Global cerebral blood flow and metabolism during acute hyperketonemia in the awake and anesthetized rat.

In the human setting, it has been shown that acute increase in the concentration of ketone bodies by infusion of beta-hydroxybutyrate increased the cerebral blood flow (CBF) without affecting the overall cerebral metabolic activity. The mechanism by which this effect of ketone bodies was mediated is not known. Alterations in several parameters may possibly explain the increase in CBF and the resetting of the relation between CBF and cerebral metabolism. To study this phenomenon further, we measured global CBF and global cerebral metabolism with the Kety-Schmidt technique in the wakeful rat before and during infusion of ketone bodies. During acute hyperketonemia (average concentration of beta-hydroxybutyrate: 6 mmol/L), global CBF increased 65% from 108 to 178 mL/100 g min and the cerebral metabolic rates for both oxygen and glucose remained constant. This resetting of the relation between CBF and cerebral metabolism could not be explained by alterations in blood pH or arterial CO2 tension. By measuring cerebral intracellular pH by 31P nuclear magnetic resonance spectroscopy, it could further be concluded that the brain pH was unchanged during acute hyperketonemia. These observations indicate that the mechanism responsible for the increase in CBF is rather a direct effect on the cerebral endothelium than via some metabolic interactions.

Sequence-specific interaction of nascent antiterminator RNA with the zinc-finger motif of Escherichia coli RNA polymerase.

The N-terminal Zn-finger motif of the beta' subunit of RNA polymerase contains two pairs of invariant cysteines flanking a moderately well-conserved segment of 13 amino acids that is rich in basic residues. Previous work showed that replacement of certain Zn-finger residues prevented transcription antitermination in response to phage HK022 put sites. Nascent put RNA binds to and modifies transcribing polymerase, so that it becomes resistant to termination. To characterize the Zn finger further, we replaced each of the basic residues with alanine and determined the effects of the substitutions on termination, antitermination and cell viability. All the mutants were defective in put-mediated antitermination. The severity of the defect depended on the mutant and on the sequence of the upstream stem-loop of put RNA. Some, but not all, mutants distinguished between put variants that differed in this region. This suggests that the Zn-finger motif interacts directly and specifically with put RNA. All the mutants in the basic residues complemented a temperature-sensitive beta' mutant for cell growth at a non-permissive temperature, and those mutant enzymes that were tested transcribed and terminated normally in vitro on a template that lacked a put site.

Regional cerebral blood flow during light sleep--a H(2)(15)O-PET study.

This is the first report on the distribution of regional cerebral blood flow (rCBF) changes during stage-1 sleep or somnolence. Two hypotheses were tested: (A) that rCBF differed between the awake relaxed state and stage-1 sleep, (B) that hypnagogic hallucinations frequently experienced at sleep onset would be accompanied by measurable changes in rCBF using positron emission tomography (PET). Eight subjects were PET-scanned with (15)O-labeled water injection in three conditions: awake, stage-1 sleep with reportable experiences and stage-1 sleep without reportable experiences. Electroencephalography (EEG) was performed continuously during the experiment. Sleep interviews were performed after each scan. The EEG was scored blindly to determine sleep stage. The sleep interviews revealed a substantial increase in how unrealistic and how leaping the thoughts were during stage-1 sleep. During sleep there was a relative flow increase in the occipital lobes and a relative flow decrease in the bilateral cerebellum, the bilateral posterior parietal cortex, the right premotor cortex and the left thalamus. Hypnagogic experiences seemed not to be associated with any relative flow changes. The topography of the occipital activation during stage-1 sleep supports a hypothesis of this state being a state of imagery. The rCBF decreases in premotor cortex, thalamus and cerebellum could be indicative of a general decline in preparedness for goal directed action during stage-1 sleep. Stage-1 sleep seems more similar to other forms of altered awareness, for example, relaxation meditation than to deeper sleep stages. We are of the opinion that stage-1 sleep represents the dreaming state of wakefulness, while rapid eye movement (REM) sleep reflects the dreaming state of the unaware, sleeping brain.

Activation-induced resetting of cerebral metabolism and flow is abolished by beta-adrenergic blockade with propranolol.

BACKGROUND AND PURPOSE: It has previously been shown that activation will increase cerebral blood flow (CBF) and cerebral glucose uptake (CMR(glc)) in excess of cerebral oxygen uptake (CMRO(2)). Our purpose was to investigate the influence of beta-adrenergic blockade with propranolol on the activation-induced uncoupling of cerebral glucose and oxygen metabolism. METHODS: Using awake rats, we determined the cerebral arteriovenous differences of oxygen [(a-v)(O2)], glucose [(a-v)(glc)], and lactate [(a-v)(lac)] both under baseline conditions and during activation. The molar ratio between CMRO(2) and CMR(glc), the oxygen-glucose index (OGI), was calculated. RESULTS: Without beta-adrenergic blockade, activation decreased the (a-v)(O2) but not the (a-v)(glc), reducing the OGI from 6.1 during baseline conditions to 4.0 under activation (P<0.01). The (a-v)(O2) decreased, indicating that the ratio CBF/CMRO(2) had increased. Under baseline conditions, a slight flux of lactate from the brain was observed. Activation increased the arterial lactate concentration, and during this condition, the lactate flux from the brain was reversed into a slight lactate uptake. Propranolol administration did not change the behavior of the animals during activation. After administration of propranolol, baseline values were unaffected, but beta-adrenergic blockade totally abolished the activation-induced uncoupling of (a-v)(O2) from (a-v)(glc), because both remained constant with an unchanged OGI. The unchanged (a-v)(O2) indicates that CBF remained unchanged compared with CMRO(2). CONCLUSIONS: beta-Adrenergic blockade by propranolol abolishes the activation-induced uncoupling of cerebral oxygen to glucose metabolism and the changes in (a-v)(O2). This may be of most significance to studies of cerebral activation by the blood oxygen level-dependent fMRI method.

Temporal transcription of the lactococcal temperate phage TP901-1 and DNA sequence of the early promoter region.

Transcriptional analysis by Northern blotting identified clusters of early, middle and late transcribed regions of the temperate lactococcal bacteriophage TP901-1 during one-step growth experiments. The latent period was found to be 65 min and the burst size 40 +/- 10. The eight early transcripts, all mapping in a 13 kb region adjacent to the attachment site of TP901-1, were present at maximal levels 10 min after infection. The four middle transcripts, observed at maximal levels 30 min after infection, are all located within a 2 kb region at the distal end of the early transcripts. The late class of transcripts were detected 40 min after infection and the amounts of these transcripts increased with time. The late transcripts were localized to the 13 kb region adjacent to the 2 kb middle transcribed region. The sequence of almost 4 kb of the early region was determined, allowing a detailed transcriptional map for the early region of which in total 6.4 kb was sequenced. Sequence analysis of the early region revealed two closely positioned but divergently orientated promoters, PL and PR, in accordance with the orientation of the ORFs and the transcriptional map. Nine ORFs were found, and similarities to a phage repressor, a single-stranded DNA-binding protein, a topoisomerase, a Cro-like protein and two other phage proteins of unknown function were detected. The gene arrangement in the early transcribed region of TP901-1 thus consists of two transcriptional units: one from PR containing four genes, of which at least two (the integrase gene and putative repressor) are needed for lysogeny, and the divergent and longer transcriptional unit from PL, presumably encoding functions required for the lytic life cycle. ORFs with homology to proteins involved in DNA replication were identified on the latter transcriptional unit.