Encoding and retrieval are differentially processed by the anterior cingulate and prelimbic cortices: a study based on trace eyeblink conditioning in the rabbit.

A growing body of literature suggests that structures along the midline of the prefrontal cortex (mPFC), including Brodmann's area 32 (prelimbic cortex) and area 24 (anterior cingulate cortex) in the rabbit play a role in retrieval of learned information. The present studies compared the effects of post-training lesions produced either immediately or 1-week following learning, to either prelimbic (area 32) or anterior cingulate (area 24) cortex on trace eyeblink (EB) conditioning. Further, because recent evidence suggests that the mPFC may play an even greater role in learning and memory when emotional arousal is low, these studies compared the effects of lesions in groups conditioned with either a relatively low-arousal corneal airpuff, or a more aversive periorbital eyeshock unconditioned stimulus (US). A total of six groups were tested, which received selective ibotenic acid or "sham" control lesions to either area 32 or 24, immediately or 1-week following asymptotic learning, and conditioned with an eyeshock US or an airpuff US. Results showed that the greatest lesion deficits were found when conditioning with the less aversive airpuff US. Further, lesions produced to area 32 one-week, but not immediately following learning, caused significant deficits in performance, while lesions produced to area 24 immediately, but not 1-week following learning, caused significant deficits in performance. These findings add to the body of evidence which shows that area 32 of the mPFC regulates retrieval, but not acquisition or storage of information, while area 24 mediates a less specific reacquisition process, but not permanent storage or retrieval of information during relearning of memories abolished by mPFC damage. These findings were, however, specific to those experiments in which the relatively non-aversive airpuff was the US.

Where does foodborne illness happen-in the home, at foodservice, or elsewhere-and does it matter?

Foodservice professionals, politicians, and the media are often cited making claims as to which locations most often expose consumers to foodborne pathogens. Many times, it is implied that most foodborne illnesses originate from food consumed where dishes are prepared to order, such as restaurants or in private homes. The manner in which the question is posed and answered frequently reveals a speculative bias that either favors homemade or foodservice meals as the most common source of foodborne pathogens. Many answers have little or no scientific grounding, while others use data compiled by passive surveillance systems. Current surveillance systems focus on the place where food is consumed rather than the point where food is contaminated. Rather than focusing on the location of consumption-and blaming consumers and others-analysis of the steps leading to foodborne illness should center on the causes of contamination in a complex farm-to-fork food safety system.

Prefrontal control of trace eyeblink conditioning in rabbits: role in retrieval of the CR?

Rabbits (Oryctolagus cuniculus) were trained on a trace eyeblink (EB) conditioning task to a criterion of 10 consecutive EB conditioned responses (CRs). One week later, ibotenic acid or sham lesions were made in the mPFC centered on the prelimbic region (Brodmann's area 32) or the cingulate cortex (Brodmann's area 24). Following a 1-week postoperative recovery period, all animals were retrained for 4 consecutive days using the same parameters as during acquisition, given 1 week off, and retrained for another 4 days. Mean EB conditioning deficits in the group with area 32 lesions occurred on the first and second days of each retraining period. However, by the third and fourth days of retraining, these lesioned animals were performing at a level comparable to that of the sham group. Lesions of area 24 did not produce deficits at either retesting period. These findings were interpreted to indicate that area 32, but not area 24, is involved in retrieval processes, rather than consolidation or storage, in that the animals were impaired at both retesting times, but were able to relearn the task.

Discriminative delay Pavlovian eyeblink conditioning in veterans with and without posttraumatic stress disorder.

BACKGROUND: Impaired eyeblink (EB) classical conditioning using a delay paradigm has previously been shown in combat veterans, as well as in a group of depressed adults, compared to normal individuals. Significant deficits in immediate memory (IM) in combat PTSD+ veterans, compared to normal controls, have also been previously shown, but these differences became non-significant after controlling for level of self-reported depression. Furthermore, EB conditioning has been shown to be significantly correlated with heart rate variability (HRV) in normal adults. The present study examined how depression (self-reported), IM, and resting HRV are related to discriminative delay classical EB conditioning in veterans with and without PTSD. METHOD: Three groups of subjects (combat PTSD+, combat PTSD-, and non-combat PTSD-) were assessed for self-report of depression and anxiety, as well as IM and HRV. Subjects received a single session of discriminative EB classical conditioning in which the conditioned stimulus (CS) was a light signal (either red or green) compounded with a tone. On CS+ trials, the light-tone compound stimulus co-terminated with a corneal airpuff (unconditioned stimulus, US), thus producing a delay paradigm. On CS- trials the appropriate light-tone stimulus was presented but not followed by the airpuff US. EB amplitude and frequency were recorded. RESULTS: PTSD+ subjects had greater self-reported depression and anxiety scores than the two control groups, as well as lower scores on a measure of IM. However, the IM difference was not significant after the effects of self-reported depression and anxiety were controlled. EB CR amplitude was significantly greater to CS+ than CS- for all three groups. EB amplitude to both the US (airpuff) and the CS+ declined over trials, but was significantly lower in the combat PTSD+ group compared to the combined PTSD- groups. Subjects who reached an EB CR acquisition criterion had significantly greater scores on IM than those who did not reach criterion. Factor analysis of the entire data set revealed four factors corresponding to (1) self-reported depression and anxiety, (2) IM, (3) HRV, and (4) EB amplitude. EB frequency was significantly predicted by IM and HRV. CONCLUSIONS: These data extend our previous results by showing deficits in EB conditioning among combat PTSD+ veterans that were associated with lower IM and resting HRV, but were not associated with self-report of depression.

Combat veterans show normal discrimination during differential trace eyeblink conditioning, but increased responsivity to the conditioned and unconditioned stimulus.

The question addressed in the present study was whether post-traumatic stress disorder (PTSD) results in associative learning impairments. To answer this question, differential trace eyeblink (EB) conditioning was studied in combat veterans with PTSD, combat veterans without PTSD, and non-combat veterans without PTSD. Veterans with PTSD showed normal EB discrimination, suggesting that associative learning is not impaired by PTSD. Veterans with PTSD also showed normal extinction. However, subjects with PTSD showed more EB conditioned responses (CRs), as well as increased CR amplitude. Increased response amplitude to the airpuff unconditioned stimulus presented alone (viz. the unconditioned response), as well as to the airpuff on CS+ trials during conditioning also occurred in the subjects with PTSD. These findings suggest increased reactivity in combat veterans with PTSD, compared to those without PTSD, but such heightened reactivity does not affect somatomotor associative learning.

Ibotenic acid lesions to ventrolateral thalamic nuclei disrupts trace and delay eyeblink conditioning in rabbits.

Intact cerebellar structures (i.e., deep nuclei and perhaps cortex) are essential for acquisition of both simple delay and trace eyeblink (EB) conditioning. However, successful trace conditioning also requires intact cortico-limbic structures (i.e., hippocampus, medial thalamus, and medial prefrontal cortex, mPFC). A direct connection between the cerebellum and ventrolateral thalamic nuclei (VLTN) has been demonstrated in several species. Since VLTN projects to both premotor and prefrontal cortex, it may be an essential link in a cerebellar-thalamic-prefrontal circuit that provides the CNS substrate for acquisition of the trace EB CR. The current studies thus assessed the role of the VLTN on trace EB conditioning in New Zealand albino rabbits. We first verified afferent connections to the mPFC (Brodmann's area 32) from the VLTN, by injecting the retrograde tracer Flourogold(c) into area 32. Strong labeling in VLTN from terminal projections to mPFC were found. We next assessed the role of VLTN in trace eyeblink conditioning in animals that received either sham or ibotenic acid VLTN lesions. EB conditioning began with 10 consecutive daily sessions of trace conditioning, followed immediately by 4 days of extinction, and then 4 days of delay conditioning. VLTN lesions significantly impaired acquisition of both trace and delay conditioning, and impaired extinction. These findings, thus confirm the importance of the VLTN in a postulated cerebellar-thalamic-prefrontal circuit that underlies successful trace, as well as delay EB conditioning.

Prefrontal control of trace versus delay eyeblink conditioning: role of the unconditioned stimulus in rabbits (Oryctolagus cuniculus).

The conditioned eyeblink (EB) response was studied with trace conditioning procedures in rabbits (Oryctolagus cuniculus) with lesions to the medial prefrontal cortex (mPFC) or sham lesions. Three experiments were performed in which either periorbital shock or a corneal airpuff served as the unconditioned stimulus (US) in separate groups of sham or mPFC-lesioned rabbits. Acquisition of the EB conditioned response (CR) was faster and reached a higher asymptote with the eyeshock US than with the airpuff US. However, mPFC lesion-induced trace conditioning deficits were obtained only in the groups that received the airpuff US. All rabbits showed normal delay conditioning and extinction. These results suggest that mPFC mediates trace EB conditioning when emotional arousal is low. However, in circumstances when emotional arousal may be high (i.e., during exposure to aversive periorbital shock), other structures (such as amygdala) may be activated to permit learning even in the absence of input from mPFC.

Nicotine modulation of cytokine induction by LPS-stimulated human monocytes and coronary artery endothelial cells.

Nicotine, the major addictive component of tobacco, is an immunomodulator that impacts on many cells, including immune cells involved in inflammatory processes. Nicotine also induces oxidative damage to the vascular endothelium and accentuates lipid peroxidation, resulting in vascular cell dysfunction. Furthermore, vascular endothelial cells produce growth factors, such as cytokines and chemokines capable of stimulating and recruiting immune cells to atheromatous lesions. In addition, bacterial products including lipopolysaccharides (LPS), a major component of Gram negative bacterial cell walls, activate gene expression resulting in inflammatory cytokine production causing further damage to the vasculature. In the present study, the combined effects of nicotine and bacterial LPS on the expression of IL-6, IL-8, GRO-alpha and MCP-1 in cell lines of human coronary artery endothelial cells (HCAEC) and pulmonary monocytes (THP-1) were examined by quantitative real-time PCR and ELISA. Results showed that nicotine suppressed the LPS induced production of IL-6 and IL-8 in both cell lines. Since cytokines which alter homeostasis of both vascular endothelial and immune cells are critical for the atherogenic process, further studies are warranted to examine in detail the role of nicotine in terms of effects on inflammatory reactions, including those induced by bacterial infection.

Medial prefrontal lesions and Pavlovian eyeblink and heart rate conditioning: effects of partial reinforcement on delay and trace conditioning in rabbits (Oryctolagus cuniculus).

Effects of continuous (100%) versus partial (25%) reinforcement were studied on Pavlovian delay and trace eyeblink conditioning in rabbits (Oryctolagus cuniculus) with either lesions to the medial prefrontal cortex (mPFC) or sham lesions. Concomitant heart rate changes evoked by the conditioned stimulus were also assessed. Partial reinforcement retarded eyeblink conditioning in both the trace and delay paradigm, but this impairment was greater during trace conditioning and in rabbits with mPFC lesions. Accompanying conditioned stimulus-evoked heart rate slowing was attenuated under all conditions by the mPFC lesions, although this result was not always statistically significant.

A behavioral stages model of classical (Pavlovian) conditioning: application to cognitive aging.

In the present article, it is argued that a five-stage sequential model of the behavioral and neurophysiological events that occur when organisms are exposed to signals predicting significant events suggests that classical conditioning produces multiple memory traces involving both excitatory and inhibitory processes. Further, these multiple brain structures and associated neurophysiological mechanisms are beginning to be understood; thus, using Pavlovian conditioning techniques to study aging and cognitive functions may provide insights into which brain structures or mechanisms are responsible for more general age-related declines in associative learning and memory. The evidence for this model is briefly reviewed and studies suggesting age-related effects on classical conditioning of various response systems are described within the context of the brain structures implicated by the model.

Age-related changes in associative learning: studies in rabbits and rats.

Two experimental models for studying age-related changes in associative learning are described. One involves classical (Pavlovian) conditioning of eyeblink and heart rate in the rabbit. The second involves Pavlovian leg flexion and heart rate conditioning in the rat. Advantages and disadvantages of each model are discussed. Results with both models suggest differential effects of aging on acquisition of autonomic and somatomotor responses, thus underlining the utility of assessing multiple response systems to adequately characterize age-related changes in learning and memory.

Leg flexion conditioning in the rat: its advantages and disadvantages as a model system of age-related changes in associative learning.

Twelve- and 28-month-old Fischer 344 rats of both sexes received five 60-trial sessions of Pavlovian conditioning in which the CS was a 75 dB, 10,000 Hz tone, and the US was a 0.5-mA, 0.5-sec duration footshock. Right foreleg flexion was measured as the conditioned response (CR). Other animals received a random sequence of unpaired tones and footshock and served as pseudoconditioning control groups. Interstimulus intervals (ISIs) of 1.5 and 3.5 sec were studied. The longer ISI resulted in higher rates of responding in both the conditioning and pseudoconditioning groups. However, with the exception of the young males, all animals showed significantly higher levels of responding in the conditioning groups. Females also showed faster acquisition and higher levels of responding than males. A significant sex by age by sessions interaction occurred, suggesting that old males may be somewhat retarded in acquiring the leg flexion CR compared to the other groups of animals. Old males were also slower to reach a criterion of 5 successive CRs than either young males or young or old females.

Chloramphenicol serum concentration falls during chloramphenicol succinate dosing.

Chloramphenicol succinate and chloramphenicol kinetics were examined on two occasions at steady state, separated by 2 to 17 days, in 10 pediatric patients on the same intravenous dose of chloramphenicol succinate. The steady-state peak serum concentration of chloramphenicol succinate fell from an average of 77.1 micrograms/ml during the first study to 42.2 micrograms/ml during the second. The steady-state peak serum concentration of chloramphenicol also decreased from an average of 27.8 micrograms/ml to 24.9 micrograms/ml. There was a marked decrease in the steady-state trough serum concentration of chloramphenicol, which averaged 8.4 micrograms/ml during the first and 5.3 micrograms/ml at the time of the second study. Mean area under the serum concentration-time curve (AUC) of chloramphenicol succinate decreased from 59.7 micrograms . hr/ml to 24.0 micrograms . hr/ml. The AUC of chloramphenicol averaged 105.7 micrograms . hr/ml at the time of the first and decreased to 79.5 micrograms . hr/ml during the second study. Mean percent decrease in the AUC of chloramphenicol was about 28% and occurred most substantially in patients with high AUCs during the first study. Mean elimination chloramphenicol half-life was 3.0 hr during the first study and fell to 2.3 hr at the time of the second study. Our data indicate that chloramphenicol serum concentration should be monitored frequently, especially in patients not responsive to a set dose.

Bioavailability and clearance of chloramphenicol after intravenous chloramphenicol succinate.

Bioavailability of chloramphenicol and kinetics of chloramphenicol succinate and chloramphenicol were studied in 12 patients. Chloramphenicol succinate, 25 mg/kg, was injected intravenously every 6 hr over 0.5 to 1 hr. Both the drug and the prodrug were analyzed by high-pressure liquid chromatography. Bioabailability of chlorampenicol ranged from 0.55 to 0.92 and total, renal, and nonrenal clearance from 6.81 to 98.22, 2.54 to 26.90, and 3.73 to 87.38 ml/m2/min, while clearances of chloramphenicol succinate ranged from 84.75 to 916.00 28.40 to 312.00, and 26.06 to 760.93 ml/m2/min. Urinary recovery of chloramphenicol was 3% to 25% and that of chloramphenicol succinate was 7% to 45%. Mean apparent volumes of distribution were 0.71 l/kg for chloramphenicol and 2.10 l/kg for chloramphenicol succinate and elimination half-lifes were 4.03 and 2.65 hr, respecitively. There were relationships between patient age and clearance of both drugs. Incomplete bioavailability of chloramphenicol and the more than 10-fold variability in clearance of both chloramphenicol and chloramphenicol succinate explain the need for individualizing doses to achieve thrapeutic effect and minimize the risk to toxicity.

Expressions of hepatic genes, especially IGF-binding protein-1, correlating with serum corticosterone in microarray analysis.

Microarray technology was evaluated for usefulness in assessing relationships between serum corticosterone and hepatic gene expression. Nine pairs of female Swiss mice were chosen to provide a wide range of serum corticosterone ratios; cDNA microarray analysis (approximately 8000 genes) was performed on their livers. A statistical method based on calculation of 99% confidence intervals discovered 32 genes which varied significantly among the livers. Five of these ratios correlated significantly with serum corticosterone ratio, including tyrosine aminotransferase, stress-induced protein, pleiotropic regulator 1 and insulin-like growth factor-binding protein-1; the latter has a potential role in cancer development. Secondly, linear regression of gene expression vs corticosterone ratios was screened for those with r> or =0.8 (P<0.01), yielding 141 genes, including some known to be corticosterone regulated and others of interest as possible glucocorticoid targets. Half of these significant correlations involved data sets where no microarray ratio exceeded +/- 1.5. These results showed that microarray may be used to survey tissues for changes in gene expression related to serum hormones, and that even small changes in expression can be of statistical significance in a study with adequate numbers of replicate samples.

Acute pulmonary blastomycosis in children: clinical course and follow-up.

The clinical courses of 14 children with acute pulmonary blastomycosis were studied. All the patients had a remarkably similar illness limited to the lungs with fever, malaise, and respiratory symptoms (cough, sputum production, chest pain, and vomiting). Despite eventual recovery with treatment in all instances, 13 of the 14 children persisted in having abnormal roentgenograms. Three children have demonstrated persistent mild obstructive airway disease for two to 12 months after completion of therapy. These data suggest that the initial illness following childhood infections with Blastomyces dematitidis is usually an acute pulmonary disease without systemic dissemination. Evidence of residual lung abnormalities conflicts with the recent concept of this being a benign, self-limited illness. Our findings suggest the importance of long-term follow-up as well as a need for more complete understanding of the full clinical spectrum and prognosis of acute pulmonary blastomycosis.

Phagocytic dysfunction in monocytes of normal newborn infants.

The kinetics of phagocytosis by monocytes isolated from cord blood and from the blood of adult volunteers was studied. Monocytes attached to glass coverslips were incubated with polystyrene spheres (1.1 mu diameter) for up to 120 minutes. In this system, the rate of phagocytosis was considerably slower in newborn monocytes than in those from adults. By the time phagocytosis had occurred in virtually all of the adult cells, only 38% of the neonatal monocytes had engulfed particles. However, this defect was not absolute, since ultimately all of the newborn cells contained engulfed spheres. Levamisole had no effect on normal adult monocytes but accelerated phagocytosis of newborn cells to a rate identical with that of adult cells. These data demonstrate that newborn monocytes are less efficient in the early stages of phagocytosis than are comparable cells from adults, raising the question of the impact of phagocytic kinetics in the development of neonatal sepsis. The correction of this defect by levamisole suggests that the differences in neonatal and adult monocytes may be evaluated more thoroughly by similar pharmacologic probes.

Experimental infection of the respiratory tract with Mycoplasma pneumoniae.

M. pneumoniae, a common human respiratory pathogen, has been studied experimentally for years using intranasal inoculation of the golden Syrian hamster. Because of recent evidence outlining the role in pulmonary immune development of particle size and depth of mycoplasma deposition in the hamster lung, we developed an aerosol chamber for the reproducible aerosolization of radiolabeled M. pneumoniae. Organisms were labeled to high specific activity by the incorporation of 3H-oleic acid and aerosolized under airflow and humidity conditions creating a mean particle diameter of 2.0 micrometers. Under these conditions, viable mycoplasmas were reproducibly and evenly distributed to all major lobes of the lung. Examination of radioactive clearance and organism viability within the lung during the first 48 hr after aerosolization have suggested a minimal role for macrophage mycoplasmacidal activity and a more prominent role for ciliary clearance. Data from aerosol infections of hamsters with radio-labeled M. pneumoniae should provide a unique opportunity to examine in a highly controlled manner the effects of air pollutants on the initial stages of infection as well as effects on the development of pulmonary immunity and histologic alterations.

Scanning electron microscopy of Malassezia furfur attachment to Broviac catheters.

Malassezia furfur has been increasingly associated with Broviac-catheter-related sepsis in infants receiving fat emulsions for parenteral alimentation. We examined by scanning electron microscopy the appearance of M. furfur attached to Broviac catheter segments mock-infected in vitro and to Broviac catheters removed from two infants with catheter-related sepsis. In vitro attachment occurred equally on external and internal surfaces of the catheters. Although some organisms were attached next to surface defects in the catheters, we could not determine if such defects were preferential sites of attachment. In the patient catheters, a dense coating of yeast cells was found adhering to the luminal surface, most abundantly near the tip. No organisms were seen on the external surface of the catheters. These findings show the need to examine the mechanisms of intraluminal catheter colonization in order to understand better the pathogenesis of M. furfur infections.

Role of the prefrontal--thalamic axis in classical conditioning.

The major conclusion to be drawn from the above-described research on the role of the PFCag in classical conditioning is obviously that it plays a primary and perhaps necessary role in the establishment of visceral cues associated with exposure to classical conditioning contingencies. Specifically, these visceral changes appear to be of an inhibitory character. This is significant, since we have postulated that inhibitory cardiac changes invariably accompany initial processing of sensory stimuli for informational value. Such visceral changes are thus not epiphenomena associated with other simultaneously occurring physiological events. A variety of lesion experiments implicate the PFCm as a central structure in this process, since damage to this area greatly attenuates, and in the case of hypothalamic knife cuts, completely eliminates learned bradycardia. Neuroanatomical tract-tracing experiments revealed that the PFCm and lag have direct projections to the NTS and DVM in the dorsomedial medulla and the nucleus ambiguous in the ventral medulla, all of which provide medullary output control of visceral activities. The nucleus ambiguous and DVM have been specifically implicated in vagal control in the rabbit (Ellenberger et al., 1983). Electrical stimulation of the PFCm provides additional evidence that this area of the brain participates in parasympathetic activities, including cardiac inhibition, since stimulation of the entire MD projection cortex, including the PFCm, produces HR decelerations accompanied by depressor responses. However, since lesions of the Iag produced relatively little effect on conditioned bradycardia, this part of the PFCag does not appear to play a major role in the development of conditioned bradycardia. Electrophysiological recording studies, including both multiple unit as well as extracellular single unit studies reinforce these conclusions. A short latency (40-180 msec) CS-evoked increase in MUA was recorded from cells in both the dorsomedial as well as central PFCm. The magnitude of these CS-evoked neuronal changes (a) was correlated with the magnitude of concomitantly occurring conditioned bradycardia; (b) was trial-related; (c) was not obtained in a similar pseudoconditioning group; and (d) declined to pretraining levels during subsequent experimental extinction. Similar, but not identical, CS-evoked changes in neuronal activity were recorded from MD. Although tone-evoked increases in MUA were also obtained from the Iag, this activity did not show the characteristics of associative learning. Single unit analysis also suggests the importance of the PFCm in elicitation of conditioned bradycardia.(ABSTRACT TRUNCATED AT 400 WORDS)