Arachnoid

The intrathecal space is located between the arachnoid and the pia mater of the spinal cord. It contains the cerebrospinal fluid, spinal nerves and blood vessels. 

Spinal cord I Epidural space Arachnoid space... 

Meninges Group of three membranes (dura mater, pia mater, arachnoid) surrounding the brain and spinal cord. 

Mizoguchi, A., Eguchi, N., Kimura, K. el al. (2001). Dominant localization of prostaglandin D receptors on arachnoid trabecular cells in mouse basal forebrain and their involvement in the regulation of non-rapid eye movement sleep. Proc. Natl. Acad. Sci. USA 98 (20). 11674-9. 

The exit of drugs from the CNS can involve (1) diffusion across the blood-brain barrier in the reverse direction at rates determined by the lipid solubility and degree of ionization of the drug, (2) drainage from the cerebrospinal fluid (CSP) into the dural blood sinuses by flowing through the wide channels of the arachnoid villi, and (2) active transport of certain organic anions and cations from the CSF to blood across the choroid plexuses... 

CRUSTACEANS AND ARACHNOIDS Copepod, Acartia tonsa 290 50% immobilized in 48 h 1... 

ARACHNOIDS Horseshoe crab, Limulus polyphemus Molting and survival adversely affected during 5-day exposure 11... 

The entire CNS is covered by the meninges, which form a protective covering. The outermost is the dura, which is tough and leathery in consistency. It is highly vascularized and innervated, so it is sensitive to pain. The arachnoid membrane is a weblike, spongy layer beneath the dura. Beneath the arachnoid is the subarachnoid space, which is filled with cerebrospinal fluid. Beneath the subarachnoid space is a thin layer of cells called the pia, which covers the brain and spinal cord. Ventricular System... 

WB shows CYP7A/induction in arachnoid, dura mater, choroid plexus, pineal gland, and pituitary of rat brain by //-naphthoflavone (Morse et al., 1998). 

The brain lacks connection with the lymphatic system. The interstitial fluid drains into the perivascular space, which surrounds arteries and veins, and from there into the sub-arachnoid space where it mixes with the cerebrospinal fluid. This is secreted by the choroid plexuses, which are capillary-rich outgrowths into cavities within the brain, known as ventricles. From the ventricles, cerebrospinal fluid flows through channels to the surface of the brain and... 

After i.c.v. injection, the rate of elimination from the CNS compartment is dominated by cerebrospinal fluid dynamics. The CSF, which is secreted by the choroid plexus epithelium across the apical membrane, circulates along the surface and convexities of the brain in a rostral to caudal direction. It is reabsorbed by bulk flow into the peripheral bloodstream at the arachnoid vUh within both cranial and spinal arachnoid spaces [62]. Of note is that the turnover rate of total CSF volume is species dependent and varies between approximately... 

The risk of severe neurotoxic reactions is sharply increased in patients with impaired renal function or prerenal azotemia. These include disturbances of vestibular and cochlear function, optic nerve dysfunction, peripheral neuritis, arachnoiditis, and encephalopathy. The incidence of clinically detectable, irreversible vestibular damage is particularly high in patients treated with streptomycin. 

CSF Alls the intracerebral (intraventricular 20%) and extracerebral (subarachnoidal 80%) space. CSF originates from plasma (ultraflltration) as well as from choroid plexus (active secretion) in the ventricles, flows through cisternae and the subarachnoid space, and finally drains through the arachnoid villi into venous blood. Equilition processes establish a physiological ratio between composition and resorption of CSF. CSF flow starts around the time of birth and reaches its maximum rate at four months after birth, following the complete maturation of the arachnoid villi. 

Fig. 1. Model of subarachnoidal space, CSF flow, and molecular flux (N1). After CSF production in choroid plexus of the ventricles (1,2,3), CSF passes the aperture (4,5), reaches the cistemae (6-9), and divides into a cortical and a lumbar branch of the subarachnoidal space. Finally, CSF drains through the arachnoid villi into venous blood. The illustration represents an idealized cross section through the subarachnoid space. Molecules diffuse from serum with a concentration C(ser) flu ough tissue along the diffusion path x into the subarachnoid space with a concentration C(csF)- Th molecular flux J depends on the local gradient Ac/Ax or dddx and the diffusion constant D. The CSF concentration increases with decreasing volume exchange, i.e., decreasing CSF volume bulk flow (F= 500 ml/day). The flow rate of a molecule in CSF is r= FIA, where A is the varying cross section of the subarachnoid space.

A blood-CSF barrier dysfunction (i.e., pathologically reduced CSF flow) can have different causes reduced CSF production rate, restricted flow in the subarachnoid space, or restricted passage through the arachnoid villi (F2, R5). 

The flow of cerebrospinal fluid is essentially unidirectional that is, it flows from its site of formation in the choroid plexus through the ventricles to its site of exit at the arachnoid villi. Drugs in this fluid can either enter the brain tissue or be returned to the venous circulation in the bulk flow of cerebrospinal fluid carried through the arachnoid villi. Some drugs, such as penicillin, wUl not leave the cerebrospinal fluid compartment by bulk flow but will be actively transported by the choroid plexus out of the fluid and back into the blood. Finally, drugs may diffuse from brain tissue directly into blood capUlaries. 

Myelosuppression is a major toxicity, as is severe bone marrow hypoplasia. Nausea and mucositis also may occur. Intrathecal administration occasionally produces arachnoiditis or more severe neurological toxicity. 

Paresthesias, weakness and paralysis of lower extremity, hypotension, high or total spinal block, urinary retention or incontinence, fecal incontinence, headache, back pain, septic meningitis, meningismus, arachnoiditis, shivering cranial nerve palsies due to traction on nerves from loss of CSF, and loss of perineal sensation and sexual function Rare... 

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