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Influence of gender and estrous cycle in the acoustic startle reflex in Wistar rats

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Marina Galleazzo Martins
Total Authors: 1
Document type: Master's Dissertation
Press: Botucatu. 2016-04-13.
Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
Defense date:
Advisor: José de Anchieta de Castro e Horta Júnior; Camila Contin Diniz de Almeida Francia

The acoustic startle reflex (ASR) is a fast and intense motor reaction that promotes skeletal striated muscles contraction of face and body, in response to an unexpected and high-intensity sound stimulus. The ASR has many modulations such as prepulse inhibition (PPI) which is characterized by reduced amplitude of ASR when the triggering sound stimulus is preceded by a lower-intensity stimulus. The ASR and PPI responses can be measured non-invasively in humans and rodents with high homology and have been used for basic and clinical research. Additionally, they are disrupted in many neurological and psychiatric conditions that show deficits in sensorimotor processing. In humans, it is known that there are gender-related differences in PPI, which reflect hormonal changes that occur during the menstrual cycle. However, studies in rodents are conflicting regarding the differences in ASR and PPI between males and females, rarely mentioning the possible variations during the estrous cycle. This fact makes it difficult to interpret experimental results in females and their translation to results obtained in humans. To assess the influence of gender and estrous cycle in ASR, 10 males and 28 females adult Wistar rats were studied. Females’ estrous cycle was monitored daily and all animals were subjected to sessions of ASR and PPI evaluation. In females, estradiol and progesterone plasmatic concentrations were determinated. The brains of 3 males and 3 females in each phase of the estrous cycle were processed for Fos protein immunohistochemistry. There was no influence of gender or estrous cycle phases on the ASR normalized amplitude and latency to maximum peak. Males do not differ from females in relation to %PPI. However, females in proestrus show lower %PPI than females in diestrous when the prepulse is greater than or equal to 70dB. Furthermore, we could observe direct association between progesterone levels and %PPI as a set.ASR short-term habituation has been observed in males and females in metestrus and transition proestrus-estrus, although there was also a significant amplitude decrease at the session’s Final Block in females in diestrus. The number of Fos immunoreactive neurons (FOS-ir) in the dorsal cochlear nucleus, locus coeruleus and central nucleus of inferior colliculus does not change between gender and estrous cycle. In the ventral and medial nucleus of the trapezoid body, pedunculopontine tegmental, cuneiform nucleus, A5 and external cortex of inferior colliculus, females in proestrous have the largest number of FOS-ir neurons. Therefore, studies interested in assessing %PPI between males and females should take into account the stage the estrous cycle for data analysis. The ideal size of the ASR/PPI evaluation session and the Initial and Final blocks set also vary depending on the estrous cycle. Our findings are important to design studies using ASR and PPI in males and females Wistar rats as tools for assessing deficits in sensorimotor integration and to improve of translational studies. (AU)

FAPESP's process: 14/03890-0 - Influence of gender and estrous cycle in the acoustic startle reflex in Wistar rats
Grantee:Marina Galleazzo Martins
Support Opportunities: Scholarships in Brazil - Master