Effect of aging on the substance P receptor, NK-1, in the spinal cord of rats with peripheral nerve injury.

Substance P (SP) levels in the spinal cords of very old rats are less than the levels in younger rats (Bergman et al., 1996). After injury to a peripheral nerve in young rats, immunoreactivity (ir) to the SP receptor, NK-1 (neurokinin-1), increases in the spinal cord ipsilateral to the injury and the increases are correlated with the development of thermal hyperalgesia (Goff et al., 1998). Thus we postulated that aged rats might display an increased sensitivity to thermal stimulation before peripheral nerve injury and that they might respond differently to injury than do younger rats. To test this hypothesis, we used the Bennett and Xie model (1988) of chronic constriction injury (CCI) to the sciatic nerve to induce a neuropathic pain condition. We investigated the effect of age on changes in NK-1 ir in superficial layers of the dorsal horn and on numbers of NK ir cells in deeper laminae at the L4-L5 levels of the spinal cord after CCI. NK-1 receptors were tagged immunohistochemically and their distribution quantified by use of computer-assisted image analysis. NK-1 ir changes were related to alterations in thermal and tactile sensitivity that developed after CCI in young, mature and aged (4-6, 14-16, and 24-26 months) Fischer F344 BNF1 hybrid rats. No differences in thermal or tactile sensitivity of young and aged rats were seen in the absence of nerve injury. After injury, aged rats developed thermal hyperalgesia and tactile allodynia more slowly than did the younger rats. NK-1 receptor ir and numbers of NK-1 ir cells in the dorsal horn increased with time post-injury in all three groups. NK-1 ir increases were correlated with the development of thermal hyperalgesia in those rats that displayed hyperalgesia. However, some rats developed an increased threshold to thermal stimuli (analgesia) and that also was correlated with increases in NK-1 ir. Thus NK-1 ir extent, while correlated with thermal sensitivity in the absence of injury, is not a specific marker for disturbances in one particular sensory modality; rather it increases with peripheral nerve injury per se.

Neuropathic pain in aged rats: behavioral responses and astrocytic activation.

We used the Bennett and Xie (1988) model of chronic neuropathic pain to study the effect of age on thermal and tactile sensitivity and on astrocytic activation in the dorsal horn of the spinal cord after nerve injury. Fischer 344 FBNF1 hybrid rats in three age groups, 4-6, 14-16, and 24-26 months, were studied. Rats were either unligated (day 0, control) or the left sciatic nerve was loosely ligated to cause a chronic constriction injury (CCI). CCI causes a neuropathic pain condition characterized by tactile allodynia and thermal hyperalgesia. Rats were behaviorally assessed for tactile and thermal sensitivity of their ligated and unligated hind paws up to 35 days postligation. Rats were sacrificed before or at various days postligation, and activated astrocytes were identified at the L4-L5 levels of their spinal cords by use of an antibody to glial fibrillary acid protein (GFAP). The number of GFAP-ir astrocytes in the dorsal horn of the spinal cord in the control, uninjured condition decreased with age (P < or = 0.001) but increased after CCI in all three age groups. After CCI, astrocytic activation in the cord was less robust in aged rats than in younger ones (P < or = 0.01). Not all the CCI rats displayed hyperalgesia to touch and to heat. Rats with an increased sensitivity to heat had increased levels of GFAP-ir in their cords; however, rats with decreased thermal sensitivity also displayed increased GFAP-ir. Thus the presence of activated astrocytes was not correlated with a single behavioral manifestation of neuropathic pain.

Gender and the behavioral manifestations of neuropathic pain.

A model of peripheral nerve injury was used to study gender differences in the development and progression of chronic constriction injury (CCI)-induced hyperalgesia and allodynia in male and female Fischer 344 FBNF1 hybrid rats. Rats were randomly assigned to one of the following treatment groups: (1) gonadally intact unligated males (male); (2) gonadally intact ligated males (male (CCI)); (3) castrated ligated males (male (CAS/CCI)); (4) gonadally intact unligated females (female); (5) gonadally intact ligated females (female (CCI)); and (6) ovariectomized ligated females (female (OVX/CCI)). A plantar analgesia meter and calibrated von Frey pressure filaments were used as the analgesiometric assays. In the absence of nerve injury, gonadally intact males responded significantly faster than females to a thermal nociceptive stimulus. The onset of the behavioral manifestations of unilateral ligation of the sciatic nerve did not differ as a function of sex or hormonal status (e.g., gonadally intact and gonadectomized male and female rats developed thermal hyperalgesia within 14 days post-CCI). Paw withdrawal latency (PWL) values of gonadally intact males returned to baseline control values after postligation day 14, whereas gonadally intact females, ovariectomized females and castrated males continued to elicit robust thermal hyperalgesic symptoms throughout the 35-day duration of the experiment. Allodynic responses to peripheral nerve injury were less variable across genders. These data suggest that the mechanisms underlying chronic nociceptive processing differ as a function of gender and gonadal hormone status.

Changes in spinal serotonin turnover mediate age-related differences in the behavioral manifestations of peripheral nerve injury.

The Bennett and Xie model of peripheral nerve injury was used to study the effects of aging on the onset and progression of sciatic nerve ligation (SNL)-induced thermal hyperalgesia and tactile-evoked allodynia in young, mature, and aged Fischer 344 FBNF1 male rats (4-6, 14-16, and 24-26 months old, respectively). A plantar analgesia meter and calibrated von Frey pressure filaments were employed as the analgesiometric assays. In the absence of nerve injury, aged rats were found to be more sensitive than younger animals to noxious thermal stimuli. Following the SNL surgery, thermal hyperalgesia was observed in all three age groups within 3 days. On post-SNL day 35, the paw-withdrawal latency values of the young and mature animals returned to presurgical baseline levels, while the aged rats continued to exhibit thermal hyperalgesia. Tactile-evoked allodynia was apparent within 3 days following peripheral nerve injury in the oldest cohort, but was delayed in the younger animals. On post-SNL days 0 (control), 3, 21, and 35, young, mature, and aged rats were sacrificed and high-performance liquid chromatography and electrochemical detection (HPLC/ECD) methods were used for neurochemical analyses of spinal serotonin (5-HT), norepinephrine (NE), and 5-hydroxyindoleacetic acid (5-HIAA). Spinal 5-HT and NE levels were not significantly altered by the aging process, nor were they affected by peripheral nerve injury. However, spinal 5-HT turnover from the aged animals was greater than that detected in spinal tissue from the younger counterparts. Differences in spinal 5-HT turnover may contribute to age-related variability in spinal nociceptive processing.

Microglial proliferation in the spinal cord of aged rats with a sciatic nerve injury.

Nerve injury may lead to chronic neuropathic pain syndromes. We determined whether the extent of central nervous system microglial activation that accompanies nerve injury is age dependent and correlated with behavioral manifestations of pain. We used the Bennett and Xie sciatic nerve chronic constriction injury model (Bennett, G.J., Xie, Y.-K., A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man, Pain, 33 (1998) 87-107) to induce neuropathic pain in three age cohorts of Fischer 344 FBNF1 hybrid rats (4-6, 14-16, and 24-26 months). Rats were assessed for thermal sensitivity (hyperalgesia) of their hind paws pre-injury (day 0) and up to 35 days post injury. On various days post injury, the L4-L5 levels of their spinal cords were reacted for localization of an antibody to OX-42, a marker for microlgia. OX-42 immunoreactivity (ir) was quantified by use of a Bioquant density analysis system. OX-42 ir was heavy in areas of sciatic nerve primary afferent terminations and in the motor columns of its neurons. Aging increases OX-42 ir in the absence of injury. After injury, OX-42 ir increased further, but the increases over control levels decreased with age. Ligation-induced analgesia and hyperalgesia were both correlated with the increases in OX-42 ir, regardless of age.

Secure cranial-mount intrathecal cannulation - a spinal administration technique in the rat.

In order to identify an acute spinally mediated pharmacological effect of a bioactive substance, without incurring untoward supraspinal effects, it is necessary to administer the agent locally onto the spinal cord. The procedure delineated herein presents a modern technique to install a stable, permanent indwelling thecal cannulae with a cranially mounted aperture, and details a simple, repeatable administration system. These methods facilitate a quick, noninvasive spinal drug microadministration that is most useful for differentiation of the locus of pharmacological action without the behavioral disruption associated with other administration methodologies.

Strain differences in neuropathic hyperalgesia.

The purpose of this study was to investigate strain-related differences in the onset and maintenance of thermal hyperalgesia following the induction of peripheral nerve injury in two inbred strains of rats (Fischer 344 and Lewis) and two outbred strains of rats (Sprague-Dawley and Wistar). Neuropathic pain was induced via unilateral ligation of the left sciatic nerve with chromic gut sutures. A plantar analgesia meter was used to measure paw-withdrawal latency from the ligated vs. unligated hind paws of inbred vs. outbred strains of rats to investigate strain-related differences in nerve injury-induced thermal hyperalgesia. The results demonstrated no significant effects of animal strain on presurgical paw-withdrawal latency values. Following the sciatic nerve ligation (SNL) surgery, a significant hyperalgesic response was elicited from the Sprague-Dawley and Wistar rats (outbred strains) for at least 28 days. Conversely, data analyses from the inbred strains failed to demonstrate significant hyperalgesic responses to peripheral nerve injury, with the exception of postsurgical day 10. These data emphasize the importance of considering the strain of the rat being investigated before extrapolating the results from animals experiments to treatment strategies for humans with chronic neuropathic pain.

Aging and neuropathic pain.

Although chronic neuropathic pain disorders are more prevalent in the senescent population, little is known about how the aging process alters the thermal hyperalgesic sensitivity to peripheral nerve injury. In this study, neuropathic pain was induced in young, mature and aged FBNF1 hybrid rats via unilateral ligation of the left sciatic nerve. The extent to which the aging process affects the thermal hyperalgesic responsiveness of these animals was investigated. The results demonstrate that the aging process differentially alters nociceptive processing.

Risk assessment of thyroid follicular cell tumors.

Thyroid follicular cell tumors arise in rodents from mutations, perturbations of thyroid and pituitary hormone status with increased stimulation of thyroid cell growth by thyroid-stimulating hormone (TSH), or a combination of the two. The only known human thyroid carcinogen is ionizing radiation. It is not known for certain whether chemicals that affect thyroid cell growth lead to human thyroid cancer. The U.S. Environmental Protection Agency applies the following science policy positions: 1) chemically induced rodent thyroid tumors are presumed to be relevant to humans; 2) when interspecies information is lacking, the default is to assume comparable carcinogenic sensitivity in rodents and humans; 3) adverse rodent noncancer thyroid effects due to chemically induced thyroid-pituitary disruption are presumed to be relevant to humans; 4) linear dose-response considerations are applied to thyroid cancer induced by chemical substances that either do not disrupt thyroid functioning or lack mode of action information; 5) nonlinear thyroid cancer dose-response considerations are applied to chemicals that reduce thyroid hormone levels, increase TSH and thyroid cell division, and are judged to lack mutagenic activity; and 6) nonlinear considerations may be applied in thyroid cancer dose-response assessments on a case-by-case basis for chemicals that disrupt thyroid-pituitary functioning and demonstrate some mutagenic activity. Required data for risk assessment purposes is mode of action information on mutagenicity, increases in follicular cell growth (cell size and number) and thyroid gland weight, thyroid-pituitary hormones, site of action, correlations between doses producing thyroid effects and cancer, and reversibility of effects when dosing ceases.

Nucleotide sequence of the inter-structural gene region of feline infectious peritonitis virus.

The sequence of the region located between the S and M glycoprotein genes of the 79-1146 strain of feline infectious peritonitis virus (FIPV) is presented. The inter-structural gene region encodes 3 open reading frames (ORFs), termed ORFs 3a, 3b and 4, with nucleotide sequences conforming to the minimum conserved transcription signal upstream of each. An additional ORF, 3x, partially overlaps the 3' end of ORF 3a. The FIPV interstructural gene region is identical in length when compared to the Insavc-1 strain of canine coronavirus (CCV) but differs from various strains of transmissible gastroenteritis virus (TGEV) by the presence of deletions and insertions. The sizes of ORF 3a and 4 are conserved in FIPV, TGEV and CCV. However, as with CCV, the FIPV ORF 3b is truncated in comparison with TGEV.

The effects of aging on mu and delta opioid receptors in the spinal cord of Fischer-344 rats.

Previous research has demonstrated that the antinociceptive efficacy of opioids decreases with advancing age. This study utilized radioligand binding techniques to determine if this decline is due to a change in the receptor density (Bmax) and/or affinity (measured as Kd) of the mu (mu) and/or delta (delta) opioid receptors in the spinal cord with advancing age. Saturation binding analysis with [3H][d-Ala2,N-methyl-Phe4,Gly5-ol]enkephalin (DAMGO: a mu-opioid selective agonist) and [3H]naltrindole (a delta-opioid selective antagonist) revealed no age-related changes in Bmax for either the mu or delta-opioid receptors. The Kd value for naltrindole was likewise unaffected by age. The Kd value for DAMGO however, was significantly higher in the aged group as compared with the young and mature groups, indicating a decreased affinity of spinal mu-opioid receptors for DAMGO.

Environmental endocrine disruption: an effects assessment and analysis.

This report is an overview of the current state of the science relative to environmental endocrine disruption in humans, laboratory testing, and wildlife species. Background information is presented on the field of endocrinology, the nature of hormones, and potential sites for endocrine disruption, with specific examples of chemicals affecting these sites. An attempt is made to present objectively the issue of endocrine disruption, consider working hypotheses, offer opposing viewpoints, analyze the available information, and provide a reasonable assessment of the problem. Emphasis is placed on disruption of central nervous system--pituitary integration of hormonal and sexual behavioral activity, female and male reproductive system development and function, and thyroid function. In addition, the potential role of environmental endocrine disruption in the induction of breast, testicular, and prostate cancers, as well as endometriosis, is evaluated. The interrelationship of the endocrine and immune system is documented. With respect to endocrine-related ecological effects, specific case examples from the peer-reviewed literature of marine invertebrates and representatives of the five classes of vertebrates are presented and discussed. The report identifies some data gaps in our understanding of the environmental endocrine disruption issue and recommends a few research needs. Finally, the report states the U.S. Environmental Protection Agency Science Policy Council's interim position on endocrine disruption and lists some of the ongoing activities to deal with this matter.

The effects of aging on spinal neurochemistry in the rat.

The purpose of this study was to investigate how the aging process alters the basal levels of serotonin, norepinephrine, dopamine, and their respective metabolites in the spinal cord using high-performance liquid chromatography and electrochemical detection. Young, mature and aged male Fischer 344 rats (5-6, 15-16, and 25-26 months old, respectively) were used in all experiments. Dorsal and ventral halves of the cervical, thoracic, lumbar and sacral vertebral sections of the rat spinal cord were analyzed. The results indicate that as chronological age increases, local spinal levels of serotonin and norepinephrine decrease. These findings are discussed in terms of how age-related changes in the endogenous levels of the biogenic amines may alter the perception of pain in the elderly.

Mammary gland neoplasia.

Determining how findings of chemically induced carcinogenic effects in rodents can properly be interpreted for human health poses a continuing challenge to the risk assessment community. One approach begins by comparing and contrasting carcinogenic process in rodents and humans, identifying biologically significant similarities and differences and gaps in scientific knowledge and understanding. Russo and Russo (in this issue) use just such an approach to evaluate the current state of scientific understanding of the comparative mechanisms of mammary tumorigenesis in humans and rodents, particularly the role of reproductive hormones. This commentary describes the basis for this review and suggests some of the implications the report may have for human health risk assessment and for future research.

Hunter's syndrome and oral manifestations: a review.

Review of the literature on Hunter's syndrome and oral manifestations in pediatric dental patients including the primary and secondary systemic manifestations are presented. Numerous oral manifestations are presented as well. Based on the cases presented in the reviewed studies, little information is available on oral considerations and treatment of these children. Early restoration of the oral cavity is important prior to treatment of the disease itself.