Klaus-Peter Ossenkopp

Intracerebroventricular injection of propionic acid, an enteric bacterial metabolic end-product, impairs social behavior in the rat: Implications for an animal model of autism

Environmental, dietary, and gastrointestinal factors may contribute to autism spectrum disorders (ASD). Propionic acid (PPA) is a short chain fatty acid, a metabolic end-product of enteric bacteria in the gut, and a common food preservative. Recent evidence indicates that PPA can cause behavioral abnormalities and a neuroinflammatory response in rats. Social behavior was examined in similarly-treated pairs of adult male Long-Evans rats placed in an open field following intracerebroventricular (ICV) injection of PPA (4 microl of 0.26 M solution) or control compounds. Behavior was analyzed using both the EthoVision behavior tracking system and by blind scoring of videotapes of social behaviors. Compared to controls, rats treated with PPA displayed social behavior impairments as indicated by significantly greater mean distance apart, reduced time spent in close proximity, reduced playful interaction, and altered responses to playful initiations. Treatment with another short chain fatty acid, sodium acetate, produced similar impairments, but treatment with the alcohol analog of PPA, 1-propanol, did not produce impairments. Immunohistochemical analysis of brain tissue taken from rats treated with PPA revealed reactive astrogliosis, indicating a neuroinflammatory response. These findings suggest that PPA can change both brain and behavior in the laboratory rat in a manner that is consistent with symptoms of human ASD.

Conditioned taste aversions and changes in motor activity in lithium-treated rats: Mediating role of the area postrema

The role of the area postrema in mediating taste aversions conditioned with the administration of lithium was examined in experiment 1. Rats with lesions of the area postrema or with sham lesions were given pairings of a novel taste with either intraperitoneally or intragastrically administered lithium chloride (LiCl; 10 mg/kg of a 0.15 M solution of lithium chloride) or a similar concentration of NaCl (control groups). Sham-lesioned rats exhibited strong taste aversions when lithium was used for the conditioning procedure and given intraperitoneally or intragastrically (P less than 0.01). Rats with lesions of the area postrema failed to develop taste aversions after the administration of lithium by either route. In experiment 2, rats with lesions of the area postrema and rats with sham lesions were given 30 min access to a 0.12 M solution of NaCl and 2 days later to a 0.12 M solution of lithium. The sham-lesioned animals drank less lithium than NaCl (P less than 0.02) and exhibited depressions in levels of activity following the ingestion of lithium. Rats with lesions of the area postrema drank more lithium than the sham-lesioned rats (P less than 0.01) and did not show behavioral depression after the ingestion of lithium. These data suggest that in the absence of the chemically-sensitive area postrema intragastrically administered lithium does not produce conditioned taste aversions or depression of activity in rats.

Exposure to rotating magnetic fields alters morphine-induced behavioral responses in two strains of mice.

An exposure for 60 min to a 0.5 Hz rotating magnetic field (1.5-90 G) significantly reduced the day-time analgesic and locomotory effects of morphine (10 mg/kg) in CF-1 and C-57BL strains of mice, respectively. Exposure to lower intensity 60 Hz magnetic fields (0.-1.0 G) had no effect on analgesia induced by morphine. The reduction in responsiveness to morphine after exposure to the greater intensity rotating field was not evident 24 hr later. No changes were seen in the latencies of basal thermal responses or levels of activity of saline-treated mice exposed to the magnetic stimuli.

Sexually dimorphic effects of neonatal immune system activation with lipopolysaccharide on the behavioural response to a homotypic adult immune challenge.

Research has shown that acute immune activation during the early postnatal period with the Gram‐negative endotoxin, lipopolysaccharide (LPS), alters a variety of physiological and behavioural processes in the adult animal. For example, neonatal LPS exposure affects disease susceptibility later in life, though these effects appear to be modulated by time of exposure, sex, and immune stimulus. The current study examined sex differences in the effect of neonatal LPS treatment on the locomotor activity response to adult LPS administration. Male and female Long‐Evans rats were treated systemically with either LPS (50 μg/kg) or saline (0.9%) on postnatal days 3 and 5. Later in adulthood (postnatal day 92), all animals were subjected to an adult LPS challenge and were injected (i.p.) with 200 μg/kg LPS. Two hours after injection, animals were placed in a non‐novel open‐field and locomotor activity was assessed for 30 min. Body weights were determined both at the time of injection and 24 h later to examine LPS‐induced weight loss. Adult males treated neonatally with LPS exhibited significantly less horizontal and vertical activity in response to the LPS challenge relative to males treated neonatally with saline. This effect was not observed in females. Thus, the current study provides important evidence of sexual dimorphism in the long‐term effects of neonatal LPS exposure on the responses to an adult homotypic immune challenge in rats. These findings have potential clinical significance given that neonatal exposure to pathogens is a fairly common occurrence and Gram‐negative bacteria are a common cause of neonatal bacterial infections.

Systemic treatment with the enteric bacterial fermentation product, propionic acid, produces both conditioned taste avoidance and conditioned place avoidance in rats.

Propionic acid, an enteric bacterial fermentation product, has received recent attention in regards to satiety and obesity in humans. The possibility that propionic acid might produce internal aversive cues was investigated in two experiments using conditioned taste avoidance and place avoidance procedures to index the potential aversive nature of systemic treatment with propionic acid in male rats. Experiment 1 examined the effect of systemic treatment with propionic acid (500 mg/kg), LiCl (95 mg/kg) or vehicle (all corrected to pH 7.5) on the formation of conditioned taste avoidance using a lickometer procedure. On 3 acquisition days three groups of rats were injected with propionic acid, LiCl or vehicle, following 30 min access to 0.3M sucrose solution. Both the Propionic acid group and the LiCl group evidenced a conditioned taste avoidance by the end of the acquisition period. During a drug free extinction phase the Propionic acid group showed extinction of the taste avoidance whereas the LiCl group did not. Experiment 2 involved place preference conditioning with propionic acid treatment associated with one novel context and vehicle with a different novel context on 6 conditioning trials for each type of injection. Place avoidance was assessed on two drug free extinction trials. Multi-variable assessment of the unconditioned (Acquisition Trials) and conditioned effects (Extinction Trials) of propionic acid on locomotor activity was quantified as was chamber choice time on the extinction trials. Propionic acid induced a significant place avoidance and significantly reduced locomotor activity on some acquisition trials. During the extinction trials rats exhibited enhanced locomotor activity levels in the propionic acid associated chamber, likely due to the conditioned aversive nature of this chamber.

Lipopolysaccharide (LPS) blocks the acquisition of LiCl-induced gaping in a rodent model of anticipatory nausea

The effects of systemic treatment with lipopolysaccharide (LPS) on conditioned gaping in a rodent model of anticipatory nausea were examined. Stimulation of the immune system has been found to enhance, impair, or have no effect on various learning and memory tasks. The development of anticipatory nausea is formed through a classically conditioned response to a context that has been paired previously with toxin-induced nausea and/or vomiting. Rats display a distinctive conditioned gaping response when injected with a nausea-inducing drug such as LiCl. In the present study, male Long-Evans rats were injected intraperitoneally with LPS (200microg/kg) or saline (NaCl) followed 90min later by an injection of the toxin LiCl or saline before being placed in a distinctive context on four conditioning days (72h apart). On the condition test day, rats (n=6/group) were placed in the distinctive context in a drug-free state and behavioral responses were videotaped. Rats given LPS followed by LiCl were found to have significantly fewer gaping responses when compared to rats given NaCl followed by LiCl. All groups were also found to have similar levels of spontaneous ingestive behaviors suggesting that the decrease in gaping was not due to motor impairment. The present results suggest that activation of the immune system with LPS administration significantly impairs the acquisition of anticipatory nausea.

Lipopolysaccharide produces dose-dependent reductions of the acoustic startle response without impairing prepulse inhibition in male rats.

This study examined the dose-dependent effects of Lipopolysaccharide (LPS) on the acoustic startle response and prepulse inhibition (PPI) in male Long-Evans rats. LPS is known to stimulate the innate immune system and result in behavior modifications referred to as sickness behaviors. The purpose of this study was to assess the ability of LPS to modulate sensorimotor reflexes (Startle-Only trials) and/or sensory processing (PPI trials). Rats were injected intraperitoneally with LPS (50, 100 or 200 microg/kg LPS, n=9/group) or saline vehicle (n=14) on 2 test days 72 h apart. Subjects were placed in a familiar startle box apparatus where startle response magnitudes were recorded following 115 dB Startle-Only trials and PPI trials (with prepulses at +3, +6 and +12 dB above background noise). Analysis of Startle-Only trials indicated a significant dose-dependent effect of LPS on Test Day 1. The 200 microg/kg LPS group exhibited significantly reduced startle response magnitude relative to all other treatments. On the PPI trials no LPS groups displayed significantly different performance from vehicle controls. Also, DayxDrug interactions for both Startle-Only and PPI trial types indicated behavioral tolerance to LPS. LPS reduced the acoustic startle response in a dose-dependent manner on Test Day 1. From the PPI data, it is evident that all treatment groups elicited near-normal inhibition levels indicating adequate sensory function. In combination, the results suggest that the range of sickness behaviors following LPS-administration to adult rats includes decreased non-voluntary motor activity as reflected by reduced startle magnitude.

Tamoxifen and raloxifene produce conditioned taste avoidance in female rats: a microstructural analysis of licking patterns.

AIMSnEstrogen receptor activation has been shown to reduce body weight and produce conditioned taste avoidance (CTA) when estradiol administration is paired with a novel tastant. This study determined if the selective estrogen receptor modulators tamoxifen and raloxifene, which effectively prevent and treat breast cancer, can induce a CTA and alter body weight in ovariectomized (OVX)-female rats.nnnMAIN METHODSnDuring conditioning, OVX-female rats were injected with tamoxifen, raloxifene, 17beta-estradiol or vehicle, or were uninjected, prior to drinking 0.3 M sucrose in a lickometer. Immediately following sucrose access, alterations in locomotor activity and thigmotaxis (anxiety) were assessed in an open field apparatus. Conditioned drug effects on drinking, locomotor activity and anxiety were examined on a separate test day.nnnKEY FINDINGSnOur results suggest that both tamoxifen and raloxifene produce CTA that is similar to that produced by estradiol. Both the number and size of bursts of licking were significantly reduced, as well as body weight gain, in OVX-female rats treated with tamoxifen or raloxifene.nnnSIGNIFICANCEnThe results of the present study suggest that tamoxifen and raloxifene may have the potential to produce CTA in breast cancer patients receiving chemoprevention care.

Tamoxifen produces conditioned taste avoidance in male rats: an analysis of microstructural licking patterns and taste reactivity.

Estrogen receptor activation has been shown to reduce body weight and produce a conditioned reduction in food intake in male rats that is putatively mediated by estradiols suggested aversive effects. Evidence has shown that the selective estrogen receptor modulator tamoxifen used in the prevention and treatment of breast cancer may also produce changes in food intake and body weight, which are known to impact cancer development and survival. The purpose of the present study was to examine whether tamoxifen produces a conditioned reduction in intake similar to estradiol by producing a conditioned aversion. A one bottle lickometer test was used to examine conditioned changes in sucrose drinking, while the taste reactivity test was used to measure rejection reactions, which serve to index aversion in rats. A backward conditioning procedure that consisted of 3 conditioning days and one vehicle test day was used to examine conditioned changes in 0.3 M sucrose intake and taste reactivity. Our results show that tamoxifen produced a conditioned reduction in sucrose drinking in a one bottle fluid intake test that was similar to the effects produced by estradiol (positive control); however, no active rejection reactions were produced by either tamoxifen (1 and 10 mg/kg) or estradiol. The present results suggest that tamoxifen, at the doses used in the present study, acts as an estrogen receptor agonist to regulate food intake and that the conditioned reduction in intake produced by tamoxifen and estradiol reflects conditioned taste avoidance rather than conditioned taste aversion.

Inhibition of LiCl-induced conditioning of anticipatory nausea in rats following immune system stimulation: comparing the immunogens lipopolysaccharide, muramyl dipeptide, and polyinosinic: polycytidylic acid.

The effects of the bacterial endotoxins, lipopolysaccharide (LPS) and muramyl dipeptide (MDP; Experiment 1), and the viral mimetic, polyinosinic: polycytidylic acid (poly I:C; Experiment 2), on the acquisition of conditioned gaping behavior in the rodent model of LiCl-induced anticipatory nausea were examined. Experimentally naïve adult male Long-Evans rats were injected (intraperitoneal, i.p.) with either 200 μg/kg LPS, 1.6 mg/kg MDP, or 0.9% saline (Experiment 1), or 4.0 mg/kg poly I:C or 0.9% saline (Experiment 2), 90 min prior to treatment with 127 mg/kg LiCl or saline control and immediately placed into a distinctive context for 30 min (repeated over 4 conditioning days, spaced 72 h apart). On a drug-free test day (72 h following conditioning day 4), each animal was re-exposed to the context for 10 min, and orofacial and aversive behavioral responses were video recorded and analyzed. The results showed that pre-treatment with LPS, MDP (Experiment 1), or poly I:C (Experiment 2) prior to LiCl+context conditioning significantly impaired the establishment of conditioned gaping behavior, thus blocking the acquisition of anticipatory nausea. Results varied in regards to peripheral acute-phase response sickness behaviors, with significantly reduced weight loss in LPS-treated animals, less robust weight loss in poly I:C-treated animals, and no significant reductions in body weight in MDP-treated animals. The learning impairments observed in the current study suggest that endotoxin treatment with bacterial and viral endotoxin may have stronger central effects on learning and memory behavior, relative to peripheral effects on body weight and other sickness-related responses.