The Role of the Limbic System in Reproduction: The Role of the Limbic System in Reproduction by . Alade Fehinti John email@example.com +2348065701493 Outline: Outline Introduction Historical Background Functional Anatomy of the Limbic System Reproduction Role of the Limbic System in Reproductive Mechanisms Pathophysiology Conclusion Introduction:
Introduction The Limbic(Latin- limbus :“border” or “edge”) System is a complex set of interconnected structures that lie on both sides and underneath the thalamus, just under the cerebrum (MacLean, 1952). It is primarily involved in various aspects of Behaviour , Emotions,
and Memory. ( Geinisman et al. 2000, McMillan et al, l987). The parts involved in reproduction include Amygdala, Septal nuclei, Ventral Tegmental Nuclei, Nucleus Accumbens and the Hypothalamus.
Historical Background (Cingulate gyrus, PHG, Hypothalamus, Septal area, Nucleus acumbens, Orbitofrontal ctx, Amygdala): Parahippocampal gyrus Mamillary Bodies Hippocampus Historical Background ( Cingulate gyrus , PHG, Hypothalamus, Septal area, Nucleus acumbens , Orbitofrontal ctx , Amygdala) Fornix Cingulate Gyrus Hypothalamus Olfactory bulb Septal Nuclei Amygdala Broca , 1878 Maclean, 1952 Figure 1:- Diagram showing some of the Parts of the Limbic system with with their interconnecting pathways Adapted from The Amygdala: The Amygdala The Amygdala is a little almond shaped, sexually dimorphic structure located at the anterior and lower end of the Hippocampus deep in the temporal lobe consisting of the Basal, Lateral, Medial, Central nuclei. It is involved in Fear, Emotion responses, Facial recognition and responses. (Anderson and Phelps, 2000, Blanchard & Blanchard, 1988). It is connected by two major bundles of fibers with other areas of the brain: the stria termanalis and the amygdalofugal pathway. Stimulation of the different parts of the Amygdala elicits emotions ranging from Violent Rage to Pleasure. Lesion of the amygdala significantly disturbs the ability to determine, discern, or identify the motivational and emotional significance of events. These connections make it possible for the amygdala to play important role on the mediation and control of major affective activities like friendship, Love, fear, Rage, Violence and Aggression. Hypothalamus: Hypothalamus The Hypothalamus is one of the smallest and busiest part of the Brain, located below the thalamus, immediately dorsal to the pituitary gland. The hypothalamus is a sexually dimorphic structure and is highly involved in all aspects of emotional, reproductive, vegetative, endocrine, visceral and autonomic functions ( Alam et al, 1995, Johnson & Gross, 1993, Markakis & Swanson, 1997, Sherin et al, 1996, Smith et al, 1990). It is connected via the medial forebrain bundle and solitary tract(Bi directional) to other areas of the brain and also through the hypothalmic-hypophyseal portal vessel to the posterior pituitary gland (Swanson, 1987,Risvold & Swanson, 1996). On the basis of the morphology and the apparent functional roles it has four subdivisions, each, consisting of various nuclei. (Swanson, 1987). The Lateral hypothalamus is involved in Emotion(rage), Motivation and food /water intake regulation. The Periventricular hypothalamus is concerned with neuroendocrine regulation through its connection to the Pituitary gland. Slide 8: The Medial Hypothalamus functions in temperature regulation, sexual differentiation, regulation of sexual behaviour and food intake. The Posterior hypothalamus these regions project to brainstem nuclei involved with cardiovascular, respiratory, and temperature regulation. Figure 3:- showing the hyp0thalamus and the connecting Pathways with other parts of the Brain Source Frank Netter Atlas of Anatomy (2011) Ventral Tegmental Area/ Nucleus Accumbens:
Ventral Tegmental Area/ Nucleus Accumbens The Ventral tegmental area is located in the mesencephalic part of the brain stem; there is a compact group of dopamine-secreting neurons whose axons end in the Nucleus accumbens ( mesolimbic dopaminergic pathway) ( Steketee , 2003).The spontaneous firing or the electrical stimulation of neurons belonging to that region produce pleasurable sensations, some of them similar to orgasm. The Nucleus accumbens (Ventral striatum) plays a key role in limbic
circuits that are responsible for motivated , goal- directed behaviours , It is said to be the interphase between the limbic and motor systems (Kelley, 1999, Groenewegen and Uylings , 2000).
Reproduction: Reproduction Reproduction is the process by which Living organisms Produce Offspring. It Generally involves :- Physiological preparation of the Body (Puberty) Seeking Fellowship (Romantic Love) Mating (Sexual Behaviour ) Physiological mechanisms in controlling Fertilization and Gestation (Regulation Gonadotropic hormones) Parturition (Pelvic Contraction) Neonatal care-1 st 28 weeks (Maternal care) The Limbic System is involved in all these processes. Regulation of Reproductive Hormones: Regulation of Reproductive Hormones The hypothalamus as the major output of the limbic system controls pituitary function thereby inflencing functions of visceral reproductive organs (Guyton and Hall, 2010). GnRH secreted independently regulates the release of both LH and FSH from the Anterior Pituitary gland. FSH and LH are very essential hormones involved in the control of Spermatogenesis, Oogenesis , Menstrual cycle and Gestation ( Jacobowitz , 1988, Ross et al,1970, Kangasniemi et al, 1995, Guyton and Hall, 2010). PIF also controls the release of prolactin from the APG which acts as a negative feedback with Dopamine and also is involved in reproductive functions such as Milk ejection (Abe et al, 1985). Oxytocin , also secreated in the hypothalamus plays crucial roles in Milk ejection, Paturition , and sexual behaviour Falk Fahrenholz , 2001, Van Kesteren , et al 1996,). Romantic Love: Romantic Love Romantic love is a cross-cultural phenomenon, and is possibly a mammalian drive to pursue preferred mates ( Jankowiak and Fischer 1992). It is associated with specific physiological indices termed “ Limerance ” ( Sprecher 1986) which includes euphoria, emotional dependency, increased energy, and craving for emotional union. Using fMRI studies, the Ventral tegmental area, Nucleus accumbens , and other Dopamine rich areas of the Brain(Basal nuclei, caudate nucleus) have been discovered to be involved in Romantic Love( Porrino et al. 1984; Esposito et al. 1984; Wise and Hoffman 1992, McBride et al. 1999; Hollerman et al. 2000; Robbins and Everitt 1996; Schultz 2000;) Romantic love uses subcortical reward and motivation systems to focus on a specific individual, that limbic cortical regions process individual emotion factors to, and is an example of the heterogeneity for reward functions in the human brain. ( Aron et al, 2005). Mating/Copulation/Sexual Behaviour: Mating/Copulation/Sexual Behaviour Sexual arousal and Orgasm in men and women is mediated by the Hypothalamus, Amygdala, and striatal areas. During mating, these areas control the release and action of some chemicals which play specific roles in the control of sexual behaviour , examples are Dopamine, Prolatin and Oxytocin . Dopamine plays a role in Pleasure derived from mating. Prolactin plays a role in sexual satiation after sexual climax. Oxytocin is responsible for the rhythmic contractions of the genital tracts and the pelvic floor during Ejaculation and Orgasm. These three peptides have been shown rhythmically change in their blood concentration immediately before, during and after sex. ( Meston and Frohlich , 2000) Slide 14: Copyright ©2010 Society for Reproduction and Fertility Bioscientifica Reproduction. 2010 Nov;140(5):643-654 Figure 4 Effect of orgasm on peripheral PRL concentrations in human males and females before, during, and after sexual intercourse (filled squares) and during a control session (open squares) Bioscienfica , Reproduction (2010) Slide 15: Figure 4 :- Adapted from Effect of orgasm on peripheral Prolactin concentrations in human males and females before, during, and after sexual intercourse Reproduction. 2010 Nov;140(5):643-654 Society for Reproduction and Fertility Bioscientifica Maternal/Parternal Behaviour: Maternal/ Parternal Behaviour The Amygdala plays an important role in Marternal care and love. Lesions and Bilateral amygdalectomy causes abolishment of infants by mothers and any attempt by the neonate to effect maternal contact usually resulted to repulsion and brutality from the Mother (Kling, 1972) The Amygdala is also concerned with Paternal behaviour , axon sparing lesions in the medial Amygdala cases abolishment of male paternal behaviour (Kirkpatrick et al, 1994). First is a recent case of a woman who strangled her baby after giving birth in the airplane toilet. A case was also reported of a man who killed his wife and his mother, after which he climbed a city tower and killed 13 other people. After he died, Post-mortem autopsy revealed a large glioblastoma Tumor compressing the amygdala and other limbic structures was found in his Brain (Charles J. Whitman Catastrophe, Medical Aspects. Report to Governor, 9/8/1966). It is therefore suggested that women who abolish or kill their babies immediately after parturition are also clinically investigated for any Limbic disorder. Clinical Correlates: Clinical Correlates Hypersexuality Kl ϋ ver-Bucy Syndrome Infertility Conclusion: Conclusion Although the Limbic system controls other important mechanisms in the Human body such as memory, its role in reproduction can not be overemphasized. For Love makes us seek fellowship so as to continue existence of our genes. Also involved in regulation of reproductive mechanisms such as menstrual cycle, spermatogenesis e.t.c . Maternal behaviour such as Breast feeding which is also important for neonate survival. It would therefore be great if we credit the Limbic system for such pleasant sensations it gives us when we involve in functions that are essential for continuity of our offspring. 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