G. Renna

Ultrasonic vocalization in response to unavoidable aversive stimuli in rats: Effects of benzodiazepines

The effects of two benzodiazepine derivatives (diazepam, 0.5-1 mg/kg; alprazolam, 1.25-2.5 mg/kg) on ultrasonic calling elicited in adult rats by unavoidable aversive stimuli (footshocks) were investigated. The results show that either diazepam or alprazolam affected the duration of ultrasonic calls. In particular, a significant decrease in the length of ultrasounds was found in the group of animals treated with these benzodiazepines. The effects of diazepam were counteracted by the benzodiazepine-antagonist Ro 15-1788. On the other hand, neither a neuroleptic agent, such as haloperidol (0.5-1 mg/kg), nor an antidepressant, such as desipramine (5-10 mg/kg) influenced the parameters of ultrasonic emission in this experimental situation. The present results suggest that ultrasonic vocalization in response to unavoidable aversive stimuli could be considered as a potential new tool for studying drugs with antianxiety properties.

Evidence that exposure to methyl mercury during gestation induces behavioral and neurochemical changes in offspring of rats

On day 15 of gestation, pregnant Sprague-Dawley rats were orally treated by gavage with 8 mg/kg of methyl mercury (MMC). At day 1 of postnatal life the levels of MMC in whole brain of exposed pups were found to be about 100 times higher than those of saline-exposed rats, while they were near to the control values at 21 days and practically normal at 60 days of age. Behavioral experiments showed that exposure to MMC in late gestation did not affect at any tested time (14, 21 and 60 days) locomotor activity or development of ultrasonic vocalization. An increased response to a challenge dose of amphetamine was, however, detected in MMC-exposed pups at day 14. This phenomenon was no longer evident at day 21 and 60 of age. In parallel, an increased density of dopamine receptors was found in the striatum at 14, but not at 21 and 60, days of age. From these data, we tentatively suggest that a high level of MMC induces a transient phenomenon of disuse-supersensitivity of the dopaminergic system. Moreover, further evidence that acute MMC exposure during prenatal life might induce permanent disturbances in learning and memory which could be partially related to a reduced functional activity of the glutamatergic system is provided.

Neurobehavioral changes produced in rats by prenatal exposure to carbon monoxide

Wistar female rats were exposed to relatively mild concentrations of carbon monoxide (75 and 150 ppm) from day 0 to day 20 of pregnancy. The results show that prenatal exposure to CO (150 ppm) produced a significant reduction in the minimum frequency of ultrasonic calls emitted by rat pups removed from their nest. Moreover, a significant decrease in the responsiveness (rate of calling) to a challenge dose of diazepam (0.25 mg/kg) was found in male pups exposed to CO (150 ppm) during gestation. Prenatal CO (75 and 150 ppm) did not significantly affect locomotor activity or D-amphetamine-induced hyperactivity in both 14- and 21-day-old animals. Furthermore, adult male rats exposed to this chemical (150 ppm) during gestation exhibited significant alterations in the acquisition of an active avoidance task. CO-induced learning disruption does not seem to be linked to changes in the emotionality of animals. These findings suggest that gestational exposure to CO induces in rat offspring both short- and long-term behavioral changes characterized by altered ontogeny of emotional responsiveness to environmental challenges and by learning impairment.

Acute exposure to methylmercury at two developmental windows: Focus on neurobehavioral and neurochemical effects in rat offspring

The neurobehavioral and neurochemical effects produced by prenatal methylmercury exposure (8 mg/kg, gestational-days 8 or 15), were investigated in rats. On postnatal day 40, animals exposed to methylmercury and tested in the open field arena, showed a reduction in the number of rearings, whereas the number of crossings and resting time was not altered with respect to the age-matched control rats. The methylmercury-exposed groups showed a lower level of exploratory behavior as well as an impairment in habituation and working memory when subjected to the novel object exploration task. The neophobia displayed by methylmercury-exposed rats is unlikely to be attributed to a higher degree of anxiety. Prenatal methylmercury exposure did not affect motor coordination or motor learning in 40-day-old rats subjected to the balance task on a rotating rod, and it did not impair the onset of reflexive behavior in pups screened for righting reflex, cliff aversion and negative geotaxis. In cortical cell cultures from pups exposed to methylmercury during gestation, basal extracellular glutamate levels were higher, whereas the KCl-evoked extracellular glutamate levels were lower than that measured in cultures from rats born to control mothers. In addition, a higher responsiveness of glutamate release to N-methyl-D-aspartic acid receptor activation was evident in cortical cell cultures from pups born from methylmercury-treated dams than in cultures obtained from control rats. The present results suggest that acute maternal methylmercury exposure induces, in rat offspring, subtle changes in short-term memory as well as in exploratory behavior. These impairments seem to be associated to alterations of cortical glutamatergic signaling.

Ontogenetic and pharmacological dissociation of various components of locomotor activity and habituation in the rat.

Sprague‐Dawley‐derived male rats were used to investigate locomotor activity and habituation in an open field as a joint function of developmental age (2–6 weeks), pattern of test exposure (single 30‐min test vs three 5‐min tests at 24‐hr intervals), and treatment conditions (i.p. saline, d‐amphetamine sulfate 1mg/kg, or scopolamine hydrocloride 0.5 mg/kg). No‐drug animals showed low activity levels in both tests at the end of the second week, intermediate response rates at the end of the third week, and a typical adult‐like pattern at later ages (high initial activity followed by marked withinsession or between‐session habituation). Amphetamine effects varied considerably depending jointly on age and type of test. At the end of the second week, the drug hyperactivity was much more marked in successive brief tests than in the single extended test. One week later, the response increase was rather uniform in both tests. At the end of the fourth week, the sensitivity profile was reversed, consisting of a large drug effect in the extended test but not in successive brief tests. Scopolamine was still without effects at this age, while a typical hyperactivity was produced by the drug in 6‐week‐old animals. These data show that, at least in the rat strain used, the functional maturation of muscarinic regulatory systems is not a necessary condition either for the appearance of an adult‐like response pattern, or for the occurrence of the age‐ and test‐related changes of the amphetamine profile. Overall, the data point (i) to the existence of some mechanism serving the suppression of locomotion during the initial phase of exposure to a novel environment at 2 weeks and (ii) to separate mechanisms for within‐session and between‐session habituation developing at later stages.

Behavioural changes in the offspring of rats exposed to diazepam during gestation

Abstract Primiparous pregnant Sprague-Dawley dams were administered a single daily sc. injection of diazepam (0.1 and 1 mg/kg) or vehicle over gestation days 14–20. No differences in neonatal mortality and weight gain were found between the control and diazepam-exposed pups. Conversely, male pups prenatally treated with this benzodiazepine exhibited subtle behavioural alterations either during early postnatal life or during adulthood. In particular, a significant decrease in the locomotor activity of the diazepam-treated groups was found at the end of the second postnatal week (14–16 days). Furthermore, the administration of diazepam during gestation produced marked changes in the length of ultrasonic calls of rat pups removed from their nest. Finally, adult male rats (120 days of age) prenatally exposed to diazepam showed a notable impairment in copulatory activity as well as a significant decrease in the duration of ultrasonic (22 kHz) post-ejaculatory calls emitted during sexual behaviour. These findings suggest that late gestational exposure to diazepam induces both short- and long-term behavioural changes in rat offspring, changes characterized by altered activity patterns and emotional-motivational responsiveness to environmental challenges.

Ultrasonic vocalization as an indicator of emotional state during active avoidance learning in rats

Adult male rats subjected to a two-way avoidance task emitted ultrasonic vocalizations (20-30 kHz) both during the presentation of the conditioned stimulus and the intertrial interval. The rate of ultrasonic calling decreased during the 75-trial session indicating that acquisition of the conditioned avoidance response (CAR) was inversely correlated with the rate of vocalization. The rate of acquisition of the CAR was most rapid in those rats that did not emit any vocalization during learning. These data suggest that ultrasonic calling during stressful situations may be sensitive indicator of underlying emotional states that interfere with the acquisition of a complex task.

Developmental omega-3 supplementation improves motor skills in juvenile-adult rats.

Long‐chain polyunsaturated fatty acids are critical for brain growth spurt during both foetal and postnatal period. They play important roles in the expression of genes regulating cell differentiation and neuronal growth, as well as in the development of synaptic processing of neural cell interaction. Foetus and placenta are dependent on maternal supply for their growth and development, and supplemented infants show significantly greater mental and psychomotor scores. In particular, it has been shown that if mothers take omega‐3 supplements, their babies are smarter and better physically coordinated. On these grounds, the aim of the present study was to investigate, in the Sprague–Dawley rat, the effects of perinatal treatment with omega‐3 on motor activity, motor coordination, motor learning and memory. From gestational day 8 throughout the lactation period, dams received either an emulsion of 0.05 g/kg body weight omega‐3 in fruit juice, or an emulsion of 1 g/kg body weight omega‐3 in fruit juice or just the fruit juice (control). Omega‐3 formula was made of 27% docosahexaenoic acid and 53% eicosapentaenoic acid. On the day of birth (postnatal day 1), all pups were weighed, and then randomly culled to eight pups per litter. Pups were weaned at 21 days of age. One male pup per litter from each litter (control, n = 6; omega‐3 0.05 g/kg, n = 5; omega‐3 1 g/kg, n = 6) was used. Both control and treated rats were tested for (i) locomotor activity using the open field paradigm, (ii) motor coordination and motor learning using the rotarod/accelerod task and (iii) memory using the passive avoidance paradigm. Rats were tested on postnatal day 21 and re‐tested on postnatal day 90. As a result, docosahexaenoic acid and eicosapentaenoic acid supplementation significantly improved motor coordination. In particular, the latency to fall at the first speed was significantly increased in the treated rats as compared to the control animals. This benefit was observed with both doses at each tested age. The rat performance in accelerating rotation speed mode, which provides an indication of motor learning ability, was not modified by the omega‐3 supply. Finally, the omega‐3 treatment did not influence motor activity in the open field‐tested rats, nor the memory ability in the passive avoidance task. In conclusion, perinatal omega‐3 supplementation exerts a long lasting beneficial effect on the rotarod performance indicating improvement in balance and motor coordination and, possibly, in the functioning of pathways governing this task.

Ultrasonic vocalization in rat pups: effects of early postnatal exposure to SCH 23390 (a DA1-receptor antagonist) and sulpiride (a DA2-receptor antagonist).

Early postnatal administration of SCH 23390 and sulpiride induced marked changes in the ultrasonic vocalization elicited by the removal of rat pups from their nest. In particular, SCH 23390 produced a significant increase in the length, as well as in the sound pressure level, of ultrasonic calls; moreover, a significant decrease in minimum and maximum frequency values was found in pups treated with this DA1-receptor antagonist. Sulpiride significantly reduced the rate of calling, as well as the pressure level of sounds, whereas it did not influence other parameters of the ultrasonic emission. These behavioural alterations seemed to be the consequence of an impaired functional maturation of the dopamine (DA) system; however, the different changes caused by SCH 23390 and sulpiride, respectively, suggest that DA1- and DA2-receptor populations could play a distinct role in the ultrasonic calling during early postnatal life.

Changes in peripheral nervous system activity produced in rats by prenatal exposure to carbon monoxide

The present experiments were designed to investigate whether alterations of peripheral nervous system activity may be produced in male Wistar rats by prenatal exposure (from day 0 to day 20 of pregnancy) to relatively low levels of CO (75 and 150 ppm). The voltage clamp analysis of ionic currents recorded from sciatic nerve fibres showed that prenatal exposure to CO produced modifications of sodium current properties. In particular, in 40-day-old rats exposed to CO (75 and 150 ppm) during gestation, the inactivation kinetics of transient sodium current were significantly slowed. Analysis of the potential dependence of steady-state Na inactivation, h∞ (V), showed that the percentage of the maximum number of activatable Na channels at the normal resting potential (−80 mV) was increased to ≈85% in CO-exposed rats. Moreover, the voltage-current relationship showed a negative shift of sodium equilibrium potential in CO treated animals. In 270-day-old CO-exposed rats, parameters of sodium inactivation were not significantly modified; the reversal potential was still lower with respect to controls. The results indicate that prenatal exposure to mild CO concentrations produces reversible changes in sodium inactivation kinetics and on irreversible change in sodium equilibrium potential. These alterations could reflect CO influence on the rate of ion channel development.