Genetic dissection of dopaminergic and noradrenergic contributions to catecholaminergic tracts in early larval zebrafish

The catecholamines dopamine and noradrenaline provide some of the major neuromodulatory systems with far‐ranging projections in the brain and spinal cord of vertebrates. However, development of these complex systems is only partially understood. Zebrafish provide an excellent model for genetic analysis of neuronal specification and axonal projections in vertebrates. Here, we analyze the ontogeny of the catecholaminergic projections in zebrafish embryos and larvae up to the fifth day of development and establish the basic scaffold of catecholaminergic connectivity. The earliest dopaminergic diencephalospinal projections do not navigate along the zebrafish primary neuron axonal scaffold but establish their own tracts at defined ventrolateral positions. By using genetic tools, we study quantitative and qualitative contributions of noradrenergic and defined dopaminergic groups to the catecholaminergic scaffold. Suppression of Tfap2a activity allows us to eliminate noradrenergic contributions, and depletion of Otp activity deletes mammalian A11‐like Otp‐dependent ventral diencephalic dopaminergic groups. This analysis reveals a predominant contribution of Otp‐dependent dopaminergic neurons to diencephalospinal as well as hypothalamic catecholaminergic tracts. In contrast, noradrenergic projections make only a minor contribution to hindbrain and spinal catecholaminergic tracts. Furthermore, we can demonstrate that, in zebrafish larvae, ascending catecholaminergic projections to the telencephalon are generated exclusively by Otp‐dependent diencephalic dopaminergic neurons as well as by hindbrain noradrenergic groups. Our data reveal the Otp‐dependent A11‐type dopaminergic neurons as the by far most prominent dopaminergic system in larval zebrafish. These findings are consistent with a hypothesis that Otp‐dependent dopaminergic neurons establish the major modulatory system for somatomotor and somatosensory circuits in larval fish. J. Comp. Neurol. 518:439–458, 2010. © 2009 Wiley‐Liss, Inc.     

Increased mRNA expression of cytochrome oxidase in dorsal raphe nucleus of depressive suicide victims

Suicidal behavior is a problem with important social repercussions. Some groups of the population show a higher risk of suicide; for example, depression, alcoholism, psychosis or drug abuse frequently precedes suicidal behavior. However, the relationship between metabolic alterations in the brain and premorbid clinical symptoms of suicide remains uncertain. The serotonergic and noradrenergic systems have frequently been, implicated in suicidal behavior and the amount of serotonin in the brain and CSF of suicide victims has been found to be low compared with normal subjects. However, there are contradictory results regarding the role of noradrenergic neurons in the mediation of suicide attempts, possibly reflecting the heterogeneity of conditions that lead to a common outcome. In the present work we focus on the subgroup of suicide victims that share a common diagnosis of major depression. Based on post-mortem studies analyzing mRNA expression by in situ hybridization, serotonergic neurons from the dorsal raphe nucleus (DRN) from depressive suicide victims are seen to over-express cytochrome oxidase mRNA. However, no corresponding changes were found in the expression of tyrosine hydroxylase (TH) mRNA in the noradrenergic neurons of the Locus Coeruleus (LC). These results suggest that, despite of the low levels of serotonin described in suicide victims, the activity of DRN neurons could increase in the suicidally depressed, probably due to the over activation of serotonin re-uptake. No alteration was found in noradrenergic neurons, suggesting that they play no crucial role in the suicidal behavior of depressive patients.     

Changes in midbrain serotonin transporter availability in atypically depressed subjects after one year of psychotherapy

BACKGROUND: Psychotherapy is an effective treatment method for depression, but no differences in the psychotherapy response have been found between the subtypes of depression. The effect of psychotherapy on neurotransmitter transporter functions has never been recorded in depressed subjects. METHODS: Depressive outpatients (N=19) received psychodynamic psychotherapy for 12 months. All subjects fulfilled the DSM-IV criteria for depression, and 8 were classified as having atypical depression. The severity of depression was assessed with the 29-item Hamilton Depression Rating Scale (HAM-D-29). Midbrain serotonin transporter (SERT) and striatum dopamine transporter (DAT) densities were recorded using single photon emission computed tomography (SPECT) brain imaging with the [123I]nor-beta-CIT radioligand before and after psychotherapy. RESULTS: Midbrain SERT density significantly increased during psychotherapy in atypicals but not in nonatypicals. There were no changes in the levels of DAT. CONCLUSIONS: The psychotherapy-related SERT elevation of atypically depressed subjects may be due to some unknown adaptive mechanisms inducing an increase in either the levels of SERT or serotonergic nerve terminals and therefore enhancing serotonergic activity and improving mood.     

Pain relief by gabapentin and pregabalin via supraspinal mechanisms after peripheral nerve injury

The antihypersensitivity actions of gabapentin and pregabalin have been well characterized in a large number of studies, although the underlying mechanisms have yet to be defined. We have been focusing on the supraspinal structure as a possible site for their action and have demonstrated that intracerebroventricular (i.c.v.) administration of gabapentin and pregabalin indeed decreases thermal and mechanical hypersensitivity in a murine chronic pain model involving partial ligation of the sciatic nerve. This novel supraspinally mediated analgesic effect was markedly suppressed by either depletion of central noradrenaline (NA) or blockade of spinal alpha(2)-adrenergic receptors. Moreover, i.c.v. injection of gabapentin and pregabalin increased spinal NA turnover in mice only after peripheral nerve injury. In locus coeruleus (LC) neurons in brainstem slices prepared from mice after peripheral nerve injury, gabapentin reduced the gamma-aminobutyric acid (GABA) type A receptor-mediated inhibitory postsynaptic currents (IPSCs). Glutamate-mediated excitatory synaptic transmission was hardly affected. Moreover, gabapentin did not reduce IPSCs in slices taken from mice given a sham operation. Although gabapentin altered neither the amplitude nor the frequency of miniature IPSCs, it reduced IPSCs together with an increase in the paired-pulse ratio, suggesting that gabapentin acts on the presynaptic GABAergic nerve terminals in the LC. Together, the data suggest that gabapentin presynaptically reduces GABAergic synaptic transmission, thereby removing the inhibitory influence on LC neurons only in neuropathic pain states, leading to activation of the descending noradrenergic system.     

Novel anti-obesity drugs

There is increasing evidence that body weight is homeostatically regulated and that in obesity this regulation maintains weight at a high level. Weight loss activates mechanisms that are designed to return individuals to their pre-existing weight. This explains the universally poor results of current strategies to maintain weight loss. On this basis, life-long drug therapy may be justified for those with significant obesity. Currently available drugs include selective serotonin re-uptake inhibitors (e.g., fluoxetine), noradrenergic re-uptake inhibitors (e.g., phentermine), a serotonin and noradrenergic re-uptake inhibitor (sibutramine) and an intestinal lipase inhibitor (orlistat). An active research program is underway to develop new agents based on the rapidly expanding knowledge of the complex mechanisms regulating body weight. Leptin, a hormone produced by adipocytes that inhibits food intake, has undergone clinical trials and analogues are currently being developed. Other agents include amylin, melanocortin-4 receptor agonists, neuropeptide Y antagonists, ₃ adrenergic agonists and glucagon-like peptide-1 agonists. As some redundancy exists in the central regulatory system controlling body weight, some agents might need to be used in combination to be effective.     

Prolactin-releasing peptide-immunoreactivity in A1 and A2 noradrenergic neurons of the rat medulla

Distribution of prolactin-releasing peptide-like immunoreactivity (PrRP-LI) was investigated in the rat medulla with the use of a rabbit polyclonal antiserum against the human PrRP-31 peptide. PrRP-positive neurons were noted mainly in two areas of the caudal medulla: ventrolateral reticular formation and commissural nucleus of the nucleus of the solitary tract (NTS), corresponding to the A1 and A2 areas. PrRP-LI neurons were absent in the medulla rostral to the area postrema. Double-labeling the sections with PrRP antisera and tyrosine hydroxylase (TH) monoclonal antibodies revealed extensive colocalization of PrRP- and TH-like immunoreactivity (TH-LI) in neurons of the A1 and A2 areas. Our results show that PrRP-LI is expressed in a population of A1 and A2 noradrenergic neurons of the rat caudal medulla.     

Comparative anatomy of alpha(2) and beta adrenoceptors in the adult and developing brain of the marine teleost the red porgy (Pagrus pagrus, Sparidae): [(3)H]clonidine and [(3)H]dihydroalprenolol quantitative autoradiography and receptor subtypes immunohistochemistry

The present study aimed to determine the anatomic distribution and developmental profile of alpha(2) and beta adrenoceptors (AR) in marine teleost brain. Alpha 2 and beta adrenoceptors were studied at different developmental stages by using [(3)H]clonidine and [(3)H]dihydroalprenolol, respectively, by means of in vitro quantitative autoradiography. Furthermore, immunohistochemical localization of the receptor subtypes was performed to determine their cellular distribution. Saturation studies determined a high-affinity component of [(3)H]clonidine and [(3)H]dihydroalprenolol binding sites. High levels of both receptors were found in preglomerular complex, ventral hypothalamus, and lateral torus. Dorsal hypothalamus and isthmus included high levels of alpha(2) AR, whereas pretectum and molecular and proliferative zone of cerebellum were specifically characterized by high densities of beta AR. From the first year of life, adult levels of both AR were found in most medial telencephalic, hypothalamic, and posterior tegmental areas. Decreases in both receptors densities with age were prominent in ventral and posterior telencephalic, pretectal, ventral thalamic, hypothalamic, and tegmental brain regions. Immunohistochemical data were well correlated with autoradiography and demonstrated the presence of alpha(2A), alpha(2C), beta(1), and beta(2) AR subtype-like immunoreactivity. Both the neuronal (perikaryal or dendritic) and the glial localization of receptors was revealed. The localization and age-dependent alterations in alpha(2) and beta AR were parallel to plasticity mechanisms, such as cell proliferation in periventricular thalamus, hypothalamus, and cerebellum. In addition, the biochemical characteristics, distribution pattern, and neuronal or glial specificity of the receptors in teleost brain support a similar profile of noradrenergic transmission in vertebrate brain evolution.     

A hypothalamic alpha-adrenergic mechanism mediating the thermogenic response to electrical stimulation of the lower brainstem in the guinea pig

Summary Electrical stimulation of the lower brain stem (ESLB) at sites presumed to be parts of the ascending noradrenergic system was carried out in unanaesthetized young guinea pigs. At neutral ambient temperature ESLB elicited a thermogenic response resembling that evoked by microinjection of noradrenaline into the hypothalamus. The response consisted of a rise in oxygen uptake (to more than 50% of the resting value) and of body temperatures, especially of the interscapular adipose tissue. In some cases shivering was also evoked. The thermogenic response to ESLB was completely blocked by additional microinjection of an adrenergic alpha-receptor blocker, phentolamine, into the hypothalamic area where the noradrenergic fibres were presumed to terminate. Subsequent intrahypothalamic injection of noradrenaline, which had formerly been shown to restore the decreased responses to repeated ESLB, failed to restore the effectiveness of ESLB after phentolamine. It is concluded that the thermogenic responses to ESLB are mediated by a noradrenergic pathway ascending to the hypothalamus and not by direct stimulation of efferent pathways controlling the peripheral target system. The hypothalamic transmission can be prevented by an alpha-adrenergic blockade.Supported by the Deutsche Forschungsgemeinschaft SFB 122, Projeckt B 1     

Effect of the hypothalamic cardioactive protein-hormonal complex on choline sensitivity of the small intestine and contraction of the vas deferens in rats

A cardioactive protein-hormonal complex capable of increasing the sensitivity of the small intestine to acetylcholine about 2.5 times was isolated from magnocellular nuclei of the hypothalamo-neurohypophyseal system. Moreover, this complex enhanced contraction of the vas deferens caused by transmural stimulation, exogenous noradrenalin, and phenylephrine. The findings indicate release of transmitters from cholinergic and adrenergic neurons under the influence of the complex. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 3, pp. 280–282, March, 1995     

The effects of lesions to ascending noradrenergic neurons on discrimination learning and performance in the rat

Three experiments examined the effect of central noradrenergic depletion on the acquisition and performance of a temporal discrimination in auditory or visual modalities. In Experiment 1, 6-hydroxydopamine-induced lesions of the dorsal noradrenergic bundle significantly retarded acquisition compared to a similarly lesioned ventral noradrenergic bundle-group, two sham-operated and one unoperated control group. In Experiment 2, the acquisition impairment produced in the dorsal noradrenergic bundle group was replicated, for both auditory and visual modalities, by lesions depleting hippocampal and neocortical noradrenaline by over 80%. In rats subsequently switched to discriminations involving the unfamiliar modality, the dorsal-bundle lesion also impaired acquisition several weeks after surgery. Experiment 3 showed significantly impaired performance in rats with dorsal bundle lesions when training prior to surgery had not resulted in better than chance performance. In rats previously trained to criterion, the dorsal bundle lesion transiently, but non-significantly, impaired performance. In rats performing better than chance, but not having reached criterion, there were no significant effects of the dorsal bundle lesion. Subsequent manipulations of deprivation and difficulty of discrimination in general failed to distinguish between the dorsal bundle lesion and sham-groups, suggesting that the acquisition impairment did not result from simple sensory or motivational effects. Reducing the interstimulus interval did impair the dorsal bundle group more than controls. However, there was no evidence of altered "distractibility" in the lesioned group when the alternative modality was introduced as a distractor. The results are discussed in terms of other acquisition deficits shown by rats with central noradrenaline depletion and their significance for determining the functions of the projections from the locus caeruleus via the dorsal noradrenergic bundle to the neocortex and hippocampus.