Sex differences in mania phenotype and ethanol consumption in the lateral hypothalamic kindled rat model

Abstract

Sex differences have been observed in mania phenotypes in humans. However the mechanisms underlying this difference are poorly understood. Activating the lateral hypothalamus is implicated in manic-like behaviors in rodents. Using newly established lateral hypothalamus kindled (LHK) rat mania model, we investigated sex differences of manic-like behaviors and its correlation with voluntary ethanol intake. We stimulated the lateral hypothalamus bilaterally in the male and female Wistar rats over five consecutive days. We recorded and quantified kindling-induced behaviors for each individual animal. We also assessed ethanol consumption using a two-bottle choice ethanol drinking as well as circadian locomotor activity counts daily throughout the experiment. We found notable sex differences in several aspects of manic-like behaviors during kindling. Males exhibited a significantly increased locomotor activity during the light phase, and reduced rest interval. On the other hand, females displayed significantly higher ethanol consumption and more frequent rearing behavior. However, no sex differences were present in the duration of sexual, feeding or grooming behaviors or in dark-phase activity counts. The excessive alcohol intake in LHK female rats is reminiscent of clinically reported sex differences in bipolar patients while the other phenotypic sex differences such as rearing and locomotor activity are less clearly described in clinical studies. Overall, our results lend further evidence for the validity of the LHK rat as a useful model to study brain region-specific molecular changes during mania and its correlation with alcohol use disorders.

Figure 1

(a) Study design: baseline phase for 7 days, followed by surgical implantation of stimulating electrode and recovery for 5 days before mania induction took place for 5 days. Each day, the animal was allowed an initial pre-kindling habituation period (pre-kindling) for 30 min followed by kindling phase consisting of seven consecutive trains starting at 1 V for the first train then increased to 2 V for the subsequent six trains. Two-minute rest intervals were allowed between trains. Each train consisted of 10 pairs of stimulation (10 s) alternating with rest (30 s). The animal remained in the monitored cage for 30 min during the post-kindling period before it was returned back to home cage for 7 days (post-mania days). Locomotor activity counts and voluntary ethanol (EtOH) consumption were monitored continuously throughout the study period. (b) An illustration of stimulating electrode tip locations plotted within the dorso-medial part of the LHA regions. AP coordinates were between −2.12 to −2.56 from bregma according to Paxinos Atlas. AP, anteroposterior; LHA, lateral hypothalamic area.

Figure 2

Change in manic-like behaviors: from the pre-kindling to kindling (Δkindling) and post-kindling (Δpost-kindling) were compared between LHK male and female rats. (a) A nonsignificant trend towards a main effect of sex (F_1,18=4.34, ^#P=0.0516) was observed in the duration of sexual behavior, and significant main effects of kindling (F_1,20=12.15, ^*P=0.002) and sex (F_1,20=9.74, ^##P=0.005) were evident in rearing behavior (b), whereas no significant effect for kindling or sex were detected in grooming behavior (c). However, a significant main effect of kindling (F_1,20=6.13, ^**P=0.02) and an interaction between kindling and sex (F_1,20=5.29, P=0.03) were evident in the duration of feeding behavior (d) by repeated measures ANOVA. ^*P<0.05 by Tukey post hoc test; n=9–10 per rat type. Data are expressed as mean±s.e.m. ANOVA, analysis of variance; LHK, lateral hypothalamus kindled.

Figure 3

Ethanol (EtOH) consumption (g kg⁻¹ per day) showed significant main effect for kindling (F_1,17=4.93, ^*P=0.04) and sex (F_1,17=10.79, ^#P=0.004) by repeated measures ANOVA. ^*P<0.05 by Tukey post hoc test; n=9–10 per rat type. Data are expressed as mean±s.e.m. ANOVA, analysis of variance; LHK, lateral hypothalamus kindled.

Figure 4

Changes in circadian locomotor activity counts from baseline to mania-induction days (Δmania) and to post-mania-induction days (Δpost-mania) were compared between LHK male and female rats in both the light and dark phases. (a) Shows changes in light phase activity counts. Significant main effect for mania induction (F_1,12=12.56, ^*P=0.004) and an interaction between mania induction and sex (F_1,12=7.82, ^#P=0.01) were evident. The changes in dark-phase activity counts (b) show significant main effect of mania induction (F_1,14=11.89, ^#P=0.003) and sex (F_1,14=9.85, ^*P=0.007). Changes in light-phase rest interval (c) showed significant effect of sex (F_1,14=30.44, ^#P<0.0001) with males exhibiting significantly less rest intervals during both mania induction (^*P=0.01) and post-mania-induction days (^*P=0.002). Dark-phase rest interval (d) showed significant effect of sex (F_1,14=8.57, ^#P=0.01) and mania induction (F_1,14=14.02, ^*P=0.002), by two-way ANOVA; ^*P<0.05 by Tukey post hoc test; n=9–10 per rat type. Data are expressed as mean±s.e.m. ANOVA, analysis of variance; LHK, lateral hypothalamus kindled.