ABSTRACT
The formation of a conditioned taste aversion (CTA) in rats results in neural changes at several levels of the gustatory system. In the nucleus of the solitary tract (NTS), the outstanding feature of the response to a CS is a brief burst of activity that is absent in unconditioned animals. The burst occurs about 1 s after stimulus onset and is seen only in neurons that respond well to sugars and the CS (0.0025 M NaSaccharin). We recorded single neuron activity in response to 12 stimuli from taste cells in the NTS of 8 rats, in which a CTA to NaSaccharin had been created and fully extinguished, and in 8 unconditioned controls. The issue was if the neural effects of the CTA in NTS were reversed with extinction. We recorded the activity of 41 neurons in controls and 55 in CTA-extinguished rats. Responses measured across all neurons were not significantly different in spontaneous activity, breadth of tuning, overall response magnitude to each of the 12 stimuli, relationship among stimuli in taste spaces, or time-course. However, cells in the sugar-sensitive subgroup showed a clear vestige of the conditioning experience. They gave a well-defined burst of activity to the CS, though of reduced amplitude and slightly longer latency than in fully conditioned rats. This burst was no longer associated with the conditioned behavior-which was fully extinguished-though it may be a permanent marker for the once-salient CS that can influence subsequent reacquisition of the aversion.
Subject(s)
Avoidance Learning/physiology , Conditioning, Psychological/physiology , Extinction, Psychological/physiology , Solitary Nucleus/physiology , Taste/physiology , Animals , Evoked Potentials , Female , Neurons/physiology , Rats , Rats, WistarABSTRACT
The literature is divided over whether a conditioned taste aversion (CTA) can be fully extinguished. In Experiment 1, we created a powerful aversion in 54 rats by pairing the taste of 0.0025 M NaSaccharin (CS) with intraperitoneal injections of 127 mg/kg LiCl (US) on 3 occasions. We then offered 23-h deprived rats NaSaccharin for 10 min/day to observe the course of recovery. Extinction occurred in three phases: static, dynamic, and asymptotic. During the static phase (mean = 9.6 days), rats consumed the CS at < 10% of their preconditioned rate. With dynamic recovery (6.0 days), they increased acceptance to > 80% of preconditioning levels. Finally, they achieved asymptote (3.1 days) at 100% acceptance. In Experiment 2, we used 8 additional conditioned rats and 8 unconditioned controls. We followed the same 1-bottle extinction procedure and, again, obtained 100% acceptance. Then we offered both NaSaccharin and water for 8 days at 23 h/day and monitored lick patterns every 6 s to determine taste preferences. The conditioned animals consumed less NaSaccharin than controls on Day 1, and less NaSaccharin as a percentage of total fluid as late as Day 3. For the last 5 days of 2-bottle preference testing, there were no significant differences between the groups with regard to 1. volume of NaSaccharin or water consumed, 2. percentage of total fluid taken as NaSaccharin, 3. consumption of each fluid associated with a meal or taken spontaneously, 4. intake during the light or dark periods, or 5. the characteristics of ingestion, including number of drinking bouts, duration of bouts, number of licks/bout, and rate of licking. Therefore, a robust CTA is subject to complete behavioral extinction.
Subject(s)
Avoidance Learning , Conditioning, Classical , Extinction, Psychological , Taste , Animals , Association Learning/physiology , Drinking/physiology , Female , Lithium Chloride/toxicity , Rats , Rats, WistarABSTRACT
An overview of the development of lasers in medicine is presented. The creation of laser light and its effects on tissue are discussed. Information on clinical application and safety is also included.
