The role of catecholamines in behavioral arousal during ontogenesis

Comparison of infant and adult rats in exploratory activity, diurnal patterns, and responses to novel and anxiety-provoking environments

Infant rats emerge from the maternal nest at Postnatal Day 17-18 to have their first critical environmental experiences; they may be particularly sensitive to experiences or experimental interventions that can affect their adult capacity. The authors address open questions on 2 components of normative environmental exploration, locomotor activity and response to anxiety-provoking locations, in Postnatal Day 18 infant and Postnatal Day 60 adult rats. The authors compare diurnal patterns of locomotor activity, wheel running, novel and familiar open-field activity, and 2 measures of anxiety. Infants have an equivalent capacity to adults for locomotor activity and wheel running and a fundamentally adult-like diurnal rhythm, except that they do not anticipate light-dark transitions, are more perturbable at their most somnolent, and are more or less active during specific limited phases than adults. Infants initially have a lower rate of locomotor activity in novel environments and have a greater willingness to be active in anxiety-provoking locations. Such differences may allow enhanced gathering of environmental information by the infant and are important to consider in the design of experiments using infants.

Effects of 2,4-dichlorophenoxyacetic acid exposure on dopamine D2-like receptors in rat brain

2,4-Dichlorophenoxyacetic acid (2,4-D), a worldwide-used herbicide, has been associated with a range of adverse health effects on humans and different animal species. Although the mechanism of 2,4-D neurotoxicity remains unknown, we had previously reported changes in various neurotransmitter systems, such as serotonin (5-HT) and dopamine (DA), which were proposed to mediate some of the behavioral effects in rats. In the present work, we examined the impact of 2,4-D exposure on the ontogeny of dopaminergic D2-type receptors in prefrontal cortex (PFc), striatum (CPu), hippocampus (H) and cerebellum (Cer). Pregnant rats were orally exposed to 70 mg/kg/day of 2,4-D from gestation day (GD) 16 to postpartum day 23. After weaning, the pups were assigned to one of the two subgroups: T1 [fed with untreated diet until postnatal day, (PD) 90] and T2 [maintained with 2,4-D diet until PD 90]. Five to eight pups per age and sex were sacrificed at 6, 15, 30, 45 or 90 days of age for membrane receptor binding assays employing [3H]nemonapride. Subchronic 2,4-D exposure (T2 group) increased DA D2-type receptor around 40% in CPu. In addition, DA D2-type receptor levels also increased in PFc (15 and 30 days) and Cer (30 and 90 days). Sex-dependent differences in D2 receptors were observed with T2 female rats being more affected than T2 male rats. When the herbicide treatment was interrupted after weaning (T1 group), DA D2-type receptor density was apparently recovered and stabilized to control level. These findings suggest a reversible vulnerability of D2-type receptors to 2,4-D exposure. Regional increases of D2-type receptor density may explain certain behaviors reported early by us, such as catalepsy and right-turning preference in rats exposed to 2,4-D.

Polybrominated diphenyl ethers: neurobehavioral effects following developmental exposure

Polybrominated diphenyl ethers (PBDEs), a class of widely used flame retardants, are becoming widespread environmental pollutants, as indicated by studies on sentinel animal species, as well as humans. Of particular concern are the reported increasingly high levels of PBDEs in human milk, as should be given that almost no information is available on their potential effects on developing organisms. In order to address this issue, studies have been conducted in mice and rats to assess the potential neurotoxic effects of perinatal exposure to PBDEs (congeners 47, 99, 153 and the penta-BDE mixture DE-71). Characteristic endpoints of PBDE neurotoxicity are, among others, endocrine disruption (e.g. decreased thyroid hormone levels), alteration in cholinergic system activity (behavioral hyporesponsivity to nicotine challenge), as well as alterations of several behavioral parameters. In particular, the main hallmark of PBDE neurotoxicity is a marked hyperactivity at adulthood. Furthermore, a deficit in learning and memory processes has been found at adulthood in neonatally exposed animals. Some of neurotoxic effects of PBDEs are comparable to those of polychlorinated biphenyls (PCBs), though the latter class of compounds seems to exert a stronger toxic effect. Available information on PBDE neurotoxicity obtained from animal studies and the possibility of neonatal exposure to PBDEs via the mother's milk suggest that these compounds may represent a potential risk for neurobehavioral development in humans.

Behavioral alterations induced in rats by a pre- and postnatal exposure to 2,4-dichlorophenoxyacetic acid

The purpose of this study was to determine whether the behavioral development pattern was altered by a pre- and postnatal exposure to 2,4-Dichlorophenoxyacetic acid (2,4-D). Pregnant rats were daily orally exposed to 70 mg/kg/day of 2,4-D from gestation day (GD) 16 to postnatal day (PND) 23. After weaning, the pups were assigned to one of the two subgroups: T1 (fed with untreated diet until PND 90) and T2 (maintained with 2,4-D diet until PND 90). Effects on offsprings were evaluated with a neurotoxicological test battery. Neuromotor reflexes, spontaneous motor activity, serotonin syndrome, circling, and catalepsy were analyzed during various postnatal ages. 2,4-D neonatal exposure induced delay of the ontogeny of righting reflex and negative geotaxis accompanied by motor abnormalities, stereotypic behaviors (excessive grooming and vertical head movements), and hyperactivity in the open field. Adult rats of both sexes (T2 group) showed a diminution of ambulation and rearing, while excessive grooming responses were only observed in T2 males. Besides, these animals manifested serotonin syndrome behaviors, catalepsy, and right-turning preference. Some behaviors were reversible, but others were permanent, and some were only expressed after pharmacological challenges.

Effects of physostigmine on male offspring sired by alcohol-treated fathers

Male rats were intubated with either 3, 2, or 0 g/kg alcohol, twice daily, for 7 months and were then bred to untreated females. At 18 and 58-62 days of age, male offspring were tested for passive avoidance learning. At 82-88 days of age, another group of male offspring were tested for open field activity after receiving 0, 0.1, or 0.4 mg/kg physostigmine, a cholinesterase inhibitor. Offspring sired by alcohol-treated fathers required more trials to reach criterion in the passive avoidance task at 18 days of age, but did not differ significantly at 58-62 days of age. These offspring were more active in the open field compared with controls after receiving vehicle, but did not differ from controls after receiving physostigmine. These results suggest animals sired by alcohol-treated fathers are more active than controls, and this effect is cholinergically mediated. These results are of interest because of their possible relevance to the hyperactivity noted in children born to alcoholic fathers.

Biochemical correlates for behavioral deficits induced by secalonic acid D in developing mice

Humoral signals (neurotransmitters and hormones) control cell division, migration, and differentiation processes which define the organization of brain pathways. Alterations in maternal, fetal, and neonatal biochemistry during critical periods of neurogenesis may irreparably alter the circuitry and, thus, postnatal behavior of young animals. Secalonic acid D (SAD), an ergochrome mycotoxin, causes behavioral and neurochemical deficits in developing mice following prenatal (transplacental) or early postnatal (transmammary) exposure. SAD-induced functional abnormalities include delays in reflex behaviors, integrated neuromuscular activity and strength, stress adaptation responses, and sensory discrimination. These behavioral changes are associated with reductions of brain monoamine neurotransmitter levels in both fetuses and neonates. SAD also alters concentrations of maternal plasma corticosteroids and fetal cyclic nucleotides during midgestation. SAD thus modulates several chemicals in pregnant mice and their fetuses which contribute to brain development, suggesting that this mycotoxin may pose a neuroteratogenic hazard to other immature mammals, including human infants.

The histopathological, behavioral and neurochemical effects of intraventricular injection of ethylcholine mustard aziridinium (AF64A) in the neonatal rat

This study investigated the histopathological, behavioral and neurochemical effects of bilateral injection of 2.0, 0.5 and 0.1 nmol/ventricle ethylcholine aziridinium (AF64A) on postnatal day (PND) 2. The rats showed a significant, but non-dose-related reduction of choline acetyltransferase (ChAT) in the hippocampus but not the cerebral cortex or the caudate nucleus when sacrificed on PND 16. No effect on ChAT was found in any region at PND 58. The group given 2 nmol/ventricle were hyperactive and showed a deficit in spatial learning when tested on the Morris water maze at PND 38-43. No such differences were observed for the rats injected with 0.1 or 0.5 nmol/ventricle AF64A. This spatial learning impairment in the 2 nmol group was associated with non-specific tissue damage seen only in animals from this group that were sacrificed at PND 40. This tissue damage was most evident in the left medial frontal cortex, the caudate nuclei and the anterior dorsal hippocampus.

Behavioral changes induced in developing rats by an early postnatal exposure to lindane

The purpose of this study was to determine whether the behavioral developmental pattern was altered by an early postnatal exposure to lindane. Male and female offspring of Wistar rats were daily orally administered with a nonconvulsant dose of lindane (10 mg/kg) during 7 days either the 1st or the 2nd postnatal week days. Effects on pups were evaluated with a reduced developmental neurotoxicological test battery. Body weight evolution, neuromotor reflexes (surface righting, cliff avoidance and tail hang reflex) and spontaneous motor activity were analyzed from day 1 after birth up to day 28. The body weight pattern was unaffected by treatment with lindane and no signs of overt toxicity were observed. Lindane-treated pups showed an increased positive response of the neuromotor reflexes. Furthermore, lindane produced hyperactivity, especially manifested between days 12 and 16. A peak of activity was reached at day 16 in lindane-treated group, while control animals had a maximum between days 20 and 24. These results suggest that low nonconvulsant doses of lindane may induce behavioral changes in developing rats.

Secalonic acid D mycotoxin affects ontogeny of brain catecholamines and swimming in mice

Suckling mice exposed to secalonic acid D (SAD) mycotoxin postnatally (by gavaging dams with 0, 15 or 25 mg/kg on postgestational days 1 to 10) or prenatally (by gavaging with 25 mg/kg on gestational day 13 to produce a positive behavioral teratogenic control group) manifested subtle preweaning neurobehavioral, neurochemical and growth deficits. Gestational length, maternal weight gain, neonatal sex ratio and physical appearance of pups at birth were unaffected by treatment. Prenatal SAD (25 mg/kg) delayed (p less than 0.05) ontogeny of swimming on postnatal days (PND) 11 and 13 and reduced norepinephrine (NE) and dopamine (DA) levels in prosencephalon on PND 7 and in cerebellum-pons on PND 7-16. In the postnatal treatment groups, pup body weight gains were decreased from PND 9-22. Swimming was delayed in the 15 mg/kg postnatal exposure group on PND 11 and 13, while 25 mg/kg delayed swimming on PND 11-15. Postnatal exposure to 25 mg/kg also reduced NE and DA levels in prosencephalon and cerebellum-pons on PND 7-16. SAD thus caused concomitant ontogenetic delays in growth, swimming behavior and brain catecholamine levels following either prenatal (transplacental) or early postnatal (transmammary) exposure. These data indicate that both in utero and lactational exposures must be considered when assessing potential risks posed to developing mammals by environmental neurotoxicants.

Behavioral and genetic interrelationships between locomotor activity and brain biogenic amines

1. Spontaneous locomotor activity of four mouse strains, the albino ICR, BALB/C, the black C57 BL/6 and the brown CDF-I, was studied in conjunction with whole brain content of select biogenic amines and major metabolites. The ICR and C57BL/6 mice scored the highest and lowest motility among the strains studied, respectively. 2. The ICR mice motility were the most sensitive to experimental stress among the mouse strains evaluated. 3. Brain dopamine concentrations were greater in ICR and CDF-I mice than the other two mouse strains. This is compared to high serotonin and 5-hydroxyindole acetic acid levels determined in C57BL/6. 4. A relationship between the ICR mouse strain with a high motility and the ratios of brain dopamine:homovanillic acid and between serotonin:5-hydroxyindole acetic acid was established. 5. An inverse relationship between ICR mice motility and the ratio of metanephrine and normetanephrine:3-methoxy-4-hydroxyphenylglycol (MHPG) was determined. 6. It is concluded that genetic predisposition may account for a relationship between motor activity and brain biogenic amines which may give insight into the susceptibility of different patients to the development of certain extrapyramidal diseases.

Paternal alcohol consumption: effects of age of testing and duration of paternal drinking in mice

Male mice consumed liquid alcohol diets containing 25, 20, 15, 10, 5, or 0% ethanol-derived calories (EDC). Animals receiving the 20-0% EDC diets were pair-fed to those consuming the 25% EDC diet. After 7 weeks of consumption males were bred to nontreated females. Offspring were tested for activity at 16-20 and 75 days of age. Offspring sired by alcohol-consuming males did not differ from controls in litter size, birth weight, or weight at weaning, but were less active than controls on several measures of activity. Many of these decreases were best defined in terms of linear trends. However, these differences were evident only for animals tested prior to 20 days of age for most activity measures. In a second experiment adult males continued to consume alcohol for another 7 weeks and were bred again. Offspring of this second breeding were tested for activity at 16 days of age and were compared with offspring sired by the same father from the previous breeding. Offspring sired after this longer duration of paternal alcohol consumption did not differ significantly from controls in any of the above-mentioned variables.

Behavioral and developmental effects in suckling mice following maternal exposure to the mycotoxin secalonic acid D

Pregnant mice (dams) were gavaged once on gestational day 13 with 4 ml/kg of dimethylsulfoxide vehicle containing 0 (groups 15, 25 and negative control) or 25 (positive behavioral teratogenic control group) mg/kg of secalonic acid D (SAD). While nursing their offspring, dams were gavaged on postgestational days 1 to 10 with vehicle containing 0 (negative and positive control groups), 15 (group 15) or 25 (group 25) mg/kg/day of SAD. Gestational lengths, maternal pregnancy weights, litter sizes, neonatal sex ratios, neonatal physical appearance and female birth weights were unaffected by prenatal treatment, but male pups born to positive control dams weighed less (p less than 0.05) than negative control group. Compared to negative control, the positive control dams gained significantly more weight while nursing their offspring. Prenatal (positive control) and postnatal (15, 25) SAD exposure delayed ontogeny of surface righting, olfactory discrimination and hindlimb grip behaviors in males and females, and testes descent in males. Negative geotaxis in male and female offspring of group 25 and male offspring of positive control group, as well as times of incisor eruptions of both sexes in groups 15 and 25 were delayed. A significant dose-response effect in olfactory discrimination existed between the groups exposed to postnatal SAD. SAD was behaviorally teratogenic following both prenatal and early postnatal exposure.

Neonatal 6-hydroxydopa, but not DSP-4, elevates brainstem monoamines and impairs inhibitory avoidance learning in developing rats

The involvement of brain monoamines in learning and memory in developing rats was studied by comparing the effects of 3 different noradrenergic neurotoxin treatments. Two experimental groups of male Sprague-Dawley rat pups were injected systemically with 50 micrograms/g of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) either on the day of birth or on postnatal days 17-18. Rats in the third experimental group were injected systemically with 60 micrograms/g of 6-hydroxydopa (6-OHDOPA) on postnatal days 0 and 2. Control littermates received vehicle. The animals were trained on an inhibitory avoidance task on postnatal days 27-29 and tested for retention 24 h later. The drug treatments produced comparable depletion of norepinephrine in the hippocampus and frontal cortex. 6-OHDOPA, but neither DSP-4 treatment, significantly elevated brainstem concentrations of norepinephrine and serotonin. In addition, 6-OHDOPA, but not DSP-4, significantly impaired retention of the inhibitory avoidance task. The impairment did not reflect insensitivity to the footshock used in training: both neonatal drug treatments tended to lower, not raise, footshock thresholds, as measured by a flinch test. High affinity choline uptake was not affected by either neonatal drug treatment in any of the brain areas examined. Thus, the 6-OHDOPA-induced behavioral deficit did not involve altered acetylcholine function. The results implicate brainstem monoamines in the modulation of learning and memory during development.

Absence of differential motoric and thermic responses to clonidine in young rats exposed prenatally to alcohol

We studied the involvement of altered noradrenergic function in the behavioral consequences of fetal ethanol exposure. Pregnant rats were fed a liquid diet containing 35% Ethanol-Derived Calories (EDC), pair-fed a 0% EDC diet with sucrose substituted isocalorically for ethanol, or fed ad lib lab chow. In Experiment 1, offspring from these prenatal treatment groups were injected with the alpha-adrenergic agonist clonidine (0.5 or 2.0 mg/kg) at 10 or 42 days of age and showed age-characteristic, dose-dependent increases in locomotor activity, exploration, forelimb treading, and catalepsy. In Experiment 2, offspring were injected with clonidine (0.25 or 1.0 mg/kg) at 10, 14, or 18 days of age, and locomotor activity and wall-climbing were observed in a warm chamber (33 degrees C). Catalepsy and rectal temperature were also scored. There were no significant differential effects of clonidine on any prenatal treatment group at any age for any measure of activity or rectal temperature. The results do not support the hypothesis that fetal ethanol exposure alters noradrenergic systems in behaviorally significant ways.

Behavioral differences in the developing rat following postnatal anoxia or postnatally injected AF-64A, a cholinergic neurotoxin

Rat pups were submitted postnatally to one of two procedures: a 25-min exposure to 100% nitrogen or an i.c.v. bilateral injection of AF-64A, 2 nmol contained in 1-microliter saline. Throughout further development of either group, their performance in passive and active avoidance tests and in amphetamine-induced stereotype behavior was followed and compared. Both groups exhibited hyperactivity which persisted until 42 days of age in the anoxia group and beyond 120 days in the AF-64A group. Both groups were equally inferior to controls in the passive avoidance test, but only the anoxia group was inferior to controls in the active avoidance test. Amphetamine-induced stereotype behavior was much less pronounced in the anoxia group relative to AF-64A-treated rats or to controls. The results suggest that the lesion induced by the neurotoxin is more specific and less widespread than the one caused by anoxia.

Effects of prenatal 5-methoxytryptamine and parachlorophenylalanine on serotonergic uptake and behavior in the neonatal rat

Parachlorophenylalanine (pCPA) or 5-methoxytryptamine (5MT) was administered to pregnant Sprague Dawley rats from day 8 (D8) of gestation till D17 and from D12 until birth respectively. Birth weights of both drug groups of neonates were approximately 20% less than the saline-injected controls. 5MT neonates showed a significant reduction of high affinity 3H-5HT uptake in the brainstem at all three time points: D1, D15, D30, and a slight reduction in the forebrain reaching significance only on D30. The pCPA animals showed a significant reduction in the brainstem and forebrain on D1 and D30, but only a small nonsignificant reduction in both areas on D15. Behaviors measured on day 15 revealed that in general activity, spontaneous alternation, and passive avoidance both drug groups of neonates showed deficits: less activity, less alternation, and less avoidance.

Developing rat brain monoamine levels following in utero exposure to a mixture of 2,4-dichlorophenoxyacetic and 2,4,5-trichlorophenoxyacetic acids

Pregnant rats were gavaged with a 1:1 mixture of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 0 (G0), 50 (G 50) and 100 (G 100) mg/kg per day on gestational days 6-15. Treatment significantly (P less than 0.05) delayed ontogeny of dopamine (DA), but not norepinephrine (NE) levels, in the thalamus-hypothalamus on postnatal day 7; in the pons-medulla on days 7,9 and 15; and in the olfactory lobes on day 9. On day 25, serotonin (5-HT) levels were significantly decreased in the pons-medulla of G 100 rats, whereas 5-hydroxyindoleacetic acid (5-HIAA) levels decreased in the thalamus-hypothalamus and pons-medulla of G 50 and G 100 rats.

Altered development of responsiveness to clonidine in severely malnourished rats

To examine the effects of malnutrition on the ontogeny of alpha 2 noradrenergic receptor function, we compared the effects of clonidine during early development in severely malnourished and well-nourished rat pups. Independent groups of pups from dams given either 6% or 25% casein diets received one of five doses of clonidine at 5, 10, 15, 20 or 25 days of age and dose-response relationships for motor activity were determined. In the 25% pups the clonidine-induced locomotor activity was greatest at 5 and 10 days, intermediate at 15 days and not elevated at 20 and 25 days. The malnourished pups exhibited a significant delay in the transition from hyperactivity to hypoactivity, being activated by clonidine until at least 25 days. Wall-climbing measures indicated similar developmental trends as overall activity. These results are discussed in terms of the proposed mechanisms mediating the developmental change in the effects of alpha 2 receptor stimulation.

Comparison of hyperactivity in adult rats induced by neonatal intraventricular 6-hydroxydopamine following pargyline or desmethylimipramine treatment

The relative roles of norepinephrine (NE) and dopamine (DA) in sustaining neonatal hyperactivity were assessed in rats given 6-hydroxydopamine (6-OHDA) neonatally into the lateral ventricles after pargyline (P) or desmethylimipramine (DMI) pretreatment. On day 5 after birth, male and female rat pups were pretreated with P (50 mg/kg IP) or DMI (25 mg/kg IP) 30 min before receiving bilateral injections of 6-OHDA (200 micrograms/5 microliters saline containing ascorbic acid 1.0 mg/ml) into the lateral ventricles. Controls were pretreated with P or DMI and then received injections of saline containing the ascorbate. Spontaneous activity was measured in a stabilimeter at ages 30-31, 42-45, 60-63, 75-77, and 120-122 days. Activity in controls and P + 6-OHDA animals was also measured at 254 days of age. The sessions lasted 45 min, except those testing activity in the 254-day-old rats which lasted 12 h. Regional assays of catecholamines carried out when the animals were 150 days old revealed that in the P + 6-OHDA group the levels of NE were reduced in frontal cortex (7% of control levels), caudate (21%), and hippocampus (14%). The NE levels were unchanged or slightly elevated in hypothalamus, ventral midbrain, and pons. The DA levels in the P + 6-OHDA group were depleted in caudate (8%) and ventral midbrain (32%), and unchanged in hypothalamus and pons. In the DMI + 6-OHDA group the NE levels were reduced in caudate (25%) and elevated in hippocampus (188%). The DA levels were depleted in caudate (3%) and ventral midbrain (22%).(ABSTRACT TRUNCATED AT 250 WORDS)

Dopaminergic but not noradrenergic mediation of hyperactivity and performance deficits in the developing rat pup

The relative contribution of dopamine (DA) and norepinephrine (NE) in behavioral arousal was examined in developing rat pups using intracisternal 6-hydroxydopamine (6-OHDA) either alone or following pretreatment with desmethylimipramine (DMI). Such treatments were designed to examine the effects of preferential reduction of DA (DA depletion), NE (NE depletion), or both catecholamines (CA depletion) in the development of motor activity and escape performance. General motor activity increased with age and, over all ages, DA-depleted pups tended to exhibit greater activity. This was most apparent at 15 days of age, where DA-depleted pups were significantly more active than controls, NE-depleted, or CA-depleted pups. DA-depleted pups failed to exhibit the steep decline in activity over time (habituation of activity) demonstrated by the control and NE-depleted pups, while pups depleted of both CA fell into an intermediate position in habituation. Escape latency in a T-maze at 20 days and shuttle box at 26 days of age indicated comparable performance to controls for NE-depleted pups, while those animals in DA-depleted and CA-depleted groups appeared unable to perform the task. Brain CA concentrations (determined by a radioenzymatic assay) indicated preferential reduction of DA in the DA-depleted group to concentrations 25% of controls, reduction of NE to 62% of controls in the NE-depleted group, and reductions of DA to 42% and NE to 60% in the CA-depleted group. These results suggest that preferential reduction of brain DA in the developing rat pup increases motor activity and impairs habituation of activity during the stage of behavioral arousal in week 3 of postnatal life.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex and strain differences in the developmental activity profile of the rat tested over clean vs home cage bedding

In the first of two experiments, CD rat litters were used to characterize activity patterns obtained in a size-adjustable, single photodetector chamber. Beginning on postnatal Day 10 or 12, pups were tested repeatedly over clean bedding (C) or over bedding removed from each pup's home cage (HC). In C rats of both sexes and in HC females, short-term activity levels peaked on Day 16. However, HC males displayed an earlier and even greater elevation in activity from Day 12 to 16. This overall pattern was found in rats tested either every second or fourth day. In the second experiment, Long-Evans pups were assigned to each testing condition (C vs HC) and activity measured beginning on Day 12. Peak levels were seen in all Long-Evans rats on Day 16 and only females showed significant alterations as a function of bedding condition. When overall activity levels of the two strains were compared, significant differences were found on Days 12, 24, 30, and 120 in males, and 12, 24, and 30 in females. Significant differences between strains in activity as a function of bedding condition were found in males on Days 12, 20, 24, and 120 and in females on Days 12, 30, and 60. These data confirm the generality of a developmental hyperactivity phase in isolated juvenile rats. However, different patterns of hyperactivity were found in male vs female rats across strains. CD males were more active in the presence of HC olfactory cues, while in Long-Evans rats, female activity was affected more by bedding condition.

Differential effects of selective dopamine, norepinephrine or catecholamine depletion on activity and learning in the developing rat

The present experiment investigated the behavioral changes which occurred following neonatal depletion of central catecholamine systems in the rat. The behavioral effects which resulted from selective dopamine (DA) depletion were compared with those resulting from selective norepinephrine (NE) depletion as well as depletion of both catecholamines (CA). Neonatal 6-hydroxydopamine (6-OHDA) was administered intracisternally at 5 days of age following pretreatment with desmethylimipramine in order to selectively deplete DA. NE levels were reduced by intraperitoneal injections of 6-OHDA at 1 and 2 days of age. Depletion of both catecholamines was effected by combining the procedures used for selective depletion of both DA and NE. Activity was time sampled during an hour at 3 preweanling ages. Avoidance and escape learning were measured in a T maze when pups were 20 days of age and in a Shuttlebox apparatus on day 28. Results revealed that DA and CA depleted animals were hyperactive in comparison to controls and displayed severe learning impairments in both T maze and Shuttlebox performance. In contrast, NE depleted animals showed activity levels which were similar to controls but were significantly impaired on both learning paradigms. These results suggest that selective lesions of DA and NE in infancy lead to a constellation of behaviors which are distinctly unique. The implications of these findings is discussed in terms of clinical research into the Attentional Deficit Disorder of childhood.

Development of receptors for dopamine and noradrenaline in rat brain

In order to examine the receptor basis for the development of spontaneous locomotion and for the effects of clonidine in the infant rat, we measured the densities of alpha 1-adrenoceptors, alpha 2-adrenoceptors and D2-dopamine receptors in various brain regions of the developing infant Wistar rat. The mesolimbic D2-dopamine receptors paralleled the rise in spontaneous locomotion of the infant rat. No alpha 1-adrenoceptors were detectable at birth in any of the four regions examined (mesolimbic, hippocampus, frontal cortex, and hypothalamus), thus providing no basis for the locomotor-stimulating action of clonidine in the first week of life. Mesolimbic alpha 2-adrenoceptors matured between 21 and 28 days (at which time clonidine yields its usual sedating action).

Effect of propranolol treatment in pregnant rats on motor activity and avoidance learning of the offspring

Rats born to mothers treated with propranolol, during days 8-22 of gestation, displayed hyperactivity in the open field which lasted up to 60 days of age and an impairment of avoidance in the shuttle box which was more marked in the male rats. Females exhibited hyperactivity in the open field but developed impaired avoidance learning only when exposed prenatally to both propranolol and hypoxia. Propranolol administration during the last term of pregnancy (days 18-22) affected mostly shuttle box performance. In contrast, hyperactivity could be induced by treatment during various stages of pregnancy, (days 8-22, 8-18, or 18-22) with the duration of hyperactivity being directly related to the length of treatment of the mothers. The possible mechanism of the disruptive effect of propranolol in the fetus and newborn is discussed.

Behavioural effects of phenobarbitone. 1. Effects in the offspring of laboratory mice

Phenobarbitone at a concentration of 187.5 mg/l in drinking fluid of breeding mice and their offspring after weaning did not affect gestation period, litter size, litter weight or pup development before weaning, although a slight retardation of weight gain after weaning occurred. This level of phenobarbitone given to mice after weaning did not affect weight gain. The average daily intake of phenobarbitone ranged from 30 to 52 mg/kg body weight depending on age and sex. Behaviour of offspring and mice treated after weaning was examined by ethological analysis of encounters between unfamiliar mice of the same sex and treatment group in a neutral enclosure. After lifelong exposure to phenobarbitone mice at 5 and 15 weeks of age showed an increased amount of scanning and exploration of the unfamiliar cage coupled with a decrease of time spent in immobility. Difference from control levels was more pronounced at 15 than at 5 weeks of age, in part because controls showed more immobility and explored less as they matured. No behavioural changes were detected in mice treated with this level of phenobarbitone after weaning. Lifelong exposure to phenobarbitone did not affect agonistic behaviour in pair-housed males at 30 weeks of age, and under these circumstances no longer stimulated exploration to a significant extent.

In utero alcohol exposure and developmental delay of response inhibition

Offspring of rats fed liquid alcohol diet during pregnancy exhibited age-related increased activity and deficits in passive avoidance learning and response perseveration which were not age-related. Alcohol-exposed offspring also elicited less maternal responsiveness from nontreated dams than did pair-fed controls. The results suggest that in utero alcohol exposure produces a developmental delay in ontogeny of response inhibition mechanisms underlying activity, but not passive avoidance learning or spontaneous alternation.

Postnatal development of a cholinergic influence on neuroleptic-induced catalepsy

The development of cholinergic influence on neuroleptic-induced catalepsy was investigated in 10-, 15- and 20-day-old rat pups. It was found that the antimuscarinic atropine was ineffective in decreasing the catalepsy produced by spiroperidol treatment at 10 and 15 days. By day 20, however, atropine attenuated cataleptic behavior in a dose-dependent manner. Atropine alone was shown paradoxically to elicit mild to moderate cataleptic responses in 10- and 15-day-olds, but not at day 20. Clozapine by itself produced the same age dependent pattern of catalepsy response as the spiroperidol and atropine combination treatment. These results suggest that cholinergic mechanisms which interact antagonistically with the dopamine systems underlying cataleptic behavior are not functionally mature until after day 15 in the rat.

Effect of dietary lipid on locomotor activity and response to psychomotor stimulants

Spontaneous locomotor activity was investigated in developing rats fed diets rich in either saturated fat (coconut oil) or polyunsaturated fat (sunflower oil). The locomotor activity response to amphetamine, methylphenidate, and atropine in the dietary groups was also measured. Rats from dams fed sunflower oil had a late developing (20 days of age) increase in basal locomotor activity when compared to rats from dams fed coconut oil and the standard laboratory diet. The locomotor activity response to d-amphetamine administered IP to 30-day-old animals was potentiated in rats exposed to coconut oil compared to the other two groups. A dose-response analysis of the effect of methylphenidate revealed no differences among the dietary groups. A low dose of atropine (2 mg/kg) decreased 1 h locomotor activity 40% below basal level in rats fed sunflower oil but increased locomotor activity 90% over basal activity in rats fed coconut oil. These results indicate that dietary lipid can have a marked effect on basal locomotor activity as well as on the response to stimulant drugs.

Effects of apomorphine on escape performance and activity in developing rat pups treated with 6-hydroxydopamine (6-OHDA)

The effects of apomorphine and excape learning were examined in normal developing rat pups and littermates preferentially depleted of brain dopamine by the intracisternal administration of 6-hydroxydopamine (6-OHDA) at 5 days of age, a treatment which resulted in a rapid and permanent reduction in brain dopamine to concentrations 12-29% of littermate controls while norepinephrine was not significantly altered. At 19 days of age both 0.1 and 1.0 mg/kg doses of apomorphine increased general motor activity in normal but not 6-OHDA treated pups (though these pups were significantly hyperactive prior to apomorphine). At 26 days only the 1.0 mg/kg dose increased motor activity in both normal and 6-OHDA pups. Exploratory activity at 30 days in both normal and 6-OHDA pups was first reduced then abolished by progressive doses of apomorphine. Stereotyped activity was increased by 0.1 and 1.0 mg/kg apomorphine at 19 days in both normal and 6-OHDA pups. By 26 days, apomorphine no longer produced intense sterotypies in normal pups, but did effect such responses in 6-OHDA treated animals. Administration of apomorphine resulted in a disruption of escape performance in a T-maze and shuttle box in normal pups only at 1.0 mg/kg but disrupted performance in 6-OHDA treated animals at both 0.1 and 1.0 mg/kg dosages. These results indicate a peak effect of apomorphine on general motor activity at three weeks of age in normal pups. Our results also suggest that apomorphine will disrupt escape learning, effects that appear to be correlated with the apomorphine induced increase in motor activity.

Effects of 6-hydroxydopamine and 6-hydroxydopa on development of behavior

Rats treated at birth with 6-hydroxydopamine (6-OHDA) (60 microgram/g, IP) or 6-hydroxydopa (6-OHDOPA X2) (60 microgram/g, IP at birth and 48 hr later) exhibited increases in general activity throughout the initial 5 weeks after birth, with peak activity occurring around 20 days postnatally. Activity changes in the 6-OHDOPAx2 group appeared to be due to increased exploratory behavior (ambulation, climbing, rearing, sniffing), while the 6-OHDA changes appeared to be due to the increased self-directed behavior (eating, grooming, scratching). Despite these behavioral differences there was no obvious difference between treated groups in norepinephrine (NE) levels in the various brain regions, i.e., all treatments resulted in a reduction in neocortical and hippocampal NE and an elevation in cerebellar NE. These findings suggest that noradrenergic neurons may be altered to different degrees by each agent in more discrete brain regions than were tested, or that other neurotransmitter systems may be more selectively altered by either of the drug treatments. Because striatal dopamine was unaltered in any of the groups, however, there is reason to question a previously suggested link between minimal brain dysfunction (MBD) and dopamine depletion in the neonatal brain.

GABA-mediated behavioral inhibition during ontogeny in the mouse

Although immature rats and mice generally demonstrate poor behavioral inhibitory capacities, some recent evidence may indicate the presence of substantial inhibitory control. The present experiment investigated the possibility that gamma-aminobutyric acid (GABA) systems may mediate some behavioral inhibition during early development. Mice 9-100 days old were injected with the GABA-elevating agent amino-oxyacetic acid (AOAA) and tested for behavioral activity. High levels of locomotor activity characteristic of immature control mice were attenuated following AOAA injection, whereas AOAA had little effect on the activity of adult mice. Moreover, AOAA produced a period of rebound hyperactivity for young but not for adult mice. These findings suggest that although GABA systems may mediate early behavioral inhibition, coordination between excitatory and inhibitory capacities matures slowly. In a second experiment the dopamine-beta-hydroxylase inhibitor FLA-63 prevented rebound hyperactivity in young mice pretreated with AOAA, suggesting that the excitatory component may be mediated by noradrenergic systems.

Ontogenesis of spontaneous activity and habituation of activity in the rat pup

Individual components of activity and habituation of activity were determined throughout the 1st month of life in the rat pup. Total activity increased from 25% at 8 days of age to 68% at 22 days before declining to 49% at 26 days. Total slight activity (predominantly sniffing) increased to a maximum of 33% at 15 days whereas total very active behavior (predominantly ambulation) reached its maximum of 38% at 22 days. Habituation of activity expressed as the mean slope of decrement of activity over the 1st 30 min of the observation period was observed in rats as young as 8 days of age. By 12 days, habituation of total activity had increased significantly reflecting a 3-fold increase ihabituation of slight activity, an effect observed at 15 days as well. However, by 19 days the slope of activity decrement had declined to half of its 15-day value, indicating an impairment of habituation and reflecting the attenuation of very active behavior, predominantly ambulation. This decline in habituation continued through 22 days but by 26 days habituation of activity had increased again reaching a maximum for the 1st month of postnatal life. Our results suggest that the phenomenon of behavioral arousal observed in the developing rat pup 19 days of age reflects an inability of the organism to modulate his activity as effectively as the 15-day- or 26-day-old animal.

Age-dependent effects of 6-hydroxydopamine on locomotor activity in the rat

This experiment examined the effects on locomotor activity of intraventricular 6-hydroxydopamine (6-OHDA) administered to developing and adult rats. 6-OHDA was administered subsequent to pargyline treatment at 3 and 6 days of age; or 6-OHDA was administered subsequent to desmethylimipramine (DMI) treatment (6-OHDA/DMI) at 3 and 6 days of age, 11 and 14 days of age, 20 and 23 days of age, or 46 and 48 days of age. Locomotor activity of vehicle-treated rats assessed in stabilimeter cages peaked between 14 and 16 days of age and subsequently declined to levels characteristic of the adult. Treatment with pargyline and 6-OHDA at 3 days of age, or 6-OHDA/DMI at 3 and 6 or 11 and 14 days of age, did not alter the early rise in locomotor activity but prevented the decline in activity normally seen during the third and fourth weeks of life. When tested as adults, locomotor activity was greater in rats that had been treated with 6-OHDA/DMI at 3 and 6 and at 11 and 14 days of age than in those that had been treated at 20 and 23 days of age. Treatment with 6-OHDA/DMI at 46 and 48 days of age was without significant effect on locomotor activity. 6-OHDA (with pargyline pretreatment) produced large decreases in NE content in telencephalon and diencephalon and in dopamine (DA) content in striatum. 6-OHDA-DMI also produced large decreases in DA content in striatum and, in some of the treatment groups, only small decreases in norepinephrine (NE) content in telencephalon, diencephalon, and brain stem. These data suggest that the maturation of neuronal systems utilizing dopamine as a neurotransmitter is essential for the suppression of locomotor activity normally seen during development. The data further suggest that dopamine depletion per se does not lead to increased locomotor activity, but rather it is the destruction of dopamine-containing fibers prior to the normal period of locomotor suppression that increases locomotor activity.

Changes in the behavioral response to a novel environment following lesioning of the central dopaminergic system in rat pups

During the third week of life, a hyperactive period for laboratory rat, the occurrence of 8 behavioral categories was recorded in individual littermates transferred to a novel environment. Neonatal destruction of the catecholaminergic system by intraventricular injection of 6-OH-DA resulted in increased motor activity during the third week of life. Selective lesioning of the dopaminergic system by the combined treatment of 6-OH-DA + desmethylimipramine also induced a significant increase in some active behavioral categories. It appeared that in contrasts to the gross behavioral sequence, as seen in controls, which compromised locomotion and rearing leads to grooming leads to sitting and lying down, the lesioned animals showed a prolonged phse of restless locomotion. These data are interpreted as a disability to habituate adequately to a novel environment after neonatal lesioning of the dopaminergic system.

Experimental studies on hatching behavior in the chick. IV. Evidence for the role of a noradrenergic mechanism

In the present experiments we have attempted to determine whether one or more of the biogenic amines are involved in the prehatching and hatching behavior of the chick. Injection of reserpine first induces a depression in ongoing spontaneous motility on day 16 of incubation. Prior to this, reserpine has no apparent effect on embryonic behavior. Reserpine injections on days 17-19 induce a similar behavioral depression that lasts for at least six hours; by 24 hours post-injection the behavior of reserpine-treated embryos is comparable to controls. Injection of reserpine on day 20 (post-pip) delays hatching by about nine hours. Injection of reserpine into the yolk-sac of eggs prior to incubation also delays hatching by eight to nine hours. It is unlikely that the well-known cardiovascular effects of reserpine are involved in the above behavioral results since spinal embryos also exhibit a behavioral depression following reserpine treatment. Biochemical estimation of norepinephrine (NE) in the brain of reserpine-treated embryos suggest that it is release, not depletion, of the catecholamines that is responsible for the behavioral effects. Additional suport for this notion comes from experiments in which 16- or 18-day old embryos were injected with NE, L-dopa or amphetamine. In each case, a behavioral depression similar to that produced by reserpine resulted. Clonidine, a NE agonist induces a depression in certain aspects of embryonic behavior (Types 1 and 2), but also selectively enhances a corrdinated motor pattern (type 3 motility) involved in prehatching behavior (tucking). Clonidine first evokes this behavior pattern one or two days prior to its spontaneous appearance on day 16. After pipping on day 19 or 20 clonidine no longer activates Type 3 behavior, even if injected during the actual hatching process (climax). Since the alpha-adrenergic blocking agent phenoxybenzamine blocks the effect of clonidine on Type 3 tucking behavior, whereas the beta-adrenergic blocker propranolol does not, we suggest that tucking and the attainment of the hatching position are mediated by an alpha-adrenergic mechanism in the brain and/or spinal cord. Furthermore, since clonidine affects the Type 3 behavior associated with tucking, but not the somewhat similar coordinated behavior involved in hatching and emergence from the shell (climax), we propose that this later behavior pattern be given a new name, Type 4 motility.

Prenatal alcohol consumption and open-field behaviour in rats: effects of age at time of testing

Throughout gestation pregnant Wistar rats consumed a nutritious liquid diet containing 35% ethanol-derived calories. Control mothers were fed lab-chow. Subsequently, the offspring of the ethanol-fed mothers displayed significantly greater activity (ambulation) in an open-field test at 28 and at 56 days of age, but not at 112 days of age. No differences in defecation were observed at any age.

Aversive prenatal stimulation: effects on behavioral, biochemical, and somatic ontogeny in the rat

Electric foot shock administered to pregnant rats altered the ontogeny of spontaneous motor activity in their pups. Prenatally stimulated (PMS) offspring were more active than controls on Days 1-10 but less active during the 3rd postpartum week. The age of peak activity, a major developmental landmark, occurred in PMS pups around 10 days of age; in controls maximum activity was not seen until the 3rd week. This effect was independent of the gender of the offspring and the timing of the gestational stimulation. Its appearance in both cross-fostered and fostered pups indicated the prenatal origin of the effect. The maturation of spontaneous alternation behavior and several reflexes and the appearance of physical features were not affected by prenatal stimulation. Moreover, both PMS and control groups exhibited an age-related increase in brain concentrations of norepinephrine, serotonin, and 5-hydroxyindoleacetic acid. These findings indicate that spontaneous motor activity is uniquely sensitive to PMS, and as far as can be determined here, PMS produces no generalized alteration in behavioral and physical ontogeny.

Genetic and ontogenetic variations in locomotor activity following treatment with scopolamine or d-amphetamine

Highly inbred mice of 3 strains (A/J, DBA/2J, and C57BL/6J) were tested in an open field at 14, 21, or 28 days of age. Ten minutes prior to testing, mice received treatment of saline, scopolamine (.5 or 1.0 mg/kg of body weight), or d-amphetamine (.5, 1.0, or 5.0 mg/kg). The d-amphetamine (5.0 mg/kg) increased activity in all strains at 14 days and 28 days of age, and at 21 days significantly increased activity in all except the C5BL/6. In contrast, increased activity with the scopolamine treatment was seen in DBA/2 at 21 days, but not in A and C57BL/6 until 28 days postnatally. The data support a caudal-rostral gradient of brain development with the inhibitory cholinergic system developing more slowly than the excitatory catecholamine system. In addition, strain-specific differences in activity levels are discussed in relation to the differential rates of chloinergic maturation.

Ontogenetic development of locomotor activity and rate of tyrosine hydroxylation

A combined biochemical and behavioral study was performed postnatally on albino rats. An almost linear increase in total motor activity was observed from 1 to 15 days of age followed by a pronounced decrease in motor activity between days 15 and 18. The in vivo rate of tyrosine hydroxylase activity in whole brain was estimated by means of measuring accumulation of L-3,4-dihydroxyphenylalanine (Dopa) after administration of an inhibitor of aromatic amino acid decarboxylase NSD 1015. Additionally, Dopa accumulation was studied in regional brain areas in 10 and 14-day-old animals. A slight gradual increase in the amount of Dopa accumulation in whole brain was observed from 1 to 10 days of age, followed by a pronounced increase between 10 and 14 days. Regional studies revealed that the increase in Dopa accumulation was primarily located to striatum. The data suggest an involvement of central catecholamine neurons possibly dopaminergic, terminating in striatum. The decrease in motor activity observed after 15 days of age is interpreted as involvement of maturing inhibitory pathways of noncatecholaminergic origin.