Retinal Input to the Primate Lateral Geniculate Nucleus Revealed by Injection of a Different Label Into Each Eye

ABSTRACT

The primate lateral geniculate nucleus has long been a favorite structure among anatomists because of its striking lamination. It has been shown that each lamina receives input from a different eye using various single label techniques but never by double labeling. Here, we illustrate the organization of retinal inputs to the lateral geniculate nucleus by injection of cholera toxin-B conjugated to Alexa Fluor-488 into the right eye and cholera toxin-B conjugated to Alexa Fluor-594 into the left eye.

Columnar and Laminar Segregation of Retinal Input to the Primate Superior Colliculus Revealed by Anterograde Tracer Injection Into Each Eye

Purpose

After the lateral geniculate nucleus, the superior colliculus is the richest target of retinal projections in primates. Hubel et al. used tritium autoradiography to show that axon terminals emanating from one eye form irregular columns in the stratum griseum superficiale. Unlabeled gaps were thought to be filled by the other eye, but this assumption was never tested directly.

Methods

Experiments were performed in two normal macaques. In monkey 1, [³H]proline was injected into the left eye and the pattern of radiolabeling was examined in serial cross-sections through the entire superior colliculus. In monkey 2, cholera toxin subunit B conjugated to Alexa 488 was injected into the right eye and cholera toxin subunit B - Alexa 594 was injected into the left eye. The two fluorescent labels were compared in a reconstruction of the superior colliculus prepared from serial sections.

Results

In monkey 1, irregular columns of axon terminals were present in the superficial grey. The projection from the peripheral retina was stronger than the projection from the macula. In monkey 2, the two fluorescent Alexa tracers mainly interdigitated: a conspicuous gap in one label was usually filled by a clump of the other label. There was also partial laminar segregation of ocular inputs. In the far peripheral field representation, the contralateral eye's input generally terminated closer to the tectal surface. In the midperiphery the eyes switched, bringing the ipsilateral input nearer the surface.

Conclusions

Direct retinal input to the macaque superior colliculus is segregated into alternating columns and strata, despite the fact that tectal cells respond robustly to stimulation of either eye.

Activation of neuronal Ras-related C3 botulinum toxin substrate 1 (Rac1) improves post-stroke recovery and axonal plasticity in mice

Long-term disability after stroke is common but the mechanisms of post-stroke recovery remain unclear. Cerebral Ras-related C3 botulinum toxin substrate (Rac) 1 contributes to functional recovery after ischemic stroke in mice. As Rac1 plays divergent roles in individual cell types after central neural system injury, we herein examined the specific role of neuronal Rac1 in post-stroke recovery and axonal regeneration. Young male mice were subjected to 60-min of middle cerebral artery occlusion (MCAO). Inducible deletion of neuronal Rac1 by daily intraperitoneal injection of tamoxifen (2 mg/40 g) into Thy1-creER/Rac1-floxed mice day 7-11 after MCAO worsened cognitive (assayed by novel object recognition test) and sensorimotor (assayed by adhesive removal and pellet reaching tests) recovery day 14-28 accompanied with the reduction of neurofilament-L (NFL) and myelin basic protein (MBP) and the elevation of glial fibrillary acidic protein (GFAP) in the peri-infarct zone assessed by immunostaining. Whereas the brain tissue loss was not altered assayed by cresyl violet staining. In another approach, delayed overexpression of neuronal Rac1 by injection of lentivirus encoding Rac1 with neuronal promotor into both the cortex and striatum (total 4 μl at 1 × 10⁹ transducing units/mL) of stroke side in C57BL/6J mice day 7 promoted stroke outcome, NFL and MBP regrowth and alleviated GFAP invasion. Furthermore, neuronal Rac1 over-expression led to the activation of p21 activating kinases (PAK) 1, mitogen-activated protein kinase kinase (MEK) 1/2 and extracellular signal-regulated kinase (ERK) 1/2, and the elevation of brain-derived neurotrophic factor (BDNF) day 14 after stroke. Finally, we observed higher counts of neuronal Rac1 in the peri-infarct zone of subacute/old ischemic stroke subjects. This work identified a neuronal Rac1 signaling in improving functional recovery and axonal regeneration after stroke, suggesting a potential therapeutic target in the recovery stage of stroke.

Stable reduction of STARD4 alters cholesterol regulation and lipid homeostasis

STARD4, a member of the evolutionarily conserved START gene family, is a soluble sterol transport protein implicated in cholesterol sensing and maintenance of cellular homeostasis. STARD4 is widely expressed and has been shown to transfer sterol between liposomes as well as organelles in cells. However, STARD4 knockout mice lack an obvious phenotype, so the overall role of STARD4 is unclear. To model long term depletion of STARD4 in cells, we use short hairpin RNA technology to stably decrease STARD4 expression in human U2OS osteosarcoma cells (STARD4-KD). We show that STARD4-KD cells display increased total cholesterol, slower cholesterol trafficking between the plasma membrane and the endocytic recycling compartment, and increased plasma membrane fluidity. These effects can all be rescued by transient expression of a short hairpin RNA-resistant STARD4 construct. Some of the cholesterol increase was due to excess storage in late endosomes or lysosomes. To understand the effects of reduced STARD4, we carried out transcriptional and lipidomic profiling of control and STARD4-KD cells. Reduction of STARD4 activates compensatory mechanisms that alter membrane composition and lipid homeostasis. Based on these observations, we propose that STARD4 functions as a critical sterol transport protein involved in sterol sensing and maintaining lipid homeostasis.

Abstract TP263: Activation of Endothelial p21-Activated Kinase 1 Provides Neuroprotection After Stroke

Stroke is a major cause of death and long-term disability. Pak1 is implicated in many neurological disorders as it has been suggested to promote neuronal survival. However, its function and mechanisms have not been investigated in stroke. We assessed the hypothesis that Pak1 provides neuroprotection in stroke by stimulating the secretion of brain-derived neurotrophic factor (BDNF) in endothelial cells.

Transient focal ischemia was induced by middle cerebral artery occlusion (MCAO, 90 mins) in young WT male mice. Two doses of IPA3, a Pak1 specific inhibitor, were injected (i.p.) at 30 minutes prior to stroke and 1.5 hours after stroke. For mechanism studies, lentivirus (LV) encoding Pak1 or IPA3 was used to overexpress or pharmacologically inhibit Pak1 in mouse primary brain microvascular endothelial culture. Then the cells were subjected to OGD (16h) with 48 h re-oxygenation and conditioned media (Endo-CM) were collected subsequently. Mouse primary cortical neuron culture was treated with Endo-CM after OGD (90 mins) and neuronal death was assessed 24 hours later.

Pak1 activation (phosphorylated Pak1) was observed in the ischemic hemispheres 6 and 72 hours after MCAO (p-Pak1: sham 94.5± 4.7% versus 6-hour stroke 192.5 ± 10.4% ; sham 94.5± 4.7% versus 72-hour stroke 254.4 ± 32.3%, n = 4 p/g, p<0.05 for both). Administration of IPA3 increased brain infarct size assessed 24 hours after MCAO stroke. In endothelial cultures, overexpression of Pak1 increased BDNF secretion in Endo-CM after OGD (LV-GFP 22.7 ± 2.8 versus LV-Pak1 48.6± 5.5, n = 4 p/g, p<0.05). Accordingly, inhibition of Pak1 attenuated levels of BDNF in Endo-CM (Vehicle 24.5 ± 1.5 versus IPA3 9.4± 0.7, n = 3 p/g, p<0.05). Finally, treatment with Endo-CM collected from Pak1 overexpressing culture reduced neuronal death after OGD (LV-GFP 36 ± 2% versus LV-Pak1 10± 1%, n = 3 p/g, p<0.05), while Endo-CM from cells treated with Pak1 inhibitor increased neuronal mortality (Vehicle 24± 7% versus IPA3 43± 2%, n = 3 p/g, p<0.05).

Taken together, we demonstrated that endothelial Pak1 provides neuroprotection after ischemia. Mechanically, our data revealed that activation of Pak1 stimulates endothelial production of a well-known potent neuroprotectant, BDNF.