Dravet syndrome (DS) is a severe form of childhood epilepsy caused by a mutation in the SCN1A gene, which encodes the NaV1.1 voltage-gated Na+ channel. This channel is present in most GABAergic neurons, the main inhibitory neurons in the brain. Reduced activity of the channel in DS leads to loss of inhibitory activity in the brain; this, in turn, leads to seizures and developmental deficits. Through previous research using the mouse model of DS, the de la Iglesia lab has demonstrated that DS also affects circadian rhythms, which are the endogenous biological rhythms synchronized to the 24 hour day. These symptoms are likely caused by the loss of NaV1.1 in a sleep regulatory center called the suprachiasmatic nucleus (SCN), a set of cells which functions as the ‘master clock’ of the circadian system of mammals. However, the de la Iglesia lab found that selective deletion of the SCN1A gene from the SCN fails to replicate the abnormal circadian phenotype. We believe that these mutant mice are phenotypically normal either because there is a compensatory increase in the expression of another sodium channel, NaV1.3, or because the targeting strategy does not reach all cells within the SCN. To test the first hypothesis we employed in-situ hybridization to visualize the expression of the genes that code for NaV1.1 and NaV1.3 channels in either SCN-specific knock outs or their wild type littermates. My results will help explain the phenotype seen in the SCN-specific SCN1A mutants and determine whether developmental compensatory mechanisms are important in the SCN of DS mice.

Most organisms show a roughly 24-h cycle in their physiological and behavioral processes, called circadian rhythms, generated endogenously through the ~24h cyclic expression of genes known as clock genes. Clock gene expression oscillates in the master circadian clock of mammals – the suprachiasmatic nucleus (SCN) - and nearly every cell of the body. Typically, circadian clocks and the rhythms they sustain are ‘entrained’ by the 24-h light-dark (LD) cycle. Our lab has found that fear can also behave as an entraining factor. We observed that when mice or rats need to leave a safe nesting area to access a foraging area, they forage and feed during the dark phase of the LD cycle. If the foraging area is rendered dangerous with random uncued footshocks during the active dark phase, the animals’ foraging and feeding activity shifts to the light phase. My goal is to understand the neural circuits and molecular processes involved in fear entrainment. I have analyzed the expression of clock genes in animals exposed to nighttime fear and control animals exposed to daytime fear; this allowed me to assess the circadian rhythm of expression of clock genes of interest (Per1 and Bmal1) in the SCN and amygdala, and I found that the amygdala entrains to fear but the SCN does not. I have also performed trials with brain-specific-knockout mice and found that nocturnal fear entrainment requires an intact molecular clock. My current experiments use a more specific knockout strategy of viral injections into the brain to determine whether a functioning circadian oscillator in the basolateral amygdala (BLA) or the SCN is needed for nocturnal fear entrainment. These experiments serve to unmask the molecular mechanism of fear entrainment and could also help understand the mechanisms linking fear and anxiety disorders to problems with circadian rhythms and sleep.

Physiological and behavioral rhythms are controlled in mammals by a central circadian clock located in suprachiasmatic nuclei of the hypothalamus (SCN). This master clock has outputs to other organs and tissues crucial to keeping the organism properly synchronized. The SCN clock is synchronized by environmental cues, most importantly is the light-dark cycle (LD). Fearful stimuli (i.e. presence of predators) can also present cyclic variations. The de la Iglesia lab has recently shown that timed fearful stimuli during the night can switch the locomotor activity rhythms of mice to the light phase, overriding their natural nocturnal behavior. Interestingly, while the expression of the so-called “clock genes” (which sustain the circadian rhythms at the molecular level) remains unchanged in the SCN, it displays a complete inversion in the amygdala, the brain region that encodes fear. Currently, we aim to determine the pattern of expression of clock-genes in peripheral organs of mice subjected to cycling fear stimuli. Using qPCR, we will assess RNA expression of the clock genes bmal1, per1, and per2 in the adrenal gland, kidney, and liver to determine whether entrainment of activity by cyclic fear also impacts peripheral clocks at the molecular level. We hypothesize that the pattern of expression the clock genes in the liver and kidneys will be modified in mice subjected to nocturnal fear, due to altered feeding and drinking patterns. However, the adrenal gland is difficult to make predictions about the pattern of expression of the clock genes given the fact that preliminary data from our lab showed that cortisol shows two peaks in mice displaying diurnal activity after nocturnal cyclic fear exposure compared to the single peak displayed by nocturnally active mice. Thus, it is unclear if we will observe an inversion peak, much like the amygdala, or a peak similar to the LD cycle.