Caba Mario, Pabello Marcela, Moreno Maria Luisa, Meza Enrique
Centro de Investigaciones Biomédicas, Universidad Veracruzana , Xalapa, Veracruz , México and.
Chronobiol Int. 2014 Oct;31(8):869-77. doi: 10.3109/07420528.2014.918625. Epub 2014 Jun 10.
The olfactory bulb (OB) has a circadian clock independent of the suprachiasmatic nucleus, but very little is known about the functional significance of its oscillations. The OB plays a major role in food intake as it contributes to the evaluation of the hedonic properties of food, it is necessary for a normal pattern of locomotor behavior and their ablation disrupts feeding patterns. Previously we demonstrated that OB of rabbit pups can be entrained by periodic nursing but it was not clear whether food was the entraining signal. Here we hypothesized that OB can be entrained by a food pulse during the day in adult rats under a restricted feeding schedule. Then we expect that OB will have a high activation before food presentation when animals show food anticipatory activity (FAA). To this aim we determined by immunohistochemistry the expression of FOS protein, as an indicator of neural activation, in the mitral and granular cell layers of the main and accessory OB. Additionally we also explored two of the OB brain targets, the piriform cortex (PC) and bed nuclei of the accessory olfactory tract (BAOT), in three groups: ad libitum (ALF), restricted feeding (RF), and fasted rats after restricted feeding (RF-F). In ALF group FOS levels in both main and accessory OB were low during the day and high during the night at the normal onset of the increase of activity, in agreement with previous reports. On the contrary in RF and RF-F groups FOS was high at the time of FAA, just before food presentation, when animals are in a state of high arousal and during food consumption but was low during the night. In their brain targets, we observed a similar pattern as OB in all groups with the only difference being that FOS levels remained high during the night in RF-F group. We conclude that the OB is entrained by food restriction by showing high activation at the time of food presentation, which persists during fasting and impose a similar FOS pattern to the two brain targets explored only in fed animals.
嗅球（OB）具有独立于视交叉上核的昼夜节律时钟，但其振荡的功能意义却知之甚少。嗅球在食物摄入中起主要作用，因为它有助于评估食物的享乐属性，对于正常的运动行为模式是必需的，并且其切除会扰乱进食模式。此前我们证明，兔幼崽的嗅球可被周期性哺乳所调节，但尚不清楚食物是否为调节信号。在此我们假设，在限制进食时间表下，成年大鼠的嗅球在白天可被食物脉冲所调节。然后我们预期，当动物表现出食物预期活动（FAA）时，嗅球在食物呈现前会有高激活。为此，我们通过免疫组织化学确定了主要和辅助嗅球的二尖瓣和颗粒细胞层中FOS蛋白的表达，作为神经激活的指标。此外，我们还在三组动物中探究了嗅球的两个脑靶点，即梨状皮质（PC）和辅助嗅束的终纹床核（BAOT）：自由进食（ALF）组、限制进食（RF）组以及限制进食后禁食的大鼠（RF - F）组。在ALF组中，主要和辅助嗅球中的FOS水平在白天较低，在夜间正常活动增加开始时较高，这与先前的报道一致。相反，在RF组和RF - F组中，FOS在FAA时、就在食物呈现前较高，此时动物处于高度兴奋状态且在进食期间，但在夜间较低。在它们的脑靶点中，我们在所有组中观察到与嗅球相似的模式，唯一的区别是RF - F组中FOS水平在夜间仍保持较高。我们得出结论，嗅球通过在食物呈现时表现出高激活而被食物限制所调节，这种激活在禁食期间持续存在，并在仅在进食动物中探究的两个脑靶点中呈现类似的FOS模式。
