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Spinal monoaminergic modulation of masculine copulatory behavior in the rat
Brain Research, 302 (1984) 315-321 Elsevier
315
BRE 10066
Spinal Monoaminergic Modulation of Masculine Copulatory Behavior in the Rat L. SVENSSON and S. HANSEN
Department of Psychology, Universityof GOteborg, Box 14158, S-40020 GOteborg (Sweden) (Accepted October 25th, 1983)
Key words: 5-HT - - aminotetraline - - dopamine - - noradrenaline - - intrathecal infusions - - sexual behavior - - spinal reflexes
The sexual behavior of male rats receiving infusions of 5-HT, dopamine and noradrenaline intrathecally in the spinal cord of intracerebroventricularly (i.c.v.) in the lateral ventricle was observed. Intrathecal infusions of 5-HT and noradrenaline inhibited penile insertions and ejaculation, noradrenaline being the more potent of the amines. Dopamine was without effect. I.c.v. amine infusions impaired to various extents the masculine mating pattern, primarily by interfering with the males' tendency to approach the females. The facilitation of mating seen after intrathecal administration of the aminotetraline, 8-OH-DPAT, was more pronounced than that observed following its i.c.v, infusion. INTRODUCTION In the neural substrate for masculine sexual behavior the importance of the medial preoptic area and related hypothalamic regions are well establishedlS,17, 31. Several lines of evidence suggest that some of the central monoamine pathways may form part of this neural system as well, their importance in the regulation of masculine sexual behavior being perhaps most dramatically shown by the pronounced lowering of the ejaculatory threshold seen after treatment with certain dopamine ( D A ) and serotonin (5-HT) receptor agonists2~,11A2, 26 or by the ability of some of these drugs to restore sexual behavior in animals made unable to mount by h o r m o n e deprivation or hypothalamic lesions2,3,20, 37. Impressive as these effects may be, we still know very little as to where in the central nervous system these types of drug effects may occur. The spinal cord, being innervated by descending serotonergic, dopaminergic and noradrenergic neuron systems originating in the brainE4,2s,36,38,4°, is one interesting candidate, as several sexual genito-pelvic reflex mechanisms are organized at the spinal level and coordinated into an integrated mating pattern by supraspinal pathwaysT, 39. Indeed, there is evidence to suggest that the facilitatory effect of the ergot derivative, li-
suride, on copulatory behavior may be exerted at least partly at the spinal level 18. Considering the importance of spinal mechanisms for copulation, it would be of interest to know how perturbations of the activity of descending monoamine systems affect sexual behavior. We have begun an analysis of this problem by studying the effects of neurotoxin-induced denervations of the serotonergic and catecholaminergic input to the spinal cord21; here, we report on the actions of 5-HT, D A and N A administered in the spinal subarachnoid space shortly before testing on the masculine mating pattern. For purposes of comparison the effect of these compounds was also assessed following intracerebroventricular (i.c.v.) infusions under comparable conditions. Finally, we compared the behavioral effect of the intrathecal (i.t.) and i.c.v, routes of administration of the aminotetraline, 8 - O H - D P A T , the intraperitoneal administration of which produces a marked facilitation of masculine sexual behavior3. MATERIALS AND METHODS
Animals Sexually experienced male rats, weighing 350-400 g, obtained from M/511egaard Breeding Laboratories (Denmark) were used. Prior to surgery they were
Correspondence: S. Hansen, Department of Psychology, University of GOteborg, Box 14158, S-400 20 Gfteborg, Sweden. 0006-8993/84/$03.00 t~) 1984 Elsevier Science Publishers B.V.
316 housed in groups of 2-3 per cage (53 x 36 x 25 cm), thereafter individually to avoid damage to the cannulae. The animals had constant access to food and water, and were subjected to a reversed light-darkness cycle (dark: 10.00-22.00 h).
Surgery Rats assigned to the intrathecal (i.t.) administration studies were implanted with an 8.0 cm length of PE10 polyethylene tubing under sodium methohexithai anesthesia (Brietal, Lilly; 20-30 mg/rat), according to LoPachin et al.'s 30 procedure. The animal was positioned in a stereotaxic apparatus and the catheter was carefully inserted in the subarachnoid space through a slit in the atlanto-occipital membrane, the free end being secured by threading it through burr holes in the occipital and interparietal bones 30. The vast majority of the subjects appeared completely unaffected by the implant; rats showing signs of spinal damage were discarded. Rats used for intracerebroventricular (i.c.v.) drug administration were implanted with a 0.7 mm in diam. guide cannula (Plastic Products, VA) in the lateral ventricle (stereotaxic coordinates: 0.3 mm behind bregma, 1.2 mm lateral to midline, 4.0 mm below the skull). Brietal anesthesia was used, and the cannulae were secured with acrylic dental cement.
400 ag DA, 9 rats were given infusions of 0, 3, 12.5 and 50/~g NA, and 7 rats infused with 0, 50 and 100 #g 8-OH-DPAT. A group of 11 males implanted with i.c.v, cannulae were given 0,200/~g 5-HT, 400/~g D A and 50/~g NA in random order with 3-4 day intervals; a separate group (n = 9) received i.c.v, infusions of 0, 50 and 100/~g 8-OH-DPAT. One hour prior to testing the males were injected i.p. with 1 mg/kg of the monoamine oxidase inhibitor FLA336(+). The i.t. and i.c.v, monoamine infusions were made over a 1 min period, using a 25/~1 syringe; the i.t. infusions were followed by a 10~tl saline flush to clear the catheter of its contents. Upon completion of the infusions the males were placed in a circular Plexiglas cage (50 cm diam.), and 10 min later an estrous female rat was introduced. The following behavioral items were recorded: mount and intromission frequency, time to first mount and intromission (intromission latency is reported in the Results), time from first intromission
Control infusions 5-HT 100t 0 50 Dopamine
Drugs The following substances were used: 5-hydroxytryptamine hydrochloride (5-HT; Sigma), 3-hydroxytyramine hydrochloride (dopamine, DA; Fluka), Lnoradrenaline hydrochloride (NA; Fluka) and 8-hydroxy-2-(di-n-propylamino)tetraline hydrobromide (8-OH-DPAT). Rats receiving i.t. or i.c.v, amine infusions were pretreated (see below) with the monoamine oxidase A inhibitor FLA336(+) (Astra Liikemedel AB) 5. All drugs were dissolved in sterile saline and the doses refer to the salt forms. Controls were given sterile saline.
Experimental protocol Behavioral observations were begun approximately 1 week after surgery and recurred with 3--4 day intervals. Ten perispinally catheterized rats received in random order i.t. infusions of 0, 50, 100 and 200/tg 5-HT, 7 rats received infusions of 0, 100 and
Intrathecal
100 200
Intracerebroventricular
200IJg
F, 50
0 100 400 I 100q Norad]enalinRl~ ~*** ~
400tJg I~
0 3 12,5 50 50IJg [] Mounts [] Intromissions• Ejaculation Fig. 1. Proportion of male rats showing mounts, intromissions and ejaculation following infusions of 5-HT, dopamine and noradrenaline either intrathecally (i.t.) in the spinal cord or intracerebroventricularly (i.c.v.) in the lateral ventricle. The rats were pretreated with the MAO inhibitor FLA336(+) (1 mg/kg) 1 h prior to testing, and received the various amine infusions 10 min before testing. * P < 0.05, ** P < 0.01.
317 TABLE I Masculine sexual behavior of the male rat following infusions in the spinal subarachnoid space with 5-HT, dopamine and noradrenaline The rats were pretreated with the MAO inhibitor FLA336(+) 1 h prior to testing, and received amine infusions 10 min before testing. Values are means ± S.E.M. Treatment
Mounts/min
lntromissions/ min
lntromission latencya
Ejaculation latentya
Postejaculatory intervala
No. rats showing tail pinch reaction
5-HT 0 50 1~ 2~
1.8±0.3 1.3±0.3 1.4±0.5 1.2±0.4
1.4±0.2 1.1±0.3 0.6±0.2* 0.1±0.0"*
1.6±0.7 1.4±0.6 2.5±1.5 2.3±0.3
7.1±1.6 11.5±2.9 11.6±3.6 13.3±2.5
5.9±0.5 6.5±0.3 6.4±0.6 6.6±0.2
10/10
D~amine 0 1~ 4~
0.8±0.2 0.6±0.2 0.8±0.2
1.6±0.3 1.6±0.5 1,0±0.3
0.3±0.2 0.6±0.3 0.6±0.2
8.8±1.6 13.9±3.1 12.7±3.4
6.5±0.8 7.5±0.8 9.3±1.6
Noradrenaline 0 3 12.5 50
1.1 + 0.2 1.5 _+0.3 0.9 + 0.2 0.7 + 0.2
1.3 + 0.7 + 0.0 ± 0.1 +
1.1 + 1.3 + 1.8 + 1.8 +
11.4 + 1.5 9.2 + 2.8 ---
7.0 + 0.5 5.4 + 0.2 ---
0.2 0.2 0.0"* 0.0"*
0.3 0.3 0.9 0.8
-3/7
9/9 6/9 0/9** 1/9"*
a minutes; b not tested. * P < 0.05; ** P < 0.01 (Wilcoxon matched-pairs signed-ranks test, preceded by Friedman two-way ANOVA; Cochran Q-test followed by binomial test for tail pinch reaction data).
to ejaculation (ejaculation latency), and the time from ejaculation to next intromission (post-ejaculatory interval). The tests were t e r m i n a t e d if intromission latency or p o s t e j a c u l a t o r y interval e x c e e d e d 15 min or if ejaculation latency was longer than 30 min (see Sachs and Barfield35 for a m o r e c o m p l e t e discussion of these behavioral measures). ~The reaction to a brief, manually applied, tail pinch (i.e. agitation, orientation, vocalization) was recorded in some of the e x p e r i m e n t s after the completion of the copulatory tests. Statistics The d a t a were analyzed n o n - p a r a m e t r i c a l l y using (i) F r i e d m a n s two-way analysis of variance followed by Wilcoxons matched-pairs signed-ranks test and (ii) Cochran Q-test followed by the binomial test. RESULTS Effects o f intrathecal 5-HT, D A and N A F!g. 1 shows that the i.t. administration of at least 200 gig 5 - H T or 12.5 p g N A significantly r e d u c e d the n u m b e r of animals showing penile intromissions and ejaculation. By contrast, the p r o p o r t i o n of rats show-
ing mounting behavior r e m a i n e d unaffected by these treatments. Infusion of 100-400/~g D A did not affect the p r o p o r t i o n of copulating animals (Fig. 1), neither was any p a r a m e t e r of their mating p a t t e r n affected, as is shown in Table I. A l s o shown in Table I is the fact that 5-HT and N A , in doses lower than those required for inhibition of intromissions, did not change appreciably the copulatory p a t t e r n leading up to ejaculation. N A , in doses of 12.5-50 ~g, reduced significantly the n u m b e r of animals showing reactions to tail pinch; a similar though non-significant trend was noted following t r e a t m e n t with 200 /~g 5-HT (Table I). Effects o f intracerebroventricular 5-HT, D A and N A Fig. 1 shows that i.c.v, infusions of 200 # g 5-HT, 400/~g D A or 50/~g N A (i.e., the highest doses used in the previous experiment) decreased the n u m b e r of ejaculating rats c o m p a r e d to tests in which vehicle was given. W h e n infused with 5-HT, this decrease was a c c o m p a n i e d by a significant reduction in the n u m b e r of rats showing mounts and intromissions; this effect was not seen following D A and N A . Table II shows, however, that i.c.v, infusions of D A and
318 TABLE II Masculine sexual behavior of the male rat following intracerebroventricular infusions of 5-HT, dopamine and noradrenaline The rats were pretreated with the MAO inhibitor FLA336(+) 1 h before testing, and received amine infusions 10 min prior to testing. Values are means _+ S.E.M. Treatment
Mounts/min
lntromissions/ min
lntromission latency a
Ejaculation latency a
Poste]aculatory interva#
No. rats showing tail pinch reaction
Saline 200/~g 5-HT 400/~g dopamine 50/~g noradrenaline
0.9 0.1 0.5 0.3
3.0 + 0.4 0.9+0.4** 1.1 + 0.4* 1.2 + 0.4*
0.3 + 0.1 0.5+0.3 2.9 + 1.8 4.0 + 2.0
5.9 + 1.4 8.4+2.9 9.3 + 4.7 7.2 + 2.7
4.7 + 0.3 5.5+0.5 5.5 + 0.5 5.8 + 0.8
11/11 11/11 11/11 11/11
+ + + +
0.2 0.1"* 0.3 0.1"*
a minutes. * P < 0.05; ** P< 0.01 (Wilcoxon matched-pairs signed-ranks test, preceded by Friedman two-way ANOVA).
N A did depress the rate at which the rats i n t r o m i t t e d ;
i n t e r m e d i o l a t e r a l c o l u m n and the v e n t r a l h o r n of
in the case of N A , m o u n t i n g rate was also sup-
the spinal gray m a t t e r all r e c e i v e a r a t h e r d e n s e
pressed.
m o n o a m i n e r g i c input originating in the d i e n c e p h a Ion,
locus
coeruleus
and
medullary
raphe
nu-
Effects o f i.t. and i.c.v, infusions o f 8 - O H - D P A T R e g a r d l e s s of a d m i n i s t r a t i o n r o u t e , 8 - O H - D P A T
clei 28,36,4°. B e c a u s e the f u n c t i o n s t h e s e spinal subdi-
facilitated sex b e h a v i o r by d e c r e a s i n g the n u m b e r of
masculine m a t i n g p a t t e r n - -
m o u n t s and i n t r o m i s s i o n s p r e c e d i n g e j a c u l a t i o n , and
sensory input by the dorsal h o r n 32, r e g u l a t i o n of erec-
visions are t h o u g h t to s u b s e r v e are all i n v o l v e d in the p r o c e s s i n g of genital
by s h o r t e n i n g e j a c u l a t i o n latency. T a b l e III shows,
tion by the a u t o n o m i c n e r v o u s system 39 and control
h o w e v e r , that the effect a p p e a r e d m o r e m a r k e d fol-
of penile muscles by m o t o n e u r o n s
lowing perispinal infusions, the i n t r o m i s s i o n f r e q u e n -
horn 9, to m e n t i o n a few e x a m p l e s - - we i n v e s t i g a t e d
cy and e j a c u l a t i o n latency b e i n g significantly l o w e r
in the p r e s e n t e x p e r i m e n t s the w a y in which infusions
following the i.t. infusion of the h i g h e r 8 - O H - D P A T
of 5 - H T , D A and N A m o d i f i e d sexual b e h a v i o r in
dose (P's < 0.02, M a n n - W h i t n e y U-tests).
male rats chronically i m p l a n t e d with a c a t h e t e r in the
in the v e n t r a l
spinal s u b a r a c h n o i d space. T h e p e r h a p s m o s t striking DISCUSSION
finding to e m e r g e out of these e x p e r i m e n t s was that perispinal infusions of 5 - H T o r N A i n h i b i t e d the at-
T h e dorsal h o r n , the a u t o n o m i c cell groups of the
t a i n m e n t of e j a c u l a t i o n , at least a j u d g e d f r o m the
TABLE III Masculine sexual behavior of male rats receiving intracerebroventricular (i.c.v.) or intrathecal (i. t.) infusions of the aminotetraline, 8-OH-DPA T, 10 min before testing Values are means + S.E.M. Treatment
Mounts
Intromissions
lntromission latency a
Ejaculation latency Q
Postejaculatory interval
No. rats showing tail pinch reaction
i. c. v. infusion 0 50 100
10.3 + 2.9 2.3 + 1.1" 2.4 + 0.7**
15.3 +__3.6 5.1 + 1.1 6.7 + 0.8**
1.2 _+ 0.5 2.6 + 1.2 1.1 + 0.7
8.6 + 1.2 4.0_+ 1.2 4.5 _+ 1.4"
5.3 + 0.3 4.9_+ 0.3 4.6 + 0.4
__b ---
i.t. infusion 0 50 100
18.1 + 5.6 2.0 + 1.1 0.4 + 0.2*
10.9 + 2.1 2.4 + 0.8 1.9 + 0.4*
0.6 + 0.2 1.2 _+ 0.6 2.2 + 1.1
8.6 + 2.2 2.7 _+ 1.2" 1.4 + 0.6*
5.5 + 0.4 4.8 _+ 0.8 5.2 + 1.1
7/7 -6/6
a minutes; b not tested. * P < 0.05; ** P < 0.01 (Wilcoxon matched-pairs signed-ranks test preceded by Friedman two-way ANOVA).
319 absence of the behavioral pattern that usually accompanies the emission of seminal fluid into the female reproductive tract. The failure to ejaculate was not a consequence of any obvious lack of sexual motivation, because the rats continued to mount the estrous females at a normal rate; the persistence of mounting also shows that the 5-HT and NA infusions did not impair with the male's ability to execute pelvic thrusts and in this way inhibit ejaculation. Infusions of 5-HT and NA at doses effective in abolishing ejaculation did, however, impair the rat's ability to achieve penile intromissions when mounting the female, and it is possible, therefore, that the amines acted to block the transmission of genital tactile cues important for eliciting ejaculation. According to current concepts, genital sensory input serves at least two functions in the male rat: firstly, it serves a detector function by guiding the penis towards the vaginal orifice during mounting and, secondly, it gradually accumulates to excite (or disinhibit) the reflexive mechanisms responsible for the emission and ejaculation of semen1, 7,35. The present study suggests that i.t. 5-HT or NA infusions interfere with the guiding action of genital sensory feedback; whether or not they also impair the ejaculation-promoting actions of penile afference remain to be determined. The inhibitory actions of 5-HT and NA were not duplicated by i.t. D A infusions, which failed altogether to modify sexual behavior in the present experiments. It also seems as if NA was considerably more effective than 5-HT in inhibiting intromissions: on a molar basis our data indicate that NA was about 15 times as potent as 5-HT. It is known that subpopulations of the spinally projecting medullary 5-HT cells also contain one or several neuropeptides (e.g substance P, thyrotropin-releasing hormone, enkephalin), suggesting that 5-HT normally is released together with a peptide in the spinal cordS,10,23,25,27,33. Evidence is accruing that these neuropeptides may potentiate or otherwise modulate the behavioral action of 5-HT 6,16 and experiments designed to assess neuropeptide/5-HT interactions in the context of sexual behavior is currently underway in our laboratory 19. Even though previous studies have shown that i.t. infusions of drugs, using procedures similar to those employed in the present experiments, largely remain in the spinal compartment14, 41, some diffusion to su-
praspinal sites does occur and we therefore administered 5-HT, D A and NA into the lateral ventricle in order to investigate the extent to which the behavioral effects seen following i.t. infusions could be attributable to supraspinal sites of action. Some similarities between the two modes of exposure were indeed observed: both i.t. and i.c.v. 5-HT reduced the number of animals showing intromission and ejaculation, and depressed intromission rate. A similar effect was observed after i.t. and i.c.v. NA administration, although no decrease in the proportion of intromitting rats was recorded. However, conspicuous differences between the i.t. and i.c.v, modes of exposure were also noted. Thus, in contrast to the behavioral effect of perispinally applied 5-HT, its i.c.v, administration resulted in a pronounced decrease in the number of subjects showing mounting behavior and in mounting rate. The failure to ejaculate may thus have different causes in the two groups of 5-HT treated rats: following i.c.v, infusions it is due primarily to a lack of drive to approach and mount the female, following i.t. infusions because of an impaired ability to locate the vaginal orifice during mating. The trend towards a diminished response to noxious tail pinch in the present s t u d y - an observation in line with previous studies on pain transmission 42 - - following i.t. but not i.c.v. 5-HT administration is consistent with this interpretation. As to the behavioral effects of i.t. vs i.c.v. NA infusions, the fact that 12.5 pg of i.t. NA produced a 100% inhibition of ejaculation, whereas 50pg NA i.c.v, produced a 54.5% inhibition only is evidence that NA acted mainly at the spinal level to inhibit ejaculation. The decreased mounting rate of the i.c.v. NA-treated males, and their retained sensitivity to tail pinch (in contrast to the i.t. NA-treated males; see also ref. 34), suggest that their partial failure to ejaculate was due primarily to a reduced sexual arousability, similar to rats receiving supraspinal 5-HT. In summary, then, our results suggest that although the effects on copulatory behavior of i.t. vs i.c.v, monoamine infusions may not be as strikingly different as e.g. for the acoustic startle reflex 13, 5-HT and NA may act principally at the spinal level to inhibit the transmission of penile sensory feedback necessary for achieving intromission and ejaculation. Previous studies have shown that the systemic treatment of the ergot congener, 8-OH-DPAT, facil-
320 itates the male mating p a t t e r n 3. T h e aminotetraline is believed to act agonistically at central serotonergic receptor sites 22, though recent failures to block its sex-promoting actions by p r e t r e a t m e n t with several 5-HT receptor antagonists 29 indicate that some other neurochemical mechanism m a y also be operative. H e r e , we a t t e m p t e d to d e t e r m i n e whether the effect on sexual behavior of the c o m p o u n d was due primarily to a spinal or supraspinal site of action by comparing the behavioral effect of i.t. and i.c.v. 8-OHD P A T administration. A significant facilitation of several components of the mating pattern was detected following both routes of administration, though the effect was m o r e p r o n o u n c e d in animals receiving i.t. infusions of the drug. Thus, while the spinal cord may be an i m p o r t a n t target for 8-OHD P A T action, the present results allow no clear separation of spinal and supraspinal sites of action. The reasons for this m a y be that 8 - O H - D P A T may spread with unusual efficacy throughout the central nervous system regardless of delivery site; occlusion of the fourth ventricle may provide one way in which to overcome this potential source of error 43. A l t e r n a tively, in analogy with the neural substrate for mor-
phine-induced analgesia 44, facilitation of sexual behavior by 8 - O H - D P A T (and other ergot-like drugs) may d e p e n d on multiplicative interactions between spinal and supraspinal sites, which at high local concentrations b e c o m e capable of sex-facilitation by ind e p e n d e n t actions. Clearly, m o r e extensive studies are required to understand the locus of action of these potent compounds. ACKNOWLEDGEMENTS This study was s u p p o r t e d by the Swedish Medical Research Council (B84-21X-06605-02A) and The B a n k of Sweden T e r c e n t e n a r y F o u n d a t i o n . W e are grateful to the A s t r a L~ikemedel A B , Sfdert~ilje, for donating F L A 3 3 6 ( + ) and to the Organic Chemistry Unit of the D e p a r t m e n t of Pharmacology, University of G f t e b o r g , for supplying 8 - O H - D P A T . Mr. V. Curbelo provided excellent technical assistance. Some of these results were c o m m u n i c a t e d at the 5th Catecholamine Symposium, G 6 t e b o r g , June 1983.
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Monogr., Oxford University Press, London, 1983, pp. 3-14. 16 Fasmer, O. B., Berge, O.-G. and Hole, K., Similar behavioural effects of 5-hydroxytryptamine and substance P injected intrathecally in mice, Neuropharmacology, 22 (1983) 485-487. 17 Hansen, S., Hypothalamic control of motivation: the medial preoptic area and masculine sexual behavior, Scand. J. Psychol., Suppl. 1 (1982) 121-126. 18 Hansen, S., Spinal control of sexual behavior: effects of intrathecal administration of lisuride, Neurosci. Lett., 33 (1982) 329-332. 19 Hansen, S., H6kfelt, T. and Svensson, L., 5-HT-TRH interactions in the spinal control of sexual behavior, submitted for publication. 20 Hansen, S., K6hler, Ch., Goldstein, M. and Steinbusch, H. W. M., Effects of ibotenic acid-induced degeneration in the medial preoptic area and lateral hypothalamic area on sexual behavior in the male rat, Brain Research, 239 (1982) 213-232. 21 Hansen, S. Svensson, L., H6kfelt, T. and Everitt, B. J., 5HT-TRH interactions in the spinal cord: effects on parameters of sexual behaviour in the rat, Neurosci. Lett., 42 (1983) 299-304. 22 Hjort, S., Carlsson, A., Lindberg, P., Sanchez, D., Wikstr6m, H., Arvidsson, L.-E., Hacksell, U. and Nilsson, J. L. G., 8-hydroxy-2-(di-n-propylamino)-tetralin, 8-OHDPAT, a potent and selective simplified ergot congener with central 5-HT receptor stimulating activity, J. neural Transm., 55 (1982) 169-188 23 H6kfelt, T., Ljungdahl, H., Steinbusch, H., Verhofstad, A., Nilsson, G., Brodin, E., Pernow, B. and Goldstein, M., Immunohistochemical evidence of substance P-like immunoreactivity in some 5-HT containing neurons in the rat central nervous system, Neuroscience, 3 (1978) 517-538. 24 HOkfelt, T., Phillipson, O. and Goldstein, M., Evidence for a dopaminergic pathway in the rat descending from the A l l cell group to the spinal cord, Acta physiol, scand., 107 (1979) 393-395. 25 H6kfelt, T., Terenius, L., Kuypers, H. G, J. M. and Dann, O., Evidence for enkephalin-immunoreactive neurons in the medulla oblongata projecting to the spinal cord, Neurosci. Lett., 14 (1979) 55--60. 26 Horowski, R. and Dorow, R., Influence of estradiol and other gonadal steroids on central effects of lisuride and comparable ergot derivatives, Exp. Brain Res., Suppl. 3 (1981) 169-181. 27 Johansson, O., H6kfelt, T., Pernow, B., Jeffcoate, S. L., White, N., Steinbusch, H. W. M., Verhofstad, A. A. J., Emson, P. C. and Spindel, E., Immunohistochemical support for three putative transmitters in one neuron: coexistence of 5-hydroxytryptamine, substance P- and TRH-like immunoreactivity in medullary neurons projecting to the spinal cord, Neuroscience, 6 (1981) 1857-1881. 28 Kojima, M., Takeuchi, Y., Goto, M. and Sano, Y., Immunohistochemical study on the distribution of serotonin fibers in the spinal cord of the dog, Cell Tissue Res., 226 (1982) 477-491.
29 Larsson, K. and Ahlenius, S., Masculine sexual behavior and brain monoamines. In M. Segal (Ed.), Psychopharmacology of Sexual Disorders, J. Libbey, New York, in press. 30 LoPachin, R. M., Rudy, T. A. and Yaksh, T. L., An improved method for chronic catheterization of the rat spinal subarachnoid space, Physiol. Behav., 27 (1981) 559-561. 31 McEwen, B. S., Davis, P. G., Parsons, B. and Pfaff, D. W., The brain as a target for steroid hormone action, Ann. Rev. Neurosci., 2 (1979) 65-112. 32 Nunez, R. and Sachs, B. D., Segmental organization and spinal projections of the dorsal penile nerves in relation to penile reflexes in rats, Paper presented at the Conference on Reproductive Behavior, Tufts University, Medford, MA, June 1983. 33 Pelletier, G., Steinbusch, H. W. M. and Verhofstad, A. A. J., Immunoreactive substance P and serotonin present in the same dense-core vesicles, Nature (Lond.), 293 (1981) 71-72. 34 Reddy, S. V. R. and Yaksh, T. L., Spinal noradrenergic terminal system mediates antinociception, Brain Research, 189 (1980) 391--401. 35 Sachs, B. D. and Barfield, R. J., Functional analysis of masculine sexual behavior in the rat. In J. S. Rosenblatt, R. A. Hinde, L. Shaw and C. Beer (Eds.), Advances in the Study Behavior, Vol. 7, Academic Press, New York, 1976, pp. 91-154. 36 Skagerberg, G., Bj6rklund, A., Lindvall, O. and Schmidt, R. H., Origin and termination of the diencephalo-spinal dopamine system in the rat, Brain Res. Bull., 9 (1982) 237-244. 37 S6dersten, P., Larsson, K., Ahlenius, S. and Engel, J., Sexual behavior in castrated male rats treated with monoamine synthesis inhibitors and testosterone, Pharmacol. Biochem. Behav., 5 (1976) 319-327. 38 Steinbusch, H. ,W. M., Distribution of serotonin-immunoreactivity in central nervous system of the rat - - cell bodies and terminals, Neuroscience, 6 (1981) 557-618. 39 Wagner, G. and Green, R., Impotence, Plenum, New York, 1981. 40 Westlund, K. N., Bowker, R. M., Ziegler, M. G. and Coulter, J. D., Noradrenergic projections to the spinal cord of the rat, Brain Research, 263 (1983) 15-31. 41 Yaksh, T. L. and Rudy, T. A., Chronic catheterization of the spinal subarachnoid space, Physiol. Behav., 17 (1976) 1031-1036. 42 Yaksh, T. L. and Wilson, P. R., Spinal serotonin terminal system mediates antinociception, J. Pharmacol. exp. Ther., 208 (1979) 446-453. 43 Yeung, J. C. and Rudy, T. A., Sites of antinociceptive action of systemically injected morphine: involvement of supraspinal loci as revealed by intracerebroventricular injection of naloxone, J. Pharmacol. exp. Ther., 215 (1980) 626--632. 44 Yeung, J. C. and Rudy, T. A., Multiplicative interaction between narcotic agonisms expressed at spinal and supraspinal sites of antinociceptive action as revealed by concurrent intrathecal and intracerebroventricular injections of morphine, J. Pharmacol. exp. Ther., 215 (1980) 633--642.
315
BRE 10066
Spinal Monoaminergic Modulation of Masculine Copulatory Behavior in the Rat L. SVENSSON and S. HANSEN
Department of Psychology, Universityof GOteborg, Box 14158, S-40020 GOteborg (Sweden) (Accepted October 25th, 1983)
Key words: 5-HT - - aminotetraline - - dopamine - - noradrenaline - - intrathecal infusions - - sexual behavior - - spinal reflexes
The sexual behavior of male rats receiving infusions of 5-HT, dopamine and noradrenaline intrathecally in the spinal cord of intracerebroventricularly (i.c.v.) in the lateral ventricle was observed. Intrathecal infusions of 5-HT and noradrenaline inhibited penile insertions and ejaculation, noradrenaline being the more potent of the amines. Dopamine was without effect. I.c.v. amine infusions impaired to various extents the masculine mating pattern, primarily by interfering with the males' tendency to approach the females. The facilitation of mating seen after intrathecal administration of the aminotetraline, 8-OH-DPAT, was more pronounced than that observed following its i.c.v, infusion. INTRODUCTION In the neural substrate for masculine sexual behavior the importance of the medial preoptic area and related hypothalamic regions are well establishedlS,17, 31. Several lines of evidence suggest that some of the central monoamine pathways may form part of this neural system as well, their importance in the regulation of masculine sexual behavior being perhaps most dramatically shown by the pronounced lowering of the ejaculatory threshold seen after treatment with certain dopamine ( D A ) and serotonin (5-HT) receptor agonists2~,11A2, 26 or by the ability of some of these drugs to restore sexual behavior in animals made unable to mount by h o r m o n e deprivation or hypothalamic lesions2,3,20, 37. Impressive as these effects may be, we still know very little as to where in the central nervous system these types of drug effects may occur. The spinal cord, being innervated by descending serotonergic, dopaminergic and noradrenergic neuron systems originating in the brainE4,2s,36,38,4°, is one interesting candidate, as several sexual genito-pelvic reflex mechanisms are organized at the spinal level and coordinated into an integrated mating pattern by supraspinal pathwaysT, 39. Indeed, there is evidence to suggest that the facilitatory effect of the ergot derivative, li-
suride, on copulatory behavior may be exerted at least partly at the spinal level 18. Considering the importance of spinal mechanisms for copulation, it would be of interest to know how perturbations of the activity of descending monoamine systems affect sexual behavior. We have begun an analysis of this problem by studying the effects of neurotoxin-induced denervations of the serotonergic and catecholaminergic input to the spinal cord21; here, we report on the actions of 5-HT, D A and N A administered in the spinal subarachnoid space shortly before testing on the masculine mating pattern. For purposes of comparison the effect of these compounds was also assessed following intracerebroventricular (i.c.v.) infusions under comparable conditions. Finally, we compared the behavioral effect of the intrathecal (i.t.) and i.c.v, routes of administration of the aminotetraline, 8 - O H - D P A T , the intraperitoneal administration of which produces a marked facilitation of masculine sexual behavior3. MATERIALS AND METHODS
Animals Sexually experienced male rats, weighing 350-400 g, obtained from M/511egaard Breeding Laboratories (Denmark) were used. Prior to surgery they were
Correspondence: S. Hansen, Department of Psychology, University of GOteborg, Box 14158, S-400 20 Gfteborg, Sweden. 0006-8993/84/$03.00 t~) 1984 Elsevier Science Publishers B.V.
316 housed in groups of 2-3 per cage (53 x 36 x 25 cm), thereafter individually to avoid damage to the cannulae. The animals had constant access to food and water, and were subjected to a reversed light-darkness cycle (dark: 10.00-22.00 h).
Surgery Rats assigned to the intrathecal (i.t.) administration studies were implanted with an 8.0 cm length of PE10 polyethylene tubing under sodium methohexithai anesthesia (Brietal, Lilly; 20-30 mg/rat), according to LoPachin et al.'s 30 procedure. The animal was positioned in a stereotaxic apparatus and the catheter was carefully inserted in the subarachnoid space through a slit in the atlanto-occipital membrane, the free end being secured by threading it through burr holes in the occipital and interparietal bones 30. The vast majority of the subjects appeared completely unaffected by the implant; rats showing signs of spinal damage were discarded. Rats used for intracerebroventricular (i.c.v.) drug administration were implanted with a 0.7 mm in diam. guide cannula (Plastic Products, VA) in the lateral ventricle (stereotaxic coordinates: 0.3 mm behind bregma, 1.2 mm lateral to midline, 4.0 mm below the skull). Brietal anesthesia was used, and the cannulae were secured with acrylic dental cement.
400 ag DA, 9 rats were given infusions of 0, 3, 12.5 and 50/~g NA, and 7 rats infused with 0, 50 and 100 #g 8-OH-DPAT. A group of 11 males implanted with i.c.v, cannulae were given 0,200/~g 5-HT, 400/~g D A and 50/~g NA in random order with 3-4 day intervals; a separate group (n = 9) received i.c.v, infusions of 0, 50 and 100/~g 8-OH-DPAT. One hour prior to testing the males were injected i.p. with 1 mg/kg of the monoamine oxidase inhibitor FLA336(+). The i.t. and i.c.v, monoamine infusions were made over a 1 min period, using a 25/~1 syringe; the i.t. infusions were followed by a 10~tl saline flush to clear the catheter of its contents. Upon completion of the infusions the males were placed in a circular Plexiglas cage (50 cm diam.), and 10 min later an estrous female rat was introduced. The following behavioral items were recorded: mount and intromission frequency, time to first mount and intromission (intromission latency is reported in the Results), time from first intromission
Control infusions 5-HT 100t 0 50 Dopamine
Drugs The following substances were used: 5-hydroxytryptamine hydrochloride (5-HT; Sigma), 3-hydroxytyramine hydrochloride (dopamine, DA; Fluka), Lnoradrenaline hydrochloride (NA; Fluka) and 8-hydroxy-2-(di-n-propylamino)tetraline hydrobromide (8-OH-DPAT). Rats receiving i.t. or i.c.v, amine infusions were pretreated (see below) with the monoamine oxidase A inhibitor FLA336(+) (Astra Liikemedel AB) 5. All drugs were dissolved in sterile saline and the doses refer to the salt forms. Controls were given sterile saline.
Experimental protocol Behavioral observations were begun approximately 1 week after surgery and recurred with 3--4 day intervals. Ten perispinally catheterized rats received in random order i.t. infusions of 0, 50, 100 and 200/tg 5-HT, 7 rats received infusions of 0, 100 and
Intrathecal
100 200
Intracerebroventricular
200IJg
F, 50
0 100 400 I 100q Norad]enalinRl~ ~*** ~
400tJg I~
0 3 12,5 50 50IJg [] Mounts [] Intromissions• Ejaculation Fig. 1. Proportion of male rats showing mounts, intromissions and ejaculation following infusions of 5-HT, dopamine and noradrenaline either intrathecally (i.t.) in the spinal cord or intracerebroventricularly (i.c.v.) in the lateral ventricle. The rats were pretreated with the MAO inhibitor FLA336(+) (1 mg/kg) 1 h prior to testing, and received the various amine infusions 10 min before testing. * P < 0.05, ** P < 0.01.
317 TABLE I Masculine sexual behavior of the male rat following infusions in the spinal subarachnoid space with 5-HT, dopamine and noradrenaline The rats were pretreated with the MAO inhibitor FLA336(+) 1 h prior to testing, and received amine infusions 10 min before testing. Values are means ± S.E.M. Treatment
Mounts/min
lntromissions/ min
lntromission latencya
Ejaculation latentya
Postejaculatory intervala
No. rats showing tail pinch reaction
5-HT 0 50 1~ 2~
1.8±0.3 1.3±0.3 1.4±0.5 1.2±0.4
1.4±0.2 1.1±0.3 0.6±0.2* 0.1±0.0"*
1.6±0.7 1.4±0.6 2.5±1.5 2.3±0.3
7.1±1.6 11.5±2.9 11.6±3.6 13.3±2.5
5.9±0.5 6.5±0.3 6.4±0.6 6.6±0.2
10/10
D~amine 0 1~ 4~
0.8±0.2 0.6±0.2 0.8±0.2
1.6±0.3 1.6±0.5 1,0±0.3
0.3±0.2 0.6±0.3 0.6±0.2
8.8±1.6 13.9±3.1 12.7±3.4
6.5±0.8 7.5±0.8 9.3±1.6
Noradrenaline 0 3 12.5 50
1.1 + 0.2 1.5 _+0.3 0.9 + 0.2 0.7 + 0.2
1.3 + 0.7 + 0.0 ± 0.1 +
1.1 + 1.3 + 1.8 + 1.8 +
11.4 + 1.5 9.2 + 2.8 ---
7.0 + 0.5 5.4 + 0.2 ---
0.2 0.2 0.0"* 0.0"*
0.3 0.3 0.9 0.8
-3/7
9/9 6/9 0/9** 1/9"*
a minutes; b not tested. * P < 0.05; ** P < 0.01 (Wilcoxon matched-pairs signed-ranks test, preceded by Friedman two-way ANOVA; Cochran Q-test followed by binomial test for tail pinch reaction data).
to ejaculation (ejaculation latency), and the time from ejaculation to next intromission (post-ejaculatory interval). The tests were t e r m i n a t e d if intromission latency or p o s t e j a c u l a t o r y interval e x c e e d e d 15 min or if ejaculation latency was longer than 30 min (see Sachs and Barfield35 for a m o r e c o m p l e t e discussion of these behavioral measures). ~The reaction to a brief, manually applied, tail pinch (i.e. agitation, orientation, vocalization) was recorded in some of the e x p e r i m e n t s after the completion of the copulatory tests. Statistics The d a t a were analyzed n o n - p a r a m e t r i c a l l y using (i) F r i e d m a n s two-way analysis of variance followed by Wilcoxons matched-pairs signed-ranks test and (ii) Cochran Q-test followed by the binomial test. RESULTS Effects o f intrathecal 5-HT, D A and N A F!g. 1 shows that the i.t. administration of at least 200 gig 5 - H T or 12.5 p g N A significantly r e d u c e d the n u m b e r of animals showing penile intromissions and ejaculation. By contrast, the p r o p o r t i o n of rats show-
ing mounting behavior r e m a i n e d unaffected by these treatments. Infusion of 100-400/~g D A did not affect the p r o p o r t i o n of copulating animals (Fig. 1), neither was any p a r a m e t e r of their mating p a t t e r n affected, as is shown in Table I. A l s o shown in Table I is the fact that 5-HT and N A , in doses lower than those required for inhibition of intromissions, did not change appreciably the copulatory p a t t e r n leading up to ejaculation. N A , in doses of 12.5-50 ~g, reduced significantly the n u m b e r of animals showing reactions to tail pinch; a similar though non-significant trend was noted following t r e a t m e n t with 200 /~g 5-HT (Table I). Effects o f intracerebroventricular 5-HT, D A and N A Fig. 1 shows that i.c.v, infusions of 200 # g 5-HT, 400/~g D A or 50/~g N A (i.e., the highest doses used in the previous experiment) decreased the n u m b e r of ejaculating rats c o m p a r e d to tests in which vehicle was given. W h e n infused with 5-HT, this decrease was a c c o m p a n i e d by a significant reduction in the n u m b e r of rats showing mounts and intromissions; this effect was not seen following D A and N A . Table II shows, however, that i.c.v, infusions of D A and
318 TABLE II Masculine sexual behavior of the male rat following intracerebroventricular infusions of 5-HT, dopamine and noradrenaline The rats were pretreated with the MAO inhibitor FLA336(+) 1 h before testing, and received amine infusions 10 min prior to testing. Values are means _+ S.E.M. Treatment
Mounts/min
lntromissions/ min
lntromission latency a
Ejaculation latency a
Poste]aculatory interva#
No. rats showing tail pinch reaction
Saline 200/~g 5-HT 400/~g dopamine 50/~g noradrenaline
0.9 0.1 0.5 0.3
3.0 + 0.4 0.9+0.4** 1.1 + 0.4* 1.2 + 0.4*
0.3 + 0.1 0.5+0.3 2.9 + 1.8 4.0 + 2.0
5.9 + 1.4 8.4+2.9 9.3 + 4.7 7.2 + 2.7
4.7 + 0.3 5.5+0.5 5.5 + 0.5 5.8 + 0.8
11/11 11/11 11/11 11/11
+ + + +
0.2 0.1"* 0.3 0.1"*
a minutes. * P < 0.05; ** P< 0.01 (Wilcoxon matched-pairs signed-ranks test, preceded by Friedman two-way ANOVA).
N A did depress the rate at which the rats i n t r o m i t t e d ;
i n t e r m e d i o l a t e r a l c o l u m n and the v e n t r a l h o r n of
in the case of N A , m o u n t i n g rate was also sup-
the spinal gray m a t t e r all r e c e i v e a r a t h e r d e n s e
pressed.
m o n o a m i n e r g i c input originating in the d i e n c e p h a Ion,
locus
coeruleus
and
medullary
raphe
nu-
Effects o f i.t. and i.c.v, infusions o f 8 - O H - D P A T R e g a r d l e s s of a d m i n i s t r a t i o n r o u t e , 8 - O H - D P A T
clei 28,36,4°. B e c a u s e the f u n c t i o n s t h e s e spinal subdi-
facilitated sex b e h a v i o r by d e c r e a s i n g the n u m b e r of
masculine m a t i n g p a t t e r n - -
m o u n t s and i n t r o m i s s i o n s p r e c e d i n g e j a c u l a t i o n , and
sensory input by the dorsal h o r n 32, r e g u l a t i o n of erec-
visions are t h o u g h t to s u b s e r v e are all i n v o l v e d in the p r o c e s s i n g of genital
by s h o r t e n i n g e j a c u l a t i o n latency. T a b l e III shows,
tion by the a u t o n o m i c n e r v o u s system 39 and control
h o w e v e r , that the effect a p p e a r e d m o r e m a r k e d fol-
of penile muscles by m o t o n e u r o n s
lowing perispinal infusions, the i n t r o m i s s i o n f r e q u e n -
horn 9, to m e n t i o n a few e x a m p l e s - - we i n v e s t i g a t e d
cy and e j a c u l a t i o n latency b e i n g significantly l o w e r
in the p r e s e n t e x p e r i m e n t s the w a y in which infusions
following the i.t. infusion of the h i g h e r 8 - O H - D P A T
of 5 - H T , D A and N A m o d i f i e d sexual b e h a v i o r in
dose (P's < 0.02, M a n n - W h i t n e y U-tests).
male rats chronically i m p l a n t e d with a c a t h e t e r in the
in the v e n t r a l
spinal s u b a r a c h n o i d space. T h e p e r h a p s m o s t striking DISCUSSION
finding to e m e r g e out of these e x p e r i m e n t s was that perispinal infusions of 5 - H T o r N A i n h i b i t e d the at-
T h e dorsal h o r n , the a u t o n o m i c cell groups of the
t a i n m e n t of e j a c u l a t i o n , at least a j u d g e d f r o m the
TABLE III Masculine sexual behavior of male rats receiving intracerebroventricular (i.c.v.) or intrathecal (i. t.) infusions of the aminotetraline, 8-OH-DPA T, 10 min before testing Values are means + S.E.M. Treatment
Mounts
Intromissions
lntromission latency a
Ejaculation latency Q
Postejaculatory interval
No. rats showing tail pinch reaction
i. c. v. infusion 0 50 100
10.3 + 2.9 2.3 + 1.1" 2.4 + 0.7**
15.3 +__3.6 5.1 + 1.1 6.7 + 0.8**
1.2 _+ 0.5 2.6 + 1.2 1.1 + 0.7
8.6 + 1.2 4.0_+ 1.2 4.5 _+ 1.4"
5.3 + 0.3 4.9_+ 0.3 4.6 + 0.4
__b ---
i.t. infusion 0 50 100
18.1 + 5.6 2.0 + 1.1 0.4 + 0.2*
10.9 + 2.1 2.4 + 0.8 1.9 + 0.4*
0.6 + 0.2 1.2 _+ 0.6 2.2 + 1.1
8.6 + 2.2 2.7 _+ 1.2" 1.4 + 0.6*
5.5 + 0.4 4.8 _+ 0.8 5.2 + 1.1
7/7 -6/6
a minutes; b not tested. * P < 0.05; ** P < 0.01 (Wilcoxon matched-pairs signed-ranks test preceded by Friedman two-way ANOVA).
319 absence of the behavioral pattern that usually accompanies the emission of seminal fluid into the female reproductive tract. The failure to ejaculate was not a consequence of any obvious lack of sexual motivation, because the rats continued to mount the estrous females at a normal rate; the persistence of mounting also shows that the 5-HT and NA infusions did not impair with the male's ability to execute pelvic thrusts and in this way inhibit ejaculation. Infusions of 5-HT and NA at doses effective in abolishing ejaculation did, however, impair the rat's ability to achieve penile intromissions when mounting the female, and it is possible, therefore, that the amines acted to block the transmission of genital tactile cues important for eliciting ejaculation. According to current concepts, genital sensory input serves at least two functions in the male rat: firstly, it serves a detector function by guiding the penis towards the vaginal orifice during mounting and, secondly, it gradually accumulates to excite (or disinhibit) the reflexive mechanisms responsible for the emission and ejaculation of semen1, 7,35. The present study suggests that i.t. 5-HT or NA infusions interfere with the guiding action of genital sensory feedback; whether or not they also impair the ejaculation-promoting actions of penile afference remain to be determined. The inhibitory actions of 5-HT and NA were not duplicated by i.t. D A infusions, which failed altogether to modify sexual behavior in the present experiments. It also seems as if NA was considerably more effective than 5-HT in inhibiting intromissions: on a molar basis our data indicate that NA was about 15 times as potent as 5-HT. It is known that subpopulations of the spinally projecting medullary 5-HT cells also contain one or several neuropeptides (e.g substance P, thyrotropin-releasing hormone, enkephalin), suggesting that 5-HT normally is released together with a peptide in the spinal cordS,10,23,25,27,33. Evidence is accruing that these neuropeptides may potentiate or otherwise modulate the behavioral action of 5-HT 6,16 and experiments designed to assess neuropeptide/5-HT interactions in the context of sexual behavior is currently underway in our laboratory 19. Even though previous studies have shown that i.t. infusions of drugs, using procedures similar to those employed in the present experiments, largely remain in the spinal compartment14, 41, some diffusion to su-
praspinal sites does occur and we therefore administered 5-HT, D A and NA into the lateral ventricle in order to investigate the extent to which the behavioral effects seen following i.t. infusions could be attributable to supraspinal sites of action. Some similarities between the two modes of exposure were indeed observed: both i.t. and i.c.v. 5-HT reduced the number of animals showing intromission and ejaculation, and depressed intromission rate. A similar effect was observed after i.t. and i.c.v. NA administration, although no decrease in the proportion of intromitting rats was recorded. However, conspicuous differences between the i.t. and i.c.v, modes of exposure were also noted. Thus, in contrast to the behavioral effect of perispinally applied 5-HT, its i.c.v, administration resulted in a pronounced decrease in the number of subjects showing mounting behavior and in mounting rate. The failure to ejaculate may thus have different causes in the two groups of 5-HT treated rats: following i.c.v, infusions it is due primarily to a lack of drive to approach and mount the female, following i.t. infusions because of an impaired ability to locate the vaginal orifice during mating. The trend towards a diminished response to noxious tail pinch in the present s t u d y - an observation in line with previous studies on pain transmission 42 - - following i.t. but not i.c.v. 5-HT administration is consistent with this interpretation. As to the behavioral effects of i.t. vs i.c.v. NA infusions, the fact that 12.5 pg of i.t. NA produced a 100% inhibition of ejaculation, whereas 50pg NA i.c.v, produced a 54.5% inhibition only is evidence that NA acted mainly at the spinal level to inhibit ejaculation. The decreased mounting rate of the i.c.v. NA-treated males, and their retained sensitivity to tail pinch (in contrast to the i.t. NA-treated males; see also ref. 34), suggest that their partial failure to ejaculate was due primarily to a reduced sexual arousability, similar to rats receiving supraspinal 5-HT. In summary, then, our results suggest that although the effects on copulatory behavior of i.t. vs i.c.v, monoamine infusions may not be as strikingly different as e.g. for the acoustic startle reflex 13, 5-HT and NA may act principally at the spinal level to inhibit the transmission of penile sensory feedback necessary for achieving intromission and ejaculation. Previous studies have shown that the systemic treatment of the ergot congener, 8-OH-DPAT, facil-
320 itates the male mating p a t t e r n 3. T h e aminotetraline is believed to act agonistically at central serotonergic receptor sites 22, though recent failures to block its sex-promoting actions by p r e t r e a t m e n t with several 5-HT receptor antagonists 29 indicate that some other neurochemical mechanism m a y also be operative. H e r e , we a t t e m p t e d to d e t e r m i n e whether the effect on sexual behavior of the c o m p o u n d was due primarily to a spinal or supraspinal site of action by comparing the behavioral effect of i.t. and i.c.v. 8-OHD P A T administration. A significant facilitation of several components of the mating pattern was detected following both routes of administration, though the effect was m o r e p r o n o u n c e d in animals receiving i.t. infusions of the drug. Thus, while the spinal cord may be an i m p o r t a n t target for 8-OHD P A T action, the present results allow no clear separation of spinal and supraspinal sites of action. The reasons for this m a y be that 8 - O H - D P A T may spread with unusual efficacy throughout the central nervous system regardless of delivery site; occlusion of the fourth ventricle may provide one way in which to overcome this potential source of error 43. A l t e r n a tively, in analogy with the neural substrate for mor-
phine-induced analgesia 44, facilitation of sexual behavior by 8 - O H - D P A T (and other ergot-like drugs) may d e p e n d on multiplicative interactions between spinal and supraspinal sites, which at high local concentrations b e c o m e capable of sex-facilitation by ind e p e n d e n t actions. Clearly, m o r e extensive studies are required to understand the locus of action of these potent compounds. ACKNOWLEDGEMENTS This study was s u p p o r t e d by the Swedish Medical Research Council (B84-21X-06605-02A) and The B a n k of Sweden T e r c e n t e n a r y F o u n d a t i o n . W e are grateful to the A s t r a L~ikemedel A B , Sfdert~ilje, for donating F L A 3 3 6 ( + ) and to the Organic Chemistry Unit of the D e p a r t m e n t of Pharmacology, University of G f t e b o r g , for supplying 8 - O H - D P A T . Mr. V. Curbelo provided excellent technical assistance. Some of these results were c o m m u n i c a t e d at the 5th Catecholamine Symposium, G 6 t e b o r g , June 1983.
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