Cerebral infarct (stroke) often causes devastating and irreversible losses of function, in part because of the brain's limited capacity for anatomical reorganization. The purine nucleoside inosine has previously been shown to induce neurons to express a set of growthassociated proteins and to extend axons in culture and in vivo. We show here that in adult rats with unilateral cortical infarcts, inosine stimulated neurons on the undamaged side of the brain to extend new projections to denervated areas of the midbrain and spinal cord. This growth was paralleled by improved performance on several behavioral measures. C erebral ischemic infarct, or stroke, affects approximately 750,000 people annually in the U.S. alone. Depending on the locus of damage and other complicating factors, stroke can result in devastating losses in sensory, motor, and cognitive functions. A limited amount of synaptic reorganization is thought to occur spontaneously in the brain after stroke (1-5) or focal injury (6, 7) and can be enhanced by training (8, 9). However, there is little evidence that undamaged neurons can extend lengthy projections to reinnervate brain regions that have lost their normal inputs, nor are any clinical methods available to improve functional outcome by stimulating axonal reorganization after stroke.The purine nucleoside inosine enters cells via facilitated diffusion or can be synthesized readily from adenosine. In at least some neurons, inosine activates an intracellular signaling pathway that regulates the expression of multiple genes involved in axon outgrowth (10,11). In vivo, inosine treatment can promote extensive sprouting of the intact corticospinal tract (CST) into areas denervated by transecting the contralateral CST (12). Here, we have investigated whether inosine treatment can stimulate axonal growth and help improve behavioral outcome after stroke. The rat's sensorimotor cortex is required for fine motor control of the contralateral limbs (5,13,14). After creating a stroke that damaged most of the sensorimotor cortex on one side of the brain, we tested whether inosine could induce neurons in the intact hemisphere to grow new connections to denervated target areas and restore cortical control to the hemiparetic side. Although a number of neural pathways may be important in this regard, we have focused on the corticorubral tract and CST, two pathways that help mediate fine motor coordination (15,16). Our results demonstrate that inosine stimulates significant axonal reorganization after stroke and leads to improved performance on several sensorimotor tasks. MethodsSurgery. Male Sprague-Dawley rats (250-325 g, age range 8-10 weeks: Charles River Breeding Laboratories) were used throughout. In a pilot study done in collaboration with Cerebrotec (Boston), we investigated whether inosine treatment would improve behavioral outcome after stroke. Under halothane anesthesia, rats were placed on their sides, and a vertical incision was made midway between the right orbit and external auditory canal. The underly...

Mammalian retinal ganglion cells (RGCs) do not normally regenerate their axons through an injured optic nerve, but can be stimulated to do so by activating macrophages intraocularly. In a cell culture model of this phenomenon, we found that a small molecule that is constitutively present in the vitreous, acting in concert with macrophage-derived proteins, stimulates mature rat RGCs to regenerate their axons if intracellular cAMP is elevated. In lower vertebrates, RGCs regenerate their axons spontaneously in vivo, and in culture, the most potent axon-promoting factor for these cells is a molecule that resembles the small vitreous-derived growth factor from the rat. This molecule was isolated chromatographically and was shown by mass spectrometry to be a carbohydrate. In agreement with this finding, D-mannose proved to be a potent axon-promoting factor for rat RGCs (ED50 approximately 10 microm); this response was cAMP-dependent and was augmented further by macrophage-derived proteins. Goldfish RGCs showed far less selectivity, responding strongly to either D-mannose or D-glucose in a cAMP-independent manner. These findings accord well with the success or failure of optic nerves to regenerate in higher and lower vertebrates in vivo. The axon-promoting effects of mannose are highly specific and are unrelated to energy metabolism or glycoprotein synthesis.

Opsonic fibronectin is known to modulate macrophage (RE cell) and neutrophil Phagocytic function. Its depletion has been documented following trauma, burn, and operation in patients with rapid restoration of normal levels unless bacteremia and/or wound sepsis intervenes. Sepsis is associated with a secondary phase of opsonic fibronectin deficiency. We have observed in burn patients that this secondary phase of opsonic fibronectin depletion following trauma and burn is seen two to three days prior to the onset of clinical sepsis, raising the question of whether this deficiency sensitized the host to the subsequent development of sepsis or whether its deplection was merely an unsuspected sensitive indication of preclinical sepsis. To address the possibility that opsonic fibronectin deficiency might lower resistance to sepsis, Sprague-Dawley rats (200 gm) were partially depleted (35%) of their opsonic fibronectin prior to intraperitoneal inoculation with Staphylococcus aureus. Mortality to S. aureus peritonitis was significantly (p < 0.05) increased in animals with fibronectin deficiency. Furthermore, in control animals, nonsurvival was also associated with significantly (p < 0.05) lower initial fibronectin levels than survival. However, peritonitis itself also resulted in an early (within one hour) depletion of opsonic fibronectin followed by a marked "hyperopsonemia" within 12 hours in both groups. Thus, opsonic fibronectin depletion decreases resistance to sepsis, and the development of sepsis itself will initiate opsonic fibronectin deficiency. Host defense against infection may depend on early restoration and maintenance of normal opsonic fibronectin levels following trauma, burn, and operation, as well as the ability of the host to mount an appropriate hyperopsonemic elevation of fibronectin levels in response to infection.