Emotional and motivational disorders in adults are often considered to be the result of altered neurodevelopment. Clinical and experimental data provide evidence that serine protease dipeptidyl peptidase-IV (DPP-IV, EC 3.4.14.5) is involved in the pathophysiology of psycho-emotional disorders. Recently, we have shown that adolescent and adult rats exhibit an increase in anxiety and depression-related behaviors after neonatal administration of a synthetic non-competitive inhibitor of DPP-IV, methionyl-2(S)-cyano-pyrrolidine. In the present study, we tested the effects of two competitive, selective DPP-IV inhibitors, sitagliptin (4 mg/kg) and diprotin A (2 mg/kg), administered at postnatal days 5 - 18 on the emotional and motivational behavior of adolescent and adult rats. We observed increased anxiety in one-month-old diprotin A- or sitagliptin-treated rats in the elevated plus maze; diprotin A also enhanced the animals’ anxiety score using a ranked scale for evaluating anxiety and phobias. In the sucrose consumption and preference test, depressive-like behavior was pronounced in both the diprotin A- and sitagliptin-treated one-month-old animals, while only the diprotin A-treated rats exhibited a decrease in sucrose consumption at the age of 2 months. The diprotin A-treated rats also demonstrated behavioral despair and decreased activity in the forced swimming test within 1 - 3 months of age. Increased aggression was observed in 1 - 3-month-old diprotin A-treated rats and in two-month-old sitagliptin-treated rats. These findings support the hypothesis that DPP-IV is involved in the genesis of emotional and motivational disorders. Additionally, the results show that diprotin А impairs the adolescent and adult rats’ behavior more significantly than sitagliptin when the animals were treated with the DPP-IV inhibitors in the early postnatal period.
The heterogeneous nature of depression is well established [
The neurobiological findings from the studies on depression [
Numerous clinical data demonstrate the negative consequences of adverse early-life events in provoking emotional and mood disorders [
Although increasing evidence proves the involvement of neuropeptides in the development of depression and anxiety, there is still a lack of data on the enzymes that cleave neuropeptides, particularly the peptides enriched in proline residues. The unique conformation of the prolyl bond protects the peptides from degradation [
To further study of the contribution of one of the peptidases―DPP-IV in the development of behavioral disturbances, we have recently applied a different approach, which is based on inhibiting of the enzyme in the early postnatal period. Kato T. et al. [
DPP-IV is a multifaceted enzyme, with specificity for unique substrates, such as neuropeptide Y, substance P, peptide YY, endomorphins, a large family of chemokines that are important in the immune system functions, and hormonal peptides belonging to the glucagon superfamily, including glucagon-like peptide-1 [
With this in mind, the current study was performed to compare the consequences of postnatal administration of two well-known competitive DPP-IV inhibitors, sitagliptin and diprotin A, on the emotional and motivational behavior of adolescent and adult rats. We evaluated the animals’ emotional and behavioral disturbances by testing their depression-like behavior, anxiety and social interactions in ontogenesis from 1 to 6 months of age. Additionally, we tested the hypothesis that postnatal modulation of DPP-IV activity may trigger the occurrence of long-lasting behavioral disorders.
The experiments were performed on 59 male Wistar rats (nursery of the Institute of General Pathology and Pathophysiology). The animals were housed in groups of 4 - 7 (each from the same litter) in standard clear plastic cages (37 × 57 × 19 cm) under a natural light/dark cycle, with water and food available ad libitum (except during the sucrose consumption and preference test). All procedures were performed in accordance with the EU Directive 2010/63/EU on the protection of animals used for scientific purposes adopted on September 22, 2010, the Rules of Laboratory Practice in the Russian Federation (Order of the Ministry of Health Care and Social Development of the Russian Federation № 708n of 23.08.2010), and approved by the Ethics Committee of the Institute of General Pathology and Pathophysiology. All behavioral testing occurred between 11:00 and 18:00 hrs.
The DPP-IV inhibitors were intraperitoneally administered to the male Wistar rat pups on postnatal days 5 - 18 (for 14 days) once daily at 0.1 ml per 10 g body weight. Freshly prepared solutions of the DPP-IV inhibitors in saline were used.
Sitagliptin (phosphate monohydrate, MW 523.32) was purchased from Sigma-Aldrich (USA). The approved maximum daily dose of sitagliptin in the clinic is 100 mg; the experimental rats received a sitagliptin dose of 4 mg/kg per day (n = 22) that corresponded to approximately half of the maximum daily dose for humans [
The rats were weighed monthly and subjected to behavioral testing at the ages of one, two, three, and six months. The battery of tests included the elevated plus maze (EPM) (see 2.3.1.), forced swimming test (FST) (see 2.3.2.), anxiety-phobic score (AFS) evaluation (see 2.3.3.), sucrose consumption and preference (SCP) test (see 2.3.4.), and social contact (SC) test (see 2.3.5.). In the majority of the tests, half of the animals in each group were examined on the first day and the other half were examined on the second day (
Days of testing | Tests | Number of rats |
---|---|---|
Days 1 - 2 | Elevated Plus Maze | A half of each group a day |
Day 3 | ? | A day-off |
Days 4 - 5 | Forced swimming test | A half of each group a day |
Days 6 - 7 | Evaluation of anxiety-phobic score | A half of each group a day |
Days 8 - 9 | Adaptation to single housing and stabilization of the consumption level in sucrose consumption/preference test | All the animals |
Days 10 - 11 - 12 | Sucrose consumption/preference test | All the animals |
Days 10 - 11 | Social contact test | A half of each group a day |
point lasted approximately two weeks.
Upon completion of behavioral testing at the age of three months, some of the animals in each group were decapitated using a guillotine, and the brain structures were isolated and frozen in liquid nitrogen for subsequent biochemical and genetic analysis (data not shown). As a result, at the age of 6 months, there were fewer animals in each group: diprotin A (n = 9), sitagliptin (n = 15), and control (n = 11).
The EPM is utilized to assess anxiety and exploration [
Unlike Porsolt’s original FST [
The anxiety-phobic state was evaluated using a method based on a ranked scale consisting of parameters that characterize the species-specific responses of a rat to a series of nine mild test stimuli that induce anxiety and fear [
In this test, the rats were placed in individual standard clear plastic cages (36.5 cm × 20.5 cm × 14 cm) and were provided dry food for four days. The animals were not subjected to food or water deprivation before the test. During the test, each rat was presented with two bottles, one containing tap water and the other containing a 10% sucrose solution. The positions of the bottles were alternated every day to prevent the development of side bias. After two days for adaptation to the chamber and stabilization of the consumption level, the quantities of sucrose (g) and water intake was measured as the difference in the weight (g) of the corresponding bottle every morning for three days. The daily liquid intake (sucrose plus water) was calculated. Sucrose preference (%) was calculated as the percentage of sucrose solution consumption out of the daily liquid intake. The relative sucrose consumption (a percent of the body weight, %) was also calculated. Reduced liquid consumption reflects a decrease in drinking motivation; reduced sucrose consumption indicates the development of anhedonia, a reliable measure of the depression-like state [
The social interaction task was performed in an unfamiliar Plexiglas test cage (37 × 57 × 19 cm) located in an experimental room with indirect red light intensity set at 7 lux above the center of the cage. The floor of the cage was not covered with sawdust, and the cage was deodorized after each test. We assessed contacts between pairs of control or experimental unfamiliar weight-matched males from different litters. The rats were singly housed for two days before testing. Social exploration was observed for 15 min. We calculated the total frequency and duration of non-aggressive and aggressive social contacts. The behaviors that represented non-aggressive social contacts included sniffing, social grooming, crawling under or over the partner and following with non-aggres- sive contact; the behaviors that represented aggressive social contact included following with aggressive contact, attacks, aggressive grooming, biting, and fights.
The statistical analyses were performed using STATISTICA 7.0 for Windows. When the data met the requirements for parametric statistics, the overall effect was first analyzed by a mixed two-way analysis of variance with the treatment as the between-subject factor and the animals’ age as the within-subject factor (repeated measures factor). The six-month-old rats were excluded from the analysis of the within-subject factor effects because there were fewer animals in each group at this time point. The differences between or within groups were evaluated using parametric one-way ANOVA or repeated measures ANOVA followed by the Newman- Keuls post hoc test. When the data did not meet the requirements for parametric statistics, a nonparametric Kruskal-Wallis ANOVA or Freidman ANOVA was employed to evaluate the between and within group effects, respectively. They were followed by a multiple comparisons analysis of the mean ranks and the Wilcoxon matched pairs test with False Discovery Rate (FDR) control [
The two-way ANOVA showed a significant age effect (F = 4139.820; p < 0.001), treatment effect (F = 11.000; p < 0.001) and age x treatment interaction (F = 6.553; p < 0.001). Repeated measures ANOVA showed that the animals’ weights increased from month 1 to month 3 in the experimental and control groups (p < 0.001 in all cases).
The body weights of the postnatal day 5 rats (the day of the first injection) did not differ between the experimental and control groups. One-way ANOVA revealed a difference in the weights of the one-month-old [F(2,56) = 10.864, p < 0.001], two-month-old [F(2,56) = 10.962, p < 0.001], and three-month-old rats [F(2,56) = 7.154, p < 0.01]. The results of the between groups post hoc analysis are shown in
Most of the effects of the DPP-IV inhibitors on anxiety and exploratory behavior in the EPM were observed in 1-month-old rats. According to the Kruskal-Wallis ANOVA, the experimental rats exhibited an increased number of closed arm entries [H (2, N = 59) = 6.598, p < 0.04] and a slightly decreased preference for the open arms [H (2, N = 59) = 6.442, p < 0.04]. The results of post hoc analysis are shown in
We did not observe the signs of anxiety in the two- and three-month-old rats. In the six-month-old diprotin A-treated rats, the Kruskal-Wallis ANOVA revealed an increase in the time spent in the closed arms [H (2, N = 35) = 11.313, p < 0.01]: 284.2 ± 4.1 s in the diprotin-treated animals vs. 249.0 ± 9.3 s in the controls (p = 0.042) and 217.7 ± 17.1 s in the sitagliptin-treated group (p = 0.003), respectively.
The analysis of the animals’ exploratory activity and grooming behavior in the EPM are shown in
Groups | Vertical rearing postures | ||||||||
---|---|---|---|---|---|---|---|---|---|
One month | Two months | Three months | Six months | ||||||
Number | Latency, s | Number | Latency, s | Number | Latency, s | Number | Latency, s | ||
Diprotin A | 11.0 ± 1.2 | 43.5 ± 7.7 | 11.5 ± 1.0* | 15.9 ± 2.9*^ | 8.4 ± 1.0 | 31.5 ± 11.4 | 3.7 ± 0.6 | 35.9 ± 20.3 | |
Sitagliptin | 10.7 ± 0.8 | 38.5 ± 5.3 | 10.3 ± 1.3 | 18.6 ± 3.4+^ | 8.6 ± 1.4 | 29.7 ± 9.8 | 10.4 ± 1.1 | 22.5 ± 4.6 | |
Saline | 9.0 ± 1.0 | 42.3 ± 6.4 | 7.7 ± 1.1 | 30.5 ± 6.6 | 8.9 ± 0.9 | 22.8 ± 6.0 | 6.1 ± 1.0 | 16.8 ± 5.1 | |
Grooming | |||||||||
Number | Latency, s | Number | Latency, s | Number | Latency, s | Number | Latency, s | ||
Diprotin A | 2.5 ± 0.6 | 141.5 ± 18.5 | 6.3 ± 0.8^ | 73.9 ± 8.8*#^ | 4.8 ± 1.0 | 86.5 ± 14.8^ | 3.0 ± 1.3 | 100.5 ± 19.1 | |
Sitagliptin | 4.6 ± 0.7 | 110.0 ± 18.1 | 7.2 ± 0.9* | 68.5 ± 10.6* | 5.1 ± 0.9* | 92.3 ± 13.1 | 4.5 ± 1.2 | 139.9 ± 19.5 | |
Saline | 2.8 ± 0.7 | 128.8 ± 14.4 | 4.3 ± 0.7 | 126.1 ± 14.3 | 2.4 ± 0.5 | 119.9 ± 16.8 | 2.1 ± 0.7 | 155.9 ± 15.7 | |
The * indicates statistically significant difference from the control group (saline-treated rats), p < 0.05; the # indicates statistically significant difference from the sitagliptin-treated group, p < 0.05; the + indicates p = 0.086 compared to the controls (Kruskal-Wallis ANOVA followed by post hoc multiple comparisons analyses of the mean ranks). The ^ indicates statistically significant difference from the values in the same group at the age of one month, p < 0.033 (Freidman ANOVA followed by Wilcoxon matched pairs test with FDR control). Values are given as mean ± SEM (standard error of the mean).
0.05]; however, there was a confirmed decrease in the latency to the first posture in the two-month-old rats [Chi-squared test (N = 17, df = 2) = 9.294, p = 0.010]. The Friedman ANOVA also revealed a significant decrease in the latency to the first vertical posture [Chi-squared test (N = 21, df = 2) = 8.667, p = 0.013] in the two-month-old sitagliptin-treated rats.
The number of grooming episodes was increased in the two-[H (2, N = 58) = 6.394, p < 0.05] and three- month-old sitagliptin-treated rats [H (2, N = 58) = 6.291, p < 0.05] compared to the controls. However, compared to the one-month-old animals from the same group, the number of grooming episodes was not significantly increased, according to the Friedman ANOVA [Chi-squared test (N = 21, df = 2) = 1.506, p > 0.05]. According to the Kruskal-Wallis ANOVA, the two-month-old rats in both experimental groups exhibited a reduced latency to the first grooming episode [H (2, N = 55) = 13.090, p < 0.01] compared to the controls. In the diprotin A-treated group, an analysis of the dynamics of the latency to the first grooming episode confirmed that the values were decreased in the two- and three-month-old rats [Chi-squared test (N = 11, df = 2) = 9.455, p = 0.009]. The decreased latency in the sitagliptin-treated group was not significant [Chi-squared test (N = 18, df = 2) = 2.333, p > 0. 05]. The results of the post hoc analysis are shown in
The total distance traveled in all regions of the EPM decreased with age in the experimental and control groups (F = 78.466, p < 0.001). However, there were no significant differences between the experimental and control groups at any age (F = 1.488, p > 0.05).
A two-way ANOVA showed a main effect of treatment (F = 5.328; p < 0.01) and age (F = 52.156; p < 0.001) on the amount of time the animals engaged in active swimming and a main effect of age (F = 29.477; p < 0.001) on the amount of time engaged in passive swimming. There was no treatment x age interaction in either case.
Only the diprotin A-treated rats exhibited depressive-like behaviors in the FST. According to the one-way ANOVA, the one-month-old rats exhibited a decrease in the amount of time spent in active swimming [F(2,56) = 4.788, p < 0.02] and an increase in the amount of time spent in passive swimming [F(2,56) = 4.767, p < 0.02]. The results of the post hoc analysis are shown in
According to the Kruskal-Wallis ANOVA, the immobility time [H (2, N = 58) = 10.354, p < 0.01] and ID [H
(2, N = 58) = 11.388, p < 0.01] of the one-month-old diprotin A-treated rats were increased compared to the controls (
The AFS only differed in the one-month-old rats [F(2,56) = 5.218, p < 0.01, one way ANOVA]. The diprotin A-treated rats demonstrated a higher anxiety and phobia score, 7.0 ± 0.6 compared to 5.1 ± 0.6 in the controls (p = 0.026, Newman-Keuls post hoc test). The diprotin A-treated rats were also more anxious than the sitagliptin- treated animals, which had an average score of 4.3 ± 0.6 (p = 0.006).
In this test, the depressive-like behavior differed between the experimental groups. The one-month-old animals treated with either diprotin A or sitagliptin demonstrated a decrease in sucrose preference [H (2, N = 59) = 15.643, p < 0.001], relative sucrose consumption [H (2, N = 59) = 15.984, p < 0.001] and daily liquid intake [H (2, N = 59) = 9.580, p < 0.01].
from the diprotin A-treated group exhibited a decrease in sucrose preference [H (2, N = 59) = 6.076, p < 0.05] and relative sucrose consumption [H (2, N = 59) = 7.175, p < 0.03] (
The Friedman ANOVA analysis did not reveal a difference in sucrose preference of the one- to three- month-old control rats: Chi-squared test (N = 20, df = 2) = 4.300, p = 0.116. The diprotin A- and sitagliptin- treated rats showed a gradual increase in sucrose preference up to the control level from one to three months of age: the Friedman ANOVA, Chi-squared test (N = 17, df = 2) = 12.118, p < 0.01 and Chi-squared test (N = 22, df = 2) = 18.909, p ≤ 0.001, respectively. The post hoc analysis revealed a difference between the preference values in the two- and three-month-old rats compared to the one-month-old rats in each experimental group (for all comparisons p < 0.02).
The relative sucrose consumption of the control group gradually decreased with age [the Friedman ANOVA, Chi-squared test (N = 20, df = 2) = 22.500, p < 0.001]. The value of this parameter in the two-month-old rats was lower than in the one-month-old animals; it was also lower in the three-month-old rats than in the one- and two-month-old rats (for all comparisons p < 0.01). The sitagliptin-treated animals also demonstrated a decrease in their relative sucrose consumption [the Friedman ANOVA, Chi-squared test (N = 22, df = 2) = 15.545, p < 0.001]. The relative sucrose consumption of the one-month-old rats exceeded the consumption of two- and three-month-old rats (in both cases p < 0.01). However, unlike the control animals, there was no difference between the values from the two- and three-month-old rats. The Friedman ANOVA analysis did not reveal a difference in the relative sucrose consumption of the one- to three-month-old rats treated with diprotin A: Chi- squared test (N = 20, df = 2) = 0.824, p = 0.662.
According to the Friedman ANOVA, there were no significant changes in the daily liquid intake of the control group from month 1 to month 3 [Chi-squared test (N = 20, df = 2) = 5.564, p = 0.062] (
At the age of one month, only the diprotin A-treated rats showed increased aggression. The time spent in aggressive social contacts was increased [H (2, N = 24) = 8.054, p < 0.02], whereas the total number of non-ag- gressive social contacts [H (2, N = 24) = 7.024, p < 0.03] and time spent in non-aggressive contacts [H (2, N = 24) = 6.142, p < 0.05] were decreased. The results of the post hoc analysis are shown in
At the age of two months, both the diprotin A- and sitagliptin-treated animals demonstrated an increase in the total number of aggressive contacts [H (2, N = 21) = 10.213, p < 0.01] and in the time spent in aggressive contacts [H (2, N = 21) = 11.941, p < 0.01] (
At the age of three months, aggression remained statistically significant only in the diprotin A-treated rats. The animals demonstrated an increased number of total aggressive contacts [H (2, N = 20) = 6.030, p < 0.05] and spent more time in aggressive contacts [H (2, N = 20) = 8.653, p < 0.02] (see
Because the pairs used for the analysis of social interaction in each test were formed by different animals, the
Groups | Two-month-old rats | Three-month-old rats |
---|---|---|
Diprotin A | 65.6 ± 6.4*# | 192.8 ± 85.4+ |
Sitagliptin | 174.8 ± 38.0 | 334.2 ± 61.7 |
Saline | 213.8 ± 57.4 | 453.3 ± 103.2 |
The * indicates statistically significant difference compared to the control group (saline-treated rats), p < 0.05; the # indicates statistically significant difference compared to the sitagliptin-treated group, p < 0.05; the + indicates p = 0.056 compared to the controls (Kruskal-Wallis ANOVA followed by post hoc multiple comparisons analyses of the mean ranks). Values are given as mean ± SEM (standard error of the mean).
analysis of the within-subject factor (age) effect was not performed.
This study is the first to compare the effects of the well-known DPP-IV inhibitors diprotin A and sitagliptin on emotional and motivational behavior in rats after subchronic intraperitoneal administration of the drugs in the early postnatal period. Previously, we have shown that postnatal methionyl-2(S)-cyano-pyrrolidine, a synthetic non-competitive irreversible inhibitor of DPP-IV, causes anxiety- and depression-related behaviors in adolescent and adult rats (from the first to the seventh month) [
Sitagliptin and diprotin A, unlike methionyl-2(S)-cyano-pyrrolidine, are reversible DPP-IV inhibitors that bind to the enzyme with a non-covalent bond. Although they have different binding interfaces on the active site of the enzyme, these DPP-IV inhibitors have similar features in their molecular interactions with the DPP-IV target through three common amino acids (Glu205, Glu206, and Try226) involved in H-bond formation and several residues involved in hydrophobic interactions [
Both the one-month-old diprotin A- and sitagliptin-treated rats demonstrated signs of increased anxiety in the EPM, based on an increased preference for the closed arms. However, only diprotin A led to a marked reduction in the preference for the open arms, while sitagliptin increased the latency to the risk-assessment behavior. The diprotin A-treated rats exhibited increased anxiety, as demonstrated by their anxiety-phobic score at the age of one month. Hence, the diprotin A-treated rats showed more pronounced anxiety compared to sitagliptin-treated animals using the present scheme of DPP-IV inhibitor administration.
Although there were no differences in animals’ locomotor activity in the EPM, the two-month-old diprotin A- and sitagliptin-treated rats did increase their exploratory activity (see
Based on the view that grooming takes place during de-arousal after a stressful experience [
We believe that the decrease in sucrose preference and relative sucrose consumption caused by the DPP-IV inhibitors indicates a decrease in one of the vital motivations to experience pleasure, i.e., anhedonia. At the age of one month, both the diprotin A- and sitagliptin-treated rats showed signs of anhedonia, whereas, at the age of two months, only the diprotin A-treated rats still showed the symptoms of decreased motivation to experience pleasure (see
In principal, both sitagliptin and diprotin A may affect glucose metabolism by enhancing the incretin axis, followed by a reduction in the blood glucose levels [
The results from the FST support the conclusion that administration of the DPP-IV inhibitors in the early postnatal period may induce depressive-like behavior in rats. This test showed the strongest differences in the behaviors of the rats treated with the different DPP-IV inhibitors. According to the data, only the diprotin A-treated animals demonstrated a depressive-like behavior at two months, which was revealed as a reduced ability to escape the aversive situation. It is worth noting that weak symptoms of depressive-like behavior remained in the three-month-old rats, when they did not exhibit reduced sucrose preference and consumption. In contrast, the putative alterations in the blood glucose levels in the sitagliptin-treated rats were not manifested as depression-like behaviors in the FST. If we assume that depressive-like behaviors are associated with changes in glucose metabolism, various tests must detect this behavior at the same time. Thus, it is unlikely that the observed changes are due to glucose metabolism. Instead, they are likely based on the other mechanisms.
On the whole, neonatal administration of diprotin A caused a more pronounced reduction of vital motivations than sitagliptin, thus having a stronger depression-like effect.
We only obtained evidence of reduced motivation for non-aggressive social contacts for the diprotin A-treated rats over a three month period (see
Of particular interest are the aggressive behaviors in the social contact test. Markedly increased aggression was observed in the diprotin A-treated rats over three months, whereas sitagliptin-treated rats only showed an increase at the age of two months. Thus, the animals treated with the different DPP-IV inhibitors develop different susceptibilities to aggression under mild isolation stress.
By comparing the appearance and maintenance of the behavioral disorders in the diprotin A- and sitagliptin- treated, we concluded that, in this study, diprotin A caused more pronounced and long-term consequences, which are comparable to the effects of methionyl-2(S)-cyano-pyrrolidine [
In the present study, we did observe a reduced weight gain in the sitagliptin-treated rats within the first three months of the survey. At first glance, the data do not agree with the data on the absence of changes in body mass index in patients with type 2 diabetes mellitus after 48 months of treatment with the clinically recommended dose of sitagliptin to achieve lower postprandial hyperglycemia [
Recently, Sharma et al. [
In general, systemic administration of the DPP-IV inhibitors diprotin A and sitagliptin in the early postnatal period alters the emotional and motivational behaviors of adolescent and adult rats. Diprotin A exhibits a more significant impact on the animals’ behaviors compared to sitagliptin. We believe that the behavioral disturbances induced by the DPP-IV inhibitors can be used as putative models of mixed anxiety-depression-like disorders with disinhibited aggression upon mild stress provocation. Additionally, the data from the present study demonstrate the involvement of DPP-IV in the genesis of emotional and motivational disorders.
One of the main limitations of this study is that the late effects of inhibitors of DPP-IV were studied in the only period of their administration-PND 5-18. Another limitation is the use of only one dose of each of the inhibitors of DPP-IV. In the present study, blood glucose and incretin levels were not examined at various time points of ontogeny after the administration of the DPP-IV inhibitors in the early postnatal period. We suppose further researches to be performed to ascertain whether neonatal modulation of DPP-IV activity contributes to the genesis of emotional and motivational disorders and through which mechanisms.
We thank Ms. Sofiya Semenyuk and Mrs. Polina Mavrenkova, the students of the Faculty of Psychology, Lomonosov Moscow State University, who kindly assisted in providing the data necessary for the analysis.
These studies were supported by the Russian Foundation for Basic Research (RFBR) (grant number: 15-04- 08784). The RFBR had no role in the design, implementation, analysis, or interpretation of the data, in the preparation of the manuscript, or in the decision to submit the paper for publication. None of the material in this paper has been submitted for publication elsewhere.
The authors have no conflicts of interest to declare.
Nataliya A. Krupina,Nadezhda N. Khlebnikova, (2016) Neonatal Exposure to the Dipeptidyl Peptidase-IV Inhibitors Diprotin A and Sitagliptin Induces Depression-Like Behavior, Anxiety, and Latent Aggression in Adolescent and Adult Rats. Journal of Behavioral and Brain Science,06,167-183. doi: 10.4236/jbbs.2016.64018