Ventromedial hypothalamic nucleus lesions disrupt olfactory mate recognition and receptivity in female ferrets.

Previous research showed that ferrets of both sexes rely on the perception of conspecifics' body odors to identify and motivate approach towards opposite-sex mating partners, and exposure to male body odors stimulated Fos expression in an olfactory projection circuit of female, but not male, ferrets that terminates in the ventromedial hypothalamic nucleus (VMH). We asked whether the female-typical preference of ferrets to approach male as opposed to female body odors in Y-maze tests would be disrupted by VMH lesions. Sexually experienced female ferrets were ovo-hysterectomized prior to receiving bilateral electrolytic lesions of the VMH, the preoptic area/anterior hypothalamus (POA/AH) or a sham operation. Subsequently, while receiving estradiol benzoate, females that received either complete or partial bilateral lesions of the VMH approached volatile odors from an anesthetized male on significantly fewer trials than females given POA/AH lesions or a sham operation. Both groups of ferrets with VMH lesion damage reliably discriminated between volatile anal scents as well as urinary odors from the 2 sexes in home cage habituation/dishabituation tests, suggesting that their odor-based sex discrimination remained intact. Females with complete bilateral VMH lesions showed significantly lower acceptance of neck gripping from a stimulus male (receptivity) and more aggression towards the male than all other groups of female subjects. Estrogen-sensitive neurons in the VMH appear to play a central role in female-typical neural processing of odor inputs leading to a preference to seek out a male sex partner, in addition to facilitating females' sexual receptivity.

Discrete electrolytic lesion of the preoptic area prevents LPS-induced behavioral fever in toads.

The preoptic area (POA) plays an important role in fever in mammals, but the role of this region in fever in ectothermic vertebrates has never been assessed. Toads, like all ectotherms, regulate their body temperature (T(b)) primarily by behavior and develop behavioral fever when injected with lipopolysaccharide (LPS). Therefore, we tested the hypothesis that the POA plays a role in the behavioral fever induced by LPS in the toad Bufo paracnemis. We made electrolytic lesions in the POA of toads (0.3 mA, 8 s) and measured preferred T(b) using a thermal gradient. After a period of 24h inside the gradient chamber, control, sham-operated and lesioned toads were systemically injected with LPS (200 micro g kg(-1)) or pyrogen-free saline. There was no significant effect of POA lesion in animals at their normal preferred T(b). LPS caused a significant increase in preferred T(b) of control and sham-operated toads, but lesions in the POA abolished this response. These results indicate that the POA is an important site in the central nervous system of toads, and perhaps of all vertebrates, involved in the development of fever.

Recovery of sleep after fetal preoptic transplantation in medial preoptic area-lesioned rats.

Changes in sleep after fetal preoptic (POA) tissue transplantation were studied in rats which had been made insomniac by a medial preoptic area (mPOA) lesion. Two days after the N-methyl D-aspartic acid (NMDA) lesion of the mPOA, fetal POA tissues (obtained from 14- to 17-day-old fetuses) were transplanted into the lesioned mPOA. Insomnia was less marked in these animals, as compared to nontransplanted lesioned rats, even on the 4th day after transplantation. The quantum of sleep nearly attained the prelesion level by the 20th day. Body weight also showed recovery after transplantation. Rectal temperature, which was increased by the lesion of the mPOA, remained unaltered even after the transplantation. These results suggest that the recovery of sleep and rectal temperature may follow different time courses. Surviving transplanted neurons were seen at the site of lesion on postmortem examination. Humoral interaction between the host and the transplant may be responsible for the early recovery of sleep, though the establishment of neural connections between the host and transplant might have contributed to the later recovery. This is the first study to show the recovery of sleep function in insomniac animals after fetal preoptic tissue transplantation. However, the specificity of the POA fetal tissue, in comparison with other neural tissues to promote sleep recovery, remains to be established.

Preoptic area grafts implanted in mammillary bodies of hypogonadal mice: patterns of GnRH neuronal projections.

Gonadotropin-releasing hormone (GnRH) axons project to the median eminence, where the peptide is released to stimulate pituitary gonadotrophs. Hypogonadal mice (hpg) do not synthesize GnRH due to a deletion in the gene. When neonatal preoptic area (POA) tissue from normal mice containing GnRH neurons is transplanted into the third ventricle of hpg mice, GnRH axons exit the graft and specifically project to the median eminence, where the release of GnRH in the portal circulation induces the stimulation of the pituitary-gonadal axis. To test the hypothesis that the median eminence region is critical to targeting, we placed POA grafts in the region of the mammillary bodies, which never contains GnRH cell bodies, but is nevertheless close to the median eminence. Control mice received bilateral grafts into the anterior hypothalamus. GnRH axons innervated the median eminence in animals with grafts in the mammillary bodies and posterior hypothalamus. Mice with such grafts for 4-5 months had gonadal development, while those with grafts for shorter periods did not. Anterior hypothalamic grafts merged into the third ventricle and, consistent with previous studies, this resulted in GnRH innervation of the median eminence and gonadal development. However, when grafts were located within dorsal regions such as the thalamus, no median eminence innervation was seen. In these cases, GnRH axons borrowed other bundles of fibers to travel within the host brain. The pattern of innervation from grafts within ventro-caudal regions of the hypothalamus vs. that from dorsal regions supported the hypothesis that the median eminence releases diffusible substances directing GnRH outgrowth.

Angiotensin II pressor activity depends on medial and lateral anterior hypothalamic pathways.

The preoptic region of hypothalamus was disconnected from caudal structures with two different-size knife cuts in rats to investigate the pathway responsible for the effects of intracerebroventricular (ICV) and intravenous (IV) angiotensin II (ang II) on blood pressure and arginine vasopressin (AVP) release. Seven days after surgery ICV ang II (125 ng) in sham-operated (sham) rats increased mean arterial pressure (MAP) (+23 +/- 3 mmHg) and decreased heart rate (HR) (-58 +/- 5 beats/minute). However, ICV ang II had no effect on MAP or HR of rats with a large (preoptic-hypothalamic disconnection) cut. Both the pressor response (+12 +/- 2 mmHg) and the bradycardia (-39 +/- 6 beats/minute) were significantly reduced by a small (medial preoptic-hypothalamic disconnection) cut. The increased plasma AVP to ICV ang II in sham rats (9.8 +/- 3.6 pg/mL) was abolished in large-cut rats and attenuated in small-cut rats (3.2 +/- 0.7 pg/mL). IV bolus injection of ang II (125 ng) in sham rats increased MAP by 43 mmHg, whereas large-cut rats showed a blunted (25%) pressor response. The pressor response to IV infusion of ang II (8 ng/20 microL/minute for 15 minutes) was diminished in large-cut rats (+4 +/- 1 mmHg) as compared with that in sham rats (+19 +/- 2 mmHg). Both cuts transected the projection between the periventricular tissue surrounding the anteroventral third ventricle and supraoptic nucleus, but the supraoptic-neurohypophyseal pathway was severed only by the large cut.(ABSTRACT TRUNCATED AT 250 WORDS)

Naloxone and initial estrogen action to induce lordosis in ovariectomized rats: the effect of a cut between the septum and preoptic area.

The effects of intra-third-ventricular (ITV) injection of naloxone (NLX), an opioid receptor antagonist, on lordosis behavior were studied in ovariectomized female rats given a horizontal half-circle cut located just above the anterior commissure (ARD) and subcutaneously (s.c.) treated with estradiol benzoate (EB) and progesterone (Prog). In ARD-sham control animals, lordosis quotient (LQ) was 78.8 +/- 4.2% (SE,n = 8). LQ (48.3 +/- 7.2%, SE, n = 8) in the ARD-sham rats significantly decreased with the ITV injection of NLX at the time of s.c. EB-priming. In contrast, lordosis reflex in the ARD-operated animals was maximally facilitated (sham versus ARD, P < 0.01). LQ in the ARD-operated rats did not decrease with the ITV injection of NLX at the s.c. EB-priming. The present results suggest that the opioidergic systems modulate an initial phase of estrogen action to induce lordosis and play a part in neural input from the forebrain structures to regulate female sexual receptivity.

Preoptic recess ablation selectively increases baroreflex sensitivity to angiotensin II in conscious rats.

Angiotensin II (ANG II) attenuates baroreflex sensitivity through central pathways. However, the specific CNS sites where ANG II inhibits baroreflexes are not completely understood. The periventricular tissue of the anteroventral third cerebral ventricle (AV3V) mediates several responses to centrally and peripherally administered ANG II. Therefore, these studies determined the effects of bilateral electrolytic ablation of AV3V periventricular tissue on reflex-induced changes in heart rate during pressor and depressor responses evoked by IV administration of phenylephrine (PE), ANG II, and nitroprusside (NP). Animals were prepared with catheters in the femoral artery and vein 10-14 days following AV3V ablation or control (CONT) surgery. The following day, baroreflex sensitivity in the conscious animals was evaluated as the slope of the regression line relating blood pressure and heart rate during IV infusion (1 min) of three doses of PE, ANG II, and NP. Baroreflex sensitivity during PE and NP infusion were equivalent in AV3V-lesioned and CONT animals. However, animals with AV3V lesions demonstrated significantly greater baroreflex sensitivity during ANG II infusion than both PE-treated AV3V-lesioned animals and ANG II-treated CONT animals. These data suggest that the impairment of baroreflex-induced bradycardia during pressor responses evoked by ANG II is mediated by tissue located in the AV3V region.

Effect of hypothalamic lesions that induce precocious puberty on the morphological and functional maturation of the luteinizing hormone-releasing hormone neuronal system.

Recent evidence has implicated the transforming growth factor-alpha (TGF alpha)/epidermal growth factor receptor (EGFR) system in the mechanism by which hypothalamic lesions accelerate female sexual development. Since acquisition and maintenance of reproductive functions depend on the secretory activity of LHRH neurons, the present studies were undertaken to characterize some of the cellular and molecular events that underlie lesion-induced activation of the LHRH neuronal network. Bilateral electrolytic lesions of the posterior portion of the preoptic region and anterior hypothalamic area (POA-AHA) in 22-day-old rats resulted in vaginal opening and ovulation within 7 days. Morphological maturation of LHRH neurons was assessed by the relative frequency of irregular and smooth neurons (the former being the predominant type in adult animals). Within 20 h after the lesion, there was a significant decrease in the proportion of LHRH neurons with spiny irregular contours, indicating reversal to a more immature morphological type. This change was followed by accelerated spine reformation, so that at the time of precocious proestrus, the incidence of irregular LHRH neurons was similar in lesioned and age-matched control rats. A striking increase in c-fos mRNA levels occurred within 1 h after the lesion in the area neighboring the site of injury, reflecting the immediate cell response to trauma. Immunohistochemical localization of the c-fos protein, used to estimate changes in cellular activity at the single cell level, demonstrated c-fos induction in unidentified cells near the lesion and astrocytes, but not in LHRH neurons 20 h after injury. In contrast, a selective increase in c-fos expression was observed in LHRH neurons during the initiation of precocious puberty 5-7 days later at the time of the first proestrus. An increase in plasma LH associated with a drop in LHRH content in the median eminence and an increase in pro-LHRH precursor in the POA-AHA, with no changes in LHRH mRNA, was found to antedate the first preovulatory surge of gonadotropins in lesioned rats. Assessment of the changes in PC2 mRNA, which encodes a novel dibasic endoprotease presumptively involved in tissue-specific processing of a class of prohormones that includes pro-LHRH, showed that the content of PC2 mRNA in the AHA-POA increases during normal puberty, but not in lesioned animals, thus providing a potential explanation for the divergent changes in pro-LHRH and mature decapeptide found in lesioned rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Norepinephrine neurons in mouse locus coeruleus express c-fos protein after N-methyl-D,L-aspartic acid (NMDA) treatment: relation to LH release.

In mouse, rat, and monkey, N-methyl-D,L-aspartic acid (NMDA) modulates gonadotropin releasing hormone (GnRH) release by an unknown mechanism. In previous studies we found that normal male mice consistently responded to NMDA administration with increased levels of plasma LH, as did most normal female mice and female hypogonadal mice with fetal preoptic area implants (HPG/POA). To investigate the mechanism of NMDA-induced GnRH release, immunocytochemistry of c-fos protein (FOS) was used for detection of neurons activated by NMDA administration. In both normal male and HPG/POA mice, FOS expression was unchanged in GnRH cells after NMDA administration. That neurosecretory cells can respond to NMDA was shown by the induction of FOS in many CRH (corticotropin-releasing hormone) cells in the paraventricular nucleus. Immunocytochemistry of beta-Endorphin, neuropeptide Y, tyrosine hydroxylase, an enzyme marker for catecholaminergic neurons, and glutamic acid decarboxylase, an enzyme marker for GABA neurons, was combined with that for FOS in normal male mice. Many noradrenergic (NA) neurons in the locus coeruleus (32-61%), and dopaminergic (DA) neurons in the mediobasal hypothalamus (15-31%) expressed FOS after NMDA administration while FOS was only rarely induced in neurons with the other neuromodulators tested. FOS was also induced in the locus coeruleus in male (43, 54%) and female (40, 55, 69%) HPG/POA mice. In contrast, few cells of the locus coeruleus expressed FOS in normal or HPG/POA mice after saline challenge. These results suggested that NMDA did not activate GnRH cells directly, but that NA neurons in the locus coeruleus were activated by NMDA and might be involved in stimulating GnRH release.(ABSTRACT TRUNCATED AT 250 WORDS)

Allografts of CNS tissue possess a blood-brain barrier. II. Angiogenesis in solid tissue and cell suspension grafts.

Angiogenesis and patency of blood vessels were analyzed qualitatively in solid CNS and peripheral tissue syngeneic, allogeneic, and xenogeneic grafts and in individual cell suspension grafts of astrocytes, fibroblasts, PC12, and three additional tumor cell lines placed intracerebrally in adult host mice. Postgrafting survival times were 1 day through 4 weeks. The patency of graft vessels was determined in sections from immersion-fixed tissues incubated to reveal the endogenous peroxidase activity of host red cells trapped within the lumen of blood vessels. Additionally, horseradish peroxidase (HRP) was administered intravenously to live hosts; HRP labels host brain and graft vessels on the luminal surface and reveals the presence or absence of a blood-brain barrier (BBB) within the grafts. The origins of blood vessels supplying solid tissue xenografts were identified immunohistochemically with primary antibodies against host (athymic AKR mice) and donor (fetal Lewis rats) major histocompatibility complex (MHC) class I. Blood vessels supplying solid CNS grafts at 1-7 days post-transplantation were identified ultrastructurally and possessed interendothelial tight junctional complexes; however, they were not perfused with either host blood or blood-borne HRP prior to 8 days. Graft vessels at 10 days were outlined consistently by peroxidase-positive red cells in immersion-fixed material and labeled with blood-borne HRP. These vessels provided a BBB to the circulating HRP and exhibited interendothelial tight junctions. Evidence of angiogenesis within solid anterior pituitary grafts and the variety of cell suspension grafts was obtained prior to 3 days post-transplantation in immersion-fixed preparations; the vessels, with the notable exception of those supplying astrocyte cell suspensions, failed to present a BBB to blood-borne peroxidase. Endothelia in the solid pituitary allografts and the PC12 cell grafts were highly fenestrated and exhibited open interendothelial junctions; those in the tumor and fibroblast cell grafts, for the most part, appeared nonfenestrated, and many possessed open interendothelial junctional complexes. Immunostaining for host and donor MHC class I revealed that donor blood vessels predominate over host vessels in CNS xenografts and supply pituitary xenografts exclusively; in both preparations, donor vessels were not identified within the host CNS. Because cell suspension grafts were derived from endothelia-free preparations grown in culture, blood vessels supplying these grafts were necessarily of host CNS origin and manifested a morphological transformation from a BBB to a non-BBB endothelium. The data suggest that angiogenesis in solid CNS grafts placed into the adult host CNS, compared to similarly placed solid peripheral tissue/cell suspension grafts, is not rapid.(ABSTRACT TRUNCATED AT 400 WORDS)

Appearance of neurons with glucocorticoid receptors and neurovascular links in the embryonal rat hypothalamus grafted in the third ventricle.

We have investigated the appearance of the transmitter phenotypes of hypothalamic neurons in grafts transplanted into the third ventricle of adult female rats. The grafts were the mediobasal hypothalamus and the preoptic area of 12.5-day-old rat embryos, and were examined 40-100 days later. Wheat germ agglutinin (WGA) was injected into the jugular vein of several animals for the examination of the existence of neurovascular associations. Three days after the injection, WGA appeared to have been incorporated into the neurons in the paraventricular, periventricular, and arcuate nuclei of the host animals. In the grafts, WGA was also seen incorporated in certain neurons which were found immunoreactive for tyrosine hydroxylase (TH), rat corticotropin-releasing factor (rCRF), substance P (SP), or somatostatin (SRIH). Neurons immunoreactive for neuropeptide Y (NPY) and ACTH did not seem to incorporate WGA. These findings suggest that the neurons containing TH, rCRF, SP, or SRIH link with fenestrated capillaries developed in the grafts. The immunoreactivity for glucocorticoid receptor (GR) was detected mainly in the nucleus of certain neurons and glial cells in the grafts as well as in the host hypothalamic neurons. In the grafts, strong GR immunoreactivity was detected in the cells immunoreactive for TH, NPY, and rCRF as in the host animals. It is concluded that the undifferentiated hypothalamic neurons differentiate to synthesize GR as well as definitive peptides and TH in the grafts.

Identification of gonadotropin releasing hormone (GnRH) neurons projecting to the median eminence from third ventricular preoptic area grafts in hypogonadal mice.

Functional gonadotropin releasing hormone (GnRH) neurosecretory activity can be restored in genetically hypogonadal (hpg) adult mice with grafts of GnRH-containing fetal or neonatal septal-preoptic area (S/POA) tissue. Neurons implanted into the third ventricle of the host brain survive and send out axons which innervate one of the normal targets of these neurons, the median eminence (ME). Fibers terminate near primary portal vessels where GnRH is available for release into the vasculature, and this axonal outgrowth is essential for the stimulation of gonadotropin secretion, gonadal and accessory sex structure growth, gametogenesis, and fertility. Although it is known that GnRH axons reach their target, it is not known if all such neurons in a graft contribute to the projection. Taking advantage of the fact that axons in the ME, the sole host target, are outside the blood-brain barrier (BBB), long-term grafted animals were injected intraperitoneally with a retrograde tracer, Fluorogold (FG). Normal male mice were injected for comparison. Animals were sacrificed 5 days after injection and brain sections in the area of the graft were stained immunocytochemically for GnRH. In the normal male mice, two-thirds of the GnRH neurons were double-labeled with FG. In grafted individuals which showed increased gonadal growth, the percentage of labeled cells ranged from 17 to 75%. The results indicate that despite tissue injury, ectopic location, and a vastly reduced population, transplanted fetal GnRH neurons recapitulate a pattern seen in normal intact mice where some but not all neurons were capable of capturing a peripherally delivered tracer.

Mild cold exposure increases survival in rats with medial preoptic lesions.

High mortality rate in rats with large medial preoptic lesions discourage their use in studies of brain function. However, virtually all such animals (six out of seven) survived indefinitely if kept at an ambient temperature of 15 degrees C for 2 hours before and 10 to 12 hours after the lesions were made. Although these rats appeared otherwise healthy, they could not maintain normal both temperatures in short-term cold tests. In contrast, five of the nine rats kept at 25 degrees C died within 10 hours after the operation, and three more died within 5 days. Rats kept at 25 degrees C had a much higher incidence of cardiac arrhythmias than did rats kept at 15 degrees C, which may be responsible for their higher moratlity rates.

A study of permanent adipsia induced by medial forebrain lesions.

Cerebral lesions involving most of the anterior wall of the ventricle, and the medial part of the septal region, induced a permanent loss of thirst in two goats. The ventral part of the lamina terminalis remained intact in one of the animals. Pronounced dehydration (10--13% loss of b.wt.) developed during periods (3--7 days) when water supplementation was omitted. Determinations of plasma arginine vasopressin in one of the animals revealed that the dehydration did not cause any significant increase in the secretion of antidiuretic hormone. However, the water deficit induced a considerable rise in plasma renin activity and tachycardia. If anything, the caroitid blood pressure became slightly elevated towards the end of 7 d dehydration periods. The lesions obviously inactivated a cerebral sensory mechanism controlling water balance. It may have been due mainly to destruction of juxtaventricular receptors in the anterior hypothalamic region, but perhaps also to a disruption of afferents from such receptors located posterior to this cerebral level.

Induction of persistent estrus by electrolytic lesions placed neonatally in the hypothalamus of the female rat.

Electrolytic lesions were placed in the hypothalamus of two-day-old female rats. Destruction of the mediobasal part of the preoptic area resulted in persistent vaginal estrus starting on the day of vaginal opening, while lesions placed laterally in the preoptic-anterior hypothalamic area did not interfere with normal cycles. Therefore, the mediobasal hypothalamus is capable of undergoing maturation without any postnatal influence from at least the mediobasal part of the anterior hypothalamus. Destruction of the anterior wall of the third ventricle also caused persistent or prolonged vaginal estrus preceded by normal cycles. The relationship between the loci of lesions and the occurrence of sexual cyclicity was discussed.

Medial preoptic area and onset of maternal behavior in the rat.

The present series of experiments examined whether the medial preoptic area (MPOA) is involved in the onset of maternal behavior in the rat. Previously, the MPOA had been shown to be important in the maintenance of maternal behavior in the lactating rat. The first experiment investigated whether estradiol benzoate (EB) acts on the MPOA to facilitate the onset of maternal behavior in the 16-day pregnant, hysterectomized, and ovariectomized female rat. Such rats when given EB implants in the MPOA had significantly shorter latencies for the onset of maternal behavior than had females implanted with cholesterol in the MPOA or with EB in the ventromedial hypothalamus, in mammillary bodies, or under the skin. A second experiment showed that estrogen-induced prolactin release was not involved in this facilitation. A third experiment indicated that MPOA lesions disrupt the onset of maternal behavior that is induced by pup stimulation in virgin females. It was concluded that the MPOA is involved not only in the maintenance of maternal behavior but in the hormonally mediated onset of maternal behavior and the onset of maternal behavior induced in virgin females by pup stimulation.

Polyuria and imparied ADH release following medial preoptic lesioning in the rat.

Studies were carried out in the rat to detemine if hypothalamic lesions which caused polydipsia and polyuria had their effect mediated through an alteration of the ability of the neurohypophyseal system to release ADH. Rats with medial preoptic lesions hadincreased water intake while on ad libitum access to water and slightly impaired ability to conserve water following dehydration, but with no impairment of urine-concentrating ability. These were associated with an increase in plasma osmolality both during ad libitum fluid intake and after dehydration. Urinary ADH excretion was at leastas great as in shamoperated controls during ad libitum water intake, but failed to increase during dehydration in spite of a marked increase in plasma osmolality. Pituitary ADH content did not differ from control animals either during ad libitum water intake of after dehydration. Animals with lesions in the lateral preoptic and septal areas did not differ from control animals during ad libitum fluid intake and after dehydration even though lateral preoptic lesions produced polydipsia. In all animals, lesions were remote from the supraoptic nuclei, which showed no histological evidence of damage. It is concluded thatareas of the central nervous system away from the supraoptic nuclei are involved in the regulation of both water intake and ADH release.