Predictive validity of a non-induced mouse model of compulsive-like behavior

A key to advancing the understanding of obsessive-compulsive disorder (OCD)-like symptoms is the development of spontaneous animal models. Over 55 generations of bidirectional selection for nest-building behavior in house mice, Mus musculus, resulted in a 40-fold difference in the amount of cotton used for a nest in high (BIG) and low (SMALL) selected lines. The nesting behavior of BIG mice appears to be compulsive-like and has initial face validity as an animal model for OCD in humans. Compulsive-like digging behavior was assessed; BIG male mice buried about three times as many marbles as SMALL male mice, strengthening face validity. Using the open field and elevated plus maze, SMALL male mice showed higher levels of anxiety/fear-like behavior than BIG male mice, indicating that compulsive-like and not anxiety-like behavior was measured. To establish predictive validity, chronic (4 weeks) oral administration of fluoxetine (30, 50 and 100mg/kg/day) and clomipramine (80 mg/kg/day), both effective in treating OCD, significantly reduced compulsive-like nest-building behavior in BIG male mice. Compulsive-like digging behavior was also significantly reduced by chronic oral fluoxetine (30 and 80 mg/kg/day) treatment in BIG male mice. General locomotor activity was not affected by chronic oral fluoxetine (30 and 80 mg/kg/day) treatment; chronic oral treatment with desipramine (30 mg/kg/day), an antidepressant not effective in treating OCD, had no effect on nesting behavior of BIG male mice, strengthening predictive validity. Together, the results indicate that these mice have good face and predictive validity as a non-induced mouse model of compulsive-like behavior relevant to OCD.

Circadian dynamics of vasopressin in mouse selection lines: translation and release in the SCN

Arg8-vasopressin (AVP), a circadian clock-controlled gene product, is released from the hypothalamic suprachiasmatic nuclei (SCN) in mice in a circadian fashion. Previously reported differences in two mouse lines, initially selected for thermoregulatory nest-building behavior (building small nests (S-mice) or big nests (B-mice)) with different circadian organization of behavior and in number of SCN-AVP immunoreactive neurons, were further investigated. We confirmed and expanded the finding that S-mice exhibited constant high levels of SCN-AVP content with no apparent circadian rhythmicity, whereas B-mice had lower numbers of AVP positive cells which varied with time of day. We found that AVP mRNA expression levels at midnight and midday were similar in both lines, as established by in situ hybridization. When AVP transport and release were blocked by colchicine, SCN-AVP immunoreactivity was similar in both lines. This suggests that differences in SCN-AVP content depend on transport or release. Organotypic SCN cultures of B-mice showed more AVP release per neuron than cultures of S-mice. These results reveal that on a mechanistic level the mouse lines differed in transport and/or release of AVP in the SCN, rather than differential regulation of AVP gene transcription or number of AVP immunoreactive neurons.

Circadian rhythm of core body temperature in two laboratory mouse lines

The circadian rhythm of core body temperature (Tb) was examined in two mouse lines bidirectionally selected for nest-building behavior (small (SNB) and big nest-builders (BNB)). This selection also resulted in more robust circadian organization of wheel-running activity in the SNB compared to the BNB mice. Tb was measured by an e-mitter implanted in the abdominal cavity. The circadian Tb rhythm of the SNB was more robust compared to the BNB regardless of whether the animals had access to a running wheel or not and regardless of the lighting conditions, i.e., 12 h:12 h light:dark (LD) cycle or constant dark (DD). Wheel-running activity rhythms of SNB were more robust in LD and DD compared to BNB. The amplitude of the circadian Tb rhythm increased significantly in response to wheel access in both mouse lines, but was not significantly different between the BNB and SNB. However, BNB tended to have lower amplitudes of circadian Tb rhythm in the absence of running wheels and a larger increase in the amplitude upon access to a running wheel compared to SNB. No differences were found in LD and DD between the lines in mean Tb and wheel-running activity levels. In addition, no differences between the two mouse lines were found in the free-running period of the Tb or wheel-running activity rhythms in DD. Overall, our findings reveal a more robust circadian phenotype of the SNB compared to the BNB.

Ca(2+)-dependent mechanisms of cell injury in cultured cortical neurons

The contributions of several Ca(2+)-dependent processes to neurotoxicity were examined in primary cultures of rat cortical neurons. The Ca2+ ionophore ionomycin induced a rapid loss of axonal morphology and concomitant release of inositol phosphates that preceded morphological alterations of neuronal cell bodies, choline and arachidonate release, and protein degradation. These events were followed by a degree of neuronal lysis proportional to the external Ca2+ concentration and exposure time. The phospholipase inhibitor neomycin decreased both arachidonate release and the phospholipid hydrolysis catalysed by phospholipases C and D. Proteolysis was abated by the protease inhibitor leupeptin, but not by lysosomal proteolysis inhibitors. Neuronal lysis was inhibited partially by either leupeptin or neomycin and almost completely by both in combination. However, neither agent, alone or in combination, affected the morphological derangements. The diacylglycerol lipase inhibitor RHC-80267 reduced arachidonate release, but not neuronal lysis. Phospholipase A2 inhibitors had no effect on either arachidonate release or lysis. Treatment of mixed cultures of neurons and glia with a Ca(2+)-dependent glutamate challenge caused similar morphological changes and a delayed neuronal lysis that was also diminished by leupeptin and neomycin, but not by inhibitors of lysosomal proteolysis. These data describe several distinct stages of Ca(2+)-dependent injury to cortical neurons, a key feature of which is the stimulation of protease, and phospholipase C and D activities. The initial stage is characterized by a rapid loss of axonal morphology and increased phosphatidylinositol hydrolysis. An intermediate stage involves changes in cell body morphology plus the degradation of neuronal protein and phosphatidylcholine. In a later stage, the loss of plasma membrane integrity denotes neuronal death.