Antinociceptive and behavioral activation responses elicited by D-Pro(2)-Endomorphin-2 in the ventrolateral periaqueductal gray are sensitive to sex and gonadectomy differences in rats

Citation
Ek. Krzanowska et al., Antinociceptive and behavioral activation responses elicited by D-Pro(2)-Endomorphin-2 in the ventrolateral periaqueductal gray are sensitive to sex and gonadectomy differences in rats, PEPTIDES, 21(5), 2000, pp. 705-715
Citations number
65
Categorie Soggetti
Biochemistry & Biophysics
Journal title
PEPTIDES
ISSN journal
01969781 → ACNP
Volume
21
Issue
5
Year of publication
2000
Pages
705 - 715
Database
ISI
SICI code
0196-9781(200005)21:5<705:AABARE>2.0.ZU;2-7
Abstract
Sex differences have been observed in antinociception after morphine admini stered into either the lateral ventricles, rostral ventromedial medulla, or ventrolateral periaqueductal gray such that male rats exhibit significantl y greater antinociception than female rats. Adult gonadectomy produced smal l, but significant changes in morphine antinociception relative to same-sex sham-operated controls. The present study examined whether sex and adult g onadectomy differences were observed in antinociceptive responses after D-P ro(2)-Endomorphin-2 (1-50 mu g) elicited from the ventrolateral periaqueduc tal gray (vIPAG) on the tail-flick and jump tests in rats, and compared the se effects with morphine antinociception. D-Pro(2)-Endomorphin-2 antinocice ption in the vIPAG was significantly greater in estrous-phase, sham-operate d and ovariectomized female rats relative to sham-operated and castrated ma le rats on the tail-flick, but not jump test that differed markedly from th e greater magnitude of morphine antinociception noted for male rats on both tests. In testing whether D-Pro(2)-Endomorphin-2's antinociceptive sex dif ferences were secondary to alterations in activity, similar decreases in th e pattern of total activity were observed after D-Pro(2)-Endomorphin-2 in t he vIPAG in male and female rats. In evaluating whether male and female rat s differed in their behavioral activation responses after D-Pro(2)-Endomorp hin-2 in the vIPAG, significantly more excessive grooming, seizures, barrel rolls and explosive running behaviors were observed after D-Pro(2)-Endomor phin-2 in male, but not female rats during the precise periods of time when they were failing to display robust antinociceptive responses on the tail- flick test. Thus, the different patterns of sex differences after D-Pro(2)- Endomorphin-2 in the vIPAG appear to be attributable to sex-dependent alter ations in behavioral activation rather than nociceptive processing per se. (C) 2000 Elsevier Science Inc. All rights reserved.