Norman E. Spear

State-dependent retention in humans induced by alterations in affective state

Three experiments were conducted to determine whether an internal negative affective state might interact with human recall of verbal material. Threat of electrical shock accompanied both or neither presentation of words and a recall test, or one but not the other. The question was whether the internal context or affective state caused by the threat, during only learning or only recall, would induce state-dependent retention (poorer recall when the internal states accompanying learning and recall are different than when they are the same). The results indicated that a shift in affective state may induce state-dependent retention, but the conditions necessary for this effect remain unclear.

Alterations in the reinforcing efficacy of cocaine in adult rats following prenatal exposure to cocaine

Adult male rats gestationally exposed to cocaine and nonexposed control offspring were examined for differences in operant responding for cocaine and sucrose reinforcement. Offspring were derived from dams that had received subcutaneous injections of 40 mg/kg/3cc cocaine hydrochloride daily on gestational Days 8-20 and nontreated control dams. Although no prenatal treatment differences were seen when the animals lever pressed for sucrose pellets on a progressive-ratio (PR) schedule, adult offspring prenatally exposed to cocaine were observed to exhibit an enhanced rate of cocaine intravenous self-administration on a fixed-ratio 5 (FR-5) schedule along with a marked decrease in break point on the PR reinforcement schedule. These results suggest that the reinforcing efficacy of cocaine may be reduced in animals with a prenatal history of cocaine exposure.

Acute alcohol exposure during gestational day 8 in the rat: Effects upon physical and behavioral parameters

Pregnant rats on the eighth day of gestation (GD 8) received 2 intraperitoneal injections (0.015 ml/g body weight) spaced by an interval of 4 hours, of either 0, 6, 12 18, or 24% (v/v) alcohol solution. Brains of pups sacrificed 24 hours after delivery revealed a dose-related impairment in hemispheric and cerebellar length, width and weight. Statistically significant differences were also observed in body weights of culled pups during Post-partum Day 1. An open field test performed when offspring were 40-45 days old demonstrated a dose-dependent increase in ambulation and rearing scores for both males and females and in defecation scores for females only. Although behavioral studies revealed no effects on acquisition or retention of an active avoidance response, there was a dose-dependent impairment in transfer to passive avoidance conditioning. The present results demonstrate that in the rat, an alcohol insult during GD 8 is sufficient to induce morphological and behavioral alterations in the offspring.

Weanlings' transfer of conditioned ethanol aversion from olfaction to ingestion depends on the unconditioned stimulus

Weanling (21-day-old) rats were exposed to an alcohol odor paired with either an interoceptive (apomorphine-induced illness) or exteroceptive (footshock-induced distress) reinforcer. Twenty-four hours later, ethanol preferences were measured in a locational olfactory test (ethanol vs lemon odor) or an ingestion test (5.6% v/v ethanol vs 0.25% v/v citric acid solution). Weanling rats expressed substantial olfactory aversions, independent of the reinforcer employed in conditioning. During the drinking test, however, only rats that had experienced the ethanol odor paired with internal malaise showed a significant reduction in the intake of the ethanol solution when compared to unpaired controls. Furthermore, rats that had experienced the ethanol odor paired with external distress drank significantly more of the ethanol solution than their controls. These results provide further evidence that olfactory experiences with ethanol can lead to changes in ethanol ingestion, and indicate that the nature of the unconditioned stimulus is critical in establishing the ingestive effect.

The presence of home-cage stimuli attenuates spontaneous-alternation deficits in rats with septal lesions

The present experiment examined the effects of the olfactory context on spontaneous-alternation performance of young adult, female rats following septal lesions. Separate groups of rats were given either septal lesions (n=24) or control surgery (n=24), and then tested on the 8th postoperative day for spontaneous alternation across three trials. Half of the rats in each surgical group were tested in the presence of home-cage nest shavings located in a tray beneath the apparatus; the other septal and control groups were tested over clean, unsoiled wood shavings. Rats tested in the novel, clean-shavings environment showed the typical perserverative deficits in spontaneous alternation associated with septal lesions. Rats with septal lesions tested in the presence of the familiar olfactory stimuli from the home-litter shavings alternated at rates similar to those of controls. The training context had no effect on the alternation performance of controls. These results were interpreted as indicating that rats with septal lesions are differentially responsive to sensory conditions. In particular, the familiar olfactory stimuli may be especially potent in reducing the “hyperreactivity” resulting from the altered sensory processing following septal lesions. Differential salience of olfactory stimuli following such lesions may be related to reports of shifts in social behavior following disruption of septal functioning.

Facilitation of long-delay conditioned taste aversion in weanling rats

The impact of prior odor or taste conditioning on long-delay conditioned taste aversion in weanling rats was examined in two experiments. In Experiment 1, target conditioning consisted of saccharin paired 1.5 h later with an injection of LiCl. Weanlings given an odor or a different taste paired immediately with LiCl prior to long-delay conditioning showed significantly stronger saccharin aversions than did subjects exposed to the odor or taste unpaired with LiCl. The results of Experiment 2 indicated that the delay facilitation was not the result of any residual effect of LiCl; LiCl alone the day before delay conditioning did not enhance conditioned saccharin aversions. The results are discussed with respect to maturational and experiential interpretations of age-related differences in transfer of training and short-term memory.