Sweet liking in patients with Parkinson's disease Halina Sienkiewicz-Jarosz a , Anna Scinska a, b , Lukasz Swiecicki c , Wanda Lipczynska-Lojkowska a , Wlodzimierz Kuran a , Danuta Ryglewicz a , Marcin Kolaczkowski d , Jerzy Samochowiec e , Przemyslaw Bienkowski b, ⁎ a Department of Neurology I, Institute of Psychiatry and Neurology, Warsaw, Poland b Department of Pharmacology, Institute of Psychiatry and Neurology, Warsaw, Poland c Department of Psychiatry II, Institute of Psychiatry and Neurology, Warsaw, Poland d Department of Medicinal Chemistry, Collegium Medicum, Jagiellonian University, Krakow, Poland e Department of Psychiatry, Pomeranian Medical University, Szczecin, Poland abstract article info Article history: Received 28 November 2012 Received in revised form 13 February 2013 Accepted 6 March 2013 Available online 3 April 2013 Keywords: Parkinson's disease Sweet liking Reward Gustation Olfaction Pleasant tastes and odors are considered phylogenetically old natural rewards and their hedonic evaluation is regarded as a good indicator of the reward system function. The primary aim of the present study was to compare pleasantness ratings of sucrose solutions (1–30%, w/w) and sweet liking/disliking status in 20 patients with Parkinson's disease (PD) and in 20 age-matched healthy controls. In addition, basic sensory aspects of gustatory (intensity ratings, electrogustometric thresholds) and olfactory function (identification abilities in the Sniffin' Stick test) were assessed in both groups. The number of odors rated as pleasant, unpleasant, and neutral was also compared. As expected, the PD patients showed a significant impairment in olfactory identification abilities. There were no differences between the PD patients and controls in electrogustometric thresholds. Rated inten- sity of higher sucrose concentrations did not differ between the groups. The PD patients tended to rate water taste as more intense in comparison with the controls. Pleasantness ratings of sucrose solutions, the proportion of subjects rating 30% sucrose as the most pleasant (sweet likers), and the number of odors rated as pleasant did not differ between the study groups. The present results suggest that PD does not lead to any obvious alterations in pleasantness ratings of chemosensory stimuli. The study requires replication in larger samples. © 2013 Published by Elsevier B.V. 1. Introduction According to the dopamine hypothesis of reward, midbrain dopa- minergic neurons constitute a critical part of the brain reward system and mediate the rewarding effects of food, water, sex, and drugs of abuse [1–5]. The dopamine hypothesis of reward postulates that the rewarding properties of any stimulus are a consequence of dopamine release evoked by this stimulus in the striatum [1,2,5]. The theory says that dopamine deficits may produce anhedonia defined as the inability to experience pleasure and/or decreased interest in pleasur- able activities [1,2,6,7]. It has been found repeatedly that Parkinson's disease (PD) leads to progressive atrophy of both nigrostriatal and mesolimbic dopaminergic pathways (e.g. [8,9]). The dopamine hypothesis of reward prompted some researchers to speculate that symptoms of anhedonia in some patients with idiopathic PD [10,11] are secondary to a hypofunction of dopaminergic neurons [1,2,4–7,11,12]. Experimental evidence linking PD with a decreased experience of pleasure after presentation of natural or chemical rewards is sparse. In fact, two recent studies have found that PD patients and healthy controls gave similar pleasantness ratings to 100-ml samples of vanil- la and chocolate milk [13] and a piece of bread [14]. In a study linking changes in regional cerebral blood flow (rCBF) to monetary reward, PD patients and age-matched controls presented distinct patterns of rCBF increases in response to monetary reward but subjective value of earnings did not differ between the two groups [15]. Sweet taste and pleasant odors are considered phylogenetically old natural rewards and their hedonic evaluation is regarded as a good in- dicator of the reward system function (for review and discussion, see [16–19]). Interestingly, there are large differences among human sub- jects in the degree to which they like highly sweetened foods. Most in- dividuals can be classified into one of two categories: “sweet dislikers”, who show dislike for highly concentrated sucrose, and “sweet likers”, who show increasing liking even for very high sucrose concentrations [20–22]. In line with a hypothesis linking drug addictions with abnor- malities in brain reward mechanisms, sweet liking can be a phenotypic marker of patients with cocaine dependence [23] and alcoholics with a paternal history of alcoholism [24]. Surprisingly, in a recent study, the proportion of sweet likers did not differ between healthy controls and unipolar or bipolar depression patients [22]. Journal of the Neurological Sciences 329 (2013) 17–22 ⁎ Corresponding author at: Department of Pharmacology, Institute of Psychiatry and Neurology, 9 Sobieskiego St., 02-957 Warsaw, Poland. Tel./fax: +48 22 842 76 44. E-mail address: bienkow@ipin.edu.pl (P. Bienkowski). 0022-510X/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.jns.2013.03.005 Contents lists available at SciVerse ScienceDirect Journal of the Neurological Sciences journal homepage: www.elsevier.com/locate/jns