Karen J. Berkley

Diencephalic mechanisms of pain sensation

‘Universite Pierre et Marie Curie (Paris VI) and Groupe de Neurobiologie Appliqute, Laboratoire de Physiologie de la Nutrition, C. N. R. 7, 78350 Jouy en Josas (France); 2Department of Psychology, Florida State University, Tallahassee, FL, 32306 (U.S.A.); 3Departments of Anatomy and Anesthesiology and Ahmanson Laboratory of Neurobiology, Brain Research Institute, UCLA Center for the Health Sciences, Los Angeles, CA, 90024 (U.S.A.); “Department of Anatomy, School of Medicine, University of California, San Fransisco, CA, 94143; and *Departments of Physiology and Biophysics and Anatomy, Marine Biomedical Institute, University of Texas Medical Branch, Galveston, TX, 77550 (U.S.A.)

Pain threshold variations in somatic wall tissues as a function of menstrual cycle, segmental site and tissue depth in non-dysmenorrheic women, dysmenorrheic women and men.

Abstract Pain symptoms of many disorders are reported to vary with menstrual stage. This study investigated how pain thresholds to electrical stimulation of the skin, subcutis and muscle tissue varied with menstrual stage in normal women and compared these variations with those in women with dysmenorrhea and in healthy men at matched intervals. Thresholds of the three tissues were measured four times during the course of one menstrual cycle at four sites. Two of the sites were on the abdomen within the uterine viscerotome (abdomen‐rectus abdominis, left and right) and two were outside it on the limbs (leg‐quadriceps, arm‐deltoid). Calculated from the beginning of menstruation (day 0), the menstrual phases studied were menstrual (days 2–6), periovulatory (days 12–16), luteal (days 17–22) and premenstrual (days 25–28). Spontaneous pain associated with menstruation was measured from diary estimates on a VAS scale. Menstrual phase, dysmenorrhea and tissue: Whereas the highest thresholds always occurred in the luteal phase regardless of segmental site or stimulus depth, the lowest thresholds occurred in the periovulatory stage for skin, whereas those for muscle/subcutis occurred perimenstrually. Dysmenorrhea accentuated the impact of menstrual phase. For non‐dysmenorrheic women menstrual trends were significant only in abdominal muscle and subcutis, but for dysmenorrheic women the trends were also significant in abdominal skin and in limb muscle and subcutis. Dysmenorrhea also lowered thresholds mainly in muscle and sometimes in subcutis, but never in skin, with the greatest hyperalgesic effects in left abdominis muscle. Segmental site: Abdominal sites were more vulnerable to menstrual influences than limb sites. Muscle thresholds, but not skin or subcutis thresholds, were significantly lower in abdomen than in limbs, particularly in dysmenorrheic women. The amount of abdominal muscle hyperalgesia correlated significantly with the amount of spontaneous menstrual pain. Sex differences: Only minor sex differences were observed for pain thresholds of the arm and leg, but there was a unanimous refusal by men, but not by women, to be tested at abdominal sites. These results indicate that menstrual phase, dysmenorrhea status, segmental site, tissue depth and sex all have unique interacting effects on pain thresholds, thus adding more items to the lengthy and still‐growing list of biological factors that enter into an individuals judgment of whether or not a stimulus is painful.

Efferent connections of the rat suprachiasmatic nucleus

Abstract The efferent projections of the suprachiasmatic nucleus were studied in rats using three different light-microscopic tracing techniques. These techniques included, (1) degeneration subsequent to lesions of the nucleus, (2) autoradiography of axoplasmically-transported molecules following injections of [ 3 H]leucine into the nucleus, and (3) autoradiography of molecules which had been transneuronally-transported following injections of [ 3 H]fucose and [ 3 H]proline into the eye. Analysis of this material demonstrated that the suprachiasmatic nucleus has sparse but widespread efferent projections that extend ipsilaterally and sometimes bilaterally throughout much of the length of the periventricular system. With some exceptions, these projections tend to be confined within 0.4 mm of the midline. Four major efferent pathways were identified. (1) A ventro-caudal projection to the retrochiasmatic area, arcuate nucleus, median eminence, the ventro-medial aspect of the dorsomedial and ventromedial hypothalamic nuclei, baso-lateral hypothalamus, prelateral mammillary nucleus and lateral interpeduncular zone. A dorsal branch of this pathway followed the periventricular system into the central grey. (2) A lateral pathway to the anterior hypothalamus, a region dorsal to the supraoptic nucleus and the supraoptic nucleus. Some lateral projections may reach the anterior amygdaloid area. (3) A dorsal pathway to the paraventricular nucleus, a rostral branch to the fimbrial and triangular septal nuclei and a caudal branch via the paraventricular thalamus to the habenula, and further caudally to the mesencephalic central grey. These dorsal projections were not labeled by transneuronal transport. (4) A sparse rostral pathway through the preoptic-suprachiasmatic region. These results agree with and extend the results of other investigators. In addition, the diffuse and extensive pattern of projections of the suprachiasmatic nucleus as demonstrated here is consistent with the suggestion that the nucleus is a major component of a system of circadian pacemakers whose destruction disrupts or abolishes the circadian rhythms of a wide range of different behaviors.

Chronic pelvic pain and endometriosis: translational evidence of the relationship and implications

BACKGROUND Many clinicians and patients believe that endometriosis-associated pain is due to the lesions. Yet causality remains an enigma, because pain symptoms attributed to endometriosis occur in women without endometriosis and because pain symptoms and severity correlate poorly with lesion characteristics. Most research and reviews focus on the lesions, not the pain. This review starts with the recognition that the experience of pain is determined by the central nervous system (CNS) and focuses on the pain symptoms. METHODS Comprehensive searches of Pubmed, Medline and Embase were conducted for current basic and clinical research on chronic pelvic pain and endometriosis. The information was mutually interpreted by a basic scientist and a clinical researcher, both in the field of endometriosis. The goal was to develop new ways to conceptualize how endometriosis contributes to pain symptoms in the context of current treatments and the reproductive tract. RESULTS Endometriotic lesions can develop their own nerve supply, thereby creating a direct and two-way interaction between lesions and the CNS. This engagement provides a mechanism by which the dynamic and hormonally responsive nervous system is brought directly into play to produce a variety of individual differences in pain that can, in some women, become independent of the disease itself. CONCLUSIONS Major advances in improving understanding and alleviating pain in endometriosis will likely occur if the focus changes from lesions to pain. In turn, how endometriosis affects the CNS would be best examined in the context of mechanisms underlying other chronic pain conditions.

Estrous and sex variations in vocalization thresholds to hindpaw and tail pressure stimulation in the rat.

This study examined sex and estrous differences in vocalization thresholds of rats to hindpaw and tail pressure stimulation tested daily throughout at least 3 weeks. When all the measures were pooled, compared to males, female rats had higher thresholds for tail pressure (499 +/- 6 g, n = 188 measures vs. 466 +/- 2 g, n = 144 measures, respectively), but equal thresholds for hindpaw pressure (321 +/- 6 g, n = 188 measures vs. 319 +/- 2 g, n = 144 measures, respectively). Thresholds of female rats in proestrus and estrus were lower than those of rats in metestrus and diestrus for both tail and hindpaw stimulation, whereas those of males did not vary systematically. Thresholds at the two stimulation sites covaried in females but not in males. These results add to the growing list of important interacting factors that underly behavioral sensitivity to noxious somatic stimulation.

Are there separate central nervous system pathways for touch and pain

Information about bodily events is conveyed by primary sensory fibres to higher brain centres through neurons in the dorsal column nuclei (DCN) and spinal dorsal horn. The DCN route is commonly considered a ‘touch pathway’, separate from the spinal ‘pain pathway’, in part because DCN neurons respond to gentle tactile stimulation of small skin areas. Here we report that DCN neurons can additionally respond to gentle and noxious stimulation of viscera and widespread skin regions. These and other experimental and clinical data suggest that the DCN and spinal routes cooperate, rather than operate separately, to produce the many perceptions of touch and pain, an ensemble view that encourages novel approaches to health care and research.

Efferent projections of the gracile nucleus in the cat

The efferent projections of different portions of the gracile nucleus in the cat were studied using both autoradiographic and degeneration tracing methods. The results suggest that there are two aspects to the functional organization of these projections. First, the somatotopic organization of the gracile n. (GR) is maintained, but inverted, by the topographic organization of its projections to VPL1. Fibers from the lateral portions of GR terminate medially in VPL1; fibers from the dorsal portions terminate ventrally. These fibers, especially those from the middle and caudal portions of GR, terminate in dense, precisely located groups of clusters. Dorsally located clusters in VPL1 (predominantly from middle-ventral portions of GR) are significantly smaller than ventrally located clusters (predominantly from middle-dorsal portions). The second aspect of this organization, involving the projections both to VPL1 and to other brain stem targets, is that some kind of functionally relevant sorting process appears to occur as fibers leave different portions of the gracile n. The afferent projections of the rostral (GRr) and middle-ventral portions (GRmv) of the gracile n. are different from those from the other portions of the nucleus. Projections to VPL1 from GRr are less dense, less likely to form clusters, less clearly topographically organized, and extend further rostrally and dorsally in VPL1 than those from the rest of GR. The clusters are small, like those from GRmv. Similarly, although all portions of GR project to several other brain stem regions, these projections appear to be derived preferentially from GRr and/or GRmv. These brain stem regions involve certain portions of the inferior olive, inferior and superior colliculi, red n., zona incerta, pretectum, thalamic posterior group and the H field of Forel. This dual organization of efferent connectivity is similar to that of the cuneate n.20, and is consistent with many of the differences in cytoarchitecture, afferent connectivity and response properties of cells within different portions of the dorsal column nuclei.

Influence of endometriosis on pain behaviors and muscle hyperalgesia induced by a ureteral calculosis in female rats.

&NA; Endometriosis and urinary calculosis can co‐occur. Clinical studies have shown that both painful and non‐painful endometriosis in women are associated with enhanced pain and referred muscle hyperalgesia from urinary calculosis, but the mechanisms underlying this phenomenon are still poorly understood. The aim of this study was to develop an animal model adequate to explore this viscero‐visceral interaction in standardized conditions. Using a model of endometriosis previously developed to study reduced fertility and vaginal hyperalgesia, endometriosis (endo) or sham‐endometriosis (sham‐endo) was induced in rats by autotransplantation of small pieces of uterus (or, for sham‐endo, fat) on cascade mesenteric arteries, ovary, and abdominal wall. After the endometrial, but not the fat autografts had produced fluid‐filled cysts (3 weeks), urinary calculosis was induced by implanting an artificial stone into one ureter. Pain behaviors were monitored by continuous 24‐h videotape recordings before and after stone implantation. Referred muscle hyperalgesia was assessed by measuring vocalization thresholds to electrical stimulation of the oblique musculature (L1 dermatome). The data were compared with previously reported data from rats that had received only the stone. Neither endo nor sham‐endo alone induced pain behaviors. Following stone implantation, in endo rats compared to sham‐endo and stone‐only rats, pain behaviors specifically associated with urinary calculosis were significantly increased and new pain behaviors specifically associated with uterine pathology became evident. Muscle hyperalgesia was also significantly increased. To explore the relationship between the amount of endometriosis and that of ureteral pain behavior, two separate groups of endo rats were treated with either a standard non‐steroidal anti‐inflammatory drugs (ketoprofen) or placebo from the 12th to the 18th day after endometriosis induction. The stone was implanted on the 21st day. Ketoprofen treatment compared to placebo significantly reduced the size of the cysts and both ureteral and uterine pain behaviors post‐stone implantation. The size of the cysts showed a significant linear correlation with the post‐stone ureteral pain behaviors. In conclusion, endo increased pain crises and muscle hyperalgesia typically induced by a ureteral calculosis, and the ureteral calculosis revealed additional pain behaviors typically induced by uterine pathophysiology; and this enhancement was a function of the degree of endometriosis. This result closely reproduces the condition observed in humans and could be due to a phenomenon of ‘viscero‐visceral’ hyperalgesia, in which increased input from the cyst implantation sites to common spinal cord segments (T10‐L1) facilitates the central effect of input from the urinary tract.

Estrous cycle variation of afferent fibers supplying reproductive organs in the female rat

Multi-unit afferent nerve activity was recorded from branches of the hypogastric and pelvic nerves in virgin female rats on different days of the estrous cycle. In each rat, the response of hypogastric nerve fibers to uterine distension and the response of pelvic nerve fibers to vaginal distension was tested. The minimal pressure necessary to evoke a response was highest in diestrus for both the hypogastric and pelvic nerve fibers. For the hypogastric nerve, the minimal necessary pressures were significantly lower during both proestrus and estrus, whereas for the pelvic nerve, the pressure was significantly lower only on the day of proestrus. These results suggest that the overall response sensitivity of afferent fibers in the pelvic and hypogastric nerves are differentially affected by hormonal variations occurring across the estrous cycle in a manner that would enhance reproduction.

A life of pelvic pain

Pelvic pain associated with menstruation, i.e., dysmenorrhea, is a chronic pelvic pain that not only interferes with a womans wellbeing for a large part of her life but also often co-occurs with other chronic painful conditions such as interstitial cystitis and irritable bowel syndrome and others. Little has been known about mechanisms underlying these chronic pelvic pains. This paper reviews 37 years of research in my laboratory at Florida State University on such mechanisms. Our research, mostly on rats, has contributed to the following findings: (1) Female reproductive organs are innervated in a topographic fashion by afferents in the pelvic (vagina/cervix) and hypogastric (cervix/uterine horn) nerves. (2) The input contributes to uterine and vaginal perceptions (nociception) that are modified by reproductive status. (3) Throughout the CNS, neurons responsive to stimulation of the reproductive tract also respond to stimulation of skin and other internal organs, in a manner modifiable by reproductive status and peripheral pathophysiology. (4) This dynamic physiological convergence may reflect extensive anatomical divergence of and interconnections between pathways entering the CNS via gateways through the spinal cord, dorsal column nuclei, and solitary nucleus. (5) The convergence also indicates the existence of extensive cross-system, viscero-visceral interactions within the CNS, that, while organized for coherent bodily functioning, serves as a substrate by which pathophysiology in one organ can influence physiology and responses to pathophysiology in other organs. (6) Some cross-system effects observed so far include: (a) Bladder inflammation reduces the rate of uterine contractions and the effects of drugs on the uterus. (b) Colon inflammation produces signs of inflammation in the otherwise healthy bladder and uterus. (c) A surgical model of endometriosis produces vaginal hyperalgesia, exacerbates pain behaviors induced by a ureteral stone, and reduces volume voiding thresholds if the bladder. These cross-system effects, which likely involve CNS mechanisms, likely also underlie co-occurrence of painful clinical conditions. Research continues on details of these mechanisms and their relevance for clinical diagnosis and therapy. None of this work could have been done without collegial support of colleagues and technical staff at Florida State University.