The Septum Pellucidum 

Septo-optic dysplasia is a disorder of early brain and eye development. The most common features are underdevelopment (hypoplasia) of the eye (optic) nerve, abnormal formation of structures along the midline of the brain such as the absence of the septum pellucidum and the corpus callosum, and a small pituitary (pituitary hypoplasia). Signs and symptoms may include blindness in one or both eyes, an abnormal pupil dilation in response to light, nystagmus (abnormal movement of the eyes), low muscular tone and hormonal problems. Additional features may include recurring seizures, delayed development, intellectual disability, jaundice (yellow-ish skin), precocious puberty, short stature, sleep problems, obesity, lack of smell (anosmia), hearing loss and heart anomalies. Although the cause is unknown in most cases, very few people with SOD may have variations in the HESX1 OTX2, SOX2 or SOX3 genes

Abnormality of the pituitary gland (also known as hypophysis), which is an endocrine gland that protrudes from the bottom of the hypothalamus at the base of the brain. The pituitary gland secretes the hormones ACTH, TSH, PRL, GH, endorphins, FSH, LH, oxytocin, and antidiuretic hormone

The septum pellucidum provides information to the rest of the body about how the body is doing. This information may include whether or not the body has received enough sleep or food, or whether the environment is safe. Therefore, an absence of the septum pellucidum may cause an individual to feel hungry even when they are not or tired when they have had enough sleep.

The interrelated functions of the septum pellucidum which are consciousness, sleep, emotional response to the environment, mental processes of self-maintenance, food-finding, sexuality, autonomic-vegetative adaptation modes for homeostasis, fight and flight, and species maintenance.

Absence of Septum Pellucidum, also known as absent septum pellucidum, is related to porencephaly, cerebellar hypoplasia, and internal malformations and de morsier's syndrome information <https://www.malacards.org/card/de_morsiers_syndrome_information>. Affiliated tissues include brain, pituitary and cortex.

Septo-optic dysplasia is a rare disorder characterized by optic nerve hypoplasia; midline developmental defects including agenesis of the septum pellucidum, thinning or absence of the corpus callosum, or both; and deficiencies of pituitary hormones. The majority of cases are sporadic but rare familial cases occur. The clinical manifestations include poor visual function in one or both eyes, developmental delay, seizures, sleep disturbances, and precocious puberty. A life-long multidisciplinary approach is crucial in the management of these patients to optimize their growth and development and to help them lead as normal lives as possible.

The septum pellucidum may be regarded as a correlative center relaying visceral information through hypothalamic autonomic system to the hippocampus , amygdala, habenula, and brainstem reticular formation. It therefore partakes in consciousness and sleep and in emotional response to the environment In this regard, it is part of the circuit that subserves the mental processes of self-maintenance, food finding, sexuality, autonomic-vegetative adaptation modes for homeostasis, fight and flight , and species maintenance. Because of the important part played by the hippocampus in memory, and because important connections occur between the septum pellucidum and the hippocampus through the limbic system learning disabilities and mental retardation can be expected when abnormalities occur in the septum pellucidum 

The septal area (medial olfactory area), consisting of the lateral septum and medial septum, is an area in the lower, posterior part of the medial surface of the frontal lobe, and refers to the nearby septum pellucidum.

The lateral septum is involved in a variety of functions, including emotional, motivational, and spatial behavior. It has been suggested that the LS may regulate interactions between the hippocampus and other regions that mediate goal directed behavior, such as the ventral tegmental area.Firing of LS neurons is modulated by both speed and acceleration and spatial location, and that firing is also related to reward and context. It has thus been suggested that the lateral septum may incorporate movement into the evaluation of environmental context with respect to motivation and reward.

Little is known about the functional role of the septum pellucidum, and it is often treated as simply an anatomical barrier in many discussions of the septum. However, its connections with the hippocampus and hypothalamus suggest a role at least as a relay station between these structures <https://www.ncbi.nlm.nih.gov/pubmed/2505543>. Although abnormalities of the septum pellucidum are associated with several neurological conditions, it is at this point unclear what role, if any, the septum pellucidum plays in directly generating the symptoms of such disorders.

A bit more is known about the actions of the septal nuclei, which seem to be involved in a variety of functions, although their exact role in many of these functions is still relatively poorly understood. Additionally, most of what we do know about the septal nuclei comes from animal studies, as there is little research available on the functions of the septal nuclei in humans.

The septal nuclei are considered part of the limbic system, a group of structures that are often linked to emotion but are really involved in a long list of functions in the human brain. The septal nuclei receive afferent (i.e. incoming) connections from other limbic structures like the hippocampus, amygdala, and hypothalamus, as well as the dopamine-rich ventral tegmental area. The septal nuclei also send projections to the hippocampus, habenula, thalamus, ventral tegmental area, and hypothalamus.

One of the first functional roles to be linked to the septal nuclei was an involvement in processing rewarding experiences. In a now-famous group of experiments, researchers James Olds and Peter Milner found that electrical stimulation of the septal nuclei and several other areas of the brain seemed to be rewarding <https://www.ncbi.nlm.nih.gov/pubmed/13233369> to rats. Rats, in fact, responded more strongly to stimulation in the septal region than any other part of the brain studied, leading Olds and Milner to hypothesize the septal region was perhaps the locus of the reward system.

Although our understanding of the reward system has since expanded and less importance has been placed on the septal nuclei in favor of other structures like the ventral tegmental area and nucleus accumbens, the septal nuclei are still thought to potentially play a role in reward processing. Neurons in the septal nuclei give rise to axons that travel in the medial forebrain bundle <https://www.ncbi.nlm.nih.gov/pubmed/15297155>, a collection of fibers that connects the nuclei with the hypothalamus and ventral tegmental area. The medial forebrain bundle is an important part of the reward system, thought to stimulate dopamine neurons in the ventral tegmental area in response to rewarding stimuli.

The septal nuclei also are densely interconnected with the hippocampus, and through these connections may play a role in learning and memory <https://www.ncbi.nlm.nih.gov/pubmed/19389457>. The septal nuclei and hippocampus are sometimes referred to as the septo-hippocampal complex, and projections to the hippocampus (which travel in a fiber bundle called the fornix and are often called septohippocampal fibers) are some of largest projections from the septal region. Although the precise role of the septal nuclei in memory functions is not yet clear, the hippocampus receives the majority of its acetylcholine projections from the septal region. These neurons are activated during learning and degenerate in conditions like Alzheimer's disease that are characterized by disruptions in memory processes.

The septal nuclei have been implicated in a number of other roles such as social behavior <https://www.ncbi.nlm.nih.gov/pubmed/26318330> and the expression of fear <http://learnmem.cshlp.org/content/17/3/134.long>, and abnormalities in septal functioning have been linked to a variety of disorders ranging from depression to schizophrenia. <https://www.ncbi.nlm.nih.gov/pubmed/15297155> The septal area, however, including both the septum pellucidum and septum verum/septal nuclei, is still relatively poorly understood; it will take more research to fully elucidate its functions and influence on behavior.

Literature has shown that schizophrenia, affective psychosis, self-mutilation, developmental delays, atypical psychosis, and bipolar disorder have been found in patients that show septum pellucidum agenesis

The absence of the septum pellucidum is a rare brain abnormality, especially when it co-occurs with schizophrenia. The relationship of the septum pellucidum to the other structures in the limbic system suggests that disturbance of the septum pellucidum may have a role in the neurological etiology of schizophrenia.

https://pubmed.ncbi.nlm.nih.gov/30150022/

Abstract

Patients with schizophrenia are known to have increased prevalence of abnormalities in midline brain structures, such as a failure of the septum pellucidum to fuse (cavum septum pellucidum) and the absence of the adhesio interthalamica. This is the first study to investigate the prevalence of these abnormalities across a large multidiagnostic sample. Presence of cavum septum pellucidum and absence of the adhesio interthalamica was assessed in 639 patients with chronic schizophrenia, delusional disorder, schizoaffective disorder, bipolar disorder, major depressive disorder, or a first episode of psychosis, mania or unipolar depression. This was compared with 223 healthy controls using logistic-regression-derived odds ratios (OR). Patients with psychotic or mood disorders showed an increased prevalence of both abnormalities (OR of cavum septum pellucidum = 2.1, OR of absence of the adhesio interthalamica = 2.6, OR of both cavum septum pellucidum and absence of the adhesio interthalamica = 3.8, all P < .001). This increased prevalence was separately observed in nearly all disorders as well as after controlling for potential confounding factors. This study supports a general increased prevalence of midline brain abnormalities across mood and psychotic disorders. This nonspecificity may suggest that these disorders share a common neurodevelopmental etiology.

https://rarediseases.info.nih.gov/diseases/7627/septo-optic-dysplasia

https://rarediseases.info.nih.gov/diseases/9253/absence-of-septum-pellucidum

https://rareguru.com/library/disease/79/absence-of-septum-pellucidum

https://www.hindawi.com/journals/crips/2020/8935986/