Sex differences in c‐Fos and EGR‐1/Zif268 activity maps of rat sacral spinal cord following cystometry‐induced micturition

Abstract

Storage and voiding of urine from the lower urinary tract (LUT) must be timed precisely to occur in appropriate behavioral contexts. A major part of the CNS circuit that coordinates this activity is found in the lumbosacral spinal cord. Immediate early gene (IEG) activity mapping has been widely used to investigate the lumbosacral LUT-related circuit, but most reports focus on the effects of noxious stimulation in anesthetized female rats. Here we use c-Fos and EGR-1 (Zif268) activity mapping of lumbosacral spinal cord to investigate cystometry-induced micturition in awake female and male rats. In females, after cystometry c-Fos neurons in spinal cord segments L5-S2 were concentrated in the sacral parasympathetic nucleus (SPN), dorsal horn laminae II-IV, and dorsal commissural nucleus (SDCom). Comparisons of cystometry and control groups in male and female revealed sex differences. Activity mapping suggested dorsal horn laminae II-IV was activated in females but showed net inhibition in males. However, inhibition in male rats was not detected by EGR-1 activity mapping, which showed low coexpression with c-Fos. A class of catecholamine neurons in SPN and SDCom neurons were also more strongly activated by micturition in females. In both sexes, most c-Fos neurons were identified as excitatory by their absence of Pax2 expression. In conclusion, IEG mapping in awake male and female rats has extended our understanding of the functional molecular anatomy of the LUT-related circuit in spinal cord. Using this approach, we have identified sex differences that were not detected by previous studies in anesthetized rats.

Recording of Electrically Evoked Neural Activity and Bladder Pressure Responses in Awake Rats Chronically Implanted With a Pelvic Nerve Array

“…This pattern of c-Fos upregulation is characteristic of responses to noxious stimuli in the bladder (Birder and de Groat, 1992de Groat, , 1993Lanteri-Minet et al, 1995;Kakizaki et al, 1996;Vizzard, 2000). Our observation of c-Fos expression in other regions of the spinal cord demonstrated non-nociceptive pathways typically activated by cystometry, as reported previously (Birder and de Groat, 1992de Groat, , 1993Wiedmann et al, 2020).…”

“…Changes in c-Fos expression was assessed (n = 3) on day 10 of implantation, following 60 min of cystometry and pelvic nerve stimulation testing. In spinal segments L5-S1, neurons with c-Fos + nuclei were most densely distributed in dorsal horn, the sacral dorsal commissural nucleus (SDCom) and the SPN of segments L6 and S1 ( Figures 5A-C), consistent with our recent activity mapping study of cystometry in awake male rats (Wiedmann et al, 2020). No difference was detected in the pattern of c-Fos between the two sides of the spinal cord ( Figure 5D).…”

“…The effects of implantation of the pelvic nerve electrode array on filling evoked voiding contractions (n = 9) are summarized in Table 1 and Figure 3C. These urodynamic parameters were comparable to published values (Zhao et al, 2010;Andersson et al, 2011;Fraser et al, 2020;Wiedmann et al, 2020). Our priority in assessing the effects of stimulation of the pelvic nerve was to determine the ability of stimulation to evoke a voiding contraction.…”

Regional Targeting of Bladder and Urethra Afferents in the Lumbosacral Spinal Cord of Male and Female Rats: A Multiscale Analysis

“…Although no chemoarchitectural markers have been identified to delineate this entire group of interneurons, a subpopulation near the SPN expresses TH ( Hou et al, 2016a , 2021 ). In the current study, we found that TH neurons extend more rostrally than preganglionic neurons and we have previously reported that cystometry evokes c-Fos expression in this region and throughout the length of L6 ( Wiedmann et al, 2021 ). However, we also note that only a minority of LUT afferents were closely associated with TH neurons.…”

“…3 A , arrowheads). This region has previously been identified as the location of inhibitory and excitatory interneurons involved in micturition ( Vizzard et al, 1995 ; Araki and de Groat, 1996 ; de Groat et al, 2015 ), some of which express TH ( Hou et al, 2016a , 2021 ; Wiedmann et al, 2021 ). Confocal microscopy confirmed close associations between LUT afferents and TH neurons in this region, however the majority of LUT afferents were not near TH neurons ( Fig.…”