Differential intracellular regulation of cortical GABAA and spinal glycine receptors in cultured neurons

Using patch-clamp techniques we studied several aspects of intracellular GABA_A and glycine Cl⁻ current regulation in cortical and spinal cord neurons, respectively. Activation of PKA with a permeable analog of cyclic AMP (cAMP) produced a potentiation of the Cl⁻ current activated with glycine, but not of the current induced with GABA. The inactive analog was without effect. Activation of PKC with 1 μM PMA reduced the amplitude of the GABA_A and glycine currents. Internal application of 1 mM cGMP, on the other hand, had no effect on the amplitude of either current. The amplitude of these inhibitory currents changed slightly during 20 min of patch-clamp recording. Internal perfusion of the neurons with 1 μM okadaic acid, a phospatase inhibitor, induced potentiation in both currents. The amplitude of GABA_A and glycine currents recorded with 1 mM internal CaCl₂ and 10 mM EGTA (10 nM free Ca²⁺) decayed by less than 30% of control. Increasing the CaCl₂ concentration to 10 mM (34 μM free Ca²⁺) induced a transient potentiation of the GABA_A current. A strong depression of current amplitude was found with longer times of dialysis. The glycine current, on the contrary, was unchanged by increasing the intracellular Ca²⁺ concentration. Activation of G proteins with internal FAl⁻₄ induced an inhibition of the GABA_A current, but potentiated the amplitude of the strychnine-sensitive Cl⁻ current. These results indicate that GABA_A and glycine receptors are differentially regulated by activation of protein kinases, G proteins and Ca²⁺. This conclusion supports the existence of selectivity in the intracellular regulation of these two receptor types.     

Lengthy regrowth of cut axons from ganglion cells after peripheral nerve transplantation into the retina of adult rats

Ganglion cell axons regrew to approximately their normal length (2 cm) when autologous peripheral nerve segments were inserted into the retina of adult rats for 4-18 weeks. Retrograde labeling from the graft with HRP or combinations of two different fluorescent dyes applied to the optic tract and graft demonstrate that axons growing into the nerve transplants originated from axotomized ganglion cells rather than by sprouting of undamaged neurons. Axonal injury and graft proximity to neuronal somata appear as requisites for the elongation of these fibers.     

Intrathecal immunoglobulin synthesis in multiple sclerosis: effect of corticosteroids and azathioprine.

The objective of this study was to investigate quantitative and qualitative intrathecal IgG synthesis in 51 patients with clinically definite multiple sclerosis, taking previous immunosuppressive treatment into account. Four formulae were used to assess quantitative synthesis. Oligoclonal bands (OB) were investigated using isoelectric focusing (IEF) and silver staining. Abnormal quantitative values were detected in 42 (82%) patients, whereas OB occurred in 38 (74.5%) patients. Steroid therapy lowered quantitative synthesis in 6 out of 9 patients when given within 3 months before lumbar puncture (LP). Untreated patients with OB systematically had abnormal formulae. Patients treated with corticosteroids 10 or more months prior to LP had abnormal formulae. This fact suggests a transient depressor effect of steroids on quantitative synthesis. OB were present in patients recently treated with corticosteroids. Quantitative synthesis was higher in patients with OB than in those without OB. Azathioprine treatment did not significantly lower quantitative synthesis. We conclude that for routine purposes evaluation of intrathecal immunoglobulin synthesis could begin by performing quantitative tests. IEF seems to be mandatory for patients with normal formulae who have recently been treated with steroids.