Apoptotic cell death in mouse models of GM2 gangliosidosis and observations on human Tay-Sachs and Sandhoff diseases

Tay-Sachs and Sandhoff diseases are autosomal recessive neurodegenerative diseases resulting from the inability to catabolize GM2 ganglioside by beta-hexosaminidase A (Hex A) due to mutations of the alpha subunit (Tay-Sachs disease) or beta subunit (Sandhoff disease) of Hex A. Hex B (beta beta homodimer) is also defective in Sandhoff disease. We previously developed mouse models of both diseases and showed that Hexa-/- (Tay-Sachs) mice remain asymptomatic to at least 1 year of age while Hexb-/- (Sandhoff) mice succumb to a profound neurodegenerative disease by 4-6 months of age. Here we find that neuron death in Hexb-/- mice is associated with apoptosis occurring throughout the CNS, while Hexa-/- mice were minimally involved at the same age. Studies of autopsy samples of brain and spinal cord from human Tay-Sachs and Sandhoff diseases revealed apoptosis in both instances, in keeping with the severe expression of both diseases. We suggest that neuron death is caused by unscheduled apoptosis, implicating accumulated GM2 ganglioside or a derivative in triggering of the apoptotic cascade.      

Increased multiclonal antibody-forming cell activity in the peripheral blood of patients with SLE

21 patients with criteria for systemic lupus erythematosus (SLE) and 12 normal controls were studied for their spontaneous circulating IgM and IgG plaque-forming cells (PFCs) reactive against sheep erythrocytes (SRBC) and against a panel of five haptens. Quantitatively defined active and mildly active SLE patients had significantly elevated IgM- and IgG-producing PFCs in their peripheral blood reactive with the panel of five chemically defined haptens. Those patients having inactive SLE also showed increased circulating IgM PFCs. Significant elevations in circulating hapten-reactive PFCs were found to correlate progressively with disease activity in the inactive, mildly active, and active SLE patient groups. Circulating IgM- and IgG-secreting PFC reactive against SRBC were both significantly elevated only in those patients with active SLE. The data support the concept that SLE patients have a generalized increase in B cell activity against a broad repertoire of determinants, even those ostensibly unrelated to natural tissue antigens.     

Functional consequences of ROMK mutants linked to antenatal Bartter's syndrome and implications for treatment

The antenatal variant of Bartter's syndrome is an autosomal recessive kidney disease characterized by polyhydramnios, premature delivery, hypokalemic alkalosis and hypercalciuria. It is genetically heterogeneous, having been linked recently to mutations in an ATP- sensitive, renal outer medullary K+channel, ROMK, and earlier to mutations in the Na-K-2Cl co-transporter, NKCC2. We characterized four of the mutations reported in three heterozygous ROMK variants of antenatal Bartter's and found that each expressed a distinct phenotype in Sf9 cells. One mutation expressed normal function and appears to be an allelic polymorphism. The other three mutations produced channels with significantly reduced K+fluxes. However, the mechanisms in each case were different and reflected abnormalities in phosphorylation, proteolytic processing or protein trafficking. The different mechanisms may be important in the design of appropriate therapy for patients with this disease.      

Do blood cultures need continuous monitoring so that clinical action can be taken outside normal working hours?

Many automated blood culture reading systems monitor bacterial growth 24 hours a day but it is unclear if reacting to prompts indicating bacterial growth outside normal laboratory hours is of clinical benefit. An analysis of 50 blood cultures from 43 patients which had organisms seen on Gram films and had triggered positive out-of-hours showed that examination of the Gram film altered management of seven patients and the results of culture or sensitivity testing altered that of a further four. However, after review, it was felt the clinical outcome would not have been influenced by earlier intervention in any of these patients. We therefore consider that an out-of-hours service for dealing with positive blood cultures is not justified in our hospital. This conclusion may not apply universally, especially in hospitals where potential pathogens show less predictable antimicrobial sensitivity patterns.     

Long-term potentiation deficits and excitability changes following traumatic brain injury

The effects of traumatic brain injury (TBI) on hippocampal long-term potentiation (LTP) and cellular excitability were assessed at postinjury days 2, 7, and 15. TBI was induced using a well-characterized central fluid-percussion model. LTP of the Schaffer collateral/commissural system was assessed in vivo in urethane-anesthetized rats. Significant LTP of the population excitatory postsynaptic potential (EPSP) slope was found only in controls, and no recovery to control levels was observed for any postinjury time point. Four measurement parameters reflecting pyramidal cell discharges (population spike) indicated that TBI significantly increased cellular excitability at postinjury day 2: (1) pretetanus baseline recording showed that TBI reduced population spike threshold and latency; (2) tetanic stimulation (400 Hz) increased population spike amplitudes to a greater degree in injured animals than in control animals; (3) tetanus-induced population spike latency shifts were greater in injured cases; and (4) tetanic stimulation elevated EPSP to spike ratios (E-S potentiation) to a greater degree in injured animals. These parameters returned to control levels, as measured on postinjury days 7 and 15. These results suggest that TBI-induced excitability changes persist at least through 2 days postinjury and involve a differential impairment of mechanisms subserving LTP of synaptic efficacy and mechanisms related to action potential generation     

Release from central auditory competition in the split-brain patient

We used dichotic digits (DD), staggered spondaic words (SSW), and frequency patterns (PATT) to study central auditory function before and after two-stage callosotomy. Preoperatively, the patient demonstrated reduced scores bilaterally on all these tests, consistent with documented bilateral hemisphere lesions. After the first operation (sectioning the posterior half of the corpus callosum), the dichotic tests (DD and SSW) revealed the expected decrease in left-ear scores, but there was improvement on the right, perhaps because there was release from central auditory competition. Our findings also suggest that the "auditory" portion of the corpus callosum may be in the posterior half of this structure.