Chronic neuroleptic treatment in rats produces persisting changes in GABAA and dopamine D-2, but not dopamine D-1 receptors

The effects of continuous treatment with haloperidol (HAL) or fluphenazine (FLU) for 10 months on dopamine and GABA receptors in the rat brain was examined using in vitro autoradiography. Rats treated with HAL, but not FLU, showed an increase in D-2 receptor binding in the caudate-putamen as revealed by [3H]spiperone. Labeling of D-1 receptors by [3H]SCH23390 revealed no changes in either drug-treated group. Both drug-treated groups, however, exhibited a significant increase in [3H]muscimol binding in substantia nigra, pars reticulata (SNR). These dopaminergic-GABAergic receptor alterations may be related to previously reported changes in oral movement activity seen in these neuroleptic-treated animals.     

Dietary restriction alters demographic but not behavioral aging in Drosophila

Dietary restriction extends lifespan substantially in numerous species including Drosophila. However, it is unclear whether dietary restriction in flies impacts age-related functional declines in conjunction with its effects on lifespan. Here, we address this issue by assessing the effect of dietary restriction on lifespan and behavioral senescence in two wild-type strains, in our standard white laboratory stock, and in short-lived flies with reduced expression of superoxide dismutase 2. As expected, dietary restriction extended lifespan in all of these strains. The effect of dietary restriction on lifespan varied with genetic background, ranging from 40 to 90% extension of median lifespan in the seven strains tested. Interestingly, despite its robust positive effects on lifespan, dietary restriction had no substantive effects on senescence of behavior in any of the strains in our studies. Our results suggest that dietary restriction does not have a global impact on aging in Drosophila and support the hypothesis that lifespan and behavioral senescence are not driven by identical mechanisms.     

Permissive role of D-1 receptor stimulation for the expression of D-2 mediated behavioral responses: a quantitative phenomenological study in rats

The syndrome of behavioral stimulation induced in male Sprague-Dawley rats by two dopaminergic agents was studied by distinguishing specific behavioral items and quantifying them in terms of their incidence. The specific D-2 agonist LY 171555 elicited yawning, genital grooming, exploratory behavior, downward sniffing and licking but failed to induce gnawing even at high doses. On the other hand, the D-1/D-2 agonist apomorphine elicited the full stereotyped syndrome including gnawing. Depletion of endogenous dopamine (DA) by alpha-methyltyrosine (alpha-MT) prevented the ability of LY 171555 to elicit all the items of behavioral stimulation including the stereotyped ones (sniffing and licking). In contrast, the ability of apomorphine to induce stereotypies was not reduced by depletion of endogenous DA by alpha-MT pretreatment. Blockade of D-1 receptors with SCH 23390 abolished the capacity of both LY 171555 and apomorphine to elicit all the items of behavioral stimulation. In alpha-MT pretreated rats, administration of low doses of the D-1 agonist SKF 38393 (2.5 mg/kg s.c.) reinstated the ability of LY 171555 to elicit behavioral stimulation and eventually conferred the ability of inducing gnawing. The results support the hypothesis that stimulation of D-1 receptors exerts a permissive role for the expression of behavioral stimulation following D-2 receptor stimulation. Endogenous DA appears to provide sufficient D-1 input to permit full expression of yawning, genital grooming, exploratory behavior, downward sniffing and licking following D-2 stimulation; pharmacological stimulation of D-1 in addition to D-2 receptors seems however necessary for full expression of the highest rank stereotypy item, gnawing.     

Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.     

Prenatal amphetamine reduces alpha but not beta adrenergic receptor binding in brain of adult rats

Adults offspring of rats treated with daily injection of d,l-amphetamine sulfate (0.5 mg/kg s.c.) during pregnancy showed a significant decrease in brain alpha but not beta adrenergic receptor binding, without apparent changes in receptor affinity. This change may be a consequence of long lasting alterations in the metabolism of brain catecholamines produced by amphetamine administration at fetal age, and may account for the behavioral alterations described in these animals.     

Late pulmonary allergic responses in actively but not passively IgE-sensitized rats

Previous studies suggested that although rats that were passively sensitized [monoclonal murine immunoglobulin E (IgE)] would respond to pulmonary antigen challenge with an immediate increase in resistance, they exhibited no late increases in resistance, unlike late changes in rats actively sensitized to preferentially produce IgE antibody. We hypothesized that passively sensitized rats also would not develop antigen-induced pulmonary inflammation. In a blinded protocol we compared immediate responses and pulmonary resistance and inflammation at 8, 19 and 24 h after challenge with placebo antigen, with dinitrophenol-bovine serum albumin (DNP-BSA) to elicit a passively sensitized response, or with ovalbumin (OA) to elicit an actively sensitized response. Despite similar immediate responses to OA and DNP-BSA, only the rats challenged with OA had marked inflammatory changes and a significant incidence of late elevations in resistance. Inflammation scores and lung resistance were significantly correlated only in the OA group. We also observed that anesthesia with fentanyl/droperidol significantly attenuated the immediate but not the late responses to antigen challenge, compared with rats anesthetized with ketamine. We conclude that IgE-mediated immediate responses to pulmonary antigen challenge are insufficient, and may be unnecessary, to initiate antigen-induced late inflammatory changes.     

Co-administration of quercetin and catechin in rats alters their absorption but not their metabolism

Quercetin and catechin are among the major flavonoids in plant foods and their intake has been associated to a risk reduction in several degenerative diseases. The aim of the present study was to bring data on the bioavailability of quercetin and catechin when administered simultaneously. The study was performed on rats adapted to diets containing (i) 0.25% quercetin, or (ii) 0.25% catechin, or (iii) 0.25% quercetin+0.25% catechin. Quercetin, catechin and their metabolites were determined in plasma, urine and liver by HPLC with UV or coulometric detection. When quercetin and catechin were fed in association, their respective plasma concentration significantly decreased (-35% and -28% respectively), whereas the urinary and hepatic concentrations were only affected for quercetin (-36%). These data may be explained by a competitive interaction between quercetin and catechin at the digestive level, leading to a reduction of the intestinal absorption of quercetin and a possible delaying of catechin absorption over time. The simultaneous administration of quercetin and catechin had no effect on the formation of their glucurono and sulfo conjugates, indicating the absence of competition between quercetin and catechin for the corresponding conjugative enzymes.     

Electric field exposure alters serum melatonin but not pineal melatonin synthesis in male rats

Sprague-Dawley male rats, maintained in a 14:10 h light:dark cycl were exposed for 30 days (starting at 56 days of age) to a 65 kV/m, 60 Hz electric field or to a sham field for 20 h/day beginning at dark onset. Pineal N-acetyltransferase (NAT), hydroxy-indole-o-methyl transferase (HIOMT), and melatonin as well as serum melatonin were assayed. Preliminary data on unexposed animals indicated that samples obtained 4 h into the dark period would reveal either a phase delay or depression in circadian melatonin synthesis and secretion. Exposure to electric fields for 30 days did not alter the expected nighttime increase in pineal NAT, HIOMT, or melatonin. Serum melatonin levels were also increased at night, but the electric field-exposed animals had lower levels than the sham-exposed animals. Concurrent exposure to red light and the electric field or exposure to the electric field at a different time of the day-night period did not reduce melatonin synthesis. These data do not support the hypothesis that chronic electric field exposure reduces pineal melatonin synthesis in young adult male rats. However, serum melatonin levels were reduced by electric field exposure, suggesting the possibility that degradation or tissue uptake of melatonin is stimulated by exposure to electric fields. © 1994 Wiley-Liss, Inc.     

Acute depletion of heme by succinylacetone alters vascular responses but does not induce hypertension

Heme plays a critical role in blood pressure regulation because it is required by a number of enzymes that synthesize vascular modulators, including nitric oxide (NO), carbon monoxide (CO), guanosine 3',5'-cyclic monophosphate (cGMP), endothelium-derived hyperpolarizing factor (EDHF), and prostacyclin. The goal of this study was to examine the vascular effects of a short-term depletion of heme achieved through administration of the heme-synthesis inhibitor succinylacetone (SA), an irreversible inhibitor of aminolevulinic acid dehydratase (ALAD). Rats were depleted of heme by using a 4-day treatment with SA. This treatment impacted hemoenzyme function, decreasing renal nitric oxide synthase (NOS) activity (as indicated by decreased in vitro NOS activity), and increasing kidney microsomal heme oxygenase (HO) activity by 27%. SA treatment also resulted in enhanced reduction in blood pressure after infusions of exogenous NO donor MAHMA NONOate (at high dose) and acetylcholine (at low doses). Nevertheless, this SA treatment was insufficient to produce an overt elevation of basal arterial pressure. This latter lack of effect may be the result of multiple compensatory mechanisms for the regulation of blood pressure.     

Chronic, but not acute, administration of morphine alters antiopiate (Tyr-MIF-1) binding sites in rat brain

Opiate addiction could involve a change in the binding of endogenous antiopiates. A candidate for such a role is Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2), a brain peptide that can antagonize exogenous and endogenous opiates and bind to opiate receptors. Its primary action, however, may be through its own binding site in brain, which we now report is altered by chronic administration of morphine. Rats given morphine pellets had reduced binding of both iodinated and tritiated Tyr-MIF-1 on day 5, when substantial tolerance is evident. In contrast, mu and delta opiate receptors were increased. Acute injection of an analgesic dose of morphine did not reduce Tyr-MIF-1 binding, indicating that chronic administration is required for the change. These findings open new approaches to the study of addiction by focusing on antiopiate activity.     

Regulation and Expression of D-1, but not D-5, Dopamine Receptors in Human SK-N-MC Neuroblastoma Cells

Abstract

Human SK-N-MC neuroblastoma cells endogenously express functional D-1-like dopamine receptors. The recent identification of at least two distinct type of D-1-like receptors, D-1 and D-5, lead us to investigate the precise molecular identity of the receptors expressed in these cells. By using specific primer sets and amplification of the mRNA by RT-PCR, we show that only D-1, but not D-5, dopamine receptors are expressed in these cells. Treatment of cells with 100 μM dopamine initially caused an upregulation in D-1 mRNA expression, followed by attenuation of the message compared to control, untreated cells. The D-1 receptors in SK-N-MC cells, whose expression is controlled by dopamine in a bimodal manner, may be important in understanding how these receptors are regulated at the molecular level.     

Perinatal lead exposure alters locomotion induced by amphetamine analogs in rats

AimsThe precise neurochemical perturbations through which perinatal (gestation/lactation) lead exposure modifies the reinforcement efficacy of various psychoactive drugs (e.g., cocaine, opiates) are unknown. The present study considers the role of altered serotonin and dopamine functionality in perinatal lead-psychostimulant interactions.Main methodsFemale rats were administered a 16-mg lead or a control solution (p.o.) for 30 days prior to breeding with non-exposed males. Lead exposure was discontinued at weaning (postnatal day [PND] 21). Starting at PND 120, male rats born to control or lead-exposed dams were injected with either PAL-287 or PAL-353, at doses of 0, 2, 4, 8, or 16 umol/kg (i.p.) with each dose given prior to an acute (45 min) locomotion test. Whereas PAL-287 is a potent releaser of serotonin, PAL-353 is not. Each drug induces comparable release of norepinephrine (NE) and of dopamine (DA).Key findingsControl and lead rats exhibited minimal locomotion to PAL-287. PAL-353 produced a dose-dependent activation of locomotion in control rats relative to the effects of PAL-287 in control rats. Lead-exposed rats exhibited a subsensitivity to PAL-353 at doses of 4 and 8 umol/kg.SignificanceThe subsensitivity of lead rats to PAL-353 is consistent with a lead-induced diminution of dopamine function, an effect noted earlier for the reuptake inhibitor cocaine (Nation et al. 2000). The similar response of lead and control rats to PAL-287 is inconsistent with diminished serotonin function.     

Estrogen alters excitability but not morphology of a sexually dimorphic neuromuscular system in adult rats

In rats, motoneurons of the spinal nucleus of the bulbocavernosus (SNB) innervate the bulbocavernosus (BC) muscle, which surrounds the base of the penis. The SNB/BC is a sexually dimorphic, steroid-sensitive neuromuscular system, which is critically important in male reproductive behavior. Androgens are necessary for the development, morphology, and function of the SNB/BC system. However, estradiol (E) is also necessary for the development of the SNB/BC system, and E is capable of maintaining BC EMG activity in adulthood. In this study, we used electrophysiological and anatomical methods to examine estrogenic effects on BC EMG activity. We used a modified H-reflex testing method to investigate polysynaptic reflex characteristics in intact males, castrates, and castrates treated short term with estradiol benzoate (EB). Measures of EMG activity, response latency, and spike count were altered in castrates, but maintained in EB-treated castrates to the levels of intact males. Furthermore, estrogenic effects were found in EMG activity that could be isolated to the periphery of the SNB/BC system. BC NMJ size and muscle fiber area have been demonstrated to be hormone sensitive, and we examined these for possible correlates of E's effects on BC EMG activity. BC muscles of intact males, castrates, and short-term EB-treated castrates were fixed and stained with zinc iodide and osmium tetroxide. NMJ size and muscle fiber area did not differ between groups. Together, these data suggest that E treatment results in changes in the neuromuscular periphery that maintain BC EMG activity, but this effect cannot be accounted for by changes in NMJ size or muscle fiber area.     

Chronic ethanol attenuates centrally-mediated hypotension elicited via α2-adrenergic,but not I1-imidazoline,receptor activation in female rats

AimsThis study dealt with the effect of chronic ethanol administration on hemodynamic responses elicited by α₂-adrenergic (α-methyldopa) or I₁-imidazoline (rilmenidine) receptor activation in telemetered female rats.Main methodsThe effects of α-methyldopa or rilmenidine on blood pressure (BP), heart rate (HR) and their variability were investigated in rats that received liquid diet without or with ethanol (5% w/v) for 12 weeks. To evaluate the effect of each drug on cardiovascular autonomic control (BP and HR variability) in the absence or presence of ethanol, three time-domain indices of hemodynamic variability were measured: (i) standard deviation of mean arterial pressure (SDMAP), (ii) standard deviation of beat-to-beat intervals, and (iii) root mean square of successive differences in R–R intervals.Key findingsIn liquid diet-fed control rats, i.p. rilmenidine (600 µg/kg) or α-methyldopa (100 mg/kg) reduced BP along with decreases and increases, respectively, in HR. Both drugs had no effect on HR variability but reduced BP variability (SDMAP), suggesting a reduced vasomotor sympathetic tone. Ethanol feeding attenuated reductions in BP and SDMAP evoked by α-methyldopa but not by rilmenidine.SignificanceWe conclude that chronic ethanol preferentially compromises α₂- but not I₁-receptor-mediated hypotension in female rats probably via modulation of vasomotor sympathetic activity. These findings highlight the adequacy of rilmenidine use to lower BP in hypertensive alcoholic females.     

Cholesterol feeding alters the metabolism of thoracic-duct lymph lipoprotein cholesterol in rabbits but not in rats

1. Labelled thoracic-duct lymph was collected from rats and rabbits after test meals containing [(14)C]cholesterol and [2-(3)H]glyceryl trioleate. 2. The metabolism of labelled cholesterol and triglyceride was studied in normally fed and cholesterol-fed rats and rabbits injected with radioactive lymph from the same species. 3. In normally fed animals of both species, 10min after intravenous administration, about 80% of lymph cholesteryl ester but only about 10% of triglyceride was recovered in the liver after clearance from the plasma. This distribution is consistent with participation of ;remnant' particles in the metabolism of dietary lymph particles. 4. The metabolism of cleared lymph lipoprotein constituents was unchanged in cholesterol-fed rats, but the recovery of cholesteryl ester in the livers of the cholesterol-fed rabbits was decreased to 30% of the cleared dose. 5. The low recovery in cholesterol-fed rabbits was accounted for mainly by increased hydrolysis of cholesteryl ester. 6. It is proposed that differences between rats and rabbits in metabolism of dietary cholesterol might be partly due to the observed enhancement of hydrolysis of lymph lipoprotein cholesteryl ester in rabbits.     

Metformin restores responses to insulin but not to growth hormone in Sprague-Dawley rats

Administration of growth hormone (GH) increases muscle mass in F344 x BN rats, but not in Sprague-Dawley (S-D) rats. S-D rats are insulin-resistant and insulin responsiveness is required for the anabolic actions of GH. We hypothesized that correction of insulin resistance with metformin might also restore anabolic effects of GH. Treatment with GH (0.25 or 1.0 mg/kg twice daily for 9 days) had limited anabolic effects, reducing weight gain by 14%, increasing muscle glycogen content by 40% and increasing exercise capacity by 24%, but failing to increase muscle mass or to reduce fat mass. GH also impaired insulin responsiveness and increased visceral fat TNF content of visceral fat by 77%. Metformin enhanced insulin responsiveness in skeletal muscle, but failed to enhance anabolic effects of GH. Rats aged 14 weeks were treated for 21 days with metformin (320 mg/kg/day) and for the last 9 days, with GH (0.25 mg/kg, twice daily). Metformin caused a 2.3-fold increase in insulin-stimulated muscle glucose transport and a 20% reduction in muscle fatty acid oxidation, indicating increased glucose utilization. However, metformin did not augment GH-induced weight reduction. Metformin decreased visceral fat by 22% and subcutaneous fat by 20%, but no decreases were observed in the GH/metformin group. GH increased muscle glycogen by 40%, but the effect was reversed by metformin. VO(2max) was increased 24% by GH and 17% by metformin, but was not elevated in the GH/metformin group. GH increased TNF in visceral fat and the effect was augmented by metformin (144% increase). We conclude that metformin enhances some aspects of insulin responsiveness, but does not enhance anabolic responses to GH. The latter may, in part, be explained by the failure of metformin to prevent GH-induced elevation of TNF in visceral fat.     

Metyrapone and fluoxetine suppress enduring behavioral but not cardiac effects of subchronic stress in rats

In humans, chronic stressors have long been recognized as potential causes for cardiac dysregulation. Despite this, the underlying mechanistic links responsible for this association are still poorly understood. The purpose of this study was to determine whether exposure to a paradigm of subchronic stress can provoke enduring changes on the heart rate of experimental rats and, if so, to reveal the autonomic and neural mechanisms that mediate these effects. The study was conducted on adult male Sprague-Dawley rats instrumented for telemetric recording of heart rate and locomotor activity. Animals were submitted to a subchronic stress protocol, consisting of a 1-h foot shock session on five consecutive days. Heart rate and locomotor activity were recorded continuously for 3 days before and for 6 days after the subchronic stress period. Subchronic foot shock produced significant and enduring reduction in heart rate both during the dark/active [Δ= -23 ± 3 beats per minute (bpm)] and light/inactive (Δ= -20 ± 3 bpm) phases of the circadian cycle, and a reduction in locomotor activity during the dark/active phase [Δ= -54 ± 6 counts per hour (cph)]. The bradycardic effect of subchronic stress was not related to a reduced locomotion. Selective sympathetic (atenolol) and vagal (methyl-scopolamine) blockades were performed to reveal which autonomic component was responsible for this effect. We found that the fall in heart rate persisted after subchronic stress in animals treated with atenolol (active phase Δ= -16 ± 3 bpm, inactive phase Δ= -19 ± 2 bpm), whereas vagal blockade with scopolamine transiently prevented this effect, suggesting that the bradycardia following subchronic stress was predominantly vagally mediated. Fluoxetine (selective serotonin reuptake inhibitor) and metyrapone (inhibitor of corticosterone synthesis) treatments did not affect heart rate changes but prevented the reduction in locomotion. We conclude that subchronic stress exposure in rats reduces heart rate via a rebound in vagal activation and that this effect is serotonin- and corticosterone-independent.     

Conditioned place preference from intra-accumbens but not intra-caudate amphetamine injections

Rats received injections of d-amphetamine sulphate (10 micrograms in 0.5 ul) in nucleus accumbens and were placed into one of two (randomly assigned) distinctive environments. The next day the rats were placed into the other environment and received either a saline injection or no treatment. This procedure was repeated six times. When the rats were allowed a free choice between the two environments they showed a significant preference for the one that had been paired with amphetamine. This finding suggests that amphetamine-stimulated release of dopamine in nucleus accumbens can increase the incentive value of neutral stimuli with which it is paired. When the same procedure was carried out with a group of rats that received amphetamine injections in the dorsolateral caudate nucleus, no preference for the side paired with the drug was evident. This suggests that there is functional differentiation between different parts of the dopaminergic terminal system.     

Acute and long-term amphetamine treatments alter extracellular ascorbate in neostriatum but not nucleus accumbens of freely moving rats

The ability of amphetamine to alter the extracellular level of ascorbate, an apparent modulator of neostriatal function, was assessed voltammetrically in the neostriatum and nucleus accumbens of awake, behaving rats. Whereas acute administration (1.0 and 5.0 mg/kg d-amphetamine) produced a dose-dependent rise in neostriatal ascorbate, there was no change in the nucleus accumbens. Vehicle injections had no significant effect on ascorbate levels in either location. Administration of 5.0 mg/kg d-amphetamine for one week enhanced neostriatal ascorbate release even further, but this effect returned to acute levels when treatment continued for a second week. Multiple amphetamine injections for up to two weeks failed to alter extracellular ascorbate in the nucleus accumbens. The results of these experiments confirm a site-specific action of amphetamine on ascorbate release and suggest complex changes in the extracellular level of this substance in the neostriatum with long-term treatment.     

A single intrategmental amphetamine exposure induces transient behavioral sensitization in the rats

Repeated treatment with psychostimulant drugs induces enduring behavioral sensitization and neuroadaptations which may play an important role in the development of drug addiction. However, different number and time course in drug administration and various lengths of drug withdrawal were employed in the literature, and there were inconsistent findings in the profile of extracellular dopamine level related to behavioral sensitization. Therefore, the effects of the number of drug exposure and the length of drug withdrawal period on the sensitized behavioral response were investigated in this study. Various lengths of amphetamine (AMPH) withdrawal (1, 3 and 5 days) after a single local administration of AMPH to bilateral ventral tegmental area (VTA) were used to observe the locomotor activity response. Besides, different amounts of administration of intra-VTA AMPH were given (1, 2 and 3 times of injection) to monitor the profile of travel distance and stereotypic movements of rats after 7 days of drug withdrawal. An early and short-lived behavioral sensitization to the single intra-VTA AMPH administration was induced. In the repeated treatment group, more drug exposures were associated with escalating and robust levels of travel distance after 7 days of drug withdrawal. The authors speculated that the transient and, a later augmented locomotor activity response might represent respective phases in the development of behavioral sensitization, which in turn contributed to the formation of more lasting behavioral and neuroplastic changes associated with drug addiction.