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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersLungs begin to produce surfactantImmune system beginningHead may position into pelvisFull TermPeriod of rapid brain growthWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madeImmune system beginningBrain convolutions beginBrain convolutions beginFetal liver is producing blood cellsSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
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Home | Pregnancy Timeline | News Alerts |News Archive Feb 24, 2015

When the female mouse is not in a receptive mood, the activity in her neurons was similar
in her social encounters with males OR females. However, when she was in a receptive
mood, the activity of her neurons was elevated ONLY when interacting with males




The neural basis for 'being in the mood'

Researchers discover that in female mice, neurons respond to social information depending on her hormonal state.

What determines your receptiveness or rejection towards a potential sex partner? In humans we consider many factors — appearance, culture, age, all are taken into account. But what part does an individual's internal mood really play? Our bodies function through a complicated system of hormonal signals. Signals that vary in accordance with our physiology — such as our menstrual cycle. Researchers in Lisbon, Portugal for the first time have captured live data, from mice, reflecting that changes in hormone-levels do affect the activity of the brain and related behavioral responses.

"It is well known that female mice change dramatically during different phases of their reproductive cycle, called the Estrous cycle. Responses to brief social interactions with males can result in radically different outcomes ranging from receptivity to aggression. In this study, we investigated the question - what is the neural basis that underlies these polar opposite behaviors?"  said Susana Lima, principal investigator of the research conducted at Champalimaud Centre for the Unknown in Lisbon, Spain. Researchers focused on the hypothalamus.

"The hypothalamus regulates many instinctive behaviours, including feeding, sleeping and sexual behavior. We recorded the activity of neurons in an area of the hypothalamus dedicated to socio-sexual behaviour. The activity of these neurons was observed while the females interacted with males or with other females."

Kensaku Nomoto, postdoctoral researcher, lab of Susana Lima

The researchers found that the activity of these neurons changed dramatically depending on the reproductive state of the female. "When the female was not in a receptive state, the activity of the neurons was similar for social encounters with either males or females. However, when the female was in the receptive state, the activity of the neurons was enhanced only when interacting with males", said Dr. Nomoto.

"This is the first time that activity of these neurons was recorded in naturally cycling females, where we investigated the effect of the reproductive cycle on neuronal physiology. It establishes that there is in fact a brain region where hormonal state and social interaction are integrated.

"In humans, the effect of hormonal state on attraction and rejection is quite controversial, studies such as this one, may help shed light on the neural circuits that mediate our behaviours."

Susana Lima PhD, research principal investigator, Champalimaud Centre for the Unknown, Lisbon, Portugal.

The study was published in the scientific journal Current Biology.

•We performed single-unit recordings in female mice interacting with conspecifics
•Social stimuli activate female VMHvl neurons, with preference to male stimuli
•The activity of most VMHvl neurons is modulated throughout social interactions
•Male-evoked VMHvl responses are enhanced during the sexually receptive state

Social encounters often start with routine investigatory behaviors before developing into distinct outcomes, such as affiliative or aggressive actions. For example, a female mouse will initially engage in investigatory behavior with a male but will then show copulation or rejection, depending on her reproductive state. To promote adaptive social behavior, her brain must combine internal ovarian signals and external social stimuli, but little is known about how socially evoked neural activity is modulated across the reproductive cycle [ 1 ]. To investigate this, we performed single-unit recordings in the ventrolateral region of the ventromedial hypothalamus (VMHvl) in freely behaving, naturally cycling, female mice interacting with conspecifics of both genders. The VMHvl has been implicated in rodent sociosexual behavior [ 2, 3 ]: it has access to social sensory stimuli [ 4–8 ] and is involved in aggression and mating [ 9–11 ]. Furthermore, many VMHvl neurons express ovarian hormone receptors [ 12, 13 ], which play a central role in female sociosexual behavior [ 14–16 ]. We found that a large fraction of VMHvl neurons was activated in the presence of conspecifics with preference to male stimuli and that the activity of most VMHvl neurons was modulated throughout social interactions rather than in response to specific social events. Furthermore, neuronal responses to male, but not female, conspecifics in the VMHvl were enhanced during the sexually receptive state. Thus, male-evoked VMHvl responses are modulated by the reproductive state, and VMHvl neural activity could drive gender-specific and reproductive state-dependent sociosexual behavior.

About Susana Lima, Principal Investigator at the Champalimaud Neuroscience Programme

About the Champalimaud Neuroscience Programme (CNP)
The CNP is an international programme which strives to unravel the neural basis of behaviour. The concept of the programme takes into account the fact that basic neuroscience research can have a significant impact on the understanding of brain function, which in turn may contribute to the understanding and possible treatment of neurological and psychiatric illnesses.

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