Hans C. Fibiger

On the role of ascending catecholaminergic systems in intravenous self-administration of cocaine

The role of ascending noradrenergic (NA) and dopaminergic (DA) systems in intravenous self-administration of cocaine in rats was investigated by examining the effects of 6-hydroxydopamine-induced lesions of these systems on responding for the drug on a FR-1 schedule of reinforcement. Lesions of the dorsal and ventral NA bundles that reduced hippocampal-cortical NA by 96% and hypothalamic NA by 72% failed to have any effects on responding for cocaine. Lesions of the nucleus accumbens that reduced the DA content of this nucleus by 90% resulted in a significant and long-lasting (15 days) reduction in self-administration of cocaine. Apomorphine self-administration was not affected in the same animals. Identical lesions of the n accumbens had only transient (2-3 days) effects on food-reinforced operant responding, suggesting that the prolonged disruption of cocaine self-administration was not the result of motor deficits. The results are discussed with reference to the possibility that DA terminals in the n accumbens may mediate some of the positive reinforcing properties of cocaine.

Extinction and recovery of cocaine self-administration following 6-hydroxydopamine lesions of the nucleus accumbens

Abstract The effect of 6-OHDA injections into the nucleus accumbens was examined on cocaine self-administration behaviour. Rats were given access to cocaine (0.75 mg/kg/inj.) for three hours/day on a continuous reinforcement schedule. After daily intake of cocaine had stabilized, rats were injected with 6-OHDA (8 μg/2 μl). When tested the day following the 6-OHDA injection most rats failed to self-administer cocaine, however this disruption did not resemble extinction. After several days self-administration recovered in many animals to near preoperative levels, and the rate of this recovery correlated (r = +0.75) with the levels of dopamine remaining in the nucleus accumbens. The animals with the greatest depletion of dopamine did not recover cocaine intake. In a separate experiment, animals were pretreated with desmethylimipramine and/or pargyline to achieve a more extensive and selective lesion. When tested five days after the lesion all animals in these 6-OHDA groups showed a significant decline in cocaine intake compared to vehicle injected control animals. Several 6-OHDA treated animals displayed a pattern of behaviour resembling extinction, where a high rate of lever pressing was followed by cessation of responding. Some animals were aalso tested for apomorphine self-administration and this was found not to be affected by the 6-OHDA treatment. These data support the hypothesis that non-striatal dopamine may subserve cocaine reward.

The nucleus basalis magnocellularis: The origin of a cholinergic projection to the neocortex of the rat

Abstract The cells of origin of a neocortical cholinergic afferent projection have been identified by anterograde and retrograde methods in the rat. Horseradish peroxidase injected into neocortex labelled large, acetylcholinesterase-rich neurons in the ventromedial extremity of the globus pallidus. This same group of neurons underwent retrograde degeneration following cortical ablations. The region in which cell depletion occurred also showed significant decreases in the activities of choline acetyltransferase and acetylcholinesterase. Discrete electrolytic and kainic acid lesions restricted to the medial part of the globus pallidus each resulted in significant depletions of neocortical choline acetyltransferase and acetylcholinesterase. Hemitransections caudal to this cell group did not result in such depletions. Taken together these observations suggest that the acetylcholinesterase-rich neurons lying in the ventromedial extremity of the globus pallidus, as mapped in this study, constitute the origin of a major subcortical cholinergic projection to the neocortex. The utility of acetylcholinesterase histochemistry in animals pretreated with di-isopropylphosphorofluoridate in identifying cholinergic neurons is discussed in the light of this example; specifically, it is proposed that high acetylcholinesterase activity 4–8 h after this pretreatment is a necessary, but not sufficient, criterion for the identification of cholinergic perikarya. The neurons in question appear to be homologous to the nucleus basalis of the substantia innominata of primates, and are thus termed ‘nucleus basalis magnocellularis’ in the rat. No evidence was obtained to support the hypothesis that nucleus of the diagonal band projects to neocortex. However, striking similarities in size and acetylcholinesterase activity were observed among the putative cholinergic perikarya of the nucleus basalis magnocellularis, the nucleus of the diagonal band, and the medial septal nucleus. Kainic acid lesions of the neocortex produced uniform and complete destruction of neuronal perikarya. These lesions decreased neocortical glutamic acid decar☐ylase activity, suggesting that there are GABAergic perikarya in the neocortex. However, the same lesions did not affect neocortical choline acetyltransferase. This observation suggests that there are no cholinergic perikarya in the neocortex, a conclusion that is consistent with the absence of intensely acetylcholinesterase-reactive neurons in the neocortex.

Ontogeny of Adrenergic Arousal and Cholinergic Inhibitory Mechanisms in the Rat

With spontaneous activity as a measure of arousal, dose response curves were established for scopolamine and amphetamine administered to 10-, 15-, 20-, 25-, and 100-day-old rats. Amphetamine always increased activity, but scopolamine had no efect on younger rats, which suggests that adrenergic excitatory areas in the brainstem mature more rapidly than cholinergic inhibitory areas in the forebrain.

A comparison of the distribution of central cholinergic neurons as demonstrated by acetylcholinesterase pharmacohistochemistry and choline acetyltransferase immunohistochemistry

The topographical distribution of cholinergic cell bodies has been studied in the rat brain and spinal cord by choline acetyltransferase (ChAT)-immunohistochemistry and acetylcholinesterase (AChE)-pharmacohistochemistry using diisopropylfluorophosphate (DFP). The ChAT-containing cells and the cells that stained intensely for AChE 4-8 hr after DFP were mapped in detail on an atlas of the forebrain (telencephalon, diencephalon) hindbrain (mesencephalon, rhombencephalon) and cervical cord (C2, C6). Striking similarities were observed between ChAT-positive cells and neuronal soma that stained intensely for AChE both in terms of cytoarchitectural characteristics, and with respect to the distribution of the labelled cells in many areas of the central nervous system (CNS). In the forebrain these areas include the caudatoputamen, nucleus accumbens, medial septum, nucleus of the diagonal band, magnocellular preoptic nucleus and nucleus basalis magnocellularis. In contrast, a marked discrepancy was observed in the hypothalamus and ventral thalamus where there were many neurons that stained intensely for AChE, but where there was an absence of ChAT-positive cells. No cholinergic perikarya were detected in the cerebral cortex, hippocampus, amygdala and dorsal diencephalon by either histochemical procedure. In the hindbrain, all the motoneurons constituting the well-established cranial nerve nuclei (III-VII, IX-XII) contained ChAT and exhibited intense staining for AChE. Further, a close correspondence was observed in the distribution of labeled neurons obtained by the two histochemical procedures in the midbrain and pontine tegmentum, including the laterodorsal tegmental nucleus, some areas in the caudal pontine and bulbar reticular formation, and the central gray of the closed medulla oblongata. On the other hand, AChE-intense cells were found in the nucleus raphe magnus, ventral part of gigantocellular reticular nucleus, and flocculus of the cerebellum, where ChAT-positive cells were rarely observed. According to both techniques, no positive cells were seen in the cerebellar nuclei, the pontine nuclei, or the nucleus reticularis tegmenti pontis. Large ventral horn motoneurons and, occasionally, cells in the intermediomedial zone of the cervical cord displayed ChAT-immunoreactivity and intense AChE staining. On the other hand, AChE-intense cells were detected in the dorsal portion of the lateral funiculus, but immunoreactive cells were not found in any portion of the spinal cord white matter.(ABSTRACT TRUNCATED AT 400 WORDS)

Conditioned defensive burying: A new paradigm for the study of anxiolytic agents

Behavioral paradigms that have been designed to mimic forms of learning that are important for the survival of animals in the wild, rather than to minimize the contributions of adaptive predispositions, may prove to be particularly useful for studying the behavioral effects of drugs. In the present experiments, the propensity of rats to bury sources of aversive stimulation was disrupted in a dose-dependent fashion by a single injection of the anxiolytic drug, diazepam. This suggested that the conditioned defensive burying paradigm could prove to be a valuable addition to the paradigms available for studying anxiolytic effects. Supporting this view were two additional observations. First, the relative potencies of diazepam, chlordiazepoxide, and pentobarbital in the burying paradigm compared favorably with their relative potencies in clinical settings. Second, the effects of anxiolytics on conditioned burying appeared to be dissociable from the effects of other drugs that disrupt this behavior.

Dopaminergic substrates of amphetamine-induced place preference conditioning.

The conditioned place preference paradigm was used to study the reinforcing properties of D-amphetamine. Rats were injected (i.p.) with D-amphetamine sulphate (0.5, 1.0 or 5.0 mg/kg) and 10 min later confined for 30 min to one side of a shuttle box in which each of the two compartments had distinctive features. On alternate (control) days they received saline injections and were confined for 30 min to the opposite side. At all doses D-amphetamine produced place preference for the distinctive compartment that previously had been associated with the drug. Pretreatment with haloperidol (0.15 or 1.0 mg/kg) antagonized the place preference produced by amphetamine (1.5 mg/kg). By itself, haloperidol (0.15 or 1.0 mg/kg) did not produce place aversion. In separate experiments the D-amphetamine-induced place preference was examined in rats that had received 6-hydroxydopamine (6-OHDA) lesions of the nucleus accumbens. Animals with the greatest depletion of dopamine did not show preference for the compartment associated with D-amphetamine. Furthermore, the time spent on the amphetamine-reinforced side correlated significantly with the levels of dopamine remaining in the nucleus accumbens but not with the dopamine content in the striatum. Depletion of peripheral catecholamines by systemic injections of 6-OHDA did not affect D-amphetamine-induced place preference conditioning. Other groups of animals that received the dopamine receptor agonist, apomorphine, also developed a conditioned preference for the compartment that had been associated with the drug treatment. These findings support the view that the reinforcing effects of D-amphetamine are mediated by central dopamine-containing neurons, and in particular those of the mesolimbic system.

NADPH-diaphorase: A selective histochemical marker for the cholinergic neurons of the pontine reticular formation

Choline acetyltransferase immunohistochemistry has identified a large group of cholinergic neurons in the pontine tegmentum. By combined immunohistochemical and enzyme histochemical studies this particular cholinergic cell group was found to contain an enzyme, NADPH-diaphorase, that can be visualized histochemically. Thus NADPH-diaphorase histochemistry provides a simple, reliable method to selectively stain the cholinergic neurons of the brainstem reticular formation. The resolution obtained by this novel histochemical technique is similar to that found with the Golgi stain, and it should therefore be of great value in morphological studies of this cholinergic cell group.

Sexual behavior increases dopamine transmission in the nucleus accumbens and striatum of male rats: comparison with novelty and locomotion.

Extracellular concentrations of dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were examined concurrently, using in vivo microdialysis, in the nucleus accumbens and dorsal striatum of sexually active male rats during tests of locomotor activity, exposure to a novel chamber, exposure to sex odors, the presentation of a sexually receptive female, and copulation. DA increased significantly in the nucleus accumbens when the males were presented with a sexually receptive female behind a screen and increased further during copulation. Although DA also increased significantly in the dorsal striatum during copulation, the magnitude of the effect was significantly lower than that observed in the nucleus accumbens. In contrast, forced locomotion on a rotating drum, exposure to a novel chamber, and exposure to sex odors did not increase DA significantly in either region, although both DOPAC and HVA increased significantly in both regions during the locomotion test. These results indicate that novelty or locomotor activity alone cannot account for the increased extracellular DA concentrations observed in the nucleus accumbens of male rats during the presentation of a sexually receptive female behind a screen, nor can they account for the increased DA concentrations observed in both the nucleus accumbens and dorsal striatum of male rats during copulation. The preferential increase in DA transmission in the nucleus accumbens, compared with that in the striatum, suggests that anticipatory and consummatory aspects of sexual activity may belong to a class of naturally occurring events with reward values that are mediated by DA release in the nucleus accumbens. Much of the evidence linking central dopamine (DA) systems to the control of mammalian sexual behavior comes from pharmacological analyses in rats. Systemic administration of DA receptor agonists stimulates anticipatory and

Sexual behavior enhances central dopamine transmission In the male rat

Central dopamine transmission was examined in the nucleus accumbens and striatum of sexually experienced male rats during mating behaviour using in vivo brain microdialysis. Dopamine release increased significantly in the nucleus accumbens when males were placed in a novel mating chamber and when a receptive female was introduced behind a screen partitioning this chamber. Subsequently, during copulation dopamine transmission increased sharply, this being followed by a gradual decrease after the female was removed. In contrast, striatal dopamine transmission increased significantly only during copulation. These data provide a neurochemical basis for the well-known interactions between dopaminergic drugs and male sexual behaviour and demonstrate the feasibility of using brain microdialysis to elucidate the neurochemical correlates of motivated behaviour.