Isoniazid-induced reduction in GABAergic neurotransmission alters the function of the cerebellar cortical circuit.

The cerebellar cortex contributes to the control of movement, coordination, and certain cognitive functions. The cerebellar network is composed of five different types of neurons that are wired together in a repetitive module. Given that four of these five neurons synthesize and release GABA, this inhibitory neurotransmitter plays a central role in regulation of the excitability and correct functioning of the cerebellar cortex. We have now used isoniazid, an inhibitor of glutamic acid decarboxylase, the enzyme responsible for the synthesis of GABA, to evaluate the contribution of GABAergic transmission in different types of cerebellar cortical neurons to the functioning of the cerebellar circuit. Parasagittal cerebellar slices were prepared from 28- to 40-day-old male rats and were subjected to patch-clamp recording in the voltage- or current-clamp mode. Exposure of the tissue slices to isoniazid (10 mM) resulted in a decrease in the level of GABAergic transmission in Purkinje cells and a consequent increase in the firing rate of spontaneous action potentials that was apparent after 40 min. In granule neurons, isoniazid reduced both tonic and phasic GABAergic currents and thereby altered the flow of information across the cerebellar cortex. Our data support the notion that the amount of GABA at the synaptic level is a major determinant of the excitability of the cerebellar cortex, and they suggest that isoniazid may be a useful tool with which to study the function of the cerebellar network.

Management of prosthetic abutments respecting peri-implant soft tissues.

Periodontal and peri-implant soft tissues are very similar in many aspects (phenotype, mucosal dimensions, biological width). In peri-implant tissue, the mucosal seal is localized apically to the gap existing between the fixture and the prosthetic abutment. This is due to mechanical trauma created by screwing and unscrewing the prosthetic components, to mechanical deformation produced under functional stress and to bacterial colonization. To reduce the effects of this gap on peri-implant soft tissues stability several options are available: supracresta fixture positioning, reduction of the fixture-abutment gap, and minimizing the prosthetic steps. A clinical case was illustrated. Abutments (Gingi-hue 3I with a fixture-abutment gap less than 2 mm and a fixture abutment angle rotation of 0.4 degrees ) were screwed on the fixtures after the second stage surgery and used as impression transfer. These abutments were prepared in the laboratory and definitively screwed after the impression session. The use of definitive abutments as transfer reduces the session number and allows the peri-implant soft tissues to heal without beeing troubled by screwing and unscrewing of the prosthetic components.