OCD-like behavior is caused by dysfunction of thalamo-amygdala circuits and upregulated TrkB/ERK-MAPK signaling as a result of SPRED2 deficiency.

Obsessive-compulsive disorder (OCD) is a common neuropsychiatric disease affecting about 2% of the general population. It is characterized by persistent intrusive thoughts and repetitive ritualized behaviors. While gene variations, malfunction of cortico-striato-thalamo-cortical (CSTC) circuits, and dysregulated synaptic transmission have been implicated in the pathogenesis of OCD, the underlying mechanisms remain largely unknown. Here we show that OCD-like behavior in mice is caused by deficiency of SPRED2, a protein expressed in various brain regions and a potent inhibitor of Ras/ERK-MAPK signaling. Excessive self-grooming, reflecting OCD-like behavior in rodents, resulted in facial skin lesions in SPRED2 knockout (KO) mice. This was alleviated by treatment with the selective serotonin reuptake inhibitor fluoxetine. In addition to the previously suggested involvement of cortico-striatal circuits, electrophysiological measurements revealed altered transmission at thalamo-amygdala synapses and morphological differences in lateral amygdala neurons of SPRED2 KO mice. Changes in synaptic function were accompanied by dysregulated expression of various pre- and postsynaptic proteins in the amygdala. This was a result of altered gene transcription and triggered upstream by upregulated tropomyosin receptor kinase B (TrkB)/ERK-MAPK signaling in the amygdala of SPRED2 KO mice. Pathway overactivation was mediated by increased activity of TrkB, Ras, and ERK as a specific result of SPRED2 deficiency and not elicited by elevated brain-derived neurotrophic factor levels. Using the MEK inhibitor selumetinib, we suppressed TrkB/ERK-MAPK pathway activity in vivo and reduced OCD-like grooming in SPRED2 KO mice. Altogether, this study identifies SPRED2 as a promising new regulator, TrkB/ERK-MAPK signaling as a novel mediating mechanism, and thalamo-amygdala synapses as critical circuitry involved in the pathogenesis of OCD.

Serotonin transporter gene variation impacts innate fear processing: Acoustic startle response and emotional startle.

Anxiety-related behaviors are closely linked to neural circuits relaying fear-specific information to the amygdala. Many of these circuits, like those underlying processing of innate fear, are remarkably well understood. Recent imaging studies have contributed to this knowledge by discriminating more detailed corticoamygdalar associations mediating processing fear and anxiety. However, little is known about the underlying molecular mechanisms. We used the acoustic startle paradigm to investigate the impact of molecular genetic variation of serotonergic function on the acoustic startle response and its fear potentiation. Startle magnitudes to noise bursts as measured with the eye blink response were recorded in 66 healthy volunteers under four conditions: presenting unpleasant and pleasant affective pictures as well as neutral pictures, and presenting the startle stimulus without additional stimuli as a baseline. Subjects were genotyped for functional polymorphism in the transcriptional control region of the serotonin transporter gene (5-hydroxytryptamine transporter gene-linked region: 5-HTTLPR). Analyses of variance revealed a significant effect of 5-HTTLPR on overall startle responses across conditions. Carriers of the short (s) allele exhibited stronger startle responses than l/l homozygotes. However, we could not confirm our hypothesis of enhanced fear potentiation of the startle in s allele carriers. In conclusion, the results provide first evidence that the startle response is sensitive to genetic variation in the serotonin pathway. Despite some issues remaining to be resolved, the startle paradigm may provide a valuable endophenotype of fear processing and underlying serotonergic influences.

A splice variant of glutamate transporter GLT1/EAAT2 expressed in neurons: cloning and localization in rat nervous system.

Rapid uptake of synaptically released glutamate via the high affinity glutamate transporter 1 (GLT1; EAAT2) is important for limiting transmitter signalling and prevents a harmful receptor overstimulation. So far, in the adult brain GLT1 protein has only been detected in astrocytes. Here, we describe the cDNA cloning of a variant of GLT1 from rat brain which is generated by alternative splicing at the 3'-end of the GLT1 cDNA. Reverse transcription-polymerase chain reaction revealed that the GLT1 variant message was present not only in brain, but also in peripheral organs. Northern blot analysis showed that in brain the mRNA of GLT1 (approximately 11 kb) is predominant while in the retina the mRNA of GLT1 variant (approximately 12.5 kb) prevails. In situ hybridization using cRNA and oligonucleotide probes, and immunocytochemistry using an antibody against a synthetic GLT1v peptide were applied in order to identify the cell types expressing GLT1 variant in the adult rat nervous system. GLT1 variant is preferentially expressed in neurons of the CNS and PNS, but is also detected in glial cells (oligodendrocytes, ependymal cells, epithelial cells of the plexus choroideus, satellite cells, and Schwann cells). In contrast to GLT1, GLT1 variant was only occasionally detected in astrocytes. Immunolabelling revealed a preferentially cytoplasmic (frequently granular) staining of neurons and glial cells, suggesting a localization of GLT1 variant protein in vesicle membranes. The studies provide evidence that the cellular expression of the GLT1 variant in the CNS is almost complementary to that of GLT1 and that the GLT1 variant does not seem to be restricted to the CNS.

Barrel pattern formation requires serotonin uptake by thalamocortical afferents, and not vesicular monoamine release.

Thalamocortical neurons innervating the barrel cortex in neonatal rodents transiently store serotonin (5-HT) in synaptic vesicles by expressing the plasma membrane serotonin transporter (5-HTT) and the vesicular monoamine transporter (VMAT2). 5-HTT knock-out (ko) mice reveal a nearly complete absence of 5-HT in the cerebral cortex by immunohistochemistry, and of barrels, both at P7 and adulthood. Quantitative electron microscopy reveals that 5-HTT ko affects neither the density of synapses nor the length of synaptic contacts in layer IV. VMAT2 ko mice, completely lacking activity-dependent vesicular release of monoamines including 5-HT, also show a complete lack of 5-HT in the cortex but display largely normal barrel fields, despite sometimes markedly reduced postnatal growth. Transient 5-HTT expression is thus required for barrel pattern formation, whereas activity-dependent vesicular 5-HT release is not.

Excessive activation of serotonin (5-HT) 1B receptors disrupts the formation of sensory maps in monoamine oxidase a and 5-ht transporter knock-out mice.

Deficiency in the monoamine degradation enzyme monoamine oxidase A (MAOA) or prenatal exposure to the monoamine uptake inhibitor cocaine alters behavior in humans and rodents, but the mechanisms are unclear. In MAOA knock-out mice, inhibiting serotonin synthesis during development can prevent abnormal segregation of axons in the retinogeniculate and somatosensory thalamocortical systems. To investigate this effect, we crossed MAOA knock-outs with mice lacking the serotonin transporter 5-HTT or the 5-HT1B receptor, two molecules present in developing sensory projections. Segregation was abnormal in 5-HTT knock-outs and MAOA/5-HTT double knock-outs but was normalized in MAOA/5-HT1B double knock-outs and MAOA/5-HTT/5-HT1B triple knock-outs. This demonstrates that the 5-HT1B receptor is a key factor in abnormal segregation of sensory projections and suggests that serotonergic drugs represent a risk for the development of these projections. We also found that the 5-HT1B receptor has an adverse developmental impact on beam-walking behavior in MAOA knock-outs. Finally, because the 5-HT1B receptor inhibits glutamate release, our results suggest that visual and somatosensory projections must release glutamate for proper segregation.

Reduction in the density and expression, but not G-protein coupling, of serotonin receptors (5-HT1A) in 5-HT transporter knock-out mice: gender and brain region differences.

The aim of the present study was to investigate the mechanisms underlying the desensitization of 5-HT(1A) receptors in the dorsal raphe and hypothalamus of serotonin (5-HT) transporter knock-out mice (5-HTT -/-). The density of 5-HT(1A) receptors in the dorsal raphe was reduced in both male and female 5-HTT -/- mice. This reduction was more extensive in female than in male 5-HTT -/- mice. 8-OH-DPAT-induced hypothermia was absent in female 5-HTT -/- and markedly attenuated in 5-HTT +/- mice. The density of 5-HT(1A) receptors also was decreased significantly in several nuclei of the hypothalamus, amygdala, and septum of female 5-HTT -/- mice. 5-HT(1A) receptor mRNA was reduced significantly in the dorsal raphe region, but not in the hypothalamus or hippocampus, of female 5-HTT +/- and 5-HTT -/- mice. G-protein coupling to 5-HT(1A) receptors and G-protein levels in most brain regions were not reduced significantly, except that G(o) and G(i1) proteins were reduced modestly in the midbrain of 5-HTT -/- mice. These data suggest that the desensitization of 5-HT(1A) receptors in 5-HTT -/- mice may be attributable to a reduction in the density of 5-HT(1A) receptors. This reduction is brain region-specific and more extensive in the female mice. The reduction in the density of 5-HT(1A) receptors may be mediated partly by reduction in the gene expression of 5-HT(1A) receptors in the dorsal raphe, but also by other mechanisms in the hypothalamus of 5-HTT -/- female mice. Finally, alterations in G-protein coupling to 5-HT(1A) receptors are unlikely to be involved in the desensitization of 5-HT(1A) receptors in 5-HTT -/- mice.

Reduction of 5-hydroxytryptamine (5-HT)(1A)-mediated temperature and neuroendocrine responses and 5-HT(1A) binding sites in 5-HT transporter knockout mice.

The aim of the present study was to determine whether alterations in 5-hydroxytryptamine (5-HT)(1A) receptors would be found in knockout mice lacking the serotonin transporter (5-HTT). Hypothermic and neuroendocrine responses to the 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) were used to examine the function of 5-HT(1A) receptors. Initial studies evaluated the dose-response and time course of 8-OH-DPAT-induced hypothermia and hormone secretion in normal CD-1 mice (the background strain of the 5-HTT knockout mice). 8-OH-DPAT dose-dependently produced hypothermic responses that peaked at 20 min postinjection. 8-OH-DPAT-induced hypothermia was blocked by the 5-HT(1A) antagonist WAY-100635. 8-OH-DPAT dose-dependently increased the concentrations of plasma oxytocin, corticotropin, and corticosterone. In the 5-HTT knockout (-/-) mice, the hypothermic response to 8-OH-DPAT (0.1 mg/kg s.c.) was completely abolished. Furthermore, 5-HTT-/- mice had significantly attenuated plasma oxytocin and corticosterone responses to 8-OH-DPAT. No significant changes in the hypothermic or hormonal responses to 8-OH-DPAT were observed in heterozygous (5-HTT+/-) mice. [(3)H]8-OH-DPAT- and [(125)I]MPPI [4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-iodobenzamido]ethyl] pip erazine]-binding sites in the hypothalamus and [(125)I]MPPI-binding sites in the dorsal raphe were significantly decreased in 5-HTT-/- mice. The results indicate that lack of the 5-HTT is associated with a functional desensitization of 5-HT(1A) receptor responses to 8-OH-DPAT, which may be a consequence, at least in part, of the decrease in density of 5-HT(1A) receptors in the hypothalamus and dorsal raphe of 5-HTT-/- mice.

Lilliputian and negative hallucinations in a patient with probable encephalomyelitis disseminata.

A patient who showed Lilliputian hallucinations and negative hallucinations in the course of probable disseminated encephalomyelitis is described. At the age of 14 years the patient experienced a transient, flaccid paresis of the right leg. Eighteen years later she suddenly developed paranoid-hallucinatory symptoms accompanied by atypical visual hallucinations. She did not recover completely and until now she has suffered at least once every year from an episode with psychotic symptoms. During the most recent of these episodes, MRI revealed several disseminated supra- and infratentorial foci in the brain. Two of them, in the left cerebral peduncle and in the left occipital white matter are discussed as the cause of her visual hallucinatory symptoms.