Biomedical subjects

E B Smalstig

Publications and source records attributed to E B Smalstig.

At least 19 recordsLinked to original sources

PubMed1996

Effects of LY231617 and angiotensin IV on ischemia-induced deficits in circular water maze and passive avoidance performance in rats.

The antioxidant LY231617 has previously been shown to offer significant protection against postischemic cell death in the hippocampus and corpus striatum of rats. The present results extend this observation by demonstrating a concomitant protection against the spatial memory deficits that accompany damage to the hippocampus, as measured by the circular water maze task. These animals were further tested for changes in associative memory by employing a passive avoidance conditioning task. No deficits in passive avoidance conditioning were measured among the 4-vessel occlusion animals treated with LY231617 or vehicle. However, the intracerebroventricular injection of angiotensin IV (Ang IV) immediately prior to foot-shock conditioning improved retention of the conditioned response during the subsequent 2-day period. These results suggest that LY231617 can offer considerable protection against global ischemia-induced cell death in the hippocampus with resulting preservation of spatial memory abilities. In addition, untreated animals that suffered cell losses in the hippocampus remained capable of responding to the facilitory effect of centrally administered Ang IV on a non-spatial memory task. The hypothesized mechanisms of the protection characteristics of LY231617, and the nootropic effect of Ang IV, are discussed.

Angiotensin II↗

PubMed1996

Induction of sulfated glycoprotein-2 (clusterin) and glial fibrillary acidic protein (GFAP) RNA expression following transient global ischemia is differentially attenuated by LY231617.

Sulfated glycoprotein-2 (SGP-2) is a secreted glycoprotein that along with GFAP has emerged as a prominent molecular marker of neurodegeneration. In the present study, we have evaluated further the relationship between SGP-2, GFAP and neurodegeneration, by examining the effects of LY231617, a potent antioxidant, on expression of SGP-2 and GFAP following four vessel occlusion (4VO). GFAP and SGP-2 RNA levels increased several fold in hippocampus and caudate nucleus in response to 30 min of 4VO. LY231617 treatment markedly attenuated the induction of GFAP RNA in both hippocampus and caudate nucleus, consistent with the significant neuroprotection observed histologically. In contrast, LY231617 treatment blunted SGP-2 RNA expression only in the hippocampus; SGP-2 RNA expression in caudate nucleus was similar to vehicle-treated 4VO, despite the marked attenuation of neuronal damage in both areas by LY231617. These data suggest region-specific differential regulation of SGP-2 and GFAP RNA induction.

Animals↗

PubMed1996

Reactive glia express cytosolic phospholipase A2 after transient global forebrain ischemia in the rat.

BACKGROUND AND PURPOSE: Phospholipid breakdown has been reported to be an early event in the brain after global cerebral ischemia. Our earlier observations showing the localization of cytosolic phospholipase A2 (cPLA2) to astrocytes in aged human brains and the intense glial activation observed after global forebrain ischemia prompted us to investigate the cellular localization of cPLA2 in the rat brain subjected to global ischemia. METHODS: Immunohistochemistry was performed in sections through the dorsal hippocampus in rats subjected to 30 minutes of four- vessel occlusion. PLA2 was localized with the use of a highly selective antiserum. Double immunofluorescent localization was performed to colocalize cPLA2 with various glial cell types. cPLA2 levels were also measured by enzymatic assay and Western blot analysis. RESULTS: A marked induction of cPLA2 was observed in activated microglia and astrocytes in the CA1 hippocampal region at 72 hours after ischemia. Only a subset of astrocytes and microglia were immunoreactive for cPLA2. Twenty-four hours after ischemia, numerous cPLA2 immunoreactive astrocytes were observed. Western blot analysis of hippocampal homogenates at 72 hours after ischemia showed induction of a 100-kD band that comigrated with purified human cPLA2, and a threefold induction in cPLA2 activity was demonstrated by enzymatic assay. CONCLUSIONS: These results indicate that both reactive astrocytes and microglia contain elevated levels of cPLA2. Induction of cPLA2 was confined to areas of neurodegeneration and likely precedes its onset. The results suggest that reactive glia may play a role in the pathophysiology of delayed neuronal death after transient global forebrain ischemia.

Animals↗

PubMed1995

Peripheral benzodiazepine receptors are colocalized with activated microglia following transient global forebrain ischemia in the rat.

In mammalian brain the expression of peripheral benzodiazepine receptors (PBRs) can be markedly induced following different types of neuronal injury. PBRs are believed to be expressed on non-neuronal cells in the brain, yet the specific cell type that expresses these receptors following CNS insult has not been defined. In the present study, we investigated the effects of transient global forebrain ischemia on PBRs by autoradiographic localization of 3H-PK11195 binding. The distribution of PBRs was compared to glial fibrillary acidic protein (GFAP) as a marker for astrocytes and OX42 as a marker for microglia. Five to 6 d following four-vessel occlusion (4-VO), an increase in PBRs was seen in the CA1 region of all 15 brains examined. In brains from rats subjected to 4-VO, microglia were selectively activated in stratum pyramidale of the CA1 layer. In contrast, astrocytes appeared to be activated in multiple hippocampal cell layers including stratum radiatum and stratum oriens. Activated astrocytes were also found in regions that did not exhibit increased 3H-PK11195 binding. In some brains, selected regions of secondary lesion, specifically necrotic thalamic nuclei and the isocortex were found to be strongly immunoreactive for OX42 but lacked GFAP immunoreactive cells. In adjacent sections, these same regions displayed high densities of 3H-PK1195 binding. These observations lend further support to the application of 3H-PK11195 binding as a marker of neuronal injury in the brain. Furthermore, the data strongly suggest that activated microglia rather than astrocytes express PBRs following ischemic insults.

Animals↗

PubMed1994

Preservation of a functionally intact neuronal network after global ischemia.

Although conventional histological techniques demonstrated preservation by drug treatment of neuronal perikarya in the hippocampal CA1 region in animals subjected to short periods of transient ischemia, uncertainty exists regarding whether the anatomical connections with these neurons are intact and functional. The hippocampal theta rhythm is dependent upon intact connections to the CA1 pyramidal neurons and is a useful predictor of functional hippocampal integrity. Hippocampal theta was quantitated by power spectral analysis in rats subjected to 30 min of 4-vessel occlusion (4-VO) and treatment with the neuroprotective antioxidant, LY231617. The 4-VO destroyed CA1 neurons and reduced the amount of theta, however, LY231617 protected CA1 neurons histologically and totally preserved the hippocampal theta rhythm. We conclude that histological preservation is indicative of functional integrity.

Animals↗

PubMed1993

Decrease in amyloid precursor protein precedes hippocampal degeneration in rat brain following transient global ischemia.

We have studied amyloid precursor protein (APP) expression in rat brain following transient global ischemia. Ischemic damage 24 h after 30 min of four-vessel occlusion (4VO) was limited to the caudate nucleus; hippocampal pyramidal neurons appeared histologically normal by light microscopy. Consistent with ongoing neurodegeneration in the caudate nucleus, microtubule-associated protein-2 (MAP-2) levels assessed by immunoblots were significantly reduced in homogenates of caudate nucleus after 4VO. MAP-2 levels In the hippocampus were comparable to control values. In contrast, full length APP levels in both the caudate nucleus and hippocampal homogenates were significantly decreased following 4VO despite normal hippocampal morphology at 24 h. These findings suggest that decrements in full length APP precede overt neuronal damage and may play a role in the subsequent delayed neurodegeneration in the hippocampus.

Amyloid beta-Protein Precursor↗

PubMed1993

LY207320 (6-methylene-4-pregnene-3,20-dione) inhibits testosterone biosynthesis, androgen uptake, 5 alpha-reductase, and produces prostatic regression in male rats.

LY207320 is an in vitro inhibitor (estimated IC50 = 0.06 microM) of steroid 5 alpha-reductase that catalyzes the conversion of testosterone (T) to dihydrotestosterone (DHT). In contrast, LY207320 was only moderately active against rat prostatic 5 alpha-reductase in vivo (32% inhibition at 50.0 mg/kg single dose). LY207320 did, however, inhibit the in vivo uptake of [3H]-T by the prostate. The antiprostatic and endocrine effects of this agent were evaluated following daily (21 days) administration to castrated, androgen-supplemented castrate, and intact rats. LY207320, which has modest progestational competitive binding activity, does not bind to rat prostatic androgen or uterine estrogen cytosolic receptors. In the castrated male rat, subcutaneously (s.c.) administered LY207320 had no androgen agonist activity, as evidenced by a lack of accessory sex organ weight gains. Administration of s.c. LY207320 to intact rats for 21 days at doses greater than 5.0 mg/kg-day produced significant (P < 0.05) reductions of seminal vesicle and ventral prostatic weights (maximal regression = -65% and -40% from control values, respectively at 50.0 mg/kg-day). The compound had no regressive activity on male accessory sex organs when administered orally. LY207320 did not alter circulating prolactin, LH, or corticosterone levels, but at high doses (> or = 50.0 mg/kg-day), lowered circulating T[-67% from intact control levels (P < 0.05)]. Histological analysis of the rat ventral prostates (RVPs) in LY207320-treated rats was consistent with an androgen-deprived state. Decreased circulating androgens and prostatic regression are associated with inhibition of testicular 17 alpha-hydroxy/C17,20-lyase enzyme activity (IC50 = 0.06 microM). These findings support the contention that LY207320 is a physiological antagonist of androgen action in male rats, and that its effects are mediated primarily through inhibition of testicular androgen production rather than accessory sex organ 5 alpha-reductase.

Aldehyde-Lyases↗

PubMed1993

Progress in the medicinal chemistry of dopaminergic agents.

Ergot alkaloids and their derivatives have long been recognized for their potent pharmacologic activity. A number of ergot derivatives, including the dopamine agonists bromocriptine and pergolide, are currently in clinical use for the treatment of CNS and endocrine disorders. In an effort to develop more selective dopamine agonists, studies were directed to elucidate the dopaminergic pharmacophore of the ergoline nucleus. During the course of this work, it was found that the tricyclic system containing only the B-, C-, and D-rings of the ergoline skeleton (2, X = CH) possessed D-2 dopamine agonist activity. As a result of this discovery, interest was stimulated in the preparation of other heteroareno[g]quinoline systems (3, "BCD partial ergolines") for investigation of their dopaminergic properties. Factors which we found to be particularly important in determining dopaminergic activity were: (1) the nature of the heteroaromatic B ring; (2) the orientation of that heteroaromatic ring; (3) the substituents on the heteroaromatic ring; and (4) the relative and absolute stereochemistry at the CD ring fusion. We report here the synthesis and pharmacologic activity of a series of BCD partial ergolines (3) and describe how the study of these new compounds allows for the delineation of structural features important in D2 dopamine receptor activation.

Animals↗

PubMed1993

Dopamine agonist activities of pergolide, its metabolites, and bromocriptine as measured by prolactin inhibition, compulsive turning, and stereotypic behavior.

Four pergolide metabolites and bromocriptine (CAS 25614-03-3) were compared to pergolide (8 beta-[(methylthio) methyl]-6-propyl-ergoline, CAS 66104-22-1) using three in vivo animal models of activity at dopamine receptors. The results obtained from these studies of prolactin inhibition, induction of compulsive turning, and stimulation of stereotypic behavior, were very consistent. Two of the metabolites, despropyl pergolide and despropyl pergolide sulfoxide, were devoid of dopamine-like effects in any of the models. Pergolide sulfone and pergolide sulfoxide, however, were found to be potent dopamine agonists, similar in activity to pergolide itself. Dopamine D2 receptors (and probably D1 receptors also) appear to be involved in the activities of these compounds. The compounds were active by both oral and i.p. routes of administration. Bromocriptine, while possessing some dopamine agonist activity at higher doses in some of these animal models, was much less potent (1/200 to 1/20) than either pergolide or its two dopaminergic metabolites.

Administration, Oral↗

PubMed1992

A phenothiazine derivative reduces rat brain damage after global or focal ischemia.

BACKGROUND AND PURPOSE: We previously reported that 2-(10H-phenothiazin-2-yloxy)-N,N-dimethylethanamine hydrochloride is a potent inhibitor of iron-dependent lipid peroxidation in vitro and can protect primary cultures of rat hippocampal neurons from hydrogen peroxide-induced toxicity. Because oxidants may play an important role in mediating postischemic tissue injury, we evaluated this agent in two rat models of transient cerebral ischemia. METHODS: In a model of global forebrain ischemia, 23 male Wistar rats were subjected to 10 minutes of four-vessel occlusion followed by 72 hours of reperfusion. The rats received three intraperitoneal injections of either vehicle (2% aqueous acacia) or test agent (40 mg/kg). In a model of focal stroke, 19 spontaneously hypertensive rats were subjected to 2 hours of tandem middle cerebral and ipsilateral common carotid artery occlusion followed by 24 hours of reperfusion. The rats received three intraperitoneal injections of either vehicle (2% aqueous acacia) or test agent (40 mg/kg). RESULTS: In the global model, the phenothiazine significantly protected the CA1 layer of the hippocampus, with a reduction in mean damage score from 2.1 +/- 0.3 for control rats to 1.0 +/- 0.4 for treated rats (p less than 0.05). In the transient focal stroke model, the compound reduced cortical infarct volume from 130.1 +/- 10.3 mm3 for control rats to 95.2 +/- 24.5 mm3 for treated rats (p less than 0.02). CONCLUSIONS: Although the primary mechanism responsible for the protective effect is unclear at the present time, our study is consistent with the hypothesis that oxidant-mediated lipid peroxidation may be involved in the pathophysiology of postischemic brain injury.

Animals↗

PubMed1989

Synthesis and evaluation of N,N-di-n-propyltetrahydrobenz[f]indol-7-amine and related congeners as dopaminergic agonists.

An evaluation of 6-[2-(di-n-propylamino)ethyl]indole (4), its rigid analogue N,N-di-n-propyl-5,6,7,8-tetrahydrobenz[f]indol-7-amine (5), and some related congeners, for ability to suppress serum prolactin in reserpinized rats, revealed modest biological activity in this in vivo model of dopaminergic activity. Although the indole N-H in these compounds can be considered to be oriented "meta" with respect to the ethylamine side chain, compounds with the indole N-H located in the other "meta" position (i.e. 4-[2-(di-n-propylamino)ethyl]indole (2) or its rigid benz[e]indole analogue 3) were much more potent dopamine agonists. The results argue for a particular orientation of the indole N-H vector. In addition, relatively potent dopamine agonists also resulted when the pyrrole portion of the indole ring was replaced by a methanesulfonamido function, supporting the idea that the indole N-H serves as a hydrogen-bond donor.

Animals↗

PubMed1987

Synthesis of D-oxa tricyclic partial ergolines as dopamine agonists.

A series of hetero fused hexahydro-1,4-benzoxazines has been synthesized and evaluated for dopamine agonist activity. This class of compounds is another example in which an oxygen substitution in the D ring of a partial ergoline or ergoline retains dopaminergic properties. Compound 10, trans-(+/-)-4,4a,5,6,8a,9-hexahydro-5-propyl-2H,7H-pyrazolo[4,3-g] [1,4]benzoxazine, is a D-ring analogue of trans-(+/-)-4,4a,5,6,7,8,8a,9-octahydro-5-propyl-2H-pyrazolo[3,4-g]qu ino line (1, LY141865) and also a des-A-ring analogue of 9-oxaergoline. Compounds 10, 2-aminohexahydrothiazolo[1,4]benzoxazine 11, and 2-aminohexahydropyrimido[1,4]benzoxazine 12 possess dopaminergic activity in prolactin inhibition and 6-hydroxydopamine lesioned rat turning assays.

Animals↗

PubMed1986

Effects of differing absolute and relative doses of progesterone and estrone on implantation and fetal survival in ovariectomized rats.

Rats were inseminated, then ovariectomized and treated with different doses of progesterone (P) and estrone (E), to determine the minimal and optimal daily doses of P and E required for implantation and fetal survival in ovariectomized rats. The minimal daily dose of P and E required for an optimal rate of implantation and fetal survival in ovariectomized rats was between 0.4 and 4.0 mg of P, and 0.1 and 1.0 microgram of E. The daily 5.0 micrograms E dose was too high to realize implantation or fetal survival when it was injected with P beginning on the day after insemination. If, however, 7 days of daily P treatment preceded the daily 5.0 micrograms E, combined with 20 mg P, delayed implantation was realized but subsequent fetal survival was not. High P doses alone did not substitute for combining E with lower P doses.

Animals↗

PubMed1984

Stimulation of presynaptic dopamine autoreceptors by 4-(2-di-n-propylaminoethyl) indole (DPAI).

The dopaminergic activity of 4-(2-di-n-propylaminoethyl)indole (DPAI) was investigated. In animal models for postsynaptic dopaminergic activity DPAI showed only very weak or no effects. In rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal tract, very weak contralateral turning behavior was induced in 4/6 rats. DPAI did not induce stereotyped behavior but caused a pronounced reduction in locomotor activity. In male rats pretreated with reserpine, DPAI lowered serum prolactin levels. Levels of homovanillic acid (HVA) were monitored in the striatum of the chloral hydrate anesthetized rat by means of in vivo voltammetry. DPAI administration reduced the faradaic peak corresponding to HVA. In rats pretreated with the decarboxylase inhibitor, NSD-1015, DPAI blocked the accumulation of dopa in response to gamma-butyrolactone. The results of this study indicate that DPAI possesses a high degree of selectivity for presynaptic dopamine autoreceptors, and little or no effect on postsynaptic dopamine receptors.

Animals↗

PubMed1983

Resolution and absolute configuration of an ergoline-related dopamine agonist, trans-4,4a,5,6,7,8,8a,9-Octahydro-5-propyl-1H(or 2H)-pyrazolo[3,4-g]quinoline.

The title compound (+/-)-5 (R = Pro) (LY141865) has been resolved into a (-) isomer and a (+) isomer as the D- and L-tartrate salts, respectively. Biological studies have shown that dopamine agonist activity is a property of only the (-) isomer. Crystallographic analysis has proven that the absolute configuration of the active (-) isomer is the same as that of the natural ergolines.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1981

Maintenance of unimplanted fertilized ova in spayed rats: effects of cortisone acetate therapy during the period of embryonic diapause.

Rat dams were ovariectomized on day 3 of pregnancy and treated with corn oil (0.25 ml/day), progesterone (4 mg/day), cortisone acetate (2 or 10 mg/day), cortisone acetate (10 mg/day) plus progesterone (4 mg/day) or progesterone (4 mg/day) plus oestrone (1 microgram/day) from days 2 to 8 or 14, followed by 6 to 11 days of treatment with progesterone (4 mg/day) plus oestrone (1 microgram/day). Implantation of ova at the normal time was realized in the animals treated from day 2 with progesterone plus oestrone. Implantation of ova was only realized subsequent to progesterone plus oestrone in the dams treated with progesterone alone, cortisone acetate alone, or progesterone plus cortisone acetate, except for one animal in the latter group. Implantation of ova was not usually realized even after progesterone plus oestrone treatment in the dams treated with corn oil. Even though cortisone acetate maintained unimplanted ova in spayed rats in much the same manner as does progesterone, it was not equivalent to progesterone in efficacy or action.

Animals↗

PubMed1981

Assessment of the progestagenic and oestrogenic activity of compounds by their effect on implantation in rats with diapausing embryos.

The oestrogenic, progestagenic and mixed oestrogenic--progestagenic activities of various compounds were assessed by their effects on implantation and its delay in the ovariectomized rat. Progesterone, norgestrel and 17 alpha-(2-butynyl)-17 beta-hydroxyestra-4,9,11-trien-3-one (R3852-3) were investigated. Progesterone and norgestrel proved to be progestagens with little or no inherent oestrogenic activity, while R3852-3 appeared to have both progestagenic and oestrogenic activity. The oestrogenic activity of R3852-3 was verified by using an Allen--Doisy type of assay system.

Animals↗

PubMed1980

Bicyclic and tricyclic ergoline partial structures. Rigid 3-(2-aminoethyl)pyrroles and 3- and 4-(2-aminoethyl)pyrazoles as dopamine agonists.

It is proposed, based upon comparisons with apomorphine, that the rigid pyrroleethylamine moiety of the ergolines is the portion of the molecule responsible for dopamine agonist activity. In support of this hypothesis, bicyclic and tricyclic ergoline partial structures 6, 11, 25, and 35 have been synthesized. In addition, some pyrazole isosters (37, 38, 40, and 45) of these rigid pyrroleethylamines have been made. All of the classes show dopaminergic activity in prolactin inhibition and in lesioned rat turning assays. The most potent drugs, the linear tricyclic pyrazoles 38 (R = Pr) and 40 (R = Pr), are comparable in potency with the highly active ergoline pergolide (41).

Animals↗