Identification of penile inputs to the rat gracile nucleus

Effect of low-threshold versus high-threshold genitalia stimuli on the cystometry parameters in male rats

The cross talk between external genitalia and urinary bladder could be used as part of management to certain pathological conditions affecting urinary bladder. Since urinary bladder function is also affected by pathologies of other organs (e.g., colon and esophagus), the effect of genitalia stimuli on parameters of bladder function in normal or under different pathological conditions needs to be characterized. Cystometry recordings in male rats were used to examine the effect of low-threshold (LT) and high-threshold (HT) stimulation of the scrotum and penis on urinary bladder function. These effects were studied in intact, colon irritation (CI), and esophagus irritation (EI) groups. Although HT penile stimulation had a significant inhibitory effect on micturition reflex in all groups, CI hypersensitized the penile-bladder inhibitory reflex. In addition, LT penile stimulation had a significant inhibitory effect on micturition, which was significant in CI group only. On the other hand, HT penile stimulation in CI group significantly increased the timing parameters of cystometry. Whereas LT and HT penile stimuli in EI group had a significantly increasing effect on all pressure parameters of cystometry. The scrotal stimuli had minimal effect on bladder function in all groups except for HT scrotal stimulation in the CI group, where it had a significant inhibitory effect on micturition reflex and significantly increased the maximum pressure and pressure amplitude of micturition cycles. These results show that CI and EI exacerbate the effects of genitalia stimuli, especially penile stimuli, on urinary bladder function.

Estradiol treatment prevents injury induced enhancement in spinal cord dynorphin expression

Administration of the ovarian steroid estradiol in male and female animals has been shown to have neuromodulatory and neuroprotective effects in a variety of experimental models. In the present study, spinal tissues from dermatomes just above (T5–T7, at level) a severe chronic spinal cord injury (SCI) at T8 were analyzed for expression levels of prodynorphin (PRDN) and phospho-(serine 369) κ-opioid receptor (KOR-P) in 17 β estradiol (EB)- and placebo-treated adult male rats. Dynorphin was targeted since (1) it has previously been shown to be elevated post-SCI, (2) intrathecal injection of dynorphin produces several of the same adverse effects seen with a SCI, and (3) its increased expression is known to occur in a variety of different experimental models of central neuropathic pain. A significant elevation of extracellular levels of both PRDN and KOR-P in the placebo-treated SCI group relative to uninjured surgical sham controls was found in spinal tissues above the injury level, indicating increased dynorphin levels. Importantly, the EB-treated SCI group did not show elevations of PRDN levels at 6 weeks post-injury. Immunohistochemical analysis of at level tissues revealed that EB treatment significantly prevented a post-SCI increase in expression of PRDN puncta co-labeling synapsin I, a nerve terminal marker. The dynorphin-containing terminals co-labeled vesicular glutamate receptor-2 (a marker of glutamatergic terminals), a finding consistent with a non-opioid basis for the adverse effects of dynorphin. These results support a beneficial role for EB treatment post-SCI through a reduction in excessive spinal cord levels of dynorphin. Studies manipulating the timing of the EB treatment post-injury along with specific functional assessments will address whether the beneficial effects are due to EB’s potential neuromodulatory or neuroprotective action.

Select spinal lesions reveal multiple ascending pathways in the rat conveying input from the male genitalia

The specific white matter location of all the spinal pathways conveying penile input to the rostral medulla is not known. Our previous studies using rats demonstrated the loss of low but not high threshold penile inputs to medullary reticular formation (MRF) neurons after acute and chronic dorsal column (DC) lesions of the T8 spinal cord and loss of all penile inputs after lesioning the dorsal three-fifths of the cord. In the present study, select T8 lesions were made and terminal electrophysiological recordings were performed 45-60 days later in a limited portion of the nucleus reticularis gigantocellularis (Gi) and Gi pars alpha. Lesions included subtotal dorsal hemisections that spared only the lateral half of the dorsal portion of the lateral funiculus on one side, dorsal and over-dorsal hemisections, and subtotal transections that spared predominantly just the ventromedial white matter. Electrophysiological data for 448 single unit recordings obtained from 32 urethane-anaesthetized rats, when analysed in groups based upon histological lesion reconstructions, revealed (1) ascending bilateral projections in the dorsal, dorsolateral and ventrolateral white matter of the spinal cord conveying information from the male external genitalia to MRF, and (2) ascending bilateral projections in the ventrolateral white matter conveying information from the pelvic visceral organs (bladder, descending colon, urethra) to MRF. Multiple spinal pathways from the penis to the MRF may correspond to different functions, including those processing affective/pleasure/motivational, nociception, and mating-specific (such as for erection and ejaculation) inputs.