Is benzodiazepine-induced amnesia due to deactivation of the left prefrontal cortex?

The amnesic properties of benzodiazepines result from an impairment in explicit (conscious) acquisition of new material.

RATIONALE

Explicit encoding of new material has consistently resulted in an increase in regional cerebral blood flow (rCBF) in the left prefrontal cortex, as measured by positron emission tomography (PET).

OBJECTIVE

PET was used to determine whether an amnesic dose of midazolam (0.075 mg/kg) attenuated activation in this area during explicit memory encoding.

METHODS

A second condition (condition A) used a task to control for the automatic processing that occurs during explicit learning (condition E).

RESULTS

The subjects who received midazolam (n=7) recognised significantly fewer words than those who received placebo (n=8), but were not impaired with regard to automatic processing. rCBF was significantly increased in the left prefrontal cortex during explicit encoding of word lists in all subjects and in the temporal lobe and parieto-occipital regions during automatic processing. rCBF was significantly decreased in the prefrontal, superior temporal and parieto-occipital regions following midazolam. The midazolam-induced deactivation in the prefrontal cortex did not affect rCBF activations induced by the explicit memory condition (E-A).

CONCLUSIONS

These results suggest that a specific interaction with prefrontal cortex activation does not underlie the amnesic effect of midazolam. However, it remains possible that a threshold level of prefrontal rCBF is necessary for encoding and that, after midazolam, this was not reached.

Memory, attention, and executive function in chronic fatigue syndrome

OBJECTIVES

To examine cognitive function in chronic fatigue syndrome.

METHODS

Twenty patients with chronic fatigue syndrome recruited from primary care and 20 matched normal controls were given CANTAB computerised tests of visuospatial memory, attention, and executive function, and verbal tests of letter and category fluency and word association learning.

RESULTS

Patients with chronic fatigue syndrome were impaired, predominantly in the domain of memory but their pattern of performance was unlike that of patients with amnesic syndrome or dementia. They were normal on tests of spatial pattern recognition memory, simultaneous and delayed matching to sample, and pattern-location association learning. They were impaired on tests of spatial span, spatial working memory, and a selective reminding condition of the pattern-location association learning test. An executive test of planning was normal. In an attentional test, eight subjects with chronic fatigue syndrome were unable to learn a response set; the remainder exhibited no impairment in the executive set shifting phase of the test. Patients with chronic fatigue syndrome were also impaired on verbal tests of unrelated word association learning and letter fluency.

CONCLUSION

Patients with chronic fatigue syndrome have reduced attentional capacity resulting in impaired performance on effortful tasks requiring planned or self ordered generation of responses from memory.

Dissociations in the expression of the sedative effects of triazolam

Fifteen normal volunteers were administered 0.250, 0.375, and 0.500 mg of triazolam and placebo in a double-blind repeated measures cross-over design. Subjects demonstrated dose-dependent impairments in free recall, a test of explicit memory requiring awareness and reflection, and sedation as assessed by objective behavioral measures (the digit symbol substitution task) and subjective visual analogue scales. The sedative drug response did not account for the impairment in free recall. Differences in performance of the two tests of sedation indicated that the effect of this drug on reflective processes accounts for impairment in episodic memory and the inability to track the sedative effects of this drug at the higher doses tested in this study.

A gene required for nutritional repression of the Bacillus subtilis dipeptide permease operon

An insertion mutation was isolated that resulted in derepressed expression of the Bacillus subtillis dipeptide transport operon (dpp) during the exponential growth phase in rich medium. DNA flanking the site of insertion was found to encode an operon (codVWXY) of four potential open reading frames (ORFs). The deduced product of the codV ORF is similar to members of the lambda Int family; CodW and CodX are homologous to HsIV and HsIU, two putative heat-shock proteins from Escherichia coli, and to LapC and LapA, two gene products of unknown function from Pasteurella haemolytica. CodX also shares homology with a family of ATPases, including ClpX, a regulatory subunit of the E. coli ClpP protease. CodY does not have any homologues in the data-bases. The insertion mutation and all previously isolated spontaneous cod mutations were found to map in codY. In-frame deletion mutations in each of the other cod genes revealed that only codY is required for repression of dpp in nutrient-rich medium. The codY mutations partially relieved amino acid repression of the histidine utilization (hut) operon but had no effect on regulation of certain other early stationary phase-induced genes, such as spoVG and gsiA.

Sympathetic denervation of resistance arteries increases contraction and decreases relaxation to flow

The effect of chronic sympathetic and possibly sensory denervation on flow-induced changes in smooth muscle tone was examined in a branch of the rabbit ear artery (200-400 microns ID). The superior cervical ganglion and 1-cm portions of the greater and anterior auricular nerves were removed from 4-wk-old rabbits while under general anesthesia, and arterial segments were studied 21 days later. Efficacy of denervation was assessed by catecholamine histochemistry and by absence of a constrictor response to transmural electrical field stimulation. Intraluminal flow of physiological saline solution was made through a pipette into matched-innervated and -denervated segments. Flow-induced contraction was increased in the denervated compared with the contralateral innervated segments. At the lowest flow rate studied (1 microliters/min), the contraction increased more than six times. This is consistent with the previously described nonspecific, nondeviational hypersensitivity of denervated vascular smooth muscle to constrictor influences. By contrast flow-related dilation at 10 and 20 microliters/min was significantly diminished. An intraluminal flow rate could be found that resulted in dilation in innervated but not the matched-denervated segments. Endothelial-mediated dilation to acetylcholine was also impaired. Chronic sympathetic denervation increased the magnitude of flow contraction and decreased that of flow relaxation.

Visual impairment in a rural Appalachian community. Prevalence and causes

A population-based survey of 1136 subjects aged 40 years and older was conducted in a rural valley of Kentucky to determine the nature and extent of visual disability in an underserved area of rural America. Data on corrected visual acuity and ocular history, along with demographic, socioeconomic, and health care utilization parameters, were gathered. Those subjects with an acuity below 20/60 in either eye underwent a comprehensive ophthalmologic examination. The prevalence of binocular blindness (acuity worse than 20/400 in the better eye) was 0.44% and of monocular blindness (acuity worse than 20/400 in one eye) was 3.3%, approximately twice the national rates. The chief cause of bilateral visual impairment was macular degeneration among men and cataract among women. Cataract, trauma, and amblyopia were the major causes of monocular visual impairment in both sexes. Risk factor analysis revealed younger age, higher education, active employment, access to a health care facility, and comprehensive health insurance coverage to be inversely associated with visual impairment.

Delusional depression following benzodiazepine withdrawal

Withdrawal from long-term treatment with benzodiazepines was followed in three patients by a severe delusional depression. The delusional depression may be related to the neurotransmitter changes accompanying benzodiazepine withdrawal. Caution should be exercised in long-term use of benzodiazepines in susceptible individuals.

Cholinergic effects on constructional abilities and on mnemonic processes: a case report

The effects of physostigmine on test performance of a patient with multiple cognitive deficits were observed in a double-blind, placebo-controlled study. Scores on tests of learning and memory and tests of visuo-spatial and constructional ability were both improved by physostigmine, while lecithin improved scores only on the former tests.

The constitutive heterochromatin of porcine chromosomes

The constitutive heterochromatin of porcine chromosomes was cytologically resolved into four types by using a combination of both C-banding techniques and base specific DNA binding fluorochromes. The four types of constitutive heterochromatin are: 1) C-band positive, A-T rich heterochromatin located in the centromeric region of acrocentric chromosomes; 2) faint C-band positive, G-C rich heterochromatin located in the centromeric region of biarm chromosomes; 3) C-band positive heterochromatin located in the long arm of the Y chromosome lacking available binding sites for either A-T or G-C specific fluorochromes; and 4) C-banding negative centromeric heterochromatin of the Y chromosome lacking available binding sites for either A-T or G-C specific fluorochromes.

Dissociation between the presynaptic dopamine-sensitive adenylate cyclase and [3H]spiperone binding sites in rat substantia nigra

[3H]Spiperone binding sites and the dopamine-sensitive adenylate cyclase were measured in rat substantia nigra (s. nigra) 7 or 14 days after various lesions. Hemisections, which resulted in a 66% decline in tyrosine hydroxylase and cyclic nucleotide phosphodiesterase and a 73% decrease in glutamate decarboxylase, led to a 50% decrease in [3H]spiperone binding and to the almost complete disappearance of the dopamine-sensitive adenylate cyclase from the s. nigra on the lesioned side. 6-Hydroxydopamine injection into the s. nigra, which depleted tyrosine hydroxylase activity within the s. nigra by 85%, while leaving phosphodiesterase unaffected, resulted in a 40% decrease in [3H]spiperone binding but no change in the dopamine-sensitive adenylate cyclase. Intrastriatal injections of kainic acid did not alter tyrosine hydroxylase activity in the s. nigra, but decreased both glutamate decarboxylase (54%) and phosphodiesterase (68%); [3H]spiperone binding was unaffected by this lesion while the dopamine-sensitive adenylate cyclase was greatly reduced (50-75%). These results suggest that within the s. nigra the dopamine receptor binding sites as defined using [3H]spiperone are located on dopamine neurones while the dopamine-sensitive adenylate cyclase is located presynaptically on striatonigral nerve terminals.