Characteristics of Electrical Synapses, C-terminals and Small-conductance Ca2+ activated Potassium Channels in the Sexually Dimorphic Cremaster Motor Nucleus in Spinal Cord of Mouse and Rat

Sexually dimorphic motoneurons (MNs) located in lower lumbar spinal cord are involved in mating and reproductive behaviours and are known to be coupled by electrical synapses. The cremaster motor nucleus in upper lumbar spinal cord has also been suggested to support physiological processes associated with sexual behaviours in addition to its thermoregulatory and protective role in maintaining testes integrity. Using immunofluorescence approaches, we investigated whether cremaster MNs also exhibit features reflecting their potential for electrical synaptic communication and examined some of their other synaptic characteristics. Both mice and rats displayed punctate immunolabelling of Cx36 associated with cremaster MNs, indicative of gap junction formation. Transgenic mice with enhanced green fluorescent protein (eGFP) reporter for connexin36 expression showed that subpopulations of cremaster MNs in both male and female mice express eGFP, with greater proportions of those in male mice. The eGFP+ MNs within the cremaster nucleus vs. eGFP- MNs inside and outside this nucleus displayed a 5-fold greater density of serotonergic innervation and exhibited a paucity of innervation by C-terminals arising from cholinergic V0c interneurons. All MNs within the cremaster motor nucleus displayed prominent patches of immunolabelling for SK3 (K+) channels around their periphery, suggestive of their identity as slow MNs, many though not all of which were in apposition to C-terminals. The results provide evidence for electrical coupling of a large proportion of cremaster MNs and suggest the existence of two populations of these MNs with possibly differential innervation of their peripheral target muscles serving different functions.

Cremaster muscle thickening: the anatomic difference in men with testicular retraction due to hyperactive cremaster muscle reflex

The objective was to assess whether men suffering from testicular retraction secondary to hyperactive cremaster muscle reflex have an anatomic difference in the thickness of the cremaster muscle in comparison to men who do not have retraction. From March 2021 to December 2021, 21 men underwent microsurgical subinguinal cremaster muscle release (MSCMR) on 33 spermatic cord units, as 12 of them had bilateral surgery, at Surgicare of South Austin Ambulatory Surgery Center in Austin, TX, USA. During that same time frame, 36 men underwent subinguinal microsurgical varicocele repair on 41 spermatic cord units, as 5 were bilateral for infertility. The thickness of cremaster muscles was measured by the operating surgeon in men undergoing MSCMR and varicocele repair. Comparison was made between the cremaster muscle thickness in men with testicular retraction due to a hyperactive cremaster muscle reflex undergoing MSCMR and the cremaster muscle thickness in men undergoing varicocele repair for infertility with no history of testicular retraction, which served as an anatomic control. The mean cremaster muscle thickness in men who underwent MSCMR was significantly greater than those undergoing varicocele repair for infertility, with a mean cremaster muscle thickness of 3.9 (standard deviation [s.d.]: 1.2) mm vs 1.0 (s.d.: 0.4) mm, respectively. Men with testicular retraction secondary to a hyperactive cremaster muscle reflex demonstrate thicker cremaster muscles than controls, those undergoing varicocele repair. An anatomic difference may be a beginning to understanding the pathology in men who struggle with testicular retraction.

CXCL9-Derived Peptides Differentially Inhibit Neutrophil Migration In Vivo through Interference with Glycosaminoglycan Interactions

Several acute and chronic inflammatory diseases are driven by accumulation of activated leukocytes due to enhanced chemokine expression. In addition to specific G protein-coupled receptor-dependent signaling, chemokine-glycosaminoglycan (GAG) interactions are important for chemokine activity in vivo. Therefore, the GAG-chemokine interaction has been explored as target for inhibition of chemokine activity. It was demonstrated that CXCL9(74-103) binds with high affinity to GAGs, competed with active chemokines for GAG binding and thereby inhibited CXCL8- and monosodium urate (MSU) crystal-induced neutrophil migration to joints. To evaluate the affinity and specificity of the COOH-terminal part of CXCL9 toward different GAGs in detail, we chemically synthesized several COOH-terminal CXCL9 peptides including the shorter CXCL9(74-93). Compared to CXCL9(74-103), CXCL9(74-93) showed equally high affinity for heparin and heparan sulfate (HS), but lower affinity for binding to chondroitin sulfate (CS) and cellular GAGs. Correspondingly, both peptides competed with equal efficiency for CXCL8 binding to heparin and HS but not to cellular GAGs. In addition, differences in anti-inflammatory activity between both peptides were detected in vivo. CXCL8-induced neutrophil migration to the peritoneal cavity and to the knee joint were inhibited with similar potency by intravenous or intraperitoneal injection of CXCL9(74-103) or CXCL9(74-93), but not by CXCL9(86-103). In contrast, neutrophil extravasation in the MSU crystal-induced gout model, in which multiple chemoattractants are induced, was not affected by CXCL9(74-93). This could be explained by (1) the lower affinity of CXCL9(74-93) for CS, the most abundant GAG in joints, and (2) by reduced competition with GAG binding of CXCL1, the most abundant ELR+ CXC chemokine in this gout model. Mechanistically we showed by intravital microscopy that fluorescent CXCL9(74-103) coats the vessel wall in vivo and that CXCL9(74-103) inhibits CXCL8-induced adhesion of neutrophils to the vessel wall in the murine cremaster muscle model. Thus, both affinity and specificity of chemokines and the peptides for different GAGs and the presence of specific GAGs in different tissues will determine whether competition can occur. In summary, both CXCL9 peptides inhibited neutrophil migration in vivo through interference with GAG interactions in several animal models. Shortening CXCL9(74-103) from the COOH-terminus limited its GAG-binding spectrum.

Visualizing calcium responses to acetylcholine convection along endothelium of arteriolar networks in Cx40BAC-GCaMP2 transgenic mice

Acetylcholine evokes endothelium-dependent vasodilation subsequent to a rise in intracellular calcium. Despite widespread application in human and animal studies, calcium responses to intravascular ACh have not been visualized in vivo. Microiontophoresis of ACh in tissue adjacent to an arteriole activates abluminal muscarinic receptors on endothelial cells within a "local" region of diffusion, but it is unknown whether ACh released in such fashion gains access to the flow stream resulting in further actions downstream. To test this hypothesis and provide new insight into calcium signaling in vivo, we studied the cremaster muscle microcirculation of anesthetized male Cx40(BAC)-GCaMP2 transgenic mice (n = 22; 5-9 mo; 33 ± 1 g) expressing the fluorescent calcium sensor GCaMP2 selectively in arteriolar endothelial cells. Submaximal ACh stimuli were delivered using microiontophoresis (1-μm pipette tip, 500 nA). With stimulus duration <500 ms or with the micropipette positioned within one vessel diameter (∼30 μm) away from an arteriole, endothelial cell calcium fluorescence was restricted to the region of ACh diffusion (<200 μm). In contrast, with the micropipette tip positioned immediately adjacent to an arteriole or within its lumen, calcium fluorescence encompassed entire networks downstream. The velocity of downstream calcium signaling in response to ACh increased with centerline velocity of fluorescent tracer microbeads (r(2) > 0.99; range: <1 mm/s to >10 mm/s). Diverting arteriolar blood flow into a side branch redirected downstream fluorescence responses to ACh; occluding flow abolished responses. Blocking luminal muscarinic receptors (intravascular glycopyrrolate; 6 μg/kg) inhibited downstream responses reversibly. Through visualizing the actions of a "local" ACh stimulus on endothelial cell calcium fluorescence in vivo, the present findings illustrate that transmural diffusion and convection of an agonist can activate entire networks of arteriolar endothelial cells concomitant with its delivery in the flow stream.

Association of testicular undescent induced by prenatal flutamide treatment with thickening of the cremaster muscle in rats

Background and Aims:  Previously, in cryptorchid rats, which were induced by prenatal exposure to flutamide, we found a thickening of the cremaster muscle. This study was undertaken to quantify the increase of the cremaster muscle thickness in the cryptorchid rats, and to examine its possible relationship with the proliferation of muscle cells. Methods:  To obtain cryptorchid rats, pregnant Wistar rats were subcutaneously injected with flutamide (100 mg/kg per day) during gestational days 16-17. Serial sections of the scrotum, containing the testis and cremaster muscle, were prepared from the control and cryptorchid rats that were 2-6 weeks of age, and stained with hematoxylin-eosin for morphometry, or stained with antibody against the proliferating cell nuclear antigen (PCNA) to analyze the cell proliferation ability. Results:  The thickened cremaster muscle was always associated with cryptorchid testis and, in the case of unilateral cryptorchidism, the cremaster muscle of the contralateral (descended testis) side exhibited normal thickness. The average thickness of the affected cremaster muscle was 0.80 and 1.89 mm at 4 and 6 weeks of age, respectively, although that of the normal muscle was 0.28 and 0.33 mm at the same time period, respectively. Conclusion:  Our results showed that the cremaster muscle of the cryptorchid rats was significantly thicker than that of the control rats. The immunohistochemical analysis revealed that a thickened cremaster muscle contained many PCNA-positive nuclei even at 4 weeks of age, in contrast to the control, which had only a few positive nuclei. Our present study indicates that continuous proliferation of the muscle cells associated with cryptorchid testis increases the thickness of cremaster cells in rats exposed to flutamide prenatally. (Reprod Med Biol 2003; 2: 109-113).

An anatomical and electrophysiological study of the genitofemoral nerve and some of its targets in the male rat

Anatomical descriptions of the genitofemoral nerve (GFn) innervating the lower pelvic area are contradictory. Here we re-examine its origin and innervation by its various branches of principal target organs in the male rat. Using gross dissection, electrophysiological techniques and retrograde tracing of motoneurones with horseradish peroxidase, we confirm that the GFn originates from lumbar spinal nerves 1 and 2, and that at the level of the common iliac artery it divides into a lateral femoral and a medial genital branch. In contrast to previous studies, we report that the genital and not the femoral branch innervates the abdominal-inguinal skin, and not only the genital but also the femoral branch innervates the cremaster muscle (Cm) surrounding the testes. Motoneurones innervating the Cm proper are located in the ventral nucleus of L1 and L2, and those innervating the muscular transition region of the rostral Cm are located in the ventral nucleus in L1 and the ventrolateral nucleus in L2. The GFn may contribute to male reproductive performance by transmitting cutaneous information during copulation and, via contraction of the Cm to promote ejaculation, the protective displacement of the testes into the abdominal cavity during fighting and as a sperm-protecting thermoregulatory measure.