Effects of central administration of insulin or l-NMMA on rat skeletal muscle microvascular perfusion

AIM

Intracerebroventricular (ICV) administration of a nitric oxide synthase (NOS) inhibitor to rats has been reported to raise blood pressure (BP) and cause insulin resistance, suggestive of a central effect of insulin that is NO dependent. Herein we test whether ICV insulin has peripheral haemodynamic and metabolic effects and whether peripheral effects of systemic insulin are affected by the ICV administration of the NOS inhibitor N(G) -methyl-l-arginine (l-NMMA).

METHODS

Anaesthetized rats were fitted with an ICV cannula for insulin, artificial cerebrospinal fluid (aCSF) or l-NMMA infusion. Rats receiving ICV l-NMMA (500 µg) underwent systemic insulin clamp (10 mU/min/kg) or saline treatment for 70 min and were compared with animals receiving an equal amount of l-NMMA infused systemically.

RESULTS

ICV aCSF or insulin (135 mU/min/kg brain) for 70 min or systemic l-NMMA (500 µg) had no effect on BP, heart rate (HR), femoral blood flow (FBF), glucose infusion rate, muscle 2-deoxyglucose uptake, microvascular perfusion or plasma insulin. However, ICV l-NMMA reduced systemic insulin-mediated increases in FBF (2.05 ± 0.08 to 1.55 ± 0.15 ml/min), 2-deoxyglucose uptake (17.7 ± 0.15 to 10.0 ± 0.03 µg/g/min) and microvascular perfusion (10.5 ± 0.5 to 6.6 ± 1.1 mol/min) (each mean ± SE, p < 0.05); plasma insulin, HR and BP were unaffected.

CONCLUSIONS

Central insulin administration had no effect on skeletal muscle haemodynamics or glucose metabolism. However, systemic insulin-mediated increases in limb blood flow, muscle microvascular perfusion and glucose uptake may be regulated by a central pathway that is NO dependent.

Olfactory ensheathing cells promote collateral axonal branching in the injured adult rat spinal cord

In recent years, injection of olfactory ensheathing cells (ECs) into the spinal cord has been used as an experimental strategy to promote regeneration of injured axons. In this study, we have compared the effects of transplanting encapsulated ECs with those injected directly into the spinal cord. The dorsal columns of adult rats were cut at T(8-9) and rats in experimental groups received either EC-filled porous polymer capsules or culture medium (CM)-filled capsules with ECs injected at the injury site. Control rats were in three groups: (1) uninjured, (2) lesion with transplantation of CM-filled capsules and (3) lesion with transplantation of CM-filled capsules and injections of CM. Three weeks after injury, Fluororuby was injected into the hindlimb motor and somatosensory cortex to label corticospinal neurons. Observations indicated that there were a few regenerating fibres, up to 10, in the EC-treated groups. In rats that received encapsulated ECs, regenerating fibres were present in close association with the capsule. Rats that received EC injections demonstrated a significant increase in the number of collateral branches from the intact ventral corticospinal tract (vCST) compared with the corresponding control, CM-injected group (P=0.003), while a trend for increased collateral branches was observed in rats that received encapsulated ECs (P=0.07).

Mice lacking alpha-synuclein display functional deficits in the nigrostriatal dopamine system

alpha-Synuclein (alpha-Syn) is a 14 kDa protein of unknown function that has been implicated in the pathophysiology of Parkinson's disease (PD). Here, we show that alpha-Syn-/- mice are viable and fertile, exhibit intact brain architecture, and possess a normal complement of dopaminergic cell bodies, fibers, and synapses. Nigrostriatal terminals of alpha-Syn-/- mice display a standard pattern of dopamine (DA) discharge and reuptake in response to simple electrical stimulation. However, they exhibit an increased release with paired stimuli that can be mimicked by elevated Ca2+. Concurrent with the altered DA release, alpha-Syn-/- mice display a reduction in striatal DA and an attenuation of DA-dependent locomotor response to amphetamine. These findings support the hypothesis that alpha-Syn is an essential presynaptic, activity-dependent negative regulator of DA neurotransmission.

Evidence for a novel neurotrophic factor for dopaminergic neurons secreted from mesencephalic glial cell lines

Our previous studies have shown that primary mesencephalic glia secrete factors that promote dopaminergic cell survival and differentiation in vitro. To obtain enough starting material to identify the neurotrophic activity, embryonic day (E)14.5 rat mesencephalic glia were stimulated with acidic fibroblast growth factor to increase number of cells. These cells were replated in the absence of neurons and immortalized by transfection with the SV 40 large T-antigen. Clonal cell lines were established and characterized for immunoreactivity (IR) to various glial and non-glial markers. Media conditioned by these cell lines were tested for survival-promoting effects on dopaminergic neurons in serum-free cultures of the dissociated E14.5 rat mesencephalon. All cell lines expressed IR for the astrocytic marker, GFAP, the oligodendroglial marker, CNP, and for A2B5, a marker for O-2A progenitor cells, but were negative for the neuronal marker, microtubule associated protein-2, and the fibroblast marker, fibronectin. Moreover, treatment of serum-free cultures of the dissociated E14.5 mesencephalon with glial cell line-CM conditioned medium (CM) delayed dopaminergic cell death in a dose-dependent manner, resulting in a maximal twofold to sixfold increase in the number of surviving tyrosine hydroxylase-IR neurons at various days in vitro. This increase in dopaminergic cell survival was not mimicked by GDNF, BDNF or NT-3 within the initial 3 days of cultivation. Moreover, initial biochemical characterization demonstrated that the neurotrophic activity is restricted to the high MW fraction of >50 kD of glial cell line-CM. Since the apparent MW of this factor exceeds the size of most known growth factors, it may represent a novel dopaminergic neurotrophic factor.