Effect of light on reproduction and sleep

By

Tay Lee Huay

D10a038

Objectives

• To understand the differences of photoperiod in different region on earth,

• To review the light stimulatory pathway in animals, the photosensitive cells and organ involved,

• To know the important mechanism involves in regulating sleep and reproduction,

• To allow better understanding of the effect of light on reproduction and sleep,

• Understand the role of light in regulating the reproduction and sleep of animals.

Effect of light on

reproduction and sleep

Photoperiod

&

Seasonality

Pineal gland

Other Photosensitive

organs

Light regulation pathway

Effect of light on

reproduction & sleep

Photoperiod & seasonality

Photoperiod & Seasonality

• Photoperiod: – the period of daily illumination received by an organism

• Circadian rhythm: – daily rhythmic activity cycle based on 24-hours intervals

exhibited by an organism in an constant conditions.

– Not found in short-lived organism such as protist.

• Entrain: • Synchronize

• Free-running: – Not entrained to the circadian rhythm

Photoperiod & Seasonality

• Differences in photoperiod depending on: – latitude

• Generally, – High latitude: short spring and autumn – Temperate, subpolar region: 4 seasons – Low latitudes & other regions: (tropical & sub-tropical) dry

& wet seasons instead of 4 seasons – Temperate country: has obvious difference in

photoperiod(SDP & LDP) – Light – most accurate environment clock – For animals not influenced by light, temperature and

electromagnetic field are better indicator for this case.

4seasons…. Vary in light intensity Vary in food availability

Dramatics fluctuations of temperature…

Some adaptive changes due to vary in photoperiod

Adaptive changes in animals??.... (Autumn & Winter)

Adaptive changes…..

Adaptive changes…

Spring….. & autumn

Breeding seasons….

Pineal gland

Pineal gland

• Pinecone-shaped

• Located caudally to the roof of the third ventricle of the brain filled with cerebrospinal fluid (CSF) .

• Consists of:

– pinealocytes

– glial cells

– perivascular phagocyte

– pineal neurons

– peptidergic neuron-like cells

Pineal gland cont.

• Avian:

– On the surface of brain, located ventrally to the skull.

• Main function:

– Secretes melatonin, serotonin, pineal peptides.

(*melatonin=darkness hormone suppressed by light)

• Lower vertebrates (fish, amphibians, reptiles):

– Similar to photoreceptor cells in retina

– Known as parietal organ (fx: endocrine)

Pineal gland of avian

Pineal gland of mammals

Other photosensitive organs

Melanopsin • Photopigment.

• Non-visual.

• Sensitive to blue light – inhibition of melatonin secretion.

• Found in: – Retinal ganglion cells (mammals)

– Widely distributed outside retina (non-mammals).

• Function: – Detects light

– unconscious visual reflexes, e.g. pupillary constriction

– regulating circadian rhythm

Parietal eye

• Embryologically, arises from the cranial evagination of pineal organ/ epithalamus (instead of encephalon which give rise to pineal gland)

• Fx: photoreceptive organ

• Absent in birds and mammals.

• Present in some reptiles, amphibians, lampreys and some fish.

• Connects to pineal gland by parietal nerve.

Light regulation pathway

Retinal pathway

Dorsal Cervical Ganglion

Non-retinal

pathway

Light penetrate through eyelid

Penetration through

skull

Parietal organ

Other pathway.

(not established)

Effect of light on reproduction and sleep

Effect of light on reproduction

Introduction

• Reproduction:

– Biological process where organism propagate its offspring.

• Most important hormone involved:

– Melatonin

• Secretion= 1

𝛼 photoperiod

Effect of light on reproduction

• Low light/ in dark: Melatonin secreted. – Inhibits secretion of LH and FSH (act on pineal

gland) - Suppress libido, reproductive ability.

– Binds to reproductive organ and causes gonadal regression – presence of melatonin receptors.

(Testis, epididymis, vas deferens, prostate of male and ovary and mammary gland of female)

• SDP: suppress breeding state of animals.

• LDP: stimulate animals into breeding seasons.

Effect of light on reproduction cont.

• LDP: – Lower level of melatonin.

– Serotonin –Inclination to leave food and search for a mate; Sexually receptive.

– LH surge oestrus

– Changes in ornamental pigmentation - ↑appeals

– Reduced antigonadotrophic effect.

↓ gonadotropin inhibitory hormone (GnIH), ↑ gonadotropin inhibitory hormone (GnIHR), ↑ testestrone

Animals not affected?

• Some hamster

• Humans – only continuous long duration of expose to melatonin– weeks-change in hypothalamic sensitivity to malatonin.

• Deer- breeding phase stimulated by SDP

Effect of light on sleep

Introduction

• Sleep: • Regularly recurring condition of body and mind in which the

nervous system is inactive, the eyes closed, the postural muscles relaxed, and consciousness practically suspended.

(Consise Oxford English Dictionary 11th ed.)

• Melatonin: – Binds & activates peripheral receptors – vasculature of

heart. – No significant change in heart rate – Alters autonomic activity - ↑ peripheral temp., ↓

body core temp. – ↑ sleep propensity

Light effect on sleep

• Melatonin secretion declines with age. • Factors affecting distorted in light entrainment:

– blindness, – short-sightedness which reduces sensitivity to light – stress – endocrine disorders – sleep disorders – stress – adolescene – Artificial light – Lesions on retinal pathway – Etc (free-running sleep can be observed. i.e. sleep-wake cycle doesn’t entrained to environmental light)

Dawn:

• Resets circadian rhythm.

• Suppress melatonin secretion > evening.

• Serotonin ↑- initiates animals to wake up.

Dusk:

• Resets circadian rhythm in opposite direction.

• Delay in melatonin secretion shorter than of in dawn.

Afternoon nap??? • Increase awareness.

• light during the day has little effect on the resetting the circadian clock.

• will not influenced circadian clock unless the animals sleep too much.

Blue & Green light

• Blue light: 435- 530 nm (480nm)

– Detected by melapnosin

– Increase in awareness – circadian rhythm most effected (melanopsin)

– Suppress melatonin production

• Green light:

– Detected by cone receptors.

– Suppress melatonin production – not as efficient as blue light.

– Effect dies off quickly then blue light

• Since serotonin is the intermediate product of melatonin from tryptophan, serotonin level ↑, ↓sleepiness, ↑ alertness.

Adaptive changes?

• Hibernation

– dormant state of animal to spend throughout the winter period.

• Physical & physiological changes according to environment.

• Changes may be abrupt – like new spp.

Hibernation • Siberian hamster:

– Grows fatter & bigger in size – deposition of fats

– Changing of fur colour – camouflague

– Exhibit dead during hibernation.

• Bear – hard to migrate.

– bulkier, short and compact body, large appetites. Thus, hibernate.

Conclusion

• Light is a important “time-telling” clock indicator that entrains animal’s biological cycle according to its environment to enhance the chances of survival and well-being of animals.

• Animals is evolved in such a way that they can live and adapt to their environment through with the help of photoperiod.

• Melapnosin is responsible for the detection of ‘light’ needed to entrain biological clock.

• Light is important indicator for reproduction and sleep-wake cycles of animals.

Thanks for your attention

Dankeshön