Food deprivation alters dopamine utilization in the rat prefrontal cortex and asymmetrically alters amphetamine-induced rotational behavior

The effects of 24 and 48 h of food deprivation on changes in the activity of dopaminergic (DAergic) neurons and D-amphetamine-induced rotational behavior were studied in male and female Long-Evans rats. Food deprivation selectively altered 3,4-dihydroxyphenylacetic acid (DOPAC) in the medial prefrontal cortex (PFC) but not in the nucleus accumbens or striatum: PFC DOPAC was significantly increased and decreased bilaterally after 24 and 48 h of food deprivation, respectively. Left greater than right hemispheric asymmetries were seen for DOPAC and DOPAC/DA in the control animals. In a separate experiment, 24 h of food deprivation enhanced right rotational behavior, while 48 h significantly increased left rotational behavior. The results are discussed in terms of food deprivation's effects on mesocortical DAergic neurons, previous work on cortical modulation of striatal function and how these effects on rotational behavior may be determined by brain asymmetry.

Exposure to low doses of the environmental chemical dieldrin causes behavioral deficits in animals prevented from coping with stress

Experiments were conducted which assessed the effects of low doses of an environmental contaminant in conjunction with various forms of stress. Rats were given acute doses (0, 0.5, 1.5, 4.5 mg/kg) of the chemical dieldrin and subsequently exposed to a series of 40 escapable shocks, identical inescapable shocks, or no shock in an operant chamber. Eight hours later, the subjects were re-exposed in a shuttlebox to footshock which was escapable upon performance of an FR-2 shuttle response. Escape deficits which were related in magnitude to the size of the dieldrin dose were found in the inescapable shock group but not in the escapable shock or no shock groups. The data suggest that experience with the lack of control over stress is critical in determining the behavioral effects of the agent and that the behavioral effects caused by uncontrollable stress may be exacerbated by concurrent exposure to such compounds. These results are discussed in terms of previous studies on the behavioral actions of dieldrin, the response to uncontrollable stress and the common neuronal systems that may be involved.

Changes in d-amphetamine elicited rotational behavior in rats exposed to uncontrollable footshock stress

Male and female rats, selected on the basis of their rotational behavior in response to d-amphetamine, were exposed to either escapable footshock stress, inescapable footshock stress or no stress and were then given a shuttlebox escape task on the subsequent day. Following testing, the magnitude and direction of the animals' rotational responses to d-amphetamine were determined again. Inescapable footshock stress induced a selective change in the direction and intensity of rotational behavior that was dependent upon the subjects' sex and preexisting rotational bias. Right-rotating males and left-rotating females shifted their directional bias toward the opposite side, while left-rotating males and right-rotating females displayed increased rotation in their pre-stress direction. Significant correlations were also noted between the intensity of pre-stress rotational behavior and performance on the shuttlebox shock escape task. The results are discussed with respect to stress' actions on the mesocortical dopamine system and how this system's sex-dependent asymmetrical organization may subserve part of the organism's general reaction to uncontrollable stress.

Food deprivation and stimulant self-administration in rats: differences between cocaine and d-amphetamine

The effects of food deprivation (24 h) on response rates of rats self-administering d-amphetamine and cocaine were compared. Food deprivation clearly increased rates of responding for both drugs but did so to a significantly greater extent for cocaine than for d-amphetamine. Consistent with other findings, the results suggest that the neural substrates underlying cocaine and d-amphetamine reinforcement are not identical.

Selective enhancement of dopamine utilization in the rat prefrontal cortex by food deprivation

Previous studies have indicated that food deprivation exerts various effects on brain neurotransmitters and that mild stress causes a selective enhancement of dopamine activity in the rat medial prefrontal cortex. In the present study it was found that in rats 24 h of food deprivation produced an increase in levels of the dopamine metabolite 3,4-dihydroxyphenylacetic acid in the medial prefrontal cortex but not in the nucleus accumbens or caudate-putamen. This selective increase in mesocortical dopamine activity is comparable to that found with mild footshock stress exposure and indicates that food deprivation may function as a stressor.

Differences in spontaneous and amphetamine-induced rotational behavior, and in sensitization to amphetamine, among Sprague-Dawley derived rats from different sources

Nocturnal rotational behavior was found to vary severalfold among Sprague-Dawley derived rats obtained from seven different breeders; net rotations per night (18 hours) varied from 5.0 to 31.0 in males and from 6.2 to 42.4 in females. Rats from three sources were tested twice (a week between tests) for rotation induced by d-amphetamine. Rats from two sources showed evidence of sensitization to d-amphetamine, there being significantly greater rotation in response to the second dose than in response to the first dose; the d-amphetamine-induced rotational behavior of rats from the third source did not significantly change from one week to the next. However, the latter rats had a greater initial response to the first dose of d-amphetamine than did rats from the other two breeders. Further analysis revealed that, among rats from all three breeders, rats rotating weakly in response to d-amphetamine on the first test tended to rotate more on the second test whereas rats rotating strongly in response to d-amphetamine on the first test tended to rotate less on the second test. This relationship was found to apply to previously collected data as well and was discussed with reference to a proposed mechanism involving asymmetry in sensitization to d-amphetamine-induced release of striatal dopamine. Interindividual differences among seemingly similar experimental subjects appear to contribute importantly to reported differences in results among laboratories.