SSADH deficiency leads to elevated extracellular GABA levels and increased GABAergic neurotransmission in the mouse cerebral cortex.

Succinic semialdehyde dehydrogenase (SSADH) deficiency is an inherited disorder in which patients display neurodevelopmental retardation, ataxia, and epileptic seizures. The recently engineered SSADH knock-out (KO) mouse models the severe form of the human disorder. The SSADH enzyme participates in the breakdown of the inhibitory neurotransmitter GABA, and studies have shown increases in brain GABA and downregulation of GABA(A) receptor beta(2) subunits in the cerebral cortex of these mice. Here, we used brain slice electrophysiology to investigate the alterations in GABA neurotransmission in SSADH KO mouse cortex. In layer 2/3 pyramidal cells, spontaneous inhibitory postsynaptic currents (IPSCs), reflecting activity of GABAergic synaptic contacts, were normal in SSADH KO mice. Also, IPSCs evoked by electrical single-axon stimulation in KO mice were normal. In contrast, tonic inhibition mediated by presumed extrasynaptic GABA(A) receptors was strongly increased, indicating significantly raised extracellular GABA levels. The excessive cortical GABAergic neurotransmission may participate in the seizure activity in SSADH deficiency.

Interaction between the P1 protein of Mycoplasma pneumoniae and receptors on HEp-2 cells.

The human pathogen Mycoplasma pneumoniae can cause atypical pneumonia through adherence to epithelial cells in the respiratory tract. The major immunogenic protein, P1, participates in the attachment of the bacteria to the host cells. To investigate the adhesion properties of P1, a recombinant protein (rP1-II) covering amino acids 1107-1518 of the P1 protein was produced. This protein inhibited the adhesion of M. pneumoniae to human HEp-2 cells, as visualized in a competitive-binding assay using immunofluorescence microscopy. Previous studies have shown that mAbs that recognize two epitopes in this region of P1 also reduce M. pneumoniae adhesion. Therefore, peptides covering these epitopes, of 8 and 13 aa, respectively, were synthesized to further investigate the adhesion region. None of these synthetic peptides reduced the binding of M. pneumoniae to the receptors on the host cells. Instead, 10 overlapping synthetic peptides covering the whole of rP1-II were evaluated in the competitive-binding assay using immunofluorescence microscopy. A reduction in the number of M. pneumoniae microcolonies was seen, which was confirmed for five peptides using a POLARstar OPTIMA reader to measure fluorescence intensity. The number of M. pneumoniae microcolonies adhering to the host cells was significantly reduced by these five peptides. Further investigations showed that inhibiting peptide 7 (amino acids 1347-1396) of the major adhesin protein P1 bound directly to host receptors, suggesting that the observed M. pneumoniae-inhibiting peptides occupied HEp-2 receptors, which are otherwise available for P1-mediated M. pneumoniae adhesion.

Gamma-hydroxybutyrate--a drug of abuse.

Gamma-hydroxybutyrate (GHB) is a drug of abuse that causes euphoria, anxiolysis, and hypnosis. The recent rise in the recreational intake of GHB, as well as its association with 'drug rape', has turned the attention to GHB in acute hospital settings. Acutely admitted GHB intoxicated patients may display various levels of sedation or coma, but may also show paradoxical agitation, combativeness, or self-injurious behaviors. The symptoms can be nonspecific and the definite diagnosis therefore normally relies on the detection of GHB in blood or body fluids, which is an analysis that may not be promptly available. As a basis for understanding the clinical features of GHB intoxication and abuse, we here review the pharmacological and neurophysiological knowledge about GHB, which stems from decades of clinical and basic GHB research. In addition, we discuss the latest discoveries in the quest for distinct GHB receptors in the brain, and their possible implications for future therapies of GHB abuse.