Nakano K, Suga S, Kondo Y, Sato T, Sakuma Y.
Estrogen-excitable forebrain projections to the ventral premammillary nucleus of the female rat. Neuroscience Letters, in press.
Retrograde labels by Nuclear Yellow from the female rat ventral premammillary nucleus (PMv) were most numerous in the lateral septum (LS) and the preoptic area (POA) and spread laterally into the substantia innominata. Other labels were in the diagonal band nucleus, the substantia innominata and the bed nucleus of the stria terminalis. Constant-current, single-pulse electrical stimulation of the PMv in urethane-anesthetized ovariectomized rats elicited antidromic action potentials in the cingulate cortex, in addition to the structures that contained labeled neurons. In the LS or cingulate cortex, but not in the POA, estrogen decreased antidromic activation thresholds and shortened refractory periods. The PMv is a way station that relays estrogen-excitable septal, but not preoptic, effects. The PMv also contains fibers of passage that originate in estrogen-excitable cingulate neurons.
Takeshi Terao, Fumitaka Okajima, and Yasuo Sakuma
FACILITATION OF THE LORDOSIS REFLEX IN ESTROGEN-PRIMED FEMALE RATS BY ELECTRICAL STIMULATION OF THE VENTRAL PREMAMMILLARY NUCLEUS
Japanese Journal of Physiology 45, Suppl. 2, S223, 1995
Presented at the 2nd Joint Meeting of the Physiological Societies of Japan, UK and Eire, April 1995, Nagoya
The ventral premammillary nucleus (PMV) has been implicated in the regulation of reproductive endocrinology and behavior, because neurons in this structure express estrogen- and androgen-receptor molecules and are densely innervated by steroid-sensitive limbic and forebrain structures. The rat PMV may also be sexually dimorphic. Projections of the PMV terminate rostrally in the preoptic and other subpallidal structures, and caudally in the pontine tegmentum and other lower brain stem structures. The PMV, therefore, occupies a strategic position in integrating neural and humoral regulation of steroid-dependent, sex-specific functions. However, concrete evidence for this speculation is surprisingly scanty. In the present study, we stimulated the PMV in conscious, estrogen-primed ovariectomized rats to identify the role of this structure in the control of female sexual behavior.
Ovariectomy and stereotaxic surgery for the chronic placement of the electrodes were carried out under Ketamine and Nembutal anesthesia (each given intraperitoneally at a dose of 25 mg/kg body weight). Each animal received a subcutaneous injection of 10 ug estradiol benzoate (EB, Sigma) in sesame oil on the day of surgery to ensure behavioral sensitivity to subsequent treatments. After a recovery period of 10 days, 5 ug EB was supplemented. The animals displayed moderate lordosis consistently in response to manual cutaneous stimulation of the flanks followed by stimulation of the rump-tail base-perineum. For each test session, the animal was placed in a clear plastic cage under a dim red light. The measure used in behavioral evaluation was the lordosis score, i.e., the reflex intensity when the flank and perineum of the animal were stimulated manually by the experimenter. Some animals were placed together with two sexually vigorous stud male rats, and the lordosis quotient, the percent lordosis occurrence per 10 mounts, was determined. The PMV was stimulated by trains of constant-current, negative square pulses. In most sessions, 0.2 ms-duration pulses at 50 uA were repeated at 10 Hz.
Electrical stimulation of the PMV and adjacent caudal hypothalamus caused a rapid and large facilitation of the lordosis reflex in response to either manual cutaneous stimuli or male mounts. Unilateral stimulation at intensities as small as 10 uA was sufficient for this effect. The facilitation increased in a graded manner to increased stimulus current, and was optimally evoked by stimuli delivered at 10 Hz. The effect disappeared immediately following the end of electrical stimulation. Electrical stimulation of the PMV specifically facilitated lordosis, without inducing aversive or motor response. The subjects remained calm during PMV stimulation, and rarely tried to escape or resisted to the manual contacts or to the males.
The PMV probably mediates estrogen-sensitive, facilitatory effect from the lateral septum on the lordosis reflex. The septal efferents with terminals in the PMV, which we have shown to be excitable by estrogen in the ovariectomized rat, may be the neural substrate for the facilitation of the lordosis reflex.
Akira Kato, Yasuhiko Kondo, Yasuo Sakuma
FACILITATION OF FEMALE RAT SEXUAL BEHAVIOR BY AN EXCITATORY AMINO ACID IN THE PREMAMMILLARY REGION.
Neuroscience Research, Supplement 20: S261, Abst 2427, 1996.
Presented at the 19th Annual Meeting of the Japan Neuroscience Society, July 1996, Kobe
The premammillary region (PMR) contains many estrogen-receptor positive neurons and receives inputs from the preoptic area, which is importantly involved in the regulation of female rat sexual behavior. In the present study, we examined effects of excitatory amino acid infusion into the PMR through microdialysis probes on various components of female rat sexual behavior. Guide cannulae for probes were implanted stereotaxically into the PMR under pentobarbital anesthesia in ovariectomized rats. Two to three weeks after the surgery, animals received a subcutaneous injection of 2 ug estradiol benzoate and were tested for sexual behavior 48h later. Whereas infusion of artificial cerebrospinal fluid had no effect at all, 1 mM homocysteic acid induced a complete set of sexual behavior, that included both receptivc and receptive components. The data suggest that the PMR contains neuronal elements that facilitates female sexual behavior.
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