Background
The neural projections from the infralimbic region of the prefrontal cortex
(IL) to the amygdala are important for the maintenance of conditioned fear extinction.
Neurons in this pathway exhibit a unique pattern of structural plasticity that is
sex-dependent, but the relationship between the morphological characteristics of these
neurons and successful extinction in males and females is unknown.
Methods
Using classic cued fear conditioning and extinction paradigm in large cohorts
of male and female rats, we identified subpopulations of both sexes that exhibited high
(HF) or low (LF) levels of freezing on an extinction retrieval test, representing failed
or successful extinction maintenance, respectively. We then combined retrograde tracing
with fluorescent intracellular microinjections to perform 3D reconstructions of IL
neurons that project to the basolateral amygdala (BLA) in these groups.
Results
HF/LF males exhibited neuroanatomical distinctions that were not observed in HF
vs. LF females. A retrospective analysis of behavior during fear conditioning and
extinction revealed that despite no overall sex differences in freezing behavior, HF/LF
phenotypes emerged in males during extinction, but in females during fear conditioning,
which does not involve IL-BLA neurons.
Conclusion
Our results suggest that the neural processes underlying successful or failed
extinction maintenance may be sex-specific. These findings are not only relevant to
future basic research on sex differences in fear conditioning and extinction, but also
to exposure-based clinical therapies, which are similar in premise to fear extinction,
and which are primarily used to treat disorders that are more common in women than in
men.
The purpose of this investigation was to study potential virulence factors associated with Escherichia coli urinary pathogens isolated from patients with urinary tract infection. These factors were compared with characteristics of normal-flora E. coli isolated from stool specimens of healthy individuals without a history of urinary tract infection. The potential virulence factor focused on in this study was hemagglutination (HA) of human type 0 erythrocytes by E. coli urinary pathogens. A total of 265 strains of E. coli isolated from patients with urinary tract infections were tested for their ability to hemagglutinate human type 0 erythrocytes; of these, 148 (56%) were HA positive. Only 6 of 36 fecal E. coli strains (17%) isolated from healthy controls were HA positive. This significant association of the presence of hemagglutinin on E. coli that causes urinary tract infections indicates the likelihood that HA is a marker of virulence. Only 12% (5 of 43) of Proteus mirabilis and 3% (3 of 104) of Klebsiella pneumoniae urinary isolates were HA positive. There was a trend for HA-positive E. coli to be isolated from patients with kidney infections and positive tests for antibody-coated bacteria rather than bladder infections and negative tests for antibody-coated bacteria, although the difference was not statistically significant. There was a significant correlation (P < 0.025) between hemolysin production and HA; 67% (69 of 103) of the isolates that produced hemolysin also hemagglutinated human type 0 erythrocytes. There was no significant correlation between HA and motility, although there was a trend for flagellated organisms to be non-hemagglutinators. There was a marked correlation between the presence of hemagglutinin and the serogroup of the E. coli isolate; serogroups 04, 07, and 050 were almost always HA positive (57 of 63; 90%). In contrast, serogroups 08 and 025 were rarely HA positive (2 of 30; 7%).
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