Ontogenetic differences in ethanol's motivational properties during infancy

Pairing a conditioned stimulus (CS) with ethanol generally produces aversion for that CS in adult rodents. However, infant rats (PD1-PD3) exposed to ethanol demonstrate appetitive reinforcement to ethanol (Nizhnikov, Varlinskaya, Petrov, & Spear, 2006; Petrov, Varlinskaya, & Spear, 2003). This sensitivity to the appetitive properties of ethanol during infancy may be transient, as during the second postnatal week rat pups tend to exhibit conditioned aversions to flavors paired with ethanol. The present study examined changes in the motivation properties of ethanol through ontogeny and the neurobiology underlying these changes. Rat pups were exposed to a taste conditioning procedure on PD4 or PD12. Rat pups were intraorally infused with 2.5% of their body weight of saccharin solution (0.1%) and immediately after injected intraperitoneolly (i.p.) with one of six doses of ethanol (0.0-2.0 g/kg). A day later pups were given saccharine infusions and percent body weight gain was used as an index of ethanol's reinforcing effects. PD4 pups expressed appetitive reinforcement to ethanol, as indicated by greater saccharin intake, as compared to control counterparts and to the older PD12 pups. Subsequent experiments revealed that PD4 pups were less sensitive to the aversive properties of the drug than PD12 pups. The older pups found high doses of ethanol aversive while PD4 rat pups did not condition aversions to this dose of ethanol after a single trial. A similar pattern of results was observed between the low doses of ethanol and the highest doses of a kappa opioid agonist. The PD12 animals did not condition to the kappa opioid agonist, while the younger rats expressed an appetitive response. These results illustrate an ontogenetic change in the motivational properties of ethanol, with sensitivity to its appetitive properties declining and responsiveness to the aversive properties increasing with age during early infancy.

Olfactory Conditioning of Positive Performance in Humans

Olfactory conditioning effects have been widely demonstrated in the animal literature but more seldom in human populations and rarely of consciously controlled human behaviors. Building upon previous work on negative performance, we report the first experimental evidence that odors can be used effectively in a classical conditioning paradigm to positively influence human behavior. In the present study, underachieving schoolchildren experienced unexpected success at a paper-and-pencil task in the presence of an ambient odor. When they later experienced the same odor again, performance on other tasks was superior to that of relevant control groups. These data substantially extend previous results on human olfactory classical conditioning and show that odors potentially can be used to exert positive influences on human behavior.

Infantile sensitivity to ethanol's motivational effects: Ethanol reinforcement during the third postnatal week

BACKGROUND

Although tests specific to newborn rats have frequently verified their susceptibility to the reinforcing properties of ethanol, demonstration of comparable reinforcing effects in older infants has been elusive. Using a second-order conditioning procedure, the present study assessed in preweanling rats whether pairing with early postabsorptive effects of ethanol would render intraorally delivered gustatory stimuli capable of positive reinforcement for association with a salient texture. Direct reinforcing effects of ethanol were also evaluated through intake tests of gustatory stimuli previously paired with the drug. Blood ethanol levels (BELs) were determined for each of the ethanol doses used.

METHODS

Pups (14 days old) were stimulated with intraoral infusion of sucrose (10% v/v), water, or quinine (0.0045% w/v) 5 minutes after being intragastrically (i.g.) administered 0.00, 0.25, 0.50, or 2.00 g/kg ethanol (Experiments 1 and 2). These stimuli were then briefly presented while pups experienced a rough texture (sandpaper). Rats were subsequently evaluated in a 2-way texture location test (sandpaper vs smooth surface). In Experiment 3, sucrose, water, or quinine was paired with early postabsorptive effects of ethanol (0.00, 0.50, or 2.0 g/kg). Consumption of these stimuli was later assessed. Motor activity patterns during the intake test were also evaluated. In Experiment 4, BELs corresponding to 0.25, 0.50, or 2.0 g/kg ethanol were determined 5 and 20 minutes after i.g. administration (time periods were in accord with the onset and offset of intraoral stimulation used in the previous experiments).

RESULTS

Intraoral infusion of sucrose, water, or quinine, while under a state of sobriety and paired with sandpaper, resulted in roughly 50% preference for this texture. Sandpaper preferences were significantly elevated in pups that had experienced sucrose or water in a nonsober state-while under the effects of ethanol (Experiments 1 and 2). This indicated reinforcing effects of the ethanol intoxication. Pairing ethanol intoxication directly with consumption of sucrose, water, or quinine did not affect their later consumption. Yet, there were clear indications that this pairing resulted in conditioned behavioral activity patterns. Blood ethanol levels corresponding to the ethanol doses used here ranged between 10 and 150 mg%.

CONCLUSIONS

Infants appear sensitive to pharmacological reinforcing properties of low and relatively high ethanol doses. This sensitivity was revealed indirectly, by pairing gustatory stimuli with ethanol intoxication and then allowing these stimuli to act as second-order reinforcement for a quite different (tactile) stimulus. Behavioral activation elicited by the gustatory stimuli previously paired with a state of intoxication seems to compete with the expression of ethanol's motivational properties as assessed through intake tests.

Repetitive exposures to a surrogate nipple providing nutritive and non-nutritive fluids: effects on suckling behavior of the newborn rat

Responsiveness to a surrogate nipple providing water, 0.1% saccharin, 10% sucrose, pedialyte, or milk was tested in naïve-to-suckling newborn rats during six 10-min exposures, one every 1.5 h over a 7.5 h period. Across a succession of exposures, newborn rats repeatedly attached to and ingested milk from a surrogate nipple, yielding significant body weight gain and increased concentration of blood plasma glucose. Initially, pups ingested considerable amounts of saccharin and sucrose, but then dramatically decreased their consumption of these fluids across the experimental sessions. Intake of milk was significantly higher than that of all other substances. Blood glucose concentration in pups treated with water, saccharin, sucrose, and pedialyte did not differ significantly from that of non-treated pups. The present data suggest a potential contribution of a fluid's palatability and nutritive value in the persistence and efficacy of diet intake for neonatal rats in the context of suckling behavior.

Classical conditioning of breathing pattern after two acquisition trials in 2-day-old mice

The aim of the present study was to test whether breathing pattern conditioning may occur just after birth. We hypothesized that sensory stimuli signaling the resumption of maternal care after separation may trigger an arousal and/or orienting response accompanied with concomitant respiratory changes. We performed a conditioning experiment in 2-day-old mice by using an odor (lemon) as the conditioned stimulus (CS) and maternal care after 1 h without the mother as the unconditioned stimulus (US). Each pup underwent two acquisition trials, in which the CS was presented immediately before (experimental paired group, n = 30) or 30 min before (control unpaired group, n = 30) contact with the mother. Conditioning was tested by using noninvasive whole body plethysmography to measure the respiratory response to the CS for 1 min. We found significantly stronger respiratory responses to the CS in the experimental group than in the control group. In contrast, somatomotor activity did not differ significantly between groups. Our results confirm the sensitivity of breathing to conditioning and indirectly support the hypothesis that learned feedforward processes may complement feedback pathways during postnatal maturation of respiratory control.