Lack of developmental neurotoxicity of MN rgp 120/HIV-1 administered subcutaneously to neonatal rats.

The potential for neurotoxic effects was evaluated in rat off-spring after exposure in utero and/or during the neonatal period to a recombinant subunit vaccine of gp120 prepared from the MN strain of HIV-1 (MN rgp 120/HIV-1). Thirty pregnant female rats were given MN rgp120/HIV-1 with alum adjuvant, and 30 rats were given vehicle, once every 3 days from Day 1 of presumed gestation until parturition. One pup/sex/litter from treated and control group dams were given a daily subcutaneous injection, from Day 1 through Day 22 postpartum (PP) of vehicle, MN rgp120/HIV-1, MN rgp120/HIV-1 with alum, or MN rgp120/HIV-1 with QS-21 adjuvant. Neurobehavioral and physical development were evaluated (preweaning reflex and development, sexual maturation, motor activity, acoustic startle, passive avoidance, functional observational battery, and water M-maze testing), and tissues were processed for anatomical examination (whole and regional brain weights, and neuropathology). Administration of MN rgp120/HIV-1, with or without adjuvant, to pups did not cause any persistent effect on any parameter evaluated. Neurohistological examination did not reveal any pathological effects related to treatment. Thus, MN rgp120/HIV-1 alone or formulated as a vaccine does not cause neurotoxicity or developmental toxicity in neonatal rats after exposure in utero and/or during the neonatal period.

Use of a rodent neurotoxicity screening battery in the preclinical safety assessment of recombinant-methionyl human brain-derived neurotrophic factor.

Recent efforts to evaluate neurobehavioral function in adult rodents as part of preclinical safety studies have typically been directed at evaluating possible environmental neurotoxicants. With considerable basic and clinical research efforts focusing on neurotrophic factors in the treatment of various neurodegenerative diseases, the application of these neurobehavioral evaluations is expected to increase. This report describes a six-month safety study of recombinant-methionyl human brain-derived neurotrophic factor (r-metHuBDNF) in rodents that included a neurotoxicity screening battery and was undertaken to evaluate safety issues that might be anticipated in the clinical setting. R-metHuBDNF was well tolerated by rats over six months of daily subcutaneous administration at doses that exceeded the highest anticipated clinical dose by 100-fold. Although statistically significant behavioral changes were noted, they were isolated and not considered to be associated with r-metHuBDNF treatment. We conclude that the inclusion of a neurotoxicity screening battery was an important study parameter in the assessment of the preclinical safety of this neurotrophin.

Reproductive effects of chronic administration of murine interferon-gamma.

Daily subcutaneous doses of 0.02, 0.2, or 2 mg/kg/d of recombinant murine interferon-gamma (rmuIFN-gamma) were given to mice on postnatal days 8 through 60 to determine effects on maturation, behavioral/ functional development, and reproductive capacity. Male mice receiving 2 mg/kg/d rmuIFN-gamma had delayed sexual maturation, reduced epididymal and testes weights, reduced sperm count and concentration, and sperm abnormalities (crimped flagellum). Mating performance and fertility were also reduced in the absence of altered histopathology of the testes. Males given 0.2 and 2 mg/kg/d had swelling and ulcerative dermatitis around the urogenital area, which were observed after sexual contact and attributed to a bacterial infection. Motor activity (time spent in movement) was decreased in all mice receiving 2 mg/kg/d. No microscopic changes observed in any organs were attributed to rmuIFN-gamma administration.

The effect of prenatal cocaine exposure on umbilical cord length in fetal rats.

Umbilical cord length has been considered a reliable indicator of fetal movement. In this study, the effect of prenatal cocaine exposure on umbilical cord length was examined in rats. Pregnant rats were intubated with either 0 or 60 mg/kg cocaine hydrochloride daily from gestation day (GD) 14-21. Fetuses were removed via Caesarean section on GD 21 and umbilical cord length, placental weight and fetal body weight were measured. Fetuses exposed to cocaine in utero had significantly shorter umbilical cords than intubated controls, although there were no differences in placental or fetal body weights. These data suggest that prenatal cocaine exposure suppresses fetal movement, which could contribute to some of the long-term effects observed in cocaine-exposed offspring.

Elicitation and modification of the acoustic startle reflex in animals prenatally exposed to cocaine.

In separate experiments, pregnant Long-Evans rats were administered cocaine orally (60 mg/kg/day) on gestation days 14-21, or subcutaneously (40 mg/kg/day) on gestational days 8-21. For each route of administration, a vehicle control group was pair-fed to the group administered cocaine and another control group was left untreated. Throughout pregnancy, the dams that received cocaine gained approximately 15% less weight than the untreated controls, but none of the dosage procedures affected the size of the litters, or the weight and growth of the offspring. When the offspring reached adulthood, various assessments of reflex function were made using the acoustic startle reflex and prepulse inhibition of startle. There were no effects on startle habituation or reflex modification that could be attributed to the prenatal exposure to cocaine.

Failure of acute cocaine administration to differentially affect acoustic startle and activity in rats prenatally exposed to cocaine.

Pregnant rats were administered 40 mg/kg of cocaine hydrochloride subcutaneously on gestation days 14 through 21. Rats in one control group were pair-fed to the cocaine group and injected with the saline vehicle during the dosing period, while an untreated control group was simply weighed throughout pregnancy. Maternal weight gain was reduced 13% in the cocaine group and pair-fed controls, but the offspring did not differ in their numbers or growth compared to the untreated controls. The offspring were examined between postnatal days 80 and 96 in tests of the acoustic startle response and open field behavior immediately following acute administration of 0, 5, or 10 mg/kg of cocaine. The acute dosages of cocaine increased the startle response and increased behavior in the open field. There was no evidence that the prenatal treatment altered the baseline in either of these tests. Adult rats exposed prenatally to cocaine entered more quadrants in the open field and reared more frequently than the other groups following the 10 mg/kg dosage of cocaine. However, there was no evidence of an effect of prenatal treatment among the groups administered the 5 mg/kg dosage in the open field test, nor was there a systematic effect of prenatal treatment on the acute effects of cocaine in the acoustic startle test. These data do not provide evidence that prenatal exposure to cocaine can produce persistent changes in the neural systems with which it interacts in the adult.

Exploratory behavior and locomotor activity: a failure to find effects in animals prenatally exposed to cocaine.

Pregnant Long-Evans rats were administered cocaine orally (60 mg/kg) on gestational days 14-21, or subcutaneously (40 mg/kg) on gestational days 8-21. The oral dosage of cocaine produced some maternal lethality and reduced maternal weight gain throughout the pregnancy by approximately 12%. The subcutaneous dosage regimen reduced the lethality but still caused a decrease in maternal weight gain. Neither dosing regimen affected the number of pups in the litter, their weight, or growth. The offspring of dams that received the oral dosage were examined as adults in an automated holeboard apparatus and were also tested at postnatal day 21 and as adults in an open field. Adult animals exposed prenatally to cocaine did not differ from untreated controls in any of the automated measures of the holeboard apparatus or in the various behaviors, including nosepokes, recorded in the open field. Animals in the vehicle control group did make fewer nosepokes in the open field than the cocaine group, which did not differ from untreated animals. The offspring of dams given the subcutaneous dosage regimen were observed in the open field at day 21. In this case, the prenatal cocaine group had a tendency to make fewer crosses into adjacent quadrants, to rear less often, and to make fewer nosepokes than the control groups. Based on these and other data from our lab, it does not appear that in the rat, prenatal cocaine exposure has pronounced effects on subsequent exploratory behavior and activity in weanling or adult animals.

The acquisition of passive avoidance, active avoidance, and spatial navigation tasks by animals prenatally exposed to cocaine.

Pregnant Long-Evans rats were administered cocaine orally (60 mg/kg) on gestational days 14-21. One control group was administered the vehicle and another left untreated. Cocaine treatment produced some maternal lethality, and the weight gain of the surviving dams was reduced approximately 15%. Offspring of mothers treated with cocaine did not differ from those of untreated mothers in their numbers, birth weight, or growth. Weanling offspring were tested in a passive avoidance task, and adult offspring were tested for two-way active avoidance and in a spatial navigation task. Although a few animals in the cocaine group showed poor retention of passive avoidance, the group differences were not statistically significant. The adult animals showed normal performance in both the active avoidance and spatial navigation tasks.

Facilitation and inhibition of the human startle blink reflexes by stimulus anticipation.

The cutaneous eyeblink has 2 electromyographic components, 1 unilateral and early (R1) and 1 bilateral and late (R2), which are served by different neural pathways. These 2 reactions were measured when the eliciting stimulus was expected or relatively surprising. Forewarning was varied in 3 ways: Subjects received notice that the stimulus was about to occur on some trials (Experiment 1); delivered the stimulus to themselves on some trials (Experiments 2 & 3); or experienced a series of trials in which a tone was paired with the eliciting stimulus, followed by tone-alone trials interspersed with test trials (Experiment 4). In each case, forewarning enhanced R1 amplitudes while depressing R2 but reduced the latency of both components. This mixed pattern of effects reveals that the preparatory state provoked by forewarning focuses excitatory and inhibitory processes simultaneously on different reflex pathways: inhibition central and excitation peripheral.

The acoustic startle response and disruption of aiming: I. Effect of stimulus repetition, intensity, and intensity changes.

Three experiments examined the disruption of perceptual motor performance by intense noise bursts. Subjects aimed a rifle at a fixed target for 15-s periods separated by 15 s of rest. This cycle was repeated 30 times in each of two series separated by a 15-min rest, each series containing five noise bursts. The noise bursts disrupted aiming for 1-2 s, an effect that increased with sound pressure level for 110, 120, and 130 dB stimuli. There was no difference between stimuli with energy centered on 250 Hz as opposed to 800 Hz. The effect diminished over the five bursts within the first series (but not to zero) and did not recover in the 15-min rest period. Some subjects received three days of testing; in these cases the effect of the noise bursts partially recovered after rest intervals of 24 hrs and then seven days. Other subjects received 15 trials with 110-dB stimuli, then five more trials with 130-dB stimuli. The disruption of aiming by 130 dB stimuli was not reduced by prior exposure to 110-dB stimuli.

The acoustic startle response and disruption of aiming: II. Modulation by forewarning and preliminary stimuli.

Four experiments examined the disruption of rifle aim by intense noise bursts. In Experiment 1 a trigger pull was followed occasionally by a noise burst. Aiming was disrupted for 1-2 s, an effect that habituated within days and recovered between days. Expected stimuli were less disruptive than were unexpected stimuli. Experiment 2 demonstrated that weak auditory prestimuli 100 ms before unexpected intense sounds also reduced noise-produced errors. Experiment 3 showed that the intratympanic reflex had not played a protective role in this effect. Experiment 4 showed that a weak tactile prestimulus increased both a muscular measure of the acoustic startle reaction and the perturbing effect of the noise burst on motor performance. In general, conditions that affect the amplitude of the acoustic startle reflex similarly influence the disruptive effect of a noise burst on motor performance, but the two measures are not correlated in the detail necessary to suggest a causative relationship.

Reflex modification as a test for sensory function.

Reflex modification is a versatile procedure for the assessment of sensory function because it can provide information about the responses of several sensory systems to both weak and intense stimuli. The procedure has two elements: The elicitation of some reflex, such as the acoustic startle reflex, and the modification of that reflex by preliminary stimuli. In these experiments we used reflex modification and reflex elicitation procedures to examine the normal development of auditory function in rats and to evaluate alterations in auditory function produced by physical and toxic insult. Adult rats exposed to octave bands of noise demonstrated frequency-specific deficits on a test of reflex modification, but not reflex elicitation. In the studies of developing rats, reflex elicitation appeared by postnatal day 12 and modification around day 14. Frequency-specific increases in both measures suggested that the phenomena were sensitive to auditory development and, not simply, motor development. Exposure to kanamycin on postnatal days 8 to 16 produced dose-related deficits in the ability to detect stimuli at 32 and 16 kHz, but not 4 and 0.8 kHz. These effects were observed in the absence of changes in reflex elicitation. The results demonstrate that reflex modification procedures provide more sensitive and specific information than that provided by the use of reflex elicitation alone.

Impairment in auditory and visual function follows perinatal viral infection in the rat.

Acoustic startle reflexes are elicited by intense tone bursts but inhibited if weak bursts precede reflex elicitation. Rats were infected by intracerebral inoculation with lymphocytic choriomeningitis virus (LCMV) at birth. Compared to control animals, infected animals had higher elicitation and inhibition thresholds and showed recruitment at intense stimulus levels. Histopathology revealed both cochlear and retinal degeneration. Like some infectious agents in humans, perinatal exposure to LCMV in the rat yields a severe polysensory neuropathy.

Conditions that affect the thresholds of the components of the eyeblink reflex in humans.

The threshold stimulus intensities for elicitation of the two EMG components of the eyeblink reflex were determined in human subjects under different conditions. In the first experiment subjects sat with eyelids open and were not warned about reflex elicitation. The threshold of R1 was substantially greater than that of R2. In four additional experiments subjects (a) triggered the eliciting stimulus, (b) were warned about the arrival of each stimulus, (c) had a conditioning stimulus presented before reflex elicitation, and (d) had their eyelids closed at the time of stimulus delivery. The conditions of these subsequent experiments reduced the difference between the reflex thresholds largely by lowering the R1 threshold. These results indicate that variations in the testing environmental contribute to the discrepancy between our data showing unequal threshold for elicitation of the R1 and R2 components and other reports showing equal thresholds. The results are also another illustration of the ability of complex psychological events to selectively affect different reflex pathways.