[Effect of Catechol-O-methyltransferase deficiency on reinforcing effects of cocaine (experimental study)].

Catechol-O-methyltransferase (COMT) remains an important regulatory element in prefrontal cortex dopamine homeostasis. The literature data suggest that individual differences in COMT activity (Val158Met polymorphism) might have indirect downstream effects on the reward system. The aim of the present study was to examine whether COMT deletion affects reinforcing effects of cocaine in mice. The study was conducted in male mice with homozygous COMT deletion as well as their C57BL/6J wild-type littermates. Animals were trained to nose-poke to receive response-contingent intravenous infusions of cocaine (0.3 mg/kg per infusion; final schedule of reinforcement - fixed ratio (FR) 3 time out 30 s). Following the initial acquisition phase, cocaine self-administration dose-effect functions (0.03, 0.1, 0.3, 1, and 3 mg/kg per infusion) were determined under FR3 and progressive ratio (PR) schedules of reinforcement. Cocaine dose-dependently maintained responding under FR3 and PR schedule of reinforcement when the unit dose of cocaine was varied across the sessions. The total cocaine intake did not differ in COMT deletion mice and wild-type mice. The results of this study suggest that individual differences in COMT activity do not affect primary reinforcing effects of cocaine in mice.

[Effect of alpha-conotoxin MII and its N-terminal derivatives on Ca2+ and Na+ signals induced by nicotine in neuroblastoma cell line SH-SY5Y].

Nicotinic acetylcholine receptors (nAChRs) are implicated in the regulation ofintracellular Ca2+-dependent processes in cells both in normal and pathological states, alpha-Conotoxins isolated from Conus snails venom are a valuable tool for the study of pharmacological properties and functional role of nAChRs. In the present study the alpha-conotoxin MII analogue with the additional tyrosine attached to the N terminus (Y0-MII) was prepared. Also we synthesized analogs with the N-terminal glycine residue labeled with the Bolton- Hunter reagent (BH-MII) or fluorestsein isothiocyanate (FITC-MII). Fluorescence microscopy studies of the neuroblastoma SH-SY5Y cells loaded with Ca2+ indicator Fura-2 or with Ca2+ and Na+ indicators Fluo-4 and SBFI were performed to examine effect of MII modification on its ability to inhibit nicotin-induced increases in intracellular free Ca2+ and Na+ concentrations ([Ca2+] and [Na+]i respectively). Monitoring of individual cell [Ca2+]i and [Na+]i signals revealed different kinetics of [Ca2+]i and [Na+]i rise and decay in responses to brief nicotine (Nic) applications (10-30 microM, 3-5 min), which indicates to different mechanisms of Ca2+ and Na+ homeostasis control in SH-SY5Y cells. MII inhibited in concentration-dependent manner the both [Ca2+]i and [Na+]i increase induced by Nic. Additional tyrosine in the Y0-MII or, especially, more sizeable label in FITC-MII significantly reduced the inhibitory effect of MII. Whereas the efficiency of the Ca2+ response inhibition by BH-MII was found to be close to the efficiency of its inhibition by natural alpha-conotoxin MII, radioiodinated derivatives BH-MII can be used in radioligand assay.

Induction of Fos-immunostaining by nicotine and nicotinic receptor antagonists in rat brain.

Using Fos protein immunohistochemistry, we have studied the effects of acute nicotine (0.5 mg/kg s.c.) and nicotinic acetylcholine receptor (nAChR) antagonists in eleven rat brain areas. Acute nicotine elevated Fos-like immunostaining (Fos IS) significantly in all studied areas except the medial prefrontal cortex. Nicotine increased the Fos IS in cortical, limbic and hypothalamic areas by 2-10-fold, and in the interpeduncular nucleus as well as in the visual areas the increases were 15-150-fold. When given alone, the nAChR antagonists mecamylamine (1.0 or 5.0 mg/kg i.p.) and dihydro-beta-erythroidine (DHE; 1.4 or 2.8 mg/kg i.p.) increased Fos IS in most brain areas maximally by 2-10-fold, but methyllycaconitine (MLA; 4.0 mg/kg i.p.) only in three areas and maximally by 4-fold. The efficacy of nAChR antagonists in blocking nicotine's effects on Fos IS varied noticeably with respect to region and antagonist, and the combined effect of nicotine+antagonist did not exceed that of either treatment alone. Mecamylamine and DHE significantly reduced nicotine-induced Fos IS in most of the studied areas, and MLA only in two areas. Thus, nAChRs seem to mediate the effects of nicotine on Fos IS, and the differences in the effects of the antagonists studied suggest that more than one subtype of nAChRs are involved. The present experiments also provide evidence that nAChR blockade itself may result in increased Fos protein expression in the brain. This could be due to blockade of presynaptic nAChRs modulating transmitter release or interruption of complex polysynaptic feedback pathways.

Effect of acute nicotine on Fos protein expression in rat brain during chronic nicotine and its withdrawal.

To study the cholinergic regulation of hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei and interpeduncular nucleus (IPN) we investigated the effects of acute nicotine (0.5 mg/kg, SC, 60 min) on Fos-like immunostaining (IS) during chronic nicotine and its withdrawal in rats. Nicotine or saline was infused to rats via osmotic minipumps (4 mg/kg/day) for 7 days; on the seventh day, the minipumps were removed surgically. In control rats, acute nicotine increased Fos IS significantly in all three brain areas studied. On the seventh day of nicotine infusion this effect partially persisted in IPN but was abolished in PVN and SON. After 72-h withdrawal nicotine-induced elevation of Fos IS was similar to that of control rats in all three areas. The observed attenuation of the response to acute nicotine during constant nicotine infusion in PVN and SON may be attributable to the desensitization of nicotinic acetylcholine receptors (nAChRs) mediating the effects of nicotine in these areas or in their input areas. IPN is connected to midbrain limbic system, so in agreement with our earlier observations, it seems that limbic nicotinic receptors do not very readily desensitize during chronic nicotine infusion. These findings support the suggestions that there are differences in the level of desensitization of nAChRs.

The effects of acute nicotine on the body temperature and striatal dopamine metabolism of mice during chronic nicotine infusion.

The effects of acute nicotine administration on body temperature and striatal dopamine metabolism of mice during chronic subcutaneous nicotine infusion were investigated. On the 7th day of nicotine infusion the hypothermic effect of 1 mg/kg nicotine s.c. but not that of 2 mg/kg was weakened suggesting that tolerance developing to nicotine's hypothermic effect during chronic nicotine can be overcome by increasing the dose of nicotine. In saline-infused control mice 1 mg/kg nicotine increased striatal 3, 4-dihydroxyphenylacetic acid (DOPAC) but not homovanillic acid (HVA) concentration whereas 2 mg/kg increased both DOPAC and HVA. On the 7th day of nicotine infusion DOPAC and HVA concentrations were similar to control; and acute nicotine did not increase them suggesting that nicotinic acetylcholine receptors (nAChRs) regulating striatal dopamine metabolism were desensitized. The results suggest that the nAChRs mediating nicotine's effects on thermoregulation and brain dopamine metabolism differ.

The effects of acute nicotine on the metabolism of dopamine and the expression of Fos protein in striatal and limbic brain areas of rats during chronic nicotine infusion and its withdrawal.

The effects of acute nicotine (0.5 mg/kg, s.c.) on dopamine (DA) metabolism and Fos protein expression in striatal and limbic areas of rats on the seventh day of chronic nicotine infusion (4 mg. kg(-1). d(-1)) and after 24 or 72 hr withdrawal were investigated. In saline-infused rats, acute nicotine elevated striatal and limbic 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations significantly. During the nicotine infusion, no such increases were seen in the striatum, but limbic HVA was somewhat elevated. After 24 hr withdrawal when no nicotine was found in the plasma, acute nicotine elevated striatal DOPAC and HVA and limbic HVA. However, the limbic DOPAC was unaffected. Acute nicotine increased Fos immunostaining (IS) in the caudate-putamen (CPU), the core of nucleus accumbens (NAcc), the cingulate cortex (Cg), and the central nucleus of amygdala (ACe) significantly. During nicotine infusion the nicotine-induced responses were attenuated in CPU and NAcc, whereas in ACe and Cg Fos immunostaining was increased as in saline-infused rats. After 24 hr withdrawal, acute nicotine did not increase Fos immunostaining in CPU, NAcc, and Cg, but increased it clearly in ACe. After 72 hr withdrawal, nicotine's effects were restored. Our findings suggest that the nicotinic receptors in the striatal areas are desensitized more easily than those in the limbic areas. Furthermore, the effects of nicotine on various DA metabolites differ. We also found evidence for long-lasting inactivation of nicotinic receptors in vivo regulating limbic dopamine metabolism and Fos expression in striatal and limbic areas. These findings might be important for the protective effects of nicotine in Parkinson's disease and in its dependence-producing properties.

Tolerance to nicotine's effects on striatal dopamine metabolism in nicotine-withdrawn mice.

After 7-week chronic administration of nicotine to mice in their drinking water, nicotine was withdrawn for 24 h. Acute nicotine challenge (1 mg/kg s.c., 60 min) elevated the striatal concentrations of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and decreased the concentration of 3-methoxytyramine significantly less in the mice withdrawn for 24 h from nicotine than in the control mice which had been drinking tap water under identical conditions for 7 weeks. Neither withdrawal nor the acute nicotine challenge altered the striatal dopamine concentration. No alterations were found in the density or affinity of the specific binding of [3H]SCH 23390 or [3H]spiperone to striatal membrane homogenates during nicotine treatment or after its withdrawal. Thus, our results show that tolerance to the acute effects of nicotine on striatal dopamine metabolism can be induced by administering nicotine to mice in the drinking water. However, neither chronic nicotine treatment nor its withdrawal seem to affect dopamine D1 and D2 receptors in the striatum.

Expression of Fos protein in various rat brain areas following acute nicotine and diazepam.

We studied the effects of an acute dose of (-)-nicotine (1 mg/kg) on Fos-like immunostaining (IS) in rat brain areas. Nicotine increased Fos IS significantly in the medial terminal nucleus of accessory optic tract (MT), and tended to increase it in the interpeduncular nucleus (i.p.), as well as in the stress-related areas, the paraventricular hypothalamic nucleus (PVN) and the supraoptic nucleus (SON). Previously nicotine was reported to increase Fos IS also in another stress-related area, the central nucleus of amygdala (ACe). This led us to study the interaction of nicotine with diazepam (10 mg/kg). Diazepam alone increased Fos IS in PVN and in SON as well as in ACe. In diazepam- and nicotine-treated rats Fos IS was increased in PVN and SON as well as in MT and i.p.. In MT and i.p. of diazepam and nicotine-treated rats Fos IS was similar to that induced by nicotine alone, and in PVN and SON of these rats Fos IS in ACe. Taken together, diazepam induced Fos IS in all stress-related areas studied (PVN, SON, ACe), but not in central visual structures, where nicotine induces Fos IS (MT, i.p.). No significant interactions on Fos expression were found between acute effects of diazepam and nicotine suggesting that these drugs activate different sets of neurons within the stress-related brain areas.

Efficient nonlinear amplitude recording of holographic gratings in electrolytically colored potassium bromide crystals.

The nonlinear amplitude recording of volume holographic gratings is theoretically and experimentally studied in electrolytically colored potassium bromide crystals. A maximum diffraction efficiency of 10.8% is obtained, which substantially exceeds the 3.7% maximum diffraction efficiency for linear recording.

Relaxation of elementary holographic gratings in As(2)S(3) films at low diffraction efficiencies.

The relaxation processes in As(2)S(3) films related to the self-enhancement effect of holographic gratings with low initial diffraction efficiencies are examined. It is demonstrated that the dark relaxation plays a noticeable role in the self-enhancement.

Influence of some development parameters on the reflection grating structure in dichromated gelatin.

We made reflection gratings by using the gelatin of Kodak 649F spectroscopic plates. The concentration of ammonium dichromate sensitizer was varied, and reflection efficiencies of fully developed plates were measured in different reconstructing angles. During the development process we varied the washing time, the time interval between the washing and isopropanol baths, and the duration of the isopropanol bath. The reflection efficiencies were measured for each processing variable. Finally, the characteristics of the gratings were tested by varying the recording geometry.