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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



and debility rather than the importance of the loca- 

 tion of the lesion. More recently Stamm (88) has re- 

 ported that relatively small lesions, involving only 

 about 1 6 per cent of the cortex, located medially 

 in the cingulate and retrosplenial cortex, interfere 

 very seriously with litter survi\al, nest building and 

 repair, retrieving young, and removing them from ex- 

 cessive heat. Similarly sized lateral lesions were with- 

 out apparent effect. Electrocon\ulsive shock treat- 

 ment from the i2th day of pregnancv to parturition 

 in rats obliterates nest-ijuildina; bcha\'ior and care of 

 the litter {75). 



In its dependence on the cortex, female maternal 

 beha\ior more closely resembles male mating be- 

 havior than female psychic estrus. Female mating 

 behavior depends less on initiative and distance re- 

 ceptors than on proprioception, tactile seitsaiion and 

 an elevated hormone titer. The reverse is true in ma- 

 ternal behavior, maze learning and male reproductive 

 activities. 



NEUR.\L MECH.ANISMS .AND CENTERS .AS REVE-ALED BY 

 STIMUL.ATION .AND RECORDING EXPERIMENTS 



Peripheral Mechanisms 



Although only a minimum of afferent innervation 

 appears to be necessary to maintain reproductive be- 

 havior, especially in female animals, the influence of 

 sex hormones on receptors must be considered as, at 

 least, auxiliary mechanisms in sex drive. 



Beach (12) and Holz have shown that castration in 

 male rats on the first day of life leads to the dexelop- 

 ment of a penis too short to permit normal repro- 

 ductive behavior on subsequent treatment with testos- 

 terone. Castration in the adult rat results in a penis 

 with a reduced number of genital papillae, making it 

 a less sensitive tactile organ (12). 



Campbell el al. (19, 54) have studied the receptors 

 and afferent nerves in the penis and clitoris of cats, 

 cattle and sheep by anatomical and electrophysio- 

 logical methods. They propose, as an hypothesis, that 

 altered sensitivity during tumescence of the genitalia 

 is modulated by an effect of the deep encapsulated 

 end organs on the fine nerve fibers emerging from 

 them. 



Partial patterns of sexual beha\ior in estrous female 

 animals can be evoked by grasping the neck or back 

 and prodding the perineum with a glass rod. As men- 

 tioned above, responsiveness to such treatment has 

 been made the basis of quantitating female sex drive 



in rats by Ball (4). Artificial stimulation of the vagina 

 induces a species-specific after-reaction which is fol- 

 lowed by ovulation in the cat (42) or the estrogen- 

 treated rabbit (77; see also below). 



There is evidence that olfactory sensibility plays a 

 unique role in .sexual behavior. Le Magnen (57) has 

 reported that, correlated with estrogen and androgen 

 titers in rat and man, there are marked alterations in 

 the subject's ability to detect odors of synthetic musk 

 and urinary steroids. These "olfactosexual' phenomena 

 appear to be of more importance in the lower mammal 

 (57)- 



Hypollialamic Mechanisms 



The diencephalon contains centers in which direct 

 electrical stimulation leads to behavioral responses 

 ranging from sleep to rage (47). Stimulation of 

 hypothalamic areas evokes a wide variety of autonomic 

 responses invoking smooth mu.scle, glands and heart 

 {72). These effector organs are so intimately involved 

 in emotional states that the hypothalamus has long 

 been considered a center of emotional expression. 

 Hypothalamic activation of the release of pituitary 

 gonadotrophin, considered in detail in Chapter 

 XXXIX by Harris in this Handbook, is facilitated by 

 sex steroids of the same order of dosage as that which 

 e\okes mating behavior. This facilitation, bv estro- 

 gen, of the release of pituitary oxulating honnone in 

 response to direct electrical stimulation of the hy- 

 pothalamus implies a hypothalamic or a hypophyseal 

 site of estrogen action. 



Among the lines of evidence implicating the hypo- 

 thalamus in mating behavior is the recording of 

 electroencephalographic (EEC) acti\ity from hypo- 

 thalamic sites during and after real or simulated 

 copulation activity. In the estrous cat, as mentioned 

 above, vaginal stimulation is followed by a dramatic 

 behavioral after-reaction, lasting several minutes. 

 Temporally related to this after-reaction are the EEG 

 changes, illustrated in figtire 7, bursts of high ampli- 

 tude activity localized in the anterior lateral hy- 

 pothalamus in and around the medial forebrain 

 bundle i)ut never in the posterior hypothalamus 

 (6g). These changes were observed only in estrotts 

 or estrogen-primed cats. If the after-reaction repre- 

 sents a behavioral expression of orgasm in the cat, 

 the changes may signify EEG concomitants of this 

 phenomenon; iiut orgasm is difficult to assess in 

 animals (6). 



In unanesthetized, unrestrained female rabbits 

 with clironically implanted electrodes. Green (38) 



