br Acknowledgement The authors are grateful for financial su

Acknowledgement The authors are grateful for financial support provided from specific university research (MSMT No 21-SVV/2018).
Introduction Several recent studies have demonstrated that planaria, flatworms notable for their regenerative capabilities, can develop conditioned place preference (CPP). CPP is a Pavlovian conditioning procedure which typically involves measuring the time an organism spends in two distinct yet concurrently accessible environments before and after one of the environments is paired with a rewarding stimulus, often a drug known to be used recreationally in humans and self-administered by laboratory organisms [1,2]. CPP is indicated when the organism allocates more time to the reward-paired environment than it did prior to the pairing. Movement toward the reward-paired environment can also be considered evidence of operant conditioning in which locomotion brings the organism into contact with a conditioned reinforcer. Most often, investigators have used vertebrate models in CPP research, but several investigators have taken advantage of the planarian’s innate and reliable negative phototaxis, which is movement away from a light source, to demonstrate CPP for environments paired with several substances including amphetamine [3] cocaine [4], ethanol [5], nicotine [6], and sucrose [7]. To do so, planaria are first given free access to both light-exposed and opaque halves of a petri dish. Initially, they reliably spend more time in the dark half. The planaria are then restricted to a light-exposed petri dish containing a putative dissolved reinforcing substance. Following this pairing, planaria are again given free access to both light and dark halves. CPP is indicated if more time is then spent in the light half than was recorded prior to the pairing. Given that CPP results with planaria show continuity with vertebrates in that the same substances known to stimulate dopaminergic activity engender CPP across species, it may be of interest to examine if similarities also exist with other transmitter systems. To the best of our knowledge, the behavioral effects of Flutamide mg in planaria has gone unexamined. In vertebrates, administration of histamine has been shown to be aversive. Several investigations have shown that vertebrates will develop a preference for an operandum that produces food alone over an operandum that produces both food and histamine [[8], [9], [10]]. Other investigators have shown that response-contingent histamine will suppress both food-maintained [[11], [12], [13], [14]] and drug-maintained responding [[14], [15], [16]]. If histamine functions as a punisher in vertebrates, we propose it may also produce conditioned place aversion (CPA) in planaria. With CPA, an organism spends less time in an environment after that environment has been paired with a stimulus [17]. We hypothesized that planaria restricted to a dark side of a petri dish containing histamine would subsequently spend more time in the light side of a petri dish than planaria restricted to the dark side of a petri dish containing fresh water.
Materials and methods
Results Fig. 1 depicts results from the individual testing. On average, histamine-exposed planaria spent twice as much time in the light-side of the petri dish as compared to fresh-water exposed controls. A t-test indicated a significant effect of histamine on percent of the session planaria allocated to the light side of the petri dish t (13) = 2.222, p =  .0447. The top panel of Fig. 2 depicts the average number of planaria visible during each observation for all cohorts in the group testing following dark exposure. For both the first and second cohorts, the average number of planaria visible per observation was higher for those exposed to histamine than to control. When the cohorts were combined, a t-test with Welch’s correction for unequal variances determined a significantly higher average count in the histamine-exposed planaria, t (103.1) = 6.835, p <  .0001. The bottom panel of Fig. 2 depicts cumulative counts (the total number of planaria counted during the choice sessions) for each group. The cumulative count for histamine-exposed planaria was 189 and the cumulative count for the control cohorts was 96.