Acute N-methyl-D-aspartate receptor hypofunction induced by MK801 evokes sex-specific changes in behaviors observed in open-field testing in adult male and proestrus female rats

Abstract

Schizophrenia is a complex constellation of positive, negative and cognitive symptoms. Acute administration of the non-competitive antagonist of the N-methyl-d-aspartate receptor (NMDAR) dizocilpine (MK801) in rats is one of few preclinical animal models of this disorder that has both face and/or construct validity for these multiple at-risk behavioral domains and predictive power for the efficacy of therapeutic drugs in treating them. This study asked whether and to what extent the rat NMDAR hypofunction model also embodies the sex differences that distinguish the symptoms of schizophrenia and their treatment. Thus, we compared the effects of acute MK801, with and without pretreatment with haloperidol or clozapine, on seven discrete spontaneous open-field activities in adult male and female rats. These analyses revealed that MK801 was more effective in stimulating ataxia and locomotion and inhibiting stationary behavior in females while more potently stimulating stereotypy and thigmotaxis and inhibiting rearing and grooming in males. Haloperidol and clozapine pretreatments had markedly different efficacies in terms of behaviors but strong similarities in their effectiveness in male and female subjects. These results bear intriguing relationships with the complex male/female differences that characterize the symptoms of schizophrenia and suggest possible applications for acute NMDAR hypofunction as a preclinical model for investigating the neurobiology that underlies them.

Figure 1

Effects of MK801 and neuroleptic pretreatments on locomotion. All data are expressed as group means ± SEM. A: Line graphs showing the number of line crosses made per minute during the 15 minute testing session by male (right side) and female (left side) rats that were either vehicle-injected (CTRL, black squares) or treated with 0.05 mg/kg MK801 (0.05 MK, open triangles), 0.1 mg/kg MK801 (0.1 MK, open diamonds) or with 0.2 mg/kg MK801 (0.2 MK, grey circles). B: Line graphs showing the mean number of lines crossed per minute during the 15 minute testing session by male (right side) and female (left side) rats that were treated with 0.2 mg/kg MK801 (0.2 MK, grey circles), or were pretreated with 0.04 mg/kg haloperidol (0.04 HDL, open triangles), 0.08 mg/kg haloperidol (0.08 HDL, open squares), 5 mg/kg clozapine (5 CLZ, inverted triangles) or with 10 mg/kg clozapine (10 CLZ, open diamonds) followed by 0.2 mg/kg MK801. C: Bar graphs showing the total number of line crosses for the 15 minute testing session by female (white bars) and male (black bars) in all treatment groups. Single asterisks (*) indicate a significant difference of p<0.05 compared to control, double asterisks (**) indicate a significant difference of p<0.001 compared to control; pound signs (#) indicate a significant difference of p<0.001 compared to MK801. Significant sex differences are indicated by horizontal bars; single asterisks indicate a significant difference of p<0.05, double asterisks indicate a significant difference of p<0.001.

Figure 2

Effects of MK801 and neuroleptic pretreatments on thigmotaxis. All data are expressed as group means ± SEM. A: Line graphs showing the percentages of locomotor time spent in thigmotaxis per minute during the 15 minute testing session by male (right side) and female (left side) rats that were either vehicle-injected (CTRL, black squares) or treated with 0.05 mg/kg MK801 (0.05 MK, open triangles), 0.1 mg/kg MK801 (0.1 MK, open diamonds) or with 0.2 mg/kg MK801 (0.2 MK, grey circles). B: Line graphs showing the percentages of locomotor time spent in thigmotaxis per minute during the 15 minute testing session by male (right side) and female (left side) rats that were treated with 0.2 mg/kg MK801 (0.2 MK, grey circles), or were pretreated with 0.04 mg/kg haloperidol (0.04 HDL, open triangles), 0.08 mg/kg haloperidol (0.08 HDL, open squares), 5 mg/kg clozapine (5 CLZ, inverted triangles) or with 10 mg/kg clozapine (10 CLZ, open diamonds) followed by 0.2 mg/kg MK801. C: Bar graphs showing the total percent time of locomotion spent in thigmotaxis for the 15 minute testing session by female (white bars) and male (black bars) in all treatment groups. Single asterisks (*) indicate a significant difference of p<0.05 compared to control, double asterisks (**) indicate a significant difference of p<0.001 compared to control; pound signs (#) indicate a significant difference of p<0.001 compared to MK801. Significant sex differences are indicated by horizontal bars; single asterisks indicate a significant difference of p<0.05, double asterisks indicate a significant difference of p<0.001.

Figure 3

Effects of MK801 and neuroleptic pretreatment on rearing. All data are expressed as group means ± SEM. A: Line graphs showing the number of rears made per minute during the 15 minute testing session by male (right side) and female (left side) rats that were either vehicle-injected (CTRL, black squares) or treated with 0.05 mg/kg MK801 (0.05 MK, open triangles), 0.1 mg/kg MK801 (0.1 MK, open diamonds) or with 0.2 mg/kg MK801 (0.2 MK, grey circles). B: Line graphs showing the mean number of rears made per minute during the 15 minute testing session by male (right side) and female (left side) rats that were treated with 0.2 mg/kg MK801 (0.2 MK, grey circles), or were pretreated with 0.04 mg/kg haloperidol (0.04 HDL, open triangles), 0.08 mg/kg haloperidol (0.08 HDL, open squares), 5 mg/kg clozapine (5 CLZ, inverted triangles) or with 10 mg/kg clozapine (10 CLZ, open diamonds) followed by 0.2 mg/kg MK801. C: Bar graphs showing the total number of rears made during the 15 minute testing session by female (white bars) and male (black bars) in all treatment groups. Single asterisks (*) indicate a significant difference of p<0.05 compared to control, double asterisks (**) indicate a significant difference of p<0.001 compared to control; pound signs (#) indicate a significant difference of p<0.001 compared to MK801. Significant sex differences are indicated by horizontal bars; single asterisks indicate a significant difference of p<0.05, double asterisks indicate a significant difference of p<0.001.

Figure 4

Effects of MK801 and neuroleptic pretreatment on grooming. All data are expressed as group means ± SEM. A: Line graphs showing the percent time spent grooming per minute during the 15 minute testing session by male (right side) and female (left side) rats that were either vehicle-injected (CTRL, black squares) or treated with 0.05 mg/kg MK801 (0.05 MK, open triangles), 0.1 mg/kg MK801 (0.1 MK, open diamonds) or with 0.2 mg/kg MK801 (0.2 MK, grey circles). B: Line graphs showing the percent time spent grooming per minute during the 15 minute testing session by male (right side) and female (left side) rats that were treated with 0.2 mg/kg MK801 (0.2 MK, grey circles), or were pretreated with 0.04 mg/kg haloperidol (0.04 HDL, open triangles), 0.08 mg/kg haloperidol (0.08 HDL, open squares), 5 mg/kg clozapine (5 CLZ, inverted triangles) or with 10 mg/kg clozapine (10 CLZ, open diamonds) followed by 0.2 mg/kg MK801. C: Bar graphs showing the total percent time spent grooming during the 15 minute testing session by female (white bars) and male (black bars) in all treatment groups. Single asterisks (*) indicate a significant difference of p<0.05 compared to control, double asterisks (**) indicate a significant difference of p<0.001 compared to control; pound signs (#) indicate a significant difference of p<0.001 compared to MK801. Significant sex differences are indicated by horizontal bars; single asterisks indicate a significant difference of p<0.05, double asterisks indicate a significant difference of p<0.001.

Figure 5

Effects of MK801 and neuroleptic pretreatment on stationary behavior. All data are expressed as group means ± SEM. A: Line graphs showing the percent time spent stationary per minute during the 15 minute testing session by male (right side) and female (left side) rats that were either vehicle-injected (CTRL, black squares) or treated with 0.05 mg/kg MK801 (0.05 MK, open triangles), 0.1 mg/kg MK801 (0.1 MK, open diamonds) or with 0.2 mg/kg MK801 (0.2 MK, grey circles). B: Line graphs showing the percent time spent stationary per minute during the 15 minute testing session by male (right side) and female (left side) rats that were treated with 0.2 mg/kg MK801 (0.2 MK, grey circles), or were pretreated with 0.04 mg/kg haloperidol (0.04 HDL, open triangles), 0.08 mg/kg haloperidol (0.08 HDL, open squares), 5 mg/kg clozapine (5 CLZ, inverted triangles) or with 10 mg/kg clozapine (10 CLZ, open diamonds) followed by 0.2 mg/kg MK801. C: Bar graphs showing the total percent time spent stationary during the 15 minute testing session by female (white bars) and male (black bars) in all treatment groups. Single asterisks (*) indicate a significant difference of p<0.05 compared to control, double asterisks (**) indicate a significant difference of p<0.001 compared to control; pound signs (#) indicate a significant difference of p<0.001 compared to MK801. Significant sex differences are indicated by horizontal bars; single asterisks indicate a significant difference of p<0.05, double asterisks indicate a significant difference of p<0.001.

Figure 6

Effects of MK801 and neuroleptic pretreatment on stereotypic behavior. All data are expressed as group means ± SEM. A: Line graphs showing the percent time engaged in stereotypy per minute during the 15 minute testing session by male (right side) and female (left side) rats that were either vehicle-injected (CTRL, black squares) or treated with 0.05 mg/kg MK801 (0.05 MK, open triangles), 0.1 mg/kg MK801 (0.1 MK, open diamonds) or with 0.2 mg/kg MK801 (0.2 MK, grey circles). B: Line graphs showing the percent time engaged in stereotypy per minute during the 15 minute testing session by male (right side) and female (left side) rats that were treated with 0.2 mg/kg MK801 (0.2 MK, grey circles), or were pretreated with 0.04 mg/kg haloperidol (0.04 HDL, open triangles), 0.08 mg/kg haloperidol (0.08 HDL, open squares), 5 mg/kg clozapine (5 CLZ, inverted triangles) or with 10 mg/kg clozapine (10 CLZ, open diamonds) followed by 0.2 mg/kg MK801. C: Bar graphs showing the total percent time engaged in stereotypy during the 15 minute testing session by female (white bars) and male (black bars) in all treatment groups. Single asterisks (*) indicate a significant difference of p<0.05 compared to control, double asterisks (**) indicate a significant difference of p<0.001 compared to control; pound signs (#) indicate a significant difference of p<0.001 compared to MK801. Significant sex differences are indicated by horizontal bars; single asterisks indicate a significant difference of p<0.05, double asterisks indicate a significant difference of p<0.001.

Figure 7

Effects of MK801 and neuroleptic pretreatment on ataxia. All data are expressed as group means ± SEM. A: Line graphs showing the number of ataxic events occurring per minute during the 15 minute testing session by male (right side) and female (left side) rats that were either vehicle-injected (CTRL, black squares) or treated with 0.05 mg/kg MK801 (0.05 MK, open triangles), 0.1 mg/kg MK801 (0.1 MK, open diamonds) or with 0.2 mg/kg MK801 (0.2 MK, grey circles). B: Line graphs showing the mean number of ataxic events occurring per minute during the 15 minute testing session by male (right side) and female (left side) rats that were treated with 0.2 mg/kg MK801 (0.2 MK, grey circles), or were pretreated with 0.04 mg/kg haloperidol (0.04 HDL, open triangles), 0.08 mg/kg haloperidol (0.08 HDL, open squares), 5 mg/kg clozapine (5 CLZ, inverted triangles) or with 10 mg/kg clozapine (10 CLZ, open diamonds) followed by 0.2 mg/kg MK801. C: Bar graphs showing the total number of ataxic events occurring during the 15 minute testing session by female (white bars) and male (black bars) in all treatment groups. Single asterisks (*) indicate a significant difference of p<0.05 compared to control, double asterisks (**) indicate a significant difference of p<0.001 compared to control; pound signs (#) indicate a significant difference of p<0.001 compared to MK801. Significant sex differences are indicated by horizontal bars; single asterisks indicate a significant difference of p<0.05, double asterisks indicate a significant difference of p<0.001.