved in shaping cortical output and movement, but the contribution of a cerebellar-thalamocortical pathway to voluntary movement initiation remains poorly understood. Here, we investigated how an auditory "go cue" transforms thalamocortical activity patterns and how these changes relate to movement initiation. Population responses in dentate/interpositus-recipient regions of motor thalamus reflect a time-locked increase in activity immediately prior to movement initiation that is temporally uncoupled from the go cue, indicative of a fixed-latency feedforward motor timing signal. Blocking cerebellar or motor thalamic output suppresses movement initiation, while stimulation triggers movements in a behavioral context-dependent manner. Our findings show how cerebellar output, via the thalamus, shapes cortical activity patterns necessary for learned context-dependent movement initiation., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Three-dimensional (3D) digital brain atlases and high-throughput brain-wide imaging techniques generate large multidimensional datasets that can be registered to a common reference frame. Generating insights from such datasets depends critically on visualization and interactive data exploration, but this a challenging task. Currently available software is dedicated to single atlases, model species or data types, and generating 3D renderings that merge anatomically registered data from diverse sources requires extensive development and programming skills. Here, we present brainrender: an open-source Python package for interactive visualization of multidimensional datasets registered to brain atlases. Brainrender facilitates the creation of complex renderings with different data types in the same visualization and enables seamless use of different atlas sources. High-quality visualizations can be used interactively and exported as high-resolution figures and animated videos. By facilitating the visualization of anatomically registered data, brainrender should accelerate the analysis, interpretation, and dissemination of brain-wide multidimensional data., Competing Interests: FC, AT, LP, TM, RP, TB No competing interests declared, (© 2021, Claudi et al.)

Upon inflammation, circulating monocytes leave the bloodstream and migrate into the tissues, where they differentiate after exposure to various growth factors, cytokines or infectious agents. The best defined macrophage polarization types are M1 and M2. However, the platelet-derived CXC chemokine CXCL4 induces the polarization of macrophages into a unique phenotype. In this study, we compared the effect of CXCL4 and its variant CXCL4L1 on the differentiation of monocytes into macrophages and into immature monocyte-derived dendritic cells (iMDDC). Differently to M-CSF and CXCL4, CXCL4L1 is not a survival factor for monocytes. Moreover, the expression of the chemokine receptors CCR2, CCR5 and CXCR3 was significantly higher on CXCL4L1-treated monocytes compared to M-CSF- and CXCL4-stimulated monocytes. IL-1 receptor antagonist (IL-1RN) expression was upregulated by CXCL4 and downregulated by CXCL4L1, respectively, whereas both chemokines reduced the expression of the mannose receptor (MRC). Furthermore, through activation of CXCR3, CXCL4L1-stimulated monocytes released significantly higher amounts of CCL2 and CXCL8 compared to CXCL4-treated monocytes, indicating more pronounced inflammatory traits for CXCL4L1. In contrast, in CXCL4L1-treated monocytes, the production of CCL22 was lower. Compared to iMDDC generated in the presence of CXCL4L1, CXCL4-treated iMDDC showed an enhanced phagocytic capacity and downregulation of expression of certain surface markers (e.g. CD1a) and specific enzymes (e.g. MMP-9 and MMP-12). CXCL4 and CXCL4L1 did not affect the chemokine receptor expression on iMDDC and cytokine production (CCL2, CCL18, CCL22, CXCL8, IL-10) by CXCL4- or CXCL4L1-differentiated iMDDC was similar. We can conclude that both CXCL4 and CXCL4L1 exert a direct effect on monocytes and iMDDC. However, the resulting phenotypes are different, which suggests a unique role for the two CXCL4 variants in physiology and/or pathology., Competing Interests: The authors have declared that no competing interests exist.

L-DOPA, the immediate biological precursor of dopamine, is still considered the drug of choice in the treatment of Parkinson's disease. However, therapy with L-DOPA is associated with a number of acute problems. With the aim to increase the bioavailability after oral administration, we designed a multi-protected L-DOPA prodrugs able to release the drug by both spontaneous chemical or enzyme catalyzed hydrolysis. The new compounds have been synthesized and preliminarily evaluated for their water solubility, log P, chemical stability, and enzymatic stability. The results indicate that the incorporation of the amino acidic moiety of L-DOPA into an imidazoline-4-one ring provides prodrugs sufficiently stable to potentially cross unchanged the acidic environment of the stomach, and to be absorbed from the intestine. They also might be able to release L-DOPA in human plasma after enzymatic hydrolysis. The ability of prodrugs 6a-b to increase basal levels of striatal DA, and influence brain neurochemistry associated with dopaminergic activity following oral administration, as well as the radical-scavenging activity against DPPH for compounds 6a-b and 15a are also reported., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Polyhydric alcohol derivatives of the anticancer agent lonidamine (LND) have been synthesized. The increased water solubility showed by prodrugs 4, 7, and 25 together with their logP values (2.19, 2.55, and 2.54, respectively) and chemical stability might be beneficial for prodrugs absorption after oral administration. Moreover, the new prodrugs undergo enzymatic hydrolysis in plasma and release LND demonstrating that they are promising candidates for in vivo investigations.

The novel 4-phenoxy-1,2,3,4-tetrahydroisoquinolines 6a-c and their rigid congeners 4,5,6,6a-tetrahydro-chromeno[2,3,4-de]isoquinolines 7a,b were synthesized in order to obtain dopamine D2-like receptor ligands. The new compounds were evaluated for their in vitro binding affinities, in vivo behavioral activities on rats, and for their effects on rat brain neurochemistry. Compounds 6b (toward both D2 and D3 dopamine receptors) and 7a,b (toward D3 only dopamine receptors) showed the most significant affinities. However none of the new compounds was able to stimulate behavioral activity in non pre-treated rats, nor to influence brain neurochemistry.

A series of 5-hydroxy- and 5,6-dihydroxy-1,2,3,7,12,12a-hexahydrobenzo[5,6]cyclohepta[1,2,3-ij]isoquinoline derivatives (5a--e and 6a--e) were synthesized as conformationally rigid analogues of 1-benzyltetrahydroisoquinoline and evaluated for their affinity at D(1) and D(2) dopamine receptors. All compounds showed lower D(1) and D(2) affinities than dopamine. The 5-hydroxy-1-methyl-2,3,12,12a-hexahydrobenzo[5,6]cyclohepta[1,2,3-ij]isoquinoline 5a and the 5,6-dihydroxy analogue 6a showed D(2) agonist activity. This was proved by their effects on prolactin release from primary cultures of rat anterior pituitary cells. Molecular modeling studies showed that the geometric parameters (namely the distances from meta and para hydroxyl oxygens to the nitrogen and the height of nitrogen from the hydroxylated phenyl ring plane) of the dopaminergic pharmacophore embedded in our compounds have lower values in comparison with those observed in D(1) and D(2) selective ligands.

A series of dimeric derivatives (+)-1, and (+)-2, and (+)-3a-d of L-Dopa diacetyl esters was synthesized and evaluated as potential L-Dopa prodrugs with improved physicochemical properties. All the new compounds showed chemical stability in aqueous buffer solutions (pH 1.3 and 7.4). A relatively slow release of L-Dopa in human plasma was observed.

The synthesis and in vitro chemical and enzymatic stability of L-(+)-3-(3-hydroxy-4-pivaloyloxybenzyl)-2,5-diketomorpholine (9) as L-Dopa prodrug are described. Prodrug 9 possesses a good lipophilicity (log P = 2.153 +/- 0.017), is stable in aqueous buffer solutions (pH 1.3 and 7.4), and in 80% rat and human plasma it is turned into L-Dopa.

The N-methyl, N-ethyl, and N-n-propyl derivatives of 5-hydoxy- and 10-hydroxy-2,3,12,12a-tetrahydro-1H-[1]benzoxepino[2,3, 4-ij]isoquinolines were prepared as monophenolic ligands for the dopamine receptor and evaluated for their affinity at D(1)-like and D(2)-like subtypes. All compounds showed very low D(1) affinities. This could be ascribed to the absence of a catechol nucleus or of the beta-phenyldopamine pharmacophore. Only the N-methyl-5-hydroxy- (5a), N-methyl-10-hydroxy- (6a), and N-methyl-4-bromo-10-methoxy-2,3, 12,12a-tetrahydro-1H-[1]benzoxepino[2,3,4-ij]isoquinolines (26a) bound the D(2) receptors with low affinity, in the same range as dopamine. In compounds 5a and 6a, the 2-(3-hydroxyphenyl)ethylamine moiety does not meet the requirements of the D(2) agonist pharmacophore: namely, the 2-(3-hydroxyphenyl)ethylamine does not reach the trans, fully extended conformation. The three compounds did not interact with recombinant human D(4) receptors, and only 5a showed low affinity for rat recombinant D(3) receptors. Analysis of the influence of Na(+) on [(3)H]spiperone binding showed that 5a displays a potential dopamine D(2) agonist profile, whereas 6a probably has a dopamine D(2) antagonist activity. The D(2) agonist activity of 5a was proved by the effects on prolactin release from primary cultures of rat anterior pituitary cells.

The present work reports the synthesis of enantiomeric pairs of the trans-2-amino-6-hydroxy-1-phenyl-2,3-dihydro-1H-indene [(+)-14a, (-)-14a] and trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1 H-indene [(+)-14b, (-)-14b] and their N,N-di-n-propyl [(+)-and (-)-15a,b], N-methyl-N-allyl [(+)-and (-)-16a,b], and N-methyl-N-n-propyl [(+) and (-)-17a,b] derivatives obtained by a combination of stereospecific reactions and optical resolution. The new compounds were evaluated for their affinity at the dopamine D1 and D2 receptors. The amines (+)- and (-)-14a, incorporating the D1 pharmacophore 2-phenyl-2-(3-hydroxyphenyl)ethylamine in a trans extended conformation, and their derivatives displayed D1 and D2 affinity in the nanomolar range. On the other hand, the enantiomers (+)- and (-)-14b, (+)- and (-)-15b displayed high affinity and selectivity for the D1 receptor. In a preliminary behavioral study on rats (+)-14b, and to a greater extent (+)-15b, promoted episodes of intense grooming, thus indicating that they act as central D1 agonists. The trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1H-indenes (+)-14b and (+)-15b represent selective D1 agonists lacking a catechol group, which should meet the prerequisites for a central nervous system penetration.

The N-n-propyl-N-(2-phenylethyl)-2-(3-hydroxyphenyl)ethylamine (1, RU 24213) had been previously identified as selective agonist of DA D2 receptor subtype. In this paper we describe the synthesis and in vitro binding affinities of several derivatives of 1 substituted with fluorine, chlorine and methyl or hydroxy groups on the phenyl ring of the N-2-phenylethyl moiety. The results obtained indicate that these substitutions do not improve the D2 binding affinity. The introduction on the phenyl ring of two fluorine or chlorine atoms decreases with D1 affinity, and the dichloro derivatives are highly selective for the D2 receptor. Preliminary behavioural tests confirm that the dichloro derivatives behave as D2 selective agonists.

The agnostic activity of Quinpirole (3a) at the D2 dopamine (DA) receptor suggested that the dopaminergic pharmacophore embedded in 3a was the 4-(2-aminoethyl)-1H-pyrazole (5) moiety. On that basis we have synthesized some derivatives of 5 bearing on the amino group alkyl and alkylaryl substituents. The affinities of 5 and its derivatives for the D1 and D2 DA receptor subtypes were evaluated in rat striatum by binding assays. None of these compounds show affinity for the D1 receptor. In the D2 binding assay only the N,N-di-(2-phenylethyl) (5i) and N-n-propyl-N-[2-(3-hydroxyphenyl)ethyl] (5j) derivatives show affinities comparable to that of Quinpirole. These results do not support the postulate that the 4-(2-aminoethyl)-1H-pyrazole is a bioisostere of the catechol nucleus of DA.

2-(4-Chloro-3-hydroxyphenyl)ethylamine (4) and some derivatives were synthesized as dopamine (DA) receptor ligands. Amine 4 retains the dopaminergic pharmacophore 2-(3-hydroxyphenyl)-ethylamine, and the chlorine atom replaces the "para" hydroxyl group of DA. The derivatives 18a-e were obtained by introducing on the nitrogen of amine 4 the n-propyl and 2-phenylethyl or 3-phenylpropyl groups which can be accommodated by the D-2 receptor lipophilic sites 3C and pi 3, respectively. The affinity and selectivity of these compounds for D-1 and D-2 subtypes was determined in radioligand competition assays for the DA receptors of rat striatum membranes using [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective) as radioligands. The amine 4 shows about 7-fold lower affinity than DA for both sites and is not able to discriminate between the two subtypes of DA receptors. The introduction of two n-propyl groups (18a) on the nitrogen atom reduces by one-half and doubles the affinity for D-1 and D-2 binding sites, respectively. The substitution of an n-propyl group with different alkylphenyl groups, to give compounds 18b-e, increases the affinity for the D-2 subtype from 19-fold to 36-fold. These compounds have the same affinity at the D-2 site as the DA agonist N-n-propyl-N-(2-phenylethyl)-2-(3-hydroxyphenyl)-ethylamine (2a) and are about 20 times more selective than DA for this binding site. In the assay for D-2 receptor mediated inhibition of adenylate cyclase activity, all the tested compounds behaved as D-2 agonists; N-n-propyl-N-[2(4-hydroxyphenyl)ethyl]- (18d) and N-n-propyl-N-(2-phenyl-ethyl)-2-(4-chloro-3-hydroxyphenyl)ethylamine (18b) were more effective than DA or 2a. On the other hand, all compounds were less effective than DA in stimulation of adenylate cyclase activity in rat striatal homogenates, a kind of effect which is mediated by the D-1 subtype of DA receptors. These results suggest that the nitrogen substitution enhances the affinity and selectivity for the D-2 receptor. In the adenylate cyclase assay, the compounds behave as potent D-2 agonists.

A series of N-n-propyl-2-(4-fluoro-3-hydroxyphenyl)ethylamine derivatives obtained by introducing on nitrogen atom a 2-phenylethyl moiety (with aromatic nucleus substituted at 3 or 4 position with fluorine, chlorine or hydroxy and methyl groups), as well as a 2-cyclohexylethyl or 3-phenylpropyl groups were synthesized. These substituents can interact with the D2 accessory binding site pi 3. The affinities of new compounds for D1 and D2 subtypes of dopamine (DA) receptor were measured in a test involving displacement of [3H]SCH 23390 and [3H]spiperone, respectively, from homogenates of rat striatum. The new derivatives are selective for D2 sites, and are more potent than the parent compound N-n-propyl-N-(2-phenylethyl)-2-(4-fluoro-3-hydroxyphenyl)ethylamine 2a. The N-n-propyl-N-[2-(4-hydroxyphenyl)ethyl]-2-(4-fluoro-3-hydroxyphenyl) ethylamine (11f) is the most potent and selective member in the series. Other derivatives are less effective but are as potent as the D2 agonist RU 24213. The results indicate that the pi 3 site is a rather large lipophilic pocket which can accommodate not only aromatic nuclei, but also the cyclohexyl group.

The IP injection of 2-(4-fluoro-3-hydroxyphenyl)ethylamines. (FDA 24), N-n-propyl-N-(2-phenylethyl)-2-(3-fluoro-4-hydroxyphenyl)ethylamine (FDA 27F) and N-n-propyl-N-(2-phenylethyl)-2-(4-fluoro-3-hydroxyphenyl) ethylamine (FDA 40) into adult male rats induced the stretching and yawning (SY) syndrome, FDA 24 being the least active. Moreover, FDA 27F and FDA 40 potentiated penile erection (PE) with respect to controls. For both signs (PE and SY), FDA 40 was the most potent of the three compounds. These effects, which are considered typical signs of central D-2-dopamine (DA) receptor stimulation, were dose-related and significantly inhibited by pretreatment with the selective D-2 DA antagonist, sulpiride, but not by domperidone, which does not cross the hematoencephalic barrier. In previous binding studies, FDA 27F and FDA 40 showed high affinity and selectivity for D-2 DA receptors, while FDA 24 had a low affinity for both D-1 and D-2 DA receptors. The present data show that FDA 27F and FDA 40 cross the blood-brain barrier and exert an agonistic effect on the central D-2 DA receptors. These results also provide evidence of the value of PE and SY tests as sensitive tools for the study of DA-neurochemical mechanisms.

The synthesis of 2-(4-fluoro-3-hydroxyphenyl)ethylamine (26) and of some N,N-dialkyl derivatives (27-30) starting from 4-fluoro-3-hydroxytoluene and their in vitro binding affinities for dopamine (DA) receptor are reported. The amine 26 can be regarded as a molecular modification of DA in which the para hydroxyl group is replaced by fluorine. The new compounds 26-30 were evaluated for their affinity at D-1 and D-2 DA receptor subtypes by displacement of [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective). The amine 26 had about 2-fold less affinity for D-1 and D-2 binding sites than DA. The substitution of the amino group with ethyl, n-propyl, and 2-phenylethyl groups decreased the affinity for D-1 binding sites but greatly enhanced the effectiveness on D-2 binding sites. The N-ethyl- (28) and N-n-propyl-N-(2-phenylethyl)-2-(4-fluoro-3- hydroxyphenyl)ethylamine (30) were the most potent members of the series with high selectivity for D-2 binding sites. A similar effect was observed with isomeric N-n-propyl-N-(2-phenylethyl)-2-(3-fluoro-4-hydroxyphenyl)ethylamine (31) which was approximately 65 times more selective for D-2 sites vs D-1 sites. The introduction of a 2-phenylethyl group on the nitrogen atom induce the highest effect, perhaps as a consequence of an increased liposolubility or of binding to a complementary lipophilic site on the receptor.

The geometrical isomers of the antineoplastic agents 2-formylpyridine and 1-formylisoquinoline thiosemicarbazones were synthesized and their structure was studied by spectroscopic methods. It was found that the compounds previously described in the literature and tested for carcinostatic activity were isomers with E configuration which probably contained minor amounts of Z isomers.

In a continuing search for new biologically active agents derived from indolizine, 3-(2-aminoethyl)-2-methylindolizine, 3-(2-aminoethyl)-2-methyl-5,6,7,8-tetrahydroindolizine, and some mono- and di-N-substituted derivatives were prepared. Initial pharmacological screening showed that these compounds possess anti-5-hydroxytryptamine, antihistamine, antiacetylcholine, and CNS-depressant activities.

The synthesis and dopamine agonist activity of some derivatives of trans-6-methyl-7a,8,9,10,11,11a-hexahydro-7H-pyrrolo[3,2,1-gh]- 4,7-phenanthroline (6a-c) are reported. These compounds can be regarded as analogues of ergoline derivatives with the indole nucleus replaced by indolizine. These congeners have been evaluated as inhibitors of prolactin release in vivo. trans-6-Methyl-8-ethyl-7a,8,9,10,11,11a-hexahydro-7H-pyrrolo[3,2,1-gh]- 4,7-phenanthroline (6b) proved to produce a dose-dependent inhibition of serum prolactin that was almost complete at the highest dose employed. Although effective, this compound was far less potent than bromocriptine. The 8-propyl derivative 6c was weakly active only at very high doses, and the 8-methyl derivative 6a proved to be completely ineffective. trans-4-Propyl-1,2,3,4,4a,5,6,10b-octahydro-4,7-phenanthroline (7), a molecular simplification of hexahydropyrrolo-4,7-phenanthroline, proved to be the most potent among the newly synthesized compounds. These results, taken together with those of previous studies, suggest that the presence of the nitrogen of the indolizine nucleus and the N-7 in the octahydro-4,7-phenanthroline 7 are significant for the interaction with the dopamine receptor involved in the control of prolactin release.

Compounds containing an N*-N*-S* tridentate ligand were synthesized and tested for antitumor activity against P-388 lymphocytic leukemia in mice. Of these, only 2,2'-bipyridyl-6-carbothioamide (1a) showed antitumor activity at relatively high dosage levels. Compound 1a was also evaluated against L-1210 and S180 cells in culture and found to have significant activity.

The 2-(3-fluoro-4-hydroxyphenyl)ethylamine and its N,N-dialkyl derivatives were synthesized. The affinity of new compounds for dopamine binding sites was measured in a test involving displacement of [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective) from homogenized rat striatal tissue. No compound proved effective in displacing [3H]SCH 23390. Two derivatives are selective displacers of [3H]spiperone.

A series of benzimidazole-4,7-dione derivatives, bearing substituents at positions 1, 2, 5, and 6 of the benzimidazole ring, has been synthesized and tested for antitumor activity in vivo on P388 leukemia. Some of the synthesized compounds show significant antitumor activity, associated with high toxicity, however. Compounds 7, 18, and 27 show the highest antitumor activity in this series, whereas 17, 19, and 22 are scarcely active. Some hypothetical biological precursors of these quinones are devoid of antitumor activity. Some structure-activity relationships are discussed.

Some N-alkyl derivatives of 2-(3-hydroxybenzyl)piperidine and of 2-(3,4-dihydroxybezyl)piperidine were synthesized and evaluated pharmacologically in vitro by competition with [3H]spiperone for binding to a homogenized rat striatal tissue, and for ability to stimulate adenylate cyclase. The N-methyl-2-(3,4-dihydroxybenzyl)piperidine shows a fairly good affinity for the D-2 dopamine receptor. The N-alkyl 2-(3,4-dihydroxybenzyl)piperidines produce a faible stimulation of adenylate cyclase activity.

The syntheses and a preliminary pharmacological evaluation of some aminopropylindolizines and aminopropyltetrahydroindolizines are reported. All compounds showed anti-5-hydroxytryptamine, anti-histamine, and antiacetylcholine activities. Some also exhibited weak CNS activity.

Synthesis and study of the antimonoamine oxidase activity of some N'-substituted hydrazides of 2-methyl-3-indolizinecarboxylic acid are reported. The activities were generally of about the same order as those of the corresponding hydrazides of 2-indolizinecarboxylic acid.

Some N,N-dialkylderivatives of 6-amino-5,6,7,8-tetrahydroquinoline were synthesized. The affinity of new compounds for dopamine binding sites was measured in a test involving displacement of [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective) from homogenized rat striatal tissue. While no compound was effective in displacing [3H]SCH 23390, in the binding assays on the D-2 receptor all tetrahydroquinolines displaced [3H]spiperone from specific binding sites, the compounds with a N-n-propyl-N-phenylethylamino group (18) or N,N-di n-propylamino group (16) being the most potent.

The synthesis and antimonoamine oxidase activity of some N'-substituted hydrazides of indolizine-2-carboxylic acid are described. They all inhibit monoamine oxidase and are more active than iproniazid. The structure-activity relationships also are discussed.