Anwar Hamdi

Decreased striatal D2 dopamine receptors in obese Zucker rats : changes during aging

The specific binding of [3H]YM-09151-2 was used to investigate the possible differences in age-associated changes in striatal D2 dopamine (DA) receptor properties in genetically obese (fa/fa) Zucker rats and their lean (Fa/?) littermates. The maximal binding sites (Bmax) of D2 DA receptors was found to decline with age in both obese and lean rats; the rate of decline in receptor Bmax was slightly higher in lean than obese rats. However, the Bmax of D2 DA receptor in 6-, 12- and 18-month-old obese rats was significantly lower compared to the age-matched lean rats. These data indicate that obesity decreases the number of striatal D2 DA receptors without affecting the rate at which receptor number decreases with age.

Chronic nicotine reverses age-associated increases in tail-flick latency and anxiety in rats

The chronic consumption of low doses of nicotine in drinking water for two years consistently increased the sensitivity of rats to a nociceptive thermal stimulus (tail-flick test), but reduced aversiveness in the elevated plus-maze test, relative to the responses of age-matched controls in these tests. The responses of aged nicotine-consuming rats were indistinguishable from those of young adult rats that did not receive nicotine. To determine whether these effects were due to a nicotine-induced retardation of age-related changes, young adult rats were similarly treated with nicotine for three months and similar changes in the tail-flick latency and performance in the plus-maze test were observed during nicotine consumption. These changes were reversed following withdrawal from nicotine. It is concluded that the maintenance of circulating low levels of nicotine (and/or its metabolites) increased the nociceptive sensitivity of the rats and reduced their aversions in the plus-maze test regardless of their age.

Antibodies against synthetic peptides predicted from the nucleotide sequence of D2 receptor recognize native dopamine receptor protein in rat striatum.

Two peptides corresponding to amino acid sequences predicted from the nucleotide sequence of the dopamine D2 receptor were synthesized. Peptide I (CGSEG‐KADRPHYC) and peptide II (NNTDQNECIIY), corresponding to 24–34 and 176–185 from the NH2 terminus, respectively, were conjugated to keyhole limpet hemocyanin and injected into rabbits. Peptide I showed a greater immunogenic response than did peptide II. Both peptide antibodies exhibited high titer for the homologous antigens, but showed little or no cross‐reactivity with heterogeneous peptides. Peptide I antibodies reacted with striatal membrane proteins of apparent molecular masses of 120, 90, 85, and 30 kDa on a western blot. Furthermore, the 90‐kDa band was identified as denatured D2 receptor by its high affinity for the D2 selective photoaffinity probe 125I‐AP‐azidospiperone (125I‐NAPS). Photoaffinity labeling of the 90‐kDa protein by 125I‐NAPS was reduced by 40% in the presence of the peptide I antibody. In addition, evidence is also presented to show the low level of 90‐kDa protein in cerebellum which contains little or no D2 ligand binding sites. The antibody to peptide I inhibited the binding of [3H] YM‐09151‐2, a dopamine D2 receptor selective antagonist, to striatal membranes in a concentration‐dependent manner, a 50% inhibition was obtained at a 1:500 dilution of the antisera with 20 pM ligand concentration. The data on the equilibrium inhibition kinetics of [3H] YM‐09151‐2 binding to striatal membranes were examined in the presence of antibody and showed a 25–30% decrease in Bmax (203.5 ± 11.0 and 164.6 ±3.3 fmol/mg of protein in presence of preimmune and immune sera, respectively) with no change in KD. These results suggest that polyclonal antisera raised against peptide I exhibited specific antibodies for the dopamine D2 receptor protein. The primary epitope for this antibody is at or near the ligand binding site which can be recognized in both denatured and native receptor protein in striatal membranes.

Bidirectional changes in striatal D1-dopamine receptor density during chronic ethanol intake

Results of previous studies on the effects of ethanol consumption on the properties of D1 dopamine receptors appear contradictory and inconclusive. In this study we have examined the time course of the effects of dietary ethanol on the properties of striatal D1 dopamine receptors. Chronic ethanol intake led to bidirectional changes in the maximum number (Bmax) of [3H]SCH-23390 binding to striatal D1 dopamine receptors measured 10 hrs after termination of the ethanol intake. A significant decrease (80% of control), increase (159% of control), increase (122% of control), and decrease (85% of control) after 1, 2, 3, and 4 weeks of ethanol intake respectively was observed. The bidirectional changes disappeared after 6 and 10 weeks of continued ethanol intake and the Bmax returned back to the control level. The receptor affinity (Kd), however, remained unaltered in all cases. These data suggest that the duration of ethanol exposure may be an important determinant in regulating D1 dopamine receptor density.

Effects of rapid eye movement sleep deprivation on the properties of striatal dopaminergic system

Using the water tank procedure, we have examined the effects of rapid eye movement (REM) sleep deprivation and associated stress on the properties of striatal dopaminergic system. While stress decreased the number of D1 and D2 dopamine receptors, a combination of REM sleep deprivation attenuated the decrease. The ratio of D1 to D2 densities, however, increased on both the stress and REM sleep deprivation groups. In contrast, the number of dopamine uptake sites remained unchanged. The enhanced behavioral responses to dopaminergic stimulants after REM sleep deprivation are discussed.

REM sleep deprivation alters dopamine D2 receptor binding in the rat frontal cortex.

REM sleep deprivation (RSD) of rats results in facilitation of dopaminergic behavior and an increase in striatal D2 receptor density. To determine whether RSD results in changes in D2 receptor in other brain regions, receptor affinity (Kd) and density (Bmax) were measured in the anteromediofrontal (AM), cingulate (CN), and sulcal cortex (SL) in four groups of rats: 1), RSD96 group (RSD for 96 h; small pedestal/water tank method), 2) RSD24 group (large pedestals for 72 h then small pedestals for 24 h), 3) tank control group (TC; large pedestals for 96 h), and 4) cage control group. In separate groups, ambulation was recorded for 30 min following treatments. Group RSD96 showed an increase in activity compared to TC, and TC was increased compared to CC (p < 0.05 for all). In group RSD24, the AM showed an increase in Bmax and Kd (p < 0.05), but there were no effects by RSD96. In the CN, Bmax and Kd were decreased by RSD96 (p < 0.05) but not RSD24. In the SL, Bmax was increased by RSD96, but not RSD24, whereas Kd was increased in both RSD groups (p < 0.05).

A low protein-high carbohydrate diet decreases D2 dopamine receptor density in rat brain

The property of D2 dopamine receptors in the rat brain was evaluated after long-term dietary manipulation. Groups of rats were pair-fed with equicaloric diet containing low protein (8%)-high carbohydrate, high protein (52%)-low carbohydrate and normal protein (20%) for 36 weeks. The low protein-high carbohydrate fed rats exhibited a significant decrease in the density (Bmax) of D2 dopamine receptor in the striatum (28%) and the mesolimbic regions (36%) with no apparent change in the receptor affinity (Kd). These findings suggest that long-term consumption of a low protein-high carbohydrate diet, by decreasing D2 dopamine receptor density, may be an important determinant of central dopaminergic function.

Differential modulation of dopaminergic systems in the rat brain by dietary protein

Rats that consume a diet 50% rich in protein exhibit hyperactivity and hyperresponsiveness to nociceptive stimuli, in which facilitation of dopaminergic activity has been implicated. We studied the regional changes in the concentrations of dopamine (DA) and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the brains of rats that were maintained on high-protein (HP, 50% casein), normal-protein (NP, 20% casein), and low-protein (LP, 8% casein) diets for 36 weeks. Brain nuclei that represented different DAergic systems were punchdissected and analyzed using HPLC. In the substantia nigra, the striatum, and the dentate gyrus, DA concentrations decreased and increased, respectively, with a decrease and increase in dietary protein (p<0.05 compared to the NP diet). Similar trends in the effect of the HP diet were observed in the ventral tegmental area, amygdala, frontal cortex, subiculum, centromedial nucleus (CM) of the thalamus, and inferior colliculi (IC), although the differences in DA concentrations were not statistically significant. These brain areas also showed a pattern of decreased DA concentration in association with the LP diet, and the differences were statistically significant (p<0.05) in the CM and IC. DA concentrations in most regions of the midbrain and brainstem were not different between the diet groups, nor were consistent trends observed in those regions. Also, there were no consistent relationships between DOPAC/DA and HVA/DA ratios and dietary protein level. These data suggest that only discrete dopaminergic neuronal circuits in the rat forebrain were sensitive to changes in dietary protein level.

Bidirectional changes in striatal D2-dopamine receptor density during chronic ethanol intake

Results of previous studies on the effects of ethanol consumption for a single fixed period on the properties of D2 dopamine receptors appear contradictory and inconclusive. In this study, we have examined the time course of the effects of dietary ethanol on the properties of striatal D2 dopamine receptor. Ethanol intake led to a significant decrease in the maximum number (Bmax) after 1 (35% of control) and 2 weeks (48% of control), but not after 3 (93% of control) or 4 weeks (97% of control) of treatment. However, there was a significant increase in Bmax after 6 (118% of control) and 10 weeks (123% of control) of ethanol consumption. The affinity (Kd) of the receptor, however, remained unaltered in all cases. In conclusion, these data show that the duration of ethanol exposure may be an important determinant regulating D2-dopamine receptor density.

Attenuation of pulsatile changes in the density of striatal [3H]GBR-12935 binding sites during chronic ethanol consumption

Using [3H]GBR-12935 as a selective ligand, we have examined the properties of rat striatal dopamine transporter complex during chronic ethanol consumption. The results of this study show a significant change in the Bmax (maximal binding capacity), but not Kd (affinity) of [3H]GBR-12935 binding sites. The observed changes were pulsatile and they exhibited an increase (144% of control), decrease (80% of control), tendency to increase (111% of control), increase (141% of control), decrease (84% of control), no change (98% of control), and decrease (80% of control) after 1, 2, 3, 4, 6, 8 and 10 weeks of ethanol consumption, respectively. Since the duration of ethanol exposure appears to be an important variable in regulating the properties of dopamine transporter complex, the behavioral changes observed during chronic ethanol intake may vary with time.