Effects of dorsolateral tegmental lesions on amphetamine- and lithium-induced taste aversions

Effects of heavy particle irradiation and diet on amphetamine- and lithium chloride-induced taste avoidance learning in rats

Rats were maintained on diets containing either 2% blueberry or strawberry extract or a control diet for 8 weeks prior to being exposed to 1.5 Gy of 56Fe particles in the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Three days following irradiation, the rats were tested for the effects of irradiation on the acquisition of an amphetamine- or lithium chloride-induced (LiCl) conditioned taste avoidance (CTA). The rats maintained on the control diet failed to show the acquisition of a CTA following injection of amphetamine. In contrast, the rats maintained on antioxidant diets (strawberry or blueberry extract) continued to show the development of an amphetamine-induced CTA following exposure to 56Fe particles. Neither irradiation nor diet had an effect on the acquisition of a LiCl-induced CTA. The results are interpreted as indicating that oxidative stress following exposure to 56Fe particles may be responsible for the disruption of the dopamine-mediated amphetamine-induced CTA in rats fed control diets; and that a reduction in oxidative stress produced by the antioxidant diets functions to reinstate the dopamine-mediated CTA. The failure of either irradiation or diet to influence LiCl-induced responding suggests that oxidative stress may not be involved in CTA learning following injection of LiCl.

Interaction of haloperidol and area postrema lesions in the disruption of amphetamine-induced conditioned taste aversion learning in rats

Two experiments were run to determine the mechanisms underlying the acquisition of an amphetamine-induced conditioned taste aversion. In the first experiment, it was shown that pretreatment with haloperidol (0.1-0.5 mg/kg, IP) attenuated. but did not prevent, taste aversion learning produced by amphetamine (3 mg/kg, IP). In the second experiment, combining area postrema lesions with haloperidol (0.5 mg/kg) pretreatment completely blocked the acquisition of an amphetamine-induced taste aversion. The results are interpreted as indicating that amphetamine-induced taste aversion learning has both a central component, which is mediated by dopaminergic receptors, and a nondopaminergic peripheral component, which is mediated by the area postrema.

Role of the area postrema in three putative measures of motion sickness in the rat

After thermal cauterization of the area postrema in rats the absence of conditioned taste aversion to sucrose paired with lithium chloride (0.15 M, 3.3 ml/kg) was used as a pharmacologic/behavioral index of area postrema damage. In a subsequent experiment the effects of area postrema lesions on three measures proposed as species-relevant measures of motion sickness were studied, using off-vertical rotation at 150 degrees/s for either 30 or 90 min. Lesions of area postrema did not alter postrotational suppression of drinking or amount of defecation during motion. The initial acquisition of conditioned taste aversion to a novel cider vinegar solution paired with motion was not affected by lesioning of the area postrema, but these taste aversions extinguished more slowly in lesioned rats than in sham-operates or intact controls. Results are discussed in terms of proposed humoral factors which may induce motion sickness and in light of recent data on the role of the area postrema in similar measures in species possessing the complete emetic reflex.

Interactions between radiation and amphetamine in taste aversion learning and the role of the area postrema in amphetamine-induced conditioned taste aversions

Three experiments were run to assess the role of the area postrema in taste aversion learning resulting from combined treatment with subthreshold unconditioned stimuli and in the acquisition of an amphetamine-induced taste aversion. In the first experiment, it was shown that combined treatment with subthreshold radiation (15 rad) and subthreshold amphetamine (0.5 mg/kg, IP) resulted in the acquisition of a taste aversion. The second experiment showed that lesions of the area postrema blocked taste aversion learning produced by two subthreshold doses of amphetamine. In the third experiment, which looked at the dose-response curve for amphetamine-induced taste aversion learning in intact rats and rats with area postrema lesions, it was shown that both groups of rats acquired taste aversions following injection of amphetamine, although the rats with lesions showed a less severe aversion than the intact rats. The results are interpreted as indicating that amphetamine-induced taste aversion learning may involve area postrema-mediated mechanisms, particularly at the lower doses, but that an intact area postrema is not a necessary condition for the acquisition of an amphetamine-induced taste aversion.

Effects of anterior basolateral amygdala lesions on taste aversions produced by high and low oral doses of LiCl and lactose in the rat

Adult male hooded rats (n = 12) with bilateral electrolytic lesions centered on the anterior basolateral amygdala (BLA) were given training using procedures meant to produce two different types of conditioned taste aversions (CTAs) to test whether the disruptive effects of such lesions on this form of learning were dependent upon the dosages of the illness-inducing agents used as unconditioned stimuli (UCSs). The CTAs were produced by either LiCl-induced toxicosis or lactose malabsorption. Comparison with sham-operated control subjects (n = 8) indicated that the disruptive effects of the lesions were inversely related to the dosage level of LiCl but not lactose: whilst the lesions disrupted CTAs produced by a low i.p. dose of LiCl and by a low, but not a high, oral dose of LiCl, they did not alter CTA learning produced by either high or low oral doses of lactose. These results were interpreted as providing further evidence that BLA mediates only certain types of CTA learning.

Orofacial and somatic responses elicited by lithium-, nicotine- and amphetamine-paired sucrose solution

Amphetamine and nicotine share the characteristics of both producing a conditioned taste avoidance response (CTA) via their action within the blood-brain-barrier (BBB) whereas lithium produces a CTA via its action outside of the BBB. Although, at the doses employed, all three drugs produced equally strong CTAs, amphetamine (3 mg/kg)- and nicotine (1 mg/kg)-paired 0.5 M sucrose solution elicited a similar pattern of orofacial and somatic responses which differed from that pattern elicited by a lithium (127.2 mg/kg)-paired sucrose solution. Sucrose paired with either amphetamine or nicotine elicited suppressed ingestion responses of tongue protrusion and paw licking, but did not elicit enhanced rejection responses. On the other hand, sucrose paired with lithium elicited not only suppressed ingestion responses, but also a pattern of enhanced rejection responses of chin rubbing and paw treading. The results suggest that the CTA established by lithium is qualitatively different than the CTA established by amphetamine or nicotine.

Mechanisms of radiation-induced conditioned taste aversion learning

The literature on taste aversion learning is reviewed and discussed, with particular emphasis on those studies that have used exposure to ionizing radiation as an unconditioned stimulus to produce a conditioned taste aversion. The primary aim of the review is to attempt to define the mechanisms that lead to the initiation of the taste aversion response following exposure to ionizing radiation. Studies using drug treatments to produce a taste aversion have been included to the extent that they are relevant to understanding the mechanisms by which exposure to ionizing radiation can affect the behavior of the organism.

Pre-exposure to flavor and conditioned taste aversion: amphetamine and lithium reinforcers

The experiment compared the influence of pre-exposure to a .1% saccharin CS on the conditioned taste aversion induced by lithium chloride (.15 M) and by d-amphetamine (2.0 mg/kg) in 44 female Long-Evans hooded rats. Nonpre-exposed rats displayed substantial lithium- and amphetamine-induced taste aversions while pre-exposed rats (6 days) displayed significant attenuation of taste aversion induced by lithium or amphetamine. Although the aversions induced by these reinforcers are anatomically and pharmacologically independent, manipulations of conditioning variables were not sufficient to dissociate these reinforcers.