Development of cholinergic inhibitory capacities in the hyperthyroid mouse

Prenatal alcohol exposure and offspring hyperactivity: effects of physostigmine and neostigmine

Rats were fed a liquid diet containing ethanol from days 6-19 of gestation. Controls were pair-fed the same diet with sucrose substituted for ethanol, or received ad lib chow and water. The activity of the offspring was observed at 10, 16, 22 or 28 days-of-age. Overall, offspring exposed to alcohol prenatally were hyperactive compared to controls at 16 and 22 days, but not at 10 or 28 days. Administration of physostigmine had no effect on the activity of any group at 10 days. At 16 days, physostigmine enhanced the activity of the alcohol group, had no effect on the sucrose group, but depressed the activity of the chow group. At 22 days it led to a dose-related decrease in activity in controls but had no effect on the activity of the alcohol treated pups. At 28 days, physostigmine decreased the activity of all three groups. Administration of the quaternary derivative, neostigmine, indicated that the effects of scopolamine at 22 days were probably central in origin. These data indicate that a putative cholinergic/inhibitory system becomes functional in control pups before 22 days, but in pups exposed to alcohol prenatally development is delayed by a number of days.

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 1 mg/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 within-session 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of mouse activity, stimulus reactivity, habituation, and response to amphetamine and scopolamine

Twenty-four litters of non-inbred Swiss-derived mice were used to study the development of locomotion and tendency to approach a novel object in an open field, as well as the effects of dl-amphetamine sulfate and scopolamine hydrochloride (1 or 2 mg/kg IP). Brief (7 min) tests repeated for three consecutive days were preferred in order to obtain information on between-session habituation. Animals tested on days 14-16 showed low levels of activity without changes in successive sessions. In contrast, an adult-like pattern with a high initial activity and marked between-session decrements prevailed on days 21-23 and 28-30. Dl-amphetamine elevated activity only on days 14-16, while scopolamine produced hyperactivity and impaired habituation only on days 21-23 and 28-30. Latency to approach a novel object by untreated animals showed a substantial reduction between the end of the second week and subsequent developmental stages. This went hand in hand with an appearance of latency increases after dl-amphetamine treatments, while an opposite trend in the scopolamine data failed to reach statistical significance. Activity tests in a photocell apparatus at 61-72 days (without prior treatment) showed a reduction of locomotion relative to the level measured in animals from other litters raised in parallel and not subjected to early testing. Overall, the present data and those of the literature indicate that some developmental phenomena in small rodents are relatively insensitive to a variety of organismic, environmental, and test factors, while others (e.g., inverted U-shaped activity trends and successive modifications of the amphetamine profile) depend on complex interactions between several variables.

Effects of serotonergic and cholinergic antagonists on suckling behavior of neonatal, infant, and weanling rat pups

In Experiment 1, Sprague-Dawley rat pups at postnatal days 3-4, 7-8, 10-11, 15-16, and 23-24 were tested for suckling behavior on their anesthesized multiparous dams following administration of metergoline or scopolamine. The serotonergic antagonist, metergoline, inhibited suckling in 3- to 4- and 7- to 8-day-old rat pups, but was not found to influence suckling in older pups. Scopolamine, a cholinergic antagonist, reduced suckling primarily in 3- to 4-day-old pups. In Experiment 2, parity of the maternal female was manipulated to assess whether this variable would influence suckling behavior and the effects of metergoline on suckling of weanlings. Baseline levels of suckling were reduced in 23- to 24-day-old pups of primiparous dams when compared with multiparous-derived offspring. Administration of metergoline increased the amount of time that these primiparous-derived pups spent attached to nipples, but did not influence suckling of offspring of multiparous dams, perhaps as a result of a ceiling effect on suckling behavior in these animals.

Detection of cholinergic mediation of behavior in 7-, 9-, and 12-day old rat pups

A training procedure that permitted infant rats (7, 9, and 12 days old) to acquire a T maze discrimination to escape footshock (Experimental 1) was used to study the effects of the cholinergic antagonist, scopolamine hydrobromide (0, 0.2 mg/kg and 0.8 mg/kg) (Experiment 2). These results indicated that (1) Scopolamine had no effect on T maze choice behavior, unlike previous results for 15- and 23-day old rats, but (2) scopolamine did increase latency to choice in the discrimination task at all ages, an effect previously seen in 15-day old animals, but opposite that seen after scopolamine administration to 23-day old animals or adults. This "paradoxical" effect of scopolamine on response latency is present approximately two weeks prior to earlier estimates of the time course of maturation of the cholinergic system.

Development of serotonin-mediated behavioral inhibition in the hyperthyroid mouse

Experimental hyperthyroidism was induced in neonatal mice by thyroxine injections at 1-3 days of age. Control and thyroxine-treated mice were subsequently tested daily for locomotor activity following injections of methysergide, a serotonin antagonist, or saline from 10 through 15 days of age. Although thyroxine-treated mice were more active than controls, the ontogeny of methysergide-induced disinhibition of locomotor activity was similar for both thyroxine-treated and control mice. The results suggest that the early maturation of serotonin-mediated inhibition of behavioral arousal is not affected by thyroxine-accelerated development. Results are discussed in terms of the specificity of the pharmacological agent, methysergide.

Ontogeny of short- and long-term memory capacities for passive avoidance training in undernourished mice

To assess the effects of early postnatal undernutrition upon the developing abilities of infant and juvenile mice to acquire and retain a passive-avoidance response, we reared mice following birth in either "normally nourished" or "undernourished" conditions by maintaining litter sizes of 6 or 16, respectively. At ages ranging from 7 to 21 days, mice from each nutritional condition were trained to withhold stepping off from a small vibrating platform in order to avoid shock. Following training to a common criterion, separate groups of mice were retained to the same criterion either 1 or 24 hr later. From the comparisons with yoked control groups at each age and retention interval, we conclude that although undernutrition results in some age-related differences in the ability to withhold responding, these are quite small during acquisition within each age group. In contrast, the retention data suggest that undernutrition delayed the development of both short- and long-term memory abilities on this task. In general, these results are similar to earlier data involving discriminated shock-escape wherein undernutrition had little apparent effect upon acquisition at the early ages but rather marked effects upon developing memory system.

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.