IGF-I and TGF-β2 have a key role on regeneration of nitric oxide synthase (NOS)-containing nerves after cavernous neurotomy in rats

Abstract

The molecular mechanism of nitric oxide synthase (NOS)-containing nerve regeneration is still unknown. It is believed that growth factors are involved in this phenomenon. We investigated the change of NOS containing nerve ®bers and the mRNA expression of insulin like growth factor (IGF)-I, nerve growth factor (NGF), transforming growth factor (TGF)-a, TGF-b 1 , TGF-b 2 , TGF-b 3 , vascular endothelial growth factor (VEGF), endothelial NOS (eNOS) and neuronal NOS (nNOS) on the penis after cavernous nerve neurotomy in rats.Male rats were divided into four groups: (1) sham operation (n 14); (2) unilateral neurotomy of a 5 mm segment of the cavernous nerve (n 21); (3) unilateral neurotomy with growth hormone (n 14); and (4) bilateral neurotomy (n 21). Electrostimulation of the intact cavernous nerve or pelvic ganglion were performed at one, three and six months. Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining and immunohistochemistry were used to identify NOS in the penis. The gene expression for growth factors, eNOS and nNOS were investigated in corporal tissue by reverse transcriptase-polymerase chain reaction (RT-PCR).One month after neurotomy, both unilateral and bilateral neurotomy groups showed signi®cant decreases in NOS-containing nerve ®bers on the dorsal and intracavernosal nerves on the side of neurotomy. Signi®cantly lower mRNA expression of nNOS, IGF-I and TGF-b 2 , higher mRNA expression of eNOS and VEGF 189 were shown in these groups. At three months, the number of NOS-containing nerve ®bers in the unilateral neurotomy group increased only slightly, while the GH-treated group showed a signi®cant increase. At six months, those in the intracavernosal nerve only increased in a signi®cant amount (P`0.0001), however mRNA expression of nNOS, IGF-I and TGF-b 2 showed a signi®cant increase as early as at three months. After bilateral neurotomy, the NOS-positive nerve ®bers in the dorsal and intracavernosal nerve were signi®cantly decreased at one month and remained so at six months; no erectile response could be elicited by pelvic ganglion stimulation. In the unilateral neurotomy group at six months, more NOS-positive neurons in the pelvic ganglia were found on the intact side than on the side of the neurotomy (P`0.003), indicating that the regeneration derived from pelvic ganglion neurons on the intact side. Furthermore, electrostimulation in the unilateral neurotomy group revealed a greater maximal intracavernosal pressure and a shorter latency period at six months than at one month (P`0.014, P`0.001, respectively).These data suggest that IGF-I and TGF-b 2 may play a key role in the regeneration of nNOScontaining nerve ®bers in the dorsal and intracavernosal nerves, and eNOS increases temporarily in the intracavernous involving VEGF 189 after unilateral cavernous nerve injury.

Is It Possible to Recover Erectile Function Spontaneously after Cavernous Nerve Injury? Time-Dependent Structural and Functional Changes in Corpus Cavernosum Following Cavernous Nerve Injury in Rats

“…Previous rat studies found no evidence of nerve regeneration up to 6 months after CN inury. 27,28 However, the present study showed that the expression of nNOS protein transiently decreased at 1 week after CN resection or crush injury and then recovered to control values, which supports the study by Fall et al 9 suggesting spontaneous nerve regeneration after bilateral CN ablation. Absence of functional recovery despite spontaneous nerve regeneration strongly suggests that other pathophysiologic mechanisms, such as increased corporal apoptosis or ROCK activity or structural alteration such as a loss of SMC or an increase in collagen content, leading to corporal fibrosis, may be key factors for post-RP ED.…”

Neurturin is a neurotrophic factor for penile parasympathetic neurons in adult rat

“…Although the similarity of penile neurons between rat and mice cannot be assumed, our results support the idea that GFR␣2-mediated signaling is important for both species. Third, trophic support by other neurotrophic factors is also a reasonable possibility (Burgers et al, 1991;Te et al, 1994;Jung et al, 1999).…”

Herpes simplex virus vector-mediated delivery of glial cell line-derived neurotrophic factor rescues erectile dysfunction following cavernous nerve injury

“…According to the previous studies, the change in the number of nNOSpositive MPG neurons was more significant 3-6 months after the nerve injury. 60 Therefore, the experimental period of our study might be too short to observe significant changes in the number of nNOS-expressing neurons.…”