Histamine is a monoamine structured signal molecule, which takes part in many functions of living organisms. It was first found in brain approximately 70 years ago. Neuronal histamine regulates for example biological rhythms, energy metabolism and thermoregulation. In the 1980's, H3-receptor was recognized in the brain. Neuronal histamine regulates functions of other transmitters for example gamma-aminobutyric acid, glutamate, acetylcholine, noradrenaline and dopamine. Currently, the interactions of histamine and dopamine are not well characterized. Though, it is known that histaminergic fibers innerviate almost every dopaminergic area of the brain. There are also several H3-receptors in the striatum and in the limbic system. These brain areas are important for the rewarding effect of dopamine. The aim of the experimental part of this Master's thesis was to examine the location of histaminergic and dopaminergic nervous systems in mouse brain by using immunohistochemistry. Primary antibodies that were produced in rabbit (anti-histamine (HA)) and in mouse (anti-tyrosine hydroxylase (TH)), and secondary anti-rabbit and anti-mouse anti-bodies, that were produced in goat and conjugated with fluorophores, were used in the study. The samples were imaged with a confocal microscope. The primary aim was to find out, in which addiction related brain areas, histamine and dopamine cells and fibers are located and how they are situated in relation to each other. H3-receptor antagonists have been shown to decrease the consumption and rewarding effect of alcohol in animal models. Therefore, it was examined if non-imidazole structured H3-receptor antagonist also inhibits the rewarding effect of amphetamine, and if it decreases the locomotor activity induced by amphetamine. JNJ-39220675, a neutral antagonist of H3-receptor, and behavioral paradigm of conditioned place preference (CPP) were used in the experiment. CPP was also used to find out if D2-receptor agonist quinpirole cause reward or aversion. The effect of JNJ-39220675 on quinpirole's place preference and change in locomotor activity was also investigated. The interactions of these two pharmacological ligands were also examined in a separate locomotor activity experiment. C57BL/6J mice were used in all experiments. The results show that there are possible synaptic connections of histaminergic and dopaminergic system in substantia nigra, supramammillary nucleus, dorsomedial hypothalamic area and ventral periaqueductal grey area. Also, histaminergic nerve fibers innerviate to the dorsal striatum, which regulates motor functions, and to the ventral striatum, which is a part of the rewarding system of the brain. Hence, it is possible that histamine regulates the actions of dopa-mine in these brain areas. The behavioral experiments showed that JNJ-39220675 inhibits acutely increased locomotor activity caused by amphetamine, and decreases desensitation of decreased locomotor action caused by repeated dose of quinpirole. However, JNJ-39220675 did not have any effect on the rewarding effect of amphetamine, which causes strong sensitization. Also, JNJ-39220675 did not have an effect on quinpirole's aversive action. It remains to be seen, if H3-receptor is a potential target for new medicines in the treatment of different brain diseases and addiction in the future.

Glutamate is the principal excitatory neurotransmitter in the central nervous system. Glutamatergic neurotransmission plays a central role in the development and maintenance of drug addiction. Glutamate interacts with other neurotransmitters such as dopamine in the actions concerning addiction. During the development of drug addiction, plastic changes in the neuronal connections related to memory and learning occur for example in the amount of synapses and in the efficacy of their action. Glutamatergic AMPA receptor and especially its GluA1 subunit are thought to be included in the neurobiological mechanisms related to drug addiction. Compulsive drug craving and relapses to drug use after a period of abstinence are central problems among people suffering drug addiction. Conditioned place preference is a technique that is used to study motivational properties of drugs in experimental animals. The aim of this master's thesis was to examine the importance of glutamatergic AMPA receptor GluA1 subunit in the morphine-induced place preference and in its extinction and reinstatement behaviour. Locomotor activity of mice was studied during all the phases of experiment. Glutamatergic AMPA receptor GluA1 subunit-deficient (GluA1-/-) and their control (wildtype) mice, based on C57BL/6J mouse strain, were used in the experiments. During the conditioning phase, the mice were trained to associate the effects of morphine (20 mg/kg) with a specific environment. After conditioning, the extinction with morphine paired conditioning environment was assessed by giving saline (0,9 % NaCl solution) to mice. The extinction phase was followed by reinstatement test, in which mice were given morphine (20 mg/kg). The seeking of animals with morphine paired conditioning environment described drug-seeking during different phases of experiment. GluA1-/- mice were more hyperactive when placed in the testing environment compared to the wildtype mice. However, the morphine-induced locomotor activity did not differ between genotypes. Locomotor activity of both genotypes was sensitized equally in consequence of repeated morphine exposures. Morphine induced place preference in both genotypes. Furthermore, the extinction of morphine place preference happened in both genotypes. However, the results of reinstatement test differed partly between genotypes. The place preference was reinstated by morphine in wildtype mice, but not in GluA1-/- mice, when using repeated testing extinction method. Instead of place preference, wildtype mice exhibited place aversion, when extinction method was saline conditioning. As a result of these experiments, extinction method can have an impact on the results of reinstatement test and conclusions cannot be done on the importance of GluA1 subunit in morphine reinstatement. In conclusion, the results of place preference experiments support the conception that GluA1 subunit is not significant in morphine conditioning. However, based on these experiments, GluA1 subunit is not important in morphine extinction, as one might assume on the basis of literature. GluA1 subunit may have an importance in morphine reinstatement, although the results of reinstatement test were partly contradictory.