The Effects of Long-term Molybdenum Exposure in Drinking Water on Molybdenum Metabolism and Production Performance of Beef Cattle Consuming a High Forage Diet

Fifty-four multiparous beef cows with calves were used to evaluate the effects of Mo source (feed or water) on reproduction, mineral status, and performance over two cow-calf production cycles (553 days). Cows were stratified by age, body weight, liver Cu, and Mo status and were then randomly assigned to one of six treatment groups. Treatments were (1) negative control (NC; basal diet with no supplemental Mo or Cu), (2) positive control (NC + Cu; 3 mg of supplemental Cu/kg DM), (3) NC + 500 µg Mo/L from Na2MoO4·2H2O supplied in drinking water, (4) NC + 1000 µg Mo/L of Na2MoO4·2H2O supplied in drinking water, (5) NC + Mo 1000-water + 3 mg of supplemental Cu/kg DM, and (6) NC + 3.0 mg of supplemental Mo/kg diet DM from Na2MoO4·2H2O. Animals were allowed ad libitum access to both harvested grass hay (DM basis: 6.6% crude protein; 0.15% S, 6.7 mg Cu/kg, 2.4 mg Mo/kg) and water throughout the experiment. Calves were weaned at approximately 6 months of age each year. Dietary Cu concentration below 10.0 mg Cu/kg DM total diet reduced liver and plasma Cu concentrations to values indicative of a marginal Cu deficiency in beef cows. However, no production parameters measured in this experiment were affected by treatment. Results suggest that Mo supplemented in water or feed at the concentrations used in this experiment had minimal impact on Cu status and overall performance.

Neurochemical and neuroinflammatory perturbations in two Gulf War Illness models: Modulation by the immunotherapeutic LNFPIII

Gulf War Illness (GWI) manifests a multitude of symptoms, including neurological and immunological, and approximately a third of the 1990-1991 Gulf War (GW) veterans suffer from it. This study sought to characterize the acute neurochemical (monoamine) and neuroinflammatory profiles of two established GWI animal models and examine the potential modulatory effects of the novel immunotherapeutic Lacto-N-fucopentaose III (LNFPIII). In Model 1, male C57BL/6 J mice were treated for 10 days with pyridostigmine bromide (PB) and permethrin (PM). In Model 2, a separate cohort of mice were treated for 14 days with PB and N,N-Diethyl-methylbenzamide (DEET), plus corticosterone (CORT) via drinking water on days 8-14 and diisopropylfluorophosphate (DFP) on day 15. LNFPIII was administered concurrently with GWI chemicals treatments. Brain and spleen monoamines and hippocampal inflammatory marker expression were examined by, respectively, HPLC-ECD and qPCR, 6 h post treatment cessation. Serotonergic (5-HT) and dopaminergic (DA) dyshomeostasis caused by GWI chemicals was apparent in multiple brain regions, primarily in the nucleus accumbens (5-HT) and hippocampus (5-HT, DA) for both models. Splenic levels of 5-HT (both models) and norepinephrine (Model 2) were also disrupted by GWI chemicals. LNFPIII treatment prevented many of the GWI chemicals induced monoamine alterations. Hippocampal inflammatory cytokines were increased in both models, but the magnitude and spread of inflammation was greater in Model 2; LNFPIII was anti-inflammatory, more so in the apparently milder Model 1. Overall, in both models, GWI chemicals led to monoamine disbalance and neuroinflammation. LNFPIII co-treatment prevented many of these disruptions in both models, which is indicative of its promise as a potential GWI therapeutic.

The effects of molybdenum water concentration on feedlot performance, tissue mineral concentrations, and carcass quality of feedlot steers,

Thirty cross-bred steers (initial BW 452.0 ± 12.1 kg) were used to investigate the effects of Mo water concentration on performance, carcass characteristics, and mineral status of feedlot steers. The experimental design was a randomized complete block design. Steers were blocked by weight and then divided into 2 weight blocks each consisting of 15 steers. Steers were randomly assigned within block to one of 5 treatments (3 steers/treatment per block). Water treatments consisted of: 1) 0.0 µg/L, 2) 160 µg/L, 3) 320 µg/L, 4) 480 µg/L, and 5) 960 µg/L of supplemental Mo added as Na2MoO4 to the drinking water. Steers were housed in individual pens (steer = experimental unit) that contained individual 265 L water tanks for monitoring water intake. Steers were fed a growing diet for 28 d and then transitioned to a finishing diet. Block 1 steers were fed for a total of 151 d and block 2 steers were fed for a total of 112 d. Daily water intake was recorded for each steer. Steers were individually weighed on 2 consecutive days at the beginning and end of the experiment and interim weights and jugular blood samples were obtained every 28 d. Liver biopsies were obtained on d 0 and 84 from each steer within each block. Steers were transported to a commercial abattoir, slaughtered, and individual carcass data and liver samples were collected. Initial BW was used as a covariate for statistical analysis of data and significance was determined at P ≤ 0.05. No differences were observed for final BW (P > 0.98). Overall ADG (P > 0.91), DMI (P > 0.92), feed efficiency (P > 0.94), water intake (P > 0.40), hot carcass weight (P > 0.98), dressing percentage (P > 0.98), yield grade (P > 0.91), and marbling score (P > 0.29) did not differ across treatments. Lastly, no treatment differences were observed for liver concentrations of Cu (P > 0.93), Mo (P > 0.90) and Zn (P > 0.86) or plasma concentrations of Cu (P > 0.42), Mo (P > 0.43) and Zn (P > 0.62). These data indicate that water Mo concentration, within the range studied, had no impact on performance, mineral status, water intake, and carcass characteristics in feedlot steers.

Nutritional depletion of total mixed rations by European starlings: Projected effects on dairy cow performance and potential intervention strategies to mitigate damage

European starlings are an invasive bird species in North America that are known to cause damage to commercial dairies through the consumption of total mixed rations (TMR) destined for dairy cows. We hypothesized that large foraging flocks of starlings alter the physical composition of TMR, and that this change may be significant enough to affect milk production. To better determine if production losses could potentially occur in commercial dairies as a consequence of feed consumption by foraging flocks of starlings, we conducted controlled feeding experiments using a TMR sourced from a commercial dairy that is chronically plagued with seasonal starling damage. European starlings selected the high-energy fraction of the TMR and reduced starch and crude fat availability. Using the dairy National Research Council production model equations, the nutritional changes measured in the controlled feeding experiments could potentially reduce the productivity of dairies. Model output suggests that for Holsteins producing 32 kg of milk/d, total required net energy intake (NE_I) was 31.5 Mcal/d. Within the reference TMR, NE_I supplied was 29.3 Mcal/d, whereas within the starling-consumed TMR NE_I supplied was 27.7 Mcal/d. Following our nutrition experiments, we assessed the efficacy of pelleted feed as a deterrent strategy for bird damage management in commercial dairies. Six different pelleted feed treatments of differing diameter were offered to starlings. All pellets of 0.95 cm diameter or larger inhibited starling consumption by ≥79%.

Genetic parameters estimated at receiving for circulating cortisol, immunoglobulin G, interleukin 8, and incidence of bovine respiratory disease in feedlot beef steers

Bovine respiratory disease complex (i.e., shipping fever and bacterial bronchopneumonia) is a multifaceted respiratory illness influenced by numerous environmental factors and microorganisms. Bovine respiratory disease (BRD) is just one component of BRD complex. Because BRD is moderately heritable, it may be possible to reduce the incidence of BRD through genetic selection. The objectives of this study were to determine the heritability and associative genetic relationships among immune system traits (i.e., cortisol, total IgG, IgG isotypes, and IL-8) in cattle monitored for BRD incidence. At an average of 83 d after weaning (219 d age and mean = 221.7 kg [SD 4.34]), crossbred Bos taurus steer calves (n = 2,869) were received at a commercial feedlot in southeastern Colorado over a 2-yr period. At receiving, jugular blood samples were collected at 212 (yr 1) and 226 d (yr 2) of age for immune trait analyses. The BRD phenotype was defined as a binomial variable (0 = no and 1 = yes) and compared with immune system traits measured at receiving (prior to illness onset). An animal identified as BRD positive exhibited ≥ 2 clinical signs (i.e., eye or nasal discharge, cough, lethargy, rapid breathing, acute interstitial pneumonia, or acute upper respiratory syndrome and/or a rectal temperature > 39.7°C). Heritability and genetic correlation estimates for categorical variable BRD, cortisol, IgG, IgG1, IgG2, and IL-8 were estimated from a sire model using ASREML. Heritability estimates were low to moderate for BRD (0.17 ± 0.08), cortisol (0.13 ± 0.05), IgG (0.15 ± 0.05), IgG1 (0.11 ± 0.05), IgG2 (0.24 ± 0.06), and IL-8 (0.30 ± 0.06). A moderate negative genetic correlation was determined between BRD and cortisol (r_g = −0.19 ± 0.32). Moderate positive correlations were found between BRD with IgG (0.42 ± 0.28), IgG1 (0.36 ± 0.32), and IL-8 (r_g = 0.26 ± 0.26). Variation in the BRD phenotype and immune system traits suggested herd health improvement may be achieved through genetic selection.

Evaluation of multiple ancillary therapies used in combination with an antimicrobial in newly received high-risk calves treated for bovine respiratory disease

Ancillary therapy (ANC) is commonly provided in conjunction with an antimicrobial when treating calves for suspected bovine respiratory disease (BRD) in an attempt to improve the response to a suspected BRD challenge. The first experiment evaluated the effects of 3 ANC in combination with an antimicrobial in high-risk calves treated for BRD during a 56-d receiving period. Newly received crossbred steers (n = 516; initial BW = 217 ± 20 kg) were monitored by trained personnel for clinical signs of BRD. Calves that met antimicrobial treatment criteria (n = 320) were then randomly assigned to experimental ANC treatment (80 steers/experimental ANC treatment): intravenous flunixin meglumine injection (NSAID), intranasal viral vaccination (VACC), intramuscular vitamin C injection (VITC), or no ANC (NOAC). Animal served as the experimental unit for all variables except DMI and G:F (pen served as the experimental unit for DMI and G:F). Within calves treated 3 times for BRD, those receiving NOAC had lower (P < 0.01) clinical severity scores (severity scores ranged from 0 to 4 on the basis of observed clinical signs and severity) and heavier (P = 0.01) BW than those receiving NSAID, VACC, or VITC at the time of third treatment. Between the second and third BRD treatments, calves receiving NOAC had decreased (P < 0.01) daily BW loss (−0.13 kg ADG) compared with those receiving NSAID, VACC, or VITC (−1.30, −1.90, and −1.41 kg ADG, respectively). There were no differences in rectal temperature, combined mortalities and removals, or overall performance among the experimental ANC treatments. Overall, morbidity and mortality attributed to BRD across treatments were 66.5% and 13.2%, respectively. After the receiving period, a subset of calves (n = 126) were allocated to finishing pens to evaluate the effects ANC administration on finishing performance, carcass characteristics, and lung scores at harvest. Ultrasound estimates, BW, and visual appraisal were used to target a common physiological end point for each pen of calves. There were no differences among the experimental ANC observed during the finishing period (P ≥ 0.11). In summary, the use of NSAID, VACC, and VITC do not appear to positively impact clinical health and could potentially be detrimental to performance during the receiving period in high-risk calves receiving antimicrobial treatment for suspected BRD.

Neurochemical and electrophysiological deficits in the ventral hippocampus and selective behavioral alterations caused by high-fat diet in female C57BL/6 mice

Mounting experimental evidence, predominantly from male rodents, demonstrates that high-fat diet (HFD) consumption and ensuing obesity are detrimental to the brain. To shed additional light on the neurological consequences of HFD consumption in female rodents and to determine the relatively early impact of HFD in the likely continuum of neurological dysfunction in the context of chronic HFD intake, this study investigated effects of HFD feeding for up to 12weeks on selected behavioral, neurochemical, and electrophysiological parameters in adult female C57BL/6 mice; particular focus was placed on the ventral hippocampus (vHIP). Selected locomotor, emotional and cognitive functions were evaluated using behavioral tests after 5weeks on HFD or control (low-fat diet) diets. One week later, mice were sacrificed and brain regional neurochemical (monoamine) analysis was performed. Behaviorally naïve mice were maintained on their respective diets for an additional 5-6weeks at which time synaptic plasticity was determined in ex vivo slices from the vHIP. HFD-fed female mice exhibited increased: (i) locomotor activity in the open field testing, (ii) mean turn time on the pole test, (iii) swimming time in the forced swim test, and (iv) number of marbles buried in the marble burying test. In contrast, the novel object recognition memory was unaffected. Mice on HFD also had decreased norepinephrine and dopamine turnover, respectively, in the prefrontal cortex and the vHIP. HFD consumption for a total of 11-12weeks altered vHIP synaptic plasticity, evidenced by significant reductions in the paired-pulse ratio and long-term potentiation (LTP) magnitude. In summary, in female mice, HFD intake for several weeks induced multiple behavioral alterations of mainly anxiety-like nature and impaired monoamine pathways in a brain region-specific manner, suggesting that in the female, certain behavioral domains (anxiety) and associated brain regions, i.e., the vHIP, are preferentially targeted by HFD.

High-dose anabolic implants are not all the same for growth and carcass traits of feedlot steers: a meta-analysis

A meta-analysis of studies evaluating feedlot steer implant programs was conducted to evaluate the differential effects of anabolic implant dosage on feedlot performance and carcass traits. The effect sizes of the implant dosage of interest vs. negative controls and vs. other implant dosages on various dependent variables (ADG, F:G, DMI, dressing percentage [DP], HCW, yield grade, percentage Choice or higher, and marbling score) were calculated. Treatments used for comparisons included no implant, EST (20 mg estradiol benzoate + 200 mg progesterone, 36 mg zeranol, or 72 mg zeranol), ET120 (24 mg estradiol 17β + 120 mg trenbolone acetate [TBA]), and ET200 (28 mg estradiol benzoate + 200 mg TBA or 20 mg estradiol-17β + 200 mg TBA). In the first analysis, the 3 implant dosages were compared to negative control. A second analysis was conducted to compare ET120 vs. ET200 using only studies that included a direct comparison of these 2 dosages. The number of studies included in the analysis for each implant dosage and response variable ranged from 34 to 7. A mixed model was used to evaluate individual implant treatments; implant dosage was a fixed effect, and individual study was included as a random effect. All dosages had greater ADG, DMI, and HCW and lower F:G, percentage Choice, and marbling score vs. negative controls (P < 0.05) In the second direct comparison analysis, ET200 tended to have greater ADG (P = 0.10) and HCW (P = 0.07) and had lower F:G (P < 0.01) and percentage of carcasses grading Choice or greater (P < 0.01) vs. ET120. Differences in HCW between ET120 and ET200 diminished numerically with increasing days of implant activity (P < 0.01). All dosages of implants evaluated herein increased performance and decreased quality grade vs. negative controls. Combination implants containing estrogen (E) and 200 mg TBA have greater potency for growth promotion than implants containing E+120 mg TBA resulting in slightly greater performance.

Evaluation of Saccharomyces cerevisiae fermentation product as an alternative to monensin on growth performance, cost of gain, and carcass characteristics of heavy-weight yearling beef steers

Two hundred fifty-two cross-bred yearling steers (406 ± 24 kg BW) were used in a completely randomized block design with a 2 × 2 factorial arrangement of treatments (7 pens/treatment) to evaluate the effects of dietary Saccharomyces cerevisiae fermentation product (SFP) and monensin (MON) on growth performance and carcass characteristics. Dietary treatments arranged as a 2 × 2 factorial were 1) with or without SFP and 2) with or without MON. Finishing diets contained 19.7% of DM as dried distiller's grains with solubles. Both SFP and MON were added in the total mixed ration in place of an equal amount of cornmeal (DM basis; target intake = 2.8 g of SFP and 33 mg of MON/kg of dietary DM). Each treatment group was offered ad libitum access to a transition ration from d 1 to 8 and then to the finishing ration from d 9 to 125. Body weights were collected on d 0, 28, 56, 84, 110, and 125. Initial and final BW was an average of 2-d weights (d -1 and 0 and d 124 and 125, respectively). Steers were shipped for harvest on d 125. Overall ADG was decreased (P = 0.03) in steers supplemented with SFP, but final BW was similar among treatments. Feeding SFP was associated with lighter (P < 0.01) HCW and a greater (P = 0.01) number of carcasses grading USDA Choice. Twelfth rib fat thickness was not affected by SFP (P = 0.82) or MON (P = 0.35), but numerical decreases in 12th rib fat thickness among cattle receiving SFP or MON alone contributed to a tendency (P = 0.07) for greater 12 rib fat thickness when SFP and MON were provided. There was no effect of treatment on cost of gain (P ≥ 0.21). The effects of SFP in the current study may have been limited in heavy yearling steers due to consumption of a finishing diet containing 19.7% dried distiller's grains with solubles.

D-serine treatment reduces cocaine-primed reinstatement in rats following extended access to cocaine self-administration

The most intractable feature of drug addiction is the high rate of relapse, even following extended periods of abstinence from drug-taking. Evidence suggests that allowing rats extended access to cocaine self-administration leads to behavioral characteristics in these animals that are consistent with the development of addiction in humans. In the current study, rats were allowed to self-administer cocaine over a total of 22 daily sessions, the final seven of which were long-access (LgA) sessions of 6 h duration. Assessments of reinstatement of drug-seeking behavior were made following reintroduction to the drug-taking environment and noncontingent priming with either conditioned stimulus (CS) or cocaine in both extinguished and abstinent subject groups. Three separate groups of rats were treated with either saline or D-serine (100 mg/kg i.p.) administered 2 h prior to, or immediately following, each extinction training session. Saline-treated LgA rats were resistant to the effects of extinction training to reduce noncontingent priming of reinstatement of drug-seeking behavior with either CS or cocaine. In contrast, treatment with D-serine either before or immediately following the sessions resulted in a significant enhancement in the ability of extinction training to reduce cocaine-primed reinstatement of drug-seeking behavior. These results suggest that D-serine can act to enhance the consolidation of extinction learning in LgA rats, and is therefore a promising adjunctive agent along with behavioral therapy for the treatment of cocaine addiction.

Effects of winter growing program on visceral organ mass, composition, and oxygen consumption of beef steers during growing and finishing

The purpose of this experiment was to investigate the effects of winter growing program on organ mass, composition, and oxygen consumption in beef steers. A total of 46 steers were used for the experiment. Four steers were randomly selected as an initial slaughter group. Remaining steers were randomly allotted to 1 of 4 treatment groups: 1) fed a high-concentrate diet for ad libitum intake (CF); 2) grazed on wheat pasture (WP); 3) fed a sorghum silage-based growing diet (SF); or 4) program fed a high-concentrate diet (PF). Steers in the WP, SF, and PF groups were managed to achieve approximately equal rates of BW gain during the growing phase. After the growing phase (112 d), steers in the WP, SF, and PF treatments were adapted to a high-concentrate diet for finishing. Steers from all treatments were slaughtered at a fat thickness of 1.27 cm as estimated by ultrasound. In addition, 6 steers from each treatment were randomly selected for slaughter at the end of the growing phase. Weights of all individual organs were measured and tissue samples of duodenum and liver collected. At the end of the growing phase, WP steers had greater (P < 0.05) small intestine, liver, and kidney mass than SF and PF steers. In contrast, mesenteric fat mass and total visceral fat content were greatest (P < 0.01) for PF, intermediate for SF, and least for WP steers. Mass of total viscera and total splanchnic tissues (TST) did not differ (P > 0.10) among treatments. At final slaughter, mass of mesenteric fat, total viscera, and TST were similar among treatments, but liver weights remained greatest (g/kg of empty BW; P < 0.01) for WP steers. There were no differences in oxygen consumption of duodenum or liver tissue on an equal weight basis (microL.min(-1.)g(-1)) at the end of either period. Growing program affected mass of components of the TST at the end of the growing phase, which contributed to differences in rate of splanchnic organ growth during finishing. We conclude that program feeding a high-concentrate diet during the growing phase may result in greater ADG and G:F during the subsequent finishing period compared with forage-based diets due to less accretion of visceral organ mass resulting in reduced maintenance energy requirements during finishing.

Effect of dietary supplemental vitamin A concentration on performance, carcass merit, serum metabolites, and lipogenic enzyme activity in yearling beef steers

A randomized complete block design experiment with 360 single-source black yearling steers (average BW = 316.1 +/- 9.1 kg) fed a 91% concentrate (steam-flaked corn base) diet was conducted to evaluate the effects of supplemental vitamin A (0, 1,103, 2,205, 4,410, or 8,820 IU/kg of dietary DM) on plasma and liver vitamin A and E concentrations, lipogenic enzyme activity, marbling score, and performance of yearling steers. Final BW (586, 580, 590, 585, and 584 kg for 0, 1,103, 2,205, 4,410, and 8,820 IU of supplemental vitamin A/kg of DM, respectively) did not differ (P = 0.39) among treatments. Feed efficiency, ADG, and daily DMI did not differ (P > 0.10) among treatments within each 28-d period or for the overall experiment. From d 57 to slaughter, average DMI (10.33, 10.28, 10.57, 9.75, and 10.22 kg/steer daily for 0, 1,103, 2,205, 4,410, and 8,820 IU of vitamin A/kg of DM, respectively) was less (P < 0.02) by steers receiving 4,410 IU of supplemental vitamin A/kg of dietary DM than for steers in the other treatments. Furthermore, DMI was greater (P = 0.06) for steers receiving 2,205 IU of supplemental vitamin A/kg of dietary DM than for steers receiving 8,820 IU of supplemental vitamin A/kg of DM. Marbling score, HCW, LM area, and 12th-rib fat thickness did not differ (P > 0.10) among treatments. Similarly, the percentage of carcasses grading >or=USDA Choice (62.6, 52.8, 64.0, 58.4, and 58.4% for 0, 1,103, 2,205, 4,410, and 8,820 IU of vitamin A/kg of DM, respectively), Select, or <or=Standard did not differ (P > 0.10) among treatments. Except for d 56 (P = 0.050; r = 0.18 for liver retinol), no correlations (P > 0.10) between marbling score and any plasma or liver tissue retinol or alpha-tocopherol concentrations or vitamin A intake were found, and no differences (P > 0.10) in lipogenic enzyme activity were detected among treatments. Taken together with previous and concurrent research, results of this experiment suggest that vitamin A supplementation at a concentration up to twice the NRC recommendation has little effect on performance, marbling, or lipogenic enzyme activity in adipose tissue samples in yearling feedlot steers, and that 2,205 IU of supplemental vitamin A/kg of DM (20,000 IU/steer daily) or less is adequate to meet the vitamin A requirements of finishing beef cattle.

Effects of calcium magnesium carbonate and roughage level on feedlot performance, ruminal metabolism, and site and extent of digestion in steers fed high-grain diets

A feedlot growth performance experiment and 2 metabolism experiments were conducted to evaluate dietary roughage concentration and calcium magnesium carbonate in steers fed a high-grain diet. In Exp. 1, one hundred ninety-two crossbred yearling steers (320 +/- 10 kg of initial BW) were fed diets based on steam-flaked corn with 0, 0.75, or 1.5% CaMg(CO(3))(2). There were no effects (P > or = 0.13) on ADG, DMI, G:F, or total water intake due to CaMg(CO(3))(2). In Exp. 2, five ruminally and duodenally fistulated steers (263 +/- 9 kg of initial BW) were used in a 5 x 5 Latin square design, with 5 dietary treatments arranged in a 2 x 2 + 1 factorial: 1) 3.8% dietary roughage and no CaMg(CO(3))(2); 2) 7.6% dietary roughage and no CaMg(CO(3))(2); 3) 11.4% dietary roughage and no CaMg(CO(3))(2); 4) 3.8% dietary roughage and 1.5% CaMg(CO(3))(2); and 5) 7.6% dietary roughage and 1.5% CaMg(CO(3))(2). Water consumption was less (quadratic, P = 0.003) when 7.6% dietary roughage was fed compared with 3.8 or 11.4% dietary roughage. Intake of DM was not affected (P > or = 0.16) by dietary roughage or by CaMg(CO(3))(2). Poststomach and total tract starch digestion decreased (linear, P < 0.01) as dietary roughage increased. Ruminal pH tended (P = 0.08) to increase as dietary roughage increased but was not affected (P = 0.60) by CaMg(CO(3))(2). In Exp. 3, DMI and ruminal pH were continuously monitored in a 6 x 6 Latin square design using 6 ruminally and duodenally fistulated Holstein steers (229 +/- 10 kg of initial BW). A 3 x 2 factorial treatment structure was utilized, with factors consisting of dietary roughage concentration (4.5, 9.0, or 13.5%) and CaMg(CO(3))(2) inclusion (0 or 1.0%) to replace MgO and partially replace lime-stone. A dietary roughage x CaMg(CO(3))(2) interaction (P = 0.01) occurred as steers consuming 13.5% roughage, 1.0% CaMg(CO(3))(2) had greater DMI per meal than those consuming 4.5% dietary roughage, no CaMg(CO(3))(2) and 9.0% dietary roughage, 1.0% CaMg(CO(3))(2). Steers consuming 13.5% dietary roughage, 1.0% CaMg(CO(3))(2) and 9.0% dietary roughage, no CaMg(CO(3))(2) had greater meal length (min/meal; P = 0.01) than steers consuming 4.5% dietary roughage, no CaMg(CO(3))(2). Total tract OM digestibility decreased linearly (P = 0.01), and ruminal pH increased linearly (P = 0.01) with increasing dietary roughage concentration. Inclusion of CaMg(CO(3))(2) can replace limestone and MgO but did not produce ruminal pH responses similar to those observed by increasing dietary roughage in high-concentrate diets.

Training strategies for the user interface of vocational assistive robots

Two different user training strategies were tested on the ProVAR (professional vocational assistant robot) system. Test subjects were either trained on the full system or first separately on the graphical user interface (UI) alone, away from the robotic arm followed by training on the full system with both the UI and robotic arm. Beginning training separately from the robot allows an introduction to the system to be initiated earlier and at the location most convenient for the user. However this extra training time is not offset by a shortening of the total training time needed to master the system. The choice to do UI only training should be selected based on other motivations such as the desire to engage a potential user during mandatory bed rest, an often otherwise underutilized time.

Modulation of long-term potentiation in the rat hippocampus following cocaine self-administration

Long-lasting neuroadaptations that occur during drug use and remain after withdrawal are thought to contribute to the persisting and compulsive nature of drug addiction and relapse. At the molecular and cellular levels, mechanisms that have been implicated in the normal process of memory formation are increasingly being identified as potential contributors to the persistence of the addicted state. To investigate the effect of cocaine self-administration on synaptic plasticity, rats were allowed to self-administer 0.5 mg/kg/infusion cocaine or 0.9% NaCl during 90 min sessions for 15 consecutive days. These cocaine and saline self-administration subjects were then restricted to their home cages for 3, 30, or 100 days (3, 30, and 100 day cocaine/saline withdrawal groups) before the assessment of the induction and reversal of long-term potentiation (LTP) in the CA1 region of hippocampal slices. The magnitude of LTP was increased in the 3-day cocaine withdrawal group as compared with the 3-day saline withdrawal group, but this effect was short lived, as the 30-day cocaine and saline withdrawal groups exhibited similar LTP magnitudes. Interestingly, LTP was significantly decreased in the 100-day cocaine withdrawal group compared with the 100-day saline withdrawal group. These results support the hypothesis that the capacity for LTP is persistently altered after withdrawal from exposure to an addictive substance. In addition, this alteration can be differentially expressed such that depending upon the duration of the withdrawal period following the last drug exposure, LTP may be enhanced, unchanged, or suppressed.

Effects of water sulfate concentration on performance, water intake, and carcass characteristics of feedlot steers

Two hundred forty single-source, cross-bred steers (304 kg) were used to evaluate the effects of various water sulfate concentrations on performance, water intake, and carcass characteristics of feedlot steers. Cattle were stratified by weight and assigned within weight blocks to five water treatments. Averaged over time, actual water sulfate concentrations (+/- SEM) were 136.1 (+/- 6.3), 291.2 (+/- 15.3), 582.6 (+/- 16.9), 1,219.2 (+/- 23.7), and 2,360.4 (+/- 68.2) mg/L, respectively. Weather-related data were recorded. Increasing water sulfate concentration resulted in linear decreases in ADG (P < 0.01) and gain:feed ratio (P < 0.01) and a quadratic effect on water intake (P = 0.02) and tended to quadratically increase then decrease DMI (P = 0.13). Sulfate x period interactions were evident for DMI (P = 0.01), ADG (P < 0.01), and feed efficiency (P < 0.01). Time had quadratic effects on DMI, water intake, ADG, and feed efficiency (P < 0.01 for all models). Increasing water sulfate concentration resulted in linear decreases in final weight, hot carcass weight, and dressing percentage, a linear increase in longissimus muscle area, and a quadratic effect on fat thickness over the 12th rib and predicted yield grade (P < 0.05 for all dependent variables). Mean daily temperature explained 25.7% of the observed variation in water intake. Other factors that explained a significant (P < 0.01) amount of variation in water intake were BW, DMI, water sulfate concentration, barometric pressure, wind speed, and humidity. High water sulfate concentrations had a significant and deleterious effect on performance and carcass characteristics of feedlot steers. Increasing the sulfate concentration in water may have resulted in a functional water restriction early in the trial when ambient temperatures were greatest. However, toward the latter stages of the trial, cattle supplied higher-sulfate water had higher ADG and FE. These improvements later in the trial may represent compensatory gain associated with decreased ambient temperature and water requirements. Averaged over time, a water sulfate concentration of greater than 583 mg/L, equivalent to 0.22% of the diet, decreased feedlot performance.

Opioid-mediated facilitation of long-term depression in rat hippocampus

Previous studies have demonstrated that opioid substances are often inhibitors of the gamma-aminobutyric acid (GABA) transmitter system in the hippocampal formation, and that GABA-mediated inhibition is a potent modulator of synaptic plasticity. Field excitatory postsynaptic potentials were recorded from the CA1 region of rat hippocampal slices in response to stimulation of the Schaffer collateral fibers to monitor the effects of acute opioid exposure on the induction of long-term depression (LTD) at excitatory synapses in the stratum radiatum. Exogenous application of a selective mu-opioid agonist resulted in a greater than 2-fold enhancement of LTD, whereas kappa- and delta-agonists did not significantly affect LTD magnitude. Costimulation of the opioid peptide-containing stratum lacunosum-moleculare during LTD induction also resulted in a facilitation of LTD in the stratum radiatum, an effect prevented by prior administration of an opioid antagonist. These results suggest that both exogenously applied and endogenously released opioids can act to facilitate LTD of the Schaffer collateral input to CA1 pyramidal neurons.

Priming-induced shift in synaptic plasticity in the rat hippocampus

The activity history of a given neuron has been suggested to influence its future responses to synaptic input in one prominent model of experience-dependent synaptic plasticity proposed by Bienenstock, Cooper, and Munro (BCM theory). Because plasticity of synaptic plasticity (i.e., metaplasticity) is similar in concept to aspects of the BCM proposal, we have tested the possibility that a form of metaplasticity induced by a priming stimulation protocol might exhibit BCM-like characteristics. CA1 field excitatory postsynaptic potentials (EPSPs) obtained from rat hippocampal slices were used to monitor synaptic responses before and after conditioning stimuli (3-100 Hz) of the Schaffer collateral inputs. A substantial rightward shift (>5-fold) in the frequency threshold between long-term depression (LTD) and long-term potentiation (LTP) was observed <1 h after priming. This change in the LTD/P crossover point occurred at both primed and unprimed synaptic pathways. These results provide new support for the existence of a rapid, heterosynaptic, experience-dependent mechanism that is capable of modifying the synaptic plasticity phenomena that are commonly proposed to be important for developmental and learning/memory processes in the brain.

N- and L-type calcium channel involvement in depolarization-induced suppression of inhibition in rat hippocampal CA1 cells

1. We investigated depolarization-induced suppression of inhibition (DSI) under whole-cell voltage clamp in CA1 pyramidal neurons of rat hippocampal slices. DSI, a transient reduction in monosynaptic evoked GABAAergic IPSCs lasting for approximately 1 min, was induced by depolarizing the pyramidal cell to -10 or 0 mV for 1 or 2 s. 2. Raising extracellular Ca2+ concentration increased DSI, and varying the DSI-inducing voltage step showed that the voltage dependence of DSI was like that of high-voltage-activated Ca2+ channels. 3. The P- and Q-type Ca2+ channel blocker omega-agatoxin TK (200 nM and 1 microM) and the R- and T-type Ca2+ channel blocker Ni2+ (100 microM) reduced IPSCs without reducing DSI. 4. The specific N-type Ca2+ channel antagonist omega-conotoxin GVIA (250 nM) reduced IPSC amplitudes and almost completely abolished DSI. 5. Blocking L-type Ca2+ channels with nifedipine (10 microM) had no effect on IPSCs or DSI induced by our standard protocol, but reduced DSI induced by the unclamped Na+- and Ca2+-dependent spikes that occurred when 2(triethylamino)-N-(2,6-dimethylphenyl)acetamide (QX-314) was omitted from the recording pipette solution. 6. Although intracellular Ca2+ stores were not measured, DSI was not affected by cyclopiazonic acid (CPA, 20-40 microM), a blocker of Ca2+ uptake into intracellular stores. 7. We conclude that DSI is initiated by Ca2+ influx through N- and, under certain conditions, L-type Ca2+ channels.

Primed facilitation of homosynaptic long-term depression and depotentiation in rat hippocampus

Previous studies have demonstrated that prior synaptic activity can influence the subsequent induction of synaptic plasticity in the brain. Such temporal modulation of synaptic plasticity has been called "metaplasticity." In this report, we describe the facilitatory effects of high-frequency stimulation on the induction of homosynaptic long-term depression (LTD) in the CA1 region of the rat hippocampus. The LTD induced by low-frequency stimulation (1 Hz) protocols was found to be homosynaptic and NMDA receptor-dependent. The facilitatory effects of the high-frequency stimulation-induced priming event itself were found to be NMDA receptor-independent and to have a duration of at least 90 min. The effects of priming also were heterosynaptic, because the induction of synaptic plasticity by low-frequency stimulation was enhanced at an unprimed synaptic pathway after the priming of an independent pathway. In addition to enhancing LTD, priming also enhanced the reversal of long-term potentiation elicited by a 5 Hz depotentiation protocol. Our results provide examples of how metaplasticity may play a key role in the ongoing modulation of the induction and stabilization of alterations in synaptic strength.

Retrograde signalling in depolarization-induced suppression of inhibition in rat hippocampal CA1 cells

1. We have investigated the phenomenon of 'depolarization-induced suppression of inhibition' (DSI) using whole-cell voltage-clamp techniques in Ca1 pyramidal cells of rat hippocampal slices. DSI was induced by eliciting voltage-dependent calcium (Ca2+) currents with 1 s voltage steps of +60 to +90 mV from the holding potential. DSI was apparent as a reduction in synaptic GABAA responses for a period of about 1 min following the voltage step. 2. TTX-sensitive spontaneous IPSCs (sIPSCs) were susceptible to DSI, while TTX-resistant miniature inhibitory postsynaptic current (mIPSCs) were not. Miniature IPSCs are ordinarily infrequent and independent of external Ca2+ in the CA1 region. To increase the frequency of mIPSCs and to induce a population of Ca(2+)-sensitive mIPSCs, we increased the bath K+ concentration to 15 mM. The increased mIPSCs were also insensitive to DSI, however. 3. T whole-cell pipette-filling solution contained 5 mM 2(triethylamino-N-(2,6-dimethyl-phenyl)acetamide (QX-314) to block voltage-dependent Na+ currents and caesium to block K+ currents. Nevertheless, bath application of 50 microM 4-aminopyridine (4-AP) or 250 nM veratridine both clearly reduced DSI, evidently by acting at presynaptic sites. 4. The amplitudes of monosynaptically evoked IPSCs (elicited in the presence of 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 50 microM 2-amino-5-phosphonovaleric acid (APV)) were dramatically reduced during the DSI period. Weak stimulation produced small IPSCs and occasional 'failures' of transmission during the control period. The percentage of failures increased markedly during the DSI period. Moderate-intensity stimulation produced larger IPSCs that were often composed of distinguishable multiquantal components. All-or-none failures of multiquantal IPSC components also occurred during DSI. 5. The degree of paired-pulse IPSC depression did not change during DSI, whereas it was decreased, as expected, by baclofen. 6. We conclude that the data represent novel evidence that DSI is mediated by a retrograde signalling process possibly involving presynaptic axonal conduction block.

Increased neuronal excitability during depolarization-induced suppression of inhibition in rat hippocampus

1. Depolarization-induced suppression of inhibition (DSI) is a form of plasticity of gamma-amino-butyric acid (GABAA)-mediated (henceforth 'GABAergic') responses in the CNS. We made whole-cell recordings from CA1 pyramidal neurons to investigate the effects of DSI on excitatory synaptic transmission in the hippocampal slice preparation. 2. Significant enhancement of the voltage-clamped excitatory postsynaptic current (EPSC) occurs during DSI of the temporally overlapping inhibitory postsynaptic current. With high levels of calcium chelators in the pipette solution, or bath application of bicuculline, EPSC enhancement is blocked, suggesting that it results from DSI and that the DSI process selectively affects GABAergic, but not glutamatergic, transmission. 3. The probability of synaptically evoked action potential firing is increased during DSI under current clamp. DSI could influence other excitatory phenomena as well.

Whole-cell voltage-clamp investigation of the role of PKC in muscarinic inhibition of IAHP in rat CA1 hippocampal neurons

Muscarinic, cholinergic inputs, largely from the medial septum, have pronounced effects on hippocampal cell excitability. A major effect of synaptically released ACh is block of the slow Ca(2+)-dependent potassium current, called IAHP. Protein kinase C exists in the hippocampus in high concentrations, its activation blocks IAHP, and it has been suggested as a mediator of the muscarinic-receptor-(mAChR)-mediated actions. Using conditions that produce a stable postspike afterhyperpolarizing current (IAHP) in whole-cell recordings from CA1 hippocampal pyramidal neurons in the slice preparation, we have investigated the role of PKC in the cholinergic inhibition of IAHP mediated by mACHRs. Bath application of the general kinase inhibitor, H7, had no effect on inhibition of IAHP by carbachol, although H7 dramatically reduced inhibition of IAHP by the phorbol ester, phorbol-12, 13-diacetate (PDA). Another muscarinic response thought to be mediated by PKC-inhibition of GABAB-mediated hyperpolarization-was reduced by extracellular H7 treatment, suggesting that the coupling between mAChRs and protein kinase activity was maintained in whole-cell recordings. We also discovered that PDA does not mediate its effects on IAHP directly. Intracellular perfusion of high concentrations of H7 (10 mM) or the specific PKC inhibitor, PKCI(19-31) (1 mM), did not prevent inhibition of IAHP by PDA. These results are consistent with an indirect, presynaptic action of phorbol esters on IAHP, possibly mediated through enhanced release of neurotransmitter from surrounding cells.

Homosynaptic LTD and depotentiation: do they differ in name only?

Long-term depression (LTD) now occupies a major place in theories of the cellular basis of learning and memory and other nervous system phenomena involving persistent changes in synaptic responsiveness. LTD can be induced using a variety of stimulation paradigms. Homosynaptic LTD in this review refers to a depression of basal responses that is restricted to the pathway that has been stimulated by a low-frequency (1 Hz) stimulus train. Despite the intensive interest in LTD, there has been controversy about the ease with which LTD can be induced and reports range from no success to routine success. There has been much less controversy about a related form of response depression now called "depotentiation" which shares many similarities with LTD. Depotentiation is the response reduction that affects, not the basal responses affected by LTD, but responses that have been increased by the process of long-term potentiation (LTP). LTD and depotentiation can be induced by similar stimulation and have many biochemical properties in common, but it has not been clear whether or not they represent the same phenomenon, in part because it often occurs that the same preparation that does not undergo LTD readily expresses depotentiation. We review work that indicates that the major differences between LTD and depotentiation involve age-dependence, the need for priming stimulation and sensitivity to GABA receptor antagonists. We present a hypothetical model that can reconcile the apparent disparities between LTD and depotentiation.

GABAergic and developmental influences on homosynaptic LTD and depotentiation in rat hippocampus

Low-frequency (1 Hz) stimulation (LFS) was used to elicit long-term depression (LTD) or depotentiation of excitatory transmission of the Schaffer collateral pathway in the CA1 region of the rat hippocampus. Both LTD and depotentiation were found to be homosynaptic and NMDA receptor (NMDAR) dependent. As NMDAR activation can be modulated by the inhibitory GABAergic system, we tested the hypothesis that GABA plays a role in regulating these phenomena. The GABAB antagonist CGP 35348 significantly inhibited LTD, but not depotentiation, in slices from young animals (indicating that the GABAB-mediated contribution was altered following HFS). The ability to express LTD was found to be developmentally dependent, as young animals (16-22 d) consistently expressed LTD, whereas LTD was not expressed in naive slices taken from mature (5-10 weeks) animals. The GABAA antagonist bicuculline did not affect LTD in the young animals, but did enhance LTD expression in slices from mature animals. LFS was also effective in decreasing, or depotentiating, responses that had undergone long-term potentiation (LTP) by high-frequency stimulation (HFS). In contrast to LTD, depotentiation was consistently expressed in slices from both the young and mature groups. Moreover, following an HFS train, LTD (compared to initial baseline response) could be induced in mature slices previously unable to express LTD in the naive state. Thus, the role of GABA in modulating the effects of LFS varied with the prior synaptic activity in the slice as well as with the maturity of the animal. Our results suggest that the influence of both age and prior synaptic activity (i.e., HFS) on LTD induction can be explained by changes in GABAergic systems in young versus mature, and naive versus tetanized slices.

Kappa opioids inhibit induction of long-term potentiation in the dentate gyrus of the guinea pig hippocampus

NMDA receptor-mediated long-term potentiation (LTP) of dentate granule cell responses to perforant path stimulation was inhibited by the kappa 1 opioid receptor agonist U69,593. This inhibition was reversed stereospecifically by naloxone and blocked by the selective kappa 1 antagonist norbinaltorphimine (NBNI). NBNI, by itself, had no effect on LTP induced by threshold stimulation but significantly enhanced LTP from more prolonged stimulation. This effect of NBNI suggests that endogenous opioids can regulate LTP in the dentate gyrus. In support of this hypothesis, stimulation of dynorphin-containing fibers also blocked LTP production in an NBNI-sensitive manner. Finally, dynorphin-mediated inhibition of LTP acts primarily on mechanisms of induction rather than maintenance or expression, since dynorphin released immediately before, but not immediately after, perforant path stimulation blocked LTP. Thus, exogenous and endogenous kappa opioids can inhibit induction of long-term potentiation at the perforant path-granule cell synapse and may therefore regulate plastic changes in synaptic transmission in a brain region thought to play an important role in processes of both learning and memory and epileptogenesis.

GTP modulates run-up of whole-cell Ca2+ channel current in a Ca(2+)-dependent manner

1. Whole-cell voltage-clamp recordings were obtained from CA1 neurons acutely dissociated from rat hippocampus to study the effects of guanosine 5'-triphosphate (GTP) on the gradual increase in Ca2+ channel current amplitude that takes place over several minutes after breaking in to whole-cell mode ("run-up"). 2. Including GTP (500 microM) in the patch pipette significantly prolonged the duration of run-up of peak Ca2+ channel current to its maximum value compared with controls without GTP when the recording solutions contained Ca2+. On the other hand, GTP significantly enhanced run-up when Mg2+ and Ba2+ were substituted for intracellular and extracellular Ca2+, respectively. 3. The enhancement of run-up of the current in the Mg/Ba condition appeared to be due both to an initial increase in current amplitude that was complete within 30 s after break in and to a more rapid initial rate of run-up when compared with the Ca2+ condition. GTP did not affect the absolute maximum amplitudes of the currents in either Ca2+ or Ba2+ conditions. 4. We conclude that an early GTP-dependent modulation of Ca2+ channel current is qualitatively altered, depending on whether Ca2+ or Ba2+ is used as the charge carrier. Evidence of this modulation is apparent within seconds after rupture of the membrane patch. Conceivably, influences occurring during the period of "equilibration" with electrode contents could alter subsequent regulatory steps.

Endogenous dynorphins inhibit excitatory neurotransmission and block LTP induction in the hippocampus

Although anatomical and neurochemical studies suggest that endogenous opioids act as neurotransmitters, their roles in normal and pathophysiological regulation of synaptic transmission are not defined. Here we examine the actions of prodynorphin-derived opioid peptides in the guinea-pig hippocampus and show that physiological stimulation of the dynorphin-containing dentate granule cells can release endogenous dynorphins, which then activate kappa 1 opioid receptors present in the molecular layer of the dentate gyrus. Activation of kappa 1 receptors by either pharmacologically applied agonist or endogenously released peptide reduces excitatory transmission in the dentate gyrus, as shown by a reduction in the excitatory postsynaptic currents evoked by stimulation of the perforant path, a principal excitatory afferent. In addition, released dynorphin peptides were found to block the induction of long-term potentiation (LTP) at the granule cell-perforant path synapse. The results indicate that endogenous dynorphins function in this hippocampal circuit as retrograde, inhibitory neurotransmitters.

Endogenous opioid regulation of norepinephrine release in guinea pig hippocampus

Release of endogenous norepinephrine was detected in guinea pig hippocampal slices using a radioligand displacement assay. Focal electrical stimulation released endogenous norepinephrine and caused a calcium-dependent reduction in specific [3H]propranolol binding at beta-adrenergic receptors in the brain slice. The mu-opioid agonist PL017 decreased norepinephrine release, and the inhibition by PL017 could be blocked by the opioid antagonist naloxone. Endogenous opioid peptides concomitantly released by tissue stimulation also decreased norepinephrine release in a naloxone-sensitive manner. These results support the hypothesis that endogenous opioids can regulate excitability in the hippocampus by presynaptic modulation of norepinephrine release.

GnRH in the infundibular stalk-median eminence is related to percentage body fat in carcasses of beef cows

Mature Hereford cows (n = 28) were used to determine the effect of percentage body fat on secretion of LH and content of GnRH in the infundibular stalk-median eminence (ISME). Cows were fed to maintain, lose, or gain weight to achieve body condition scores (BCS; 1 = emaciated; 9 = obese) of 3 to 7. Then cows were fed to maintain weight and body condition. Before slaughter, estrus was synchronized using two injections of prostaglandin F2 alpha(PGF) 11 d apart. Five d after the second PGF injection, cows were given 100 micrograms of GnRH (im) and serum samples were obtained. LH was quantified using RIA. The anterior pituitary and ISME were obtained within 45 min of death. Anterior pituitary weight and LH concentration, total GnRH in the ISME, total carcass fat, and percentage carcass fat were determined. BCS of cows at the time of slaughter influenced percentage carcass fat (P less than .001), total GnRH in the ISME (P less than .02), and maximum LH after GnRH treatment (P less than .09), but did not influence pituitary weight or concentration of LH in the pituitary. Content of GnRH in the ISME averaged 76 +/- 12, 32 +/- 14, 27 +/- 13, and 24 +/- 13 ng for cows with BCS of 3, 5, 6, and 7, respectively. BCS was correlated (P less than .001) with percentage carcass fat (r = .94) and total fat in the carcass (r = .92). Total GnRH in the ISME was negatively correlated (P less than .005) with BCS (r = -.54), percentage carcass fat (r = -.55), and total carcass fat (r = -.49).(ABSTRACT TRUNCATED AT 250 WORDS)

Kappa-opioids decrease excitatory transmission in the dentate gyrus of the guinea pig hippocampus

In the guinea pig hippocampus, kappa 1-opioid binding sites were primarily localized in the molecular layer of the dentate gyrus as shown by autoradiography using either the kappa 1-selective radioligand 3H-U69,593 or the nonselective radioligand 3H-diprenorphine in the presence of unlabeled mu- and delta-blocking ligands. In this region, the electrophysiological effects of kappa 1-receptor activation were identified using extracellular and intracellular recordings of dentate granule cell responses. The amplitude of the extracellularly recorded population spike was reduced by U69,593 with an EC50 of 26 nM; this effect was reversible and blocked by the opioid antagonist naloxone. The kappa 1-selective antagonist norbinaltorphimine also blocked the effect of U69,593 with an apparent equilibrium dissociation constant (Ki) of 0.26 nM determined by Schild analysis in the physiologic assay. This value agreed well with the Ki for norbinaltorphimine at kappa 1-binding sites measured by radioligand binding displacement (0.24 nM). These results indicate that the electrophysiologic response observed was likely mediated by kappa 1-receptors. As seen with U69,593, dynorphin B, an endogenous opioid peptide that is present in the dentate gyrus, also inhibited the population spike response. mu- and delta-selective opioid agonists had no effect on the amplitude of the maximally evoked response. Intracellular recordings of dentate granule cells showed no direct effects of U69,593 on the granule cells themselves. However, analysis of synaptic potentials revealed that U69,593 significantly reduced the amplitude of glutaminergic EPSPs evoked by afferent stimulation without affecting IPSP amplitudes. The specific effect of U69,593 application on granule cell EPSPs indicates that presynaptic kappa 1-receptor activation inhibits glutamate release from perforant path terminals in the molecular layer of the dentate gyrus. These results suggest that endogenous dynorphins present in the granule cells may act as feedback inhibitors of the major excitatory input to the dentate gyrus.

Endogenous opioids released from perforant path modulate norepinephrine actions and inhibitory postsynaptic potentials in guinea pig CA3 pyramidal cells

The stimulus parameters needed for the release of endogenous opioid peptides were investigated using an in vitro radioligand displacement assay in living guinea pig hippocampal slices. Electrical stimulation of the enkephalin-containing fibers in the perforant path caused the release of endogenous opioid peptides and the subsequent displacement of [3H]-[D-Ala2,N-methyl-Phe4,glyol5]enkephalin binding. High frequency trains of stimuli (10 Hz for 1 sec every 10 sec) were more effective than lower frequency stimulation (1 Hz continuous) at evoking opioid peptide release. Having identified an effective stimulation paradigm able to release endogenous opioids, the electrophysiological effects of endogenous opioids on CA3 pyramidal cells were measured in the guinea pig hippocampal slice preparation. Unlike exogenously applied opioids, stimulated release of endogenous opioid peptides from the perforant path did not significantly reduce inhibitory postsynaptic potential (IPSP) amplitudes recorded in CA3 pyramidal cells. However, perforant path stimulation in the presence of naloxone did cause a dramatic increase in IPSP amplitudes. CA3 pyramidal cells were not directly affected by perforant path stimulation. The naloxone-sensitive increase in IPSPs was delayed 3 min in onset and lasted for several minutes. In addition, the increase in the IPSPs was specifically blocked either by the beta adrenergic antagonist propranolol or by pretreating the animals with reserpine. These findings indicate that endogenous opioids regulate the effects of norepinephrine in the CA3 region of the guinea pig hippocampus. In addition, endogenously released norepinephrine appeared to act on GABAergic interneurons to increase the amplitude of the IPSP recorded in CA3 pyramidal cells.

Focal stimulation of the mossy fibers releases endogenous dynorphins that bind kappa 1-opioid receptors in guinea pig hippocampus

Physiological release of endogenous opioids in guinea pig hippocampal slices was detected in an in vitro competition binding assay using [3H]U69,593, a kappa 1-selective radioligand. Veratridine-induced opioid release caused a decrease in [3H]U69,593 binding that was blocked by either tetrodotoxin addition or the removal of calcium from the incubation buffer. Focal electrical stimulation of opioid peptide-containing afferent pathways resulted in a decrease in [3H]U69,593 binding, whereas stimulation of a major afferent lacking endogenous opioid immunoreactivity had no effect. The addition of 6-cyano-7-nitroquinoxaline-2,3-dione blocked the reduction in [3H]U69,593 binding caused by perforant path stimulation, but not the reduction caused by mossy fiber stimulation, suggesting that the primary source of endogenous kappa ligands was likely to be the dentate granule cells. Antisera against dynorphin A(1-8) or dynorphin B peptides inhibited the effects of mossy fiber stimulation in the [3H]U69,593 displacement assay. Antisera against other prodynorphin- and proenkephalin-derived opioid peptides had no effect. As shown by receptor autoradiography, the distribution of kappa 1 binding sites was limited to the molecular layer of the dentate gyrus and the presubiculum region of temporal hippocampal slices. These results indicate that prodynorphin-derived opioids released under physiological conditions from the mossy fibers act at kappa 1 receptors in the guinea pig dentate gyrus.