Population density-dependent regulation of the Bradyrhizobium japonicum nodulation genes

The nodulation genes of Bradyrhizobium japonicum are essential for infection and establishment of a nitrogen-fixing symbiosis. Here, we demonstrate that plant-produced isoflavones induce nodulation gene expression in a population density-dependent fashion. Nodulation gene induction is highest at a low population density and significantly reduced in more dense cultures. A quorum signal molecule in the conditioned medium of B. japonicum cultures mediates this repression. Repression in response to the quorum signal results from the induction of NolA which, in turn, induces NodD2 leading to inhibition of nod gene expression. Consistent with this, nolA-lacZ and nodD2-lacZ expression increased with increasing population density. Unlike the wild type, the ability to induce nodY-lacZ expression did not decline with population density in a NolA mutant. Normally, nod gene expression is repressed in planta (i.e. within nodules). However, expression of a nodY-GUS fusion was not repressed in a NolA mutant, suggesting that quorum-sensing control may mediate in planta repression of the nod genes. Addition of conditioned medium to cultures significantly reduced nod gene expression. Treatment of inoculant cultures with conditioned medium also reduced the ability of B. japonicum to nodulate soybean plants.

Child and adolescent traumatic brain injury: correlates of disruptive behaviour disorders

A record review focused on children and adolescents, with a history of traumatic brain injury (TBI), who were consecutively admitted to a brain injury clinic in which all new patients are psychiatrically evaluated. Correlates of post-injury oppositional defiant disorder/conduct disorder (ODD/CD) and post-injury attention deficit hyperactivity disorder (AHD) were investigated. Subjects who developed ODD/CD following TBI, when compared to subjects without a lifetime history of the disorder, had significantly more impaired family functioning, showed a trend toward a greater family history of alcohol dependence/abuse and suffered a milder TBI. In contrast, there were no variables which discriminated between subjects who developed ADHD following injury and those with no lifetime history of ADHD. It is difficult to determine whether ODD, CD and ADHD occurring after TBI in the patient is related to the TBI, directly or indirectly. Appropriate clinical assessment requires consideration of the important mediating role of family functioning, severity of injury and family psychiatric history.

Child and adolescent traumatic brain injury: correlates of injury severity

A record review focused on children and adolescents, with a history of traumatic brain injury, who were consecutively admitted to a brain injury clinic in which all new patients are psychiatrically evaluated. Significant correlates of severity of injury in the cognitive, education and communication domains of functioning included Performance IQ but not Verbal IQ nor standardized ratings of language or learning disability. Current organic personality syndrome (OPS) but not attention deficit hyperactivity disorder or oppositional defiant disorder/conduct disorder diagnostic status was significantly related to severity. In conclusion, the findings in this referred sample are similar to prospective studies indicating that Performance IQ appears sensitive in reflecting brain damage. The finding linking OPS to severity of injury is not surprising. This is because OPS is a diagnosis which is dependent on the clinician's judgment of the likelihood that the organic factor is etiologically related to a defined behavioural syndrome. The diagnosis therefore requires a clinical judgment that the threshold of severity of a presumed organic etiological factor has been reached.

Child and adolescent traumatic brain injury: psychiatric findings from a paediatric outpatient specialty clinic

A record review focused on children and adolescents, with a history of traumatic brain injury, who were consecutively admitted to a brain injury clinic in which all new patients are psychiatrically evaluated. The development of a 'novel' psychiatric disorder (not present before injury) occurred in 76% (38/50) of the cohort and was correlated significantly with family psychiatric history and family function, but not with severity of injury, preinjury psychiatric status, intellectual/educational functioning, or socioeconomic status. Psychiatric consultation is often necessary in this paediatric population even though much of the psychopathology, particularly following mild injury, may not be directly related to brain trauma.