Loss of neuronal GSK3ß reduces dendritic spine stability and attenuates excitatory synaptic transmission via ß-catenin.

Central nervous glycogen synthase kinase 3ß (GSK3ß) is implicated in a number of neuropsychiatric diseases, such as bipolar disorder, depression, schizophrenia, fragile X syndrome or anxiety disorder. Many drugs employed to treat these conditions inhibit GSK3ß either directly or indirectly. We studied how conditional knockout of GSK3ß affected structural synaptic plasticity. Deletion of the GSK3ß gene in a subset of cortical and hippocampal neurons in adult mice led to reduced spine density. In vivo imaging revealed that this was caused by a loss of persistent spines, whereas stabilization of newly formed spines was reduced. In electrophysiological recordings, these structural alterations correlated with a considerable drop in the frequency and amplitude of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-dependent miniature excitatory postsynaptic currents. Expression of constitutively active ß-catenin caused reduction in spine density and electrophysiological alterations similar to GSK3ß knockout, suggesting that the effects of GSK3ß knockout were mediated by the accumulation of ß-catenin. In summary, changes of dendritic spines, both in quantity and in morphology, are correlates of experience-dependent synaptic plasticity; thus, these results may help explain the mechanism of action of psychotropic drugs inhibiting GSK3ß.

Innocuous full-length botulinum neurotoxin targets and promotes the expression of lentiviral vectors in central and autonomic neurons.

Fragments of botulinum neurotoxin (BoNT) have been explored as potential targeting moieties and carriers of biomolecules into neurons, although with lower binding and translocation efficiency compared with intact proteins. This study exploits a detoxified recombinant form of full-length BoNT/B (BoTIM/B) fused with core streptavidin (CS-BoTIM/B) for lentiviral targeting to central and autonomic neurons. CS-BoTIM/B underwent an activity-dependent entry into cultured spinal cord neurons. Coupling CS-BoTIM/B to biotinylated lentivirus-encoding green fluorescent protein (GFP) endowed considerable neuron selectivity to the vector as evident from the preferential expression of the reporter in neurons co-cultured with skeletal muscle cells. CS-BoTIM/B-guided lentiviral transduction with the expression of a SNARE protein, SNAP-25 (S25), rendered non-susceptible to proteolysis by three BoNT serotypes, yielded a sizable decrease in cleaved S25 upon exposure of spinal cord neurons to these toxins. This was accompanied by synaptic transmission being spared from blockade by BoNT/A or BoNT/E, reflecting adequate translation and functional competence of recombinant multi-toxin-resistant S25. The augmented neurotropism conveyed on the lentivirus by CS-BoTIM/B was also demonstrated in vivo through enhanced expression of a reporter in intramural ganglionic neurons in the rat trachea, after injection of the targeted GFP-encoding lentivirus. Thus, a novel and realistic prospect for gene therapy of peripheral neuropathies is offered in this study through lentiviral targeting to neurons by CS-BoTIM/B.

Dual effect of GABA on descending monosynaptic excitatory postsynaptic potential in frog lumbar motoneurons.

Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by stimulating ipsilateral ventrolateral column (VLC) in the thoracic section were recorded in lumbar motoneurons within the isolated spinal cord of the frog Rana ridibunda. Bath application of the selective GABAB receptor agonist (-)-baclofen (0.05 mM) caused a reduction in the peak amplitude of VLC EPSP. Baclofen did not cause any consistent change in the membrane potential or in the EPSP waveform within frog motoneurones. The selective GABA(B) receptor antagonist saclofen (0.1 mM) completely blocked the effect of (-)-baclofen on VLC EPSP. A decrease in VLC EPSP peak amplitude was also observed during GABA (0.5 mM) application. Unlike (-)-baclofen, inhibition of VLC EPSP induced by GABA was accompanied by a shortening of the EPSP time course and a reduction in membrane input resistance within lumbar motoneurons. The decrease in VLC EPSP peak amplitude induced by (-)-baclofen and GABA was accompanied by an increase in the paired-pulse facilitation. These data provide evidence for a dual pre- and postsynaptic GABAergic inhibition of the VLC monosynaptic EPSP in lumbar motoneurons within the frog spinal cord.

[Intracellular recording of the frog dorsal root single fibres' responses mediated by the GABAA and 5-HT-receptors]. / Vnutrikletochnaia registratsiia reaktsii odinochnykh volokon dorsal'nogo koreshka liagushki, oposredovannykh GAMKA- i 5-HT-retseptorami.

The effects of GABA, bicuculline and 5-HT on primary afferents in the isolated spinal cord of the frog Rana ridibunda were studied. Bath application of GABA (1 mM) reduced the primary afferent depolarisation (PAD) in IX segment of the spinal cord evoked by X dorsal root stimulation (57 +/- 8% of initial level, n = 5, p < 0.05). The action potentials (AP) recorded in dorsal root afferents was also suppressed under the GABA action (74 +/- 9%, p < 0.05). Bath application of bicuculline (50 microM) reduced the PAD (21 +/- 7%), n = 6, p < 0.05), meanwhile the AP in dorsal root afferents was resistant against the bicuculline action. Bath application of 5-HT (25 microM) depressed the PAD (34 +/- 7%, n = 7, p < 0.05) and the amplitude of the AP recorded from the single afferent fibre in dorsal column (76 +/- 6%, n = 7, p < 0.05). In contrast to GABA, 5-HT more effectively suppressed the late phase of the PAD evoked by X dorsal root stimulation and caused (76 +/- 6%, n = 7, p < 0.05) an alteration of the AP shape. All effects induced by these drugs were reversible. The mechanisms of GABA and 5-HT modulation of spinal cord afferent income are discussed.

[Participation of the GABA B receptors in presynaptic inhibition of the spinal cord descending projections fibers in the frog Rana ridibunda]. / Uchastie GAMK B-retseptorov v presinapticheskom tormozhenii volokon niskhodiashchikh proektsii spinnogo mozga liagushki Rana ridibunda.

(-)-Baclophen was found to depress in a dose-dependent and reversible way the excitatory post-synaptic potentials (EPSPS) of motor neurons and the ventral root potentials evoked by stimulation of fibres of the ipsi- and contralateral ventral columns. The (-)-baclophen depressing effect could be eliminated with saclophen. Picrotoxin eliminated the depressing effect of the GABA on the descending EPSPS. Depressing effects of (-)-baclophen and GABA upon the ventral root potentials were also shown. The data obtained in pharmacological analysis corroborate to a certain extent existence of the GABAB receptor presynaptic inhibition in descending fibres monosynaptically corrected with the spinal cord motor neurons in the frog Rana ridibunda.