Hypothalamic Grafts Research Articles

Correction of genetic diabetes insipidus by adult hypothalamic grafts.

Brattleboro rats manifest chronic diabetes insipidus as a result of the genetic deficiency of hypothalamic vasopressin. When basal hypothalamic tissue derived from adult F344 rats was implanted as cell suspensions or tissue blocks in the supraoptic regions of these animals, concentration of urine together with reduced urine output and water intake was observed in some animals. Histologic examination of the grafted brains from the responding animals revealed neuronal cells at the implant sites and vasopressin-staining fibers in the median eminence. This study demonstrates the feasibility of the grafting of adult cerebral tissues to correct a genetic hormonal deficiency.

Rathke's pouch grafts in adult brain sites.

Donor tissue containing Rathke's pouch (RP) with its associated mesenchyme and neural lobe was isolated from 15-day fetal rats and stereotaxically transplanted either to hypothalamic hypophysiotropic sites or to cerebral cortex of adult females for 30 days. Hosts either were intact or had been hypophysectomized 2-4 weeks prior to transplantation of Rathke's pouch. Grafts in the hypothalamus of either intact or hypophysectomized hosts were pleomorphic and large, often as wide as 1-2 mm, and occasionally larger. Grafts in the cortex of either intact or hypophysectomized hosts were nodular and occasionally projected upward in association with the meninges (cortex/meninges grafts). Certain features were characteristic of the grafts in all experimental groups, i.e., development of histotypic pars distalis with cell cords and fenestrated capillaries. In all experimental groups gonadotrophs and somatotrophs, when present, were localized at the graft margin adjacent to the connective-tissue interface; mammotrophs, when present, were distributed throughout the graft. Features specific to each experimental group also were apparent. Grafts in the hypothalamus of both intact and hypophysectomized hosts typically were encapsulated by a labyrinthine meshwork of cell processes, whereas cortex/meninges grafts directly abutted dense connective tissue or neural tissue. In hypothalamic grafts in intact hosts, moderately differentiated mammotrophs, gonadotrophs, and somatotrophs could be identified by their cytological features and immunopositivity for prolactin, luteinizing hormone, and growth hormone, respectively. In hypothalamic grafts in hypophysectomized hosts, mammotrophs were absent, and gonadotrophs and somatotrophs were poorly granulated and not abundant. Grafts in the cortex of intact hosts contained numerous, well-differentiated mammotrophs, gonadotrophs, and somatotrophs. Many of the mammotrophs in these grafts were hypertrophied, and profiles of exocytosis were common. In grafts in the cortex of hypophysectomized hosts, mammotrophs were either absent or very few, whereas gonadotrophs and somatotrophs were numerous. Gonadotrophs in these grafts were dramatically hypertrophied, although exocytosis was rare. The results indicate that development of histotypic pars distalis may occur in hypophysiotropic and non-hypophysiotropic brain sites and that the hormonal state of the host as well as implantation site modulate cytodifferentiation of specific pars distalis cell types.

Pituitary and gonadal function in hypogonadotrophic hypogonadal (hpg) mice bearing hypothalamic implants

GnRH receptor values are 30-50% of normal in pituitaries of hpg male mice, and testicular LH receptors only 8% of normal (160.4 +/- 17.6 and 2013 +/- 208.1 fmol/testis respectively). In male hpg mice bearing fetal preoptic area (POA) hypothalamic implants for 10 days there was no change in pituitary GnRH receptors, pituitary gonadotrophin content, or seminal vesicle weight. However, testicular weights and LH receptors were doubled in 4/10 mice and 2 had increased serum FSH levels. Between 26 and 40 days after implantation pituitary GnRH receptors and pituitary LH increased to normal male levels, although at 40 days serum and pituitary FSH concentrations had reached only 50% of normal values. Testicular and seminal vesicle weights increased more than 10-fold by 40 days after implantation and LH receptors to 70% of normal. In hpg female mice bearing hypothalamic implants for 30-256 days pituitary gonadotrophin concentrations were normal, even though GnRH receptors reached only 60% of normal values (6.18 +/- 0.4 and 9.8 +/- 0.4 fmol/pituitary respectively). Serum FSH was substantially increased from values of less than 30 ng/ml in hpg mice to within the normal female range in hypothalamic implant recipients. Ovarian and uterine weights increased after hypothalamic grafting from only 4-5% to over 74% of normal values. LH receptors increased from 6.5 +/- 1.3 fmol/ovary for hpg mice to 566.9 +/- 39.2 fmol/ovary for implant recipients. Vaginal opening occurred about 23 days after implantation and these animals displayed prolonged periods of oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine blockade reverses the inhibition of prolactin which results from intrahypothalamic pituitary grafts.

When mated with fertile bucks, rats with anterior pituitary (AP) tissue grafted into the hypothalamus did not exhibit prolongation of the diestrous cycle. Treatment of these rats with alpha-methyl-p-tyrosine, reserpine, or haloperidol for 1 or 2 days after mating increased the interestrous interval by a few days in all rats and to more than 8 days (leading to pseudopregnancy or pregnancy) in 20% of the cases. The same treatment in unmated normals resulted in 80% becoming pseudopregnant. To get more than 70% of rats with hypothalamic AP grafts pregnant or pseudopregnant required dopamine-blocking drugs for 3 or 4 consecutive days. Pregnancy was prolonged in 50% and lactation was impaired in 78% of the grafted rats which littered. Both impairments, like the original failure of the luteotrophic response, are attributed to the effects of PRL autofeedback from the hypothalamic AP grafts. These experiments provide further evidence that the mechanism whereby PRL in the hypothalamus inhibits PRL secretion involves elevation of dopamine.

A procedure for small-volume brain grafting; vasopressin cells in neonatal and adult Brattleboro rats

A simple and reliable technique is described for the transplantation of fetal vasopressin (VP) neurons in the third ventricle of the brain of homozygous Brattleboro neonates. Small-volume grafting is introduced by microdissection of paraventricular and supraoptic areas and by pelleting the minced tissue for insertion into the transplantation cannula. Morphological and immunocytochemical evaluation yielded results in both neonatal and adult host brain that were similar to those described for anterior hypothalamic grafts in adult Brattleboro brain. The present protocol circumvents some of the general problems encountered when the use of small grafts is imperative, and is also applicable to the implantation of pelleted cell suspensions.

A model system for analyzing functional development of transplanted peptidergic neurons

Numerous studies have shown that transplants of fetal central nervous system tissue develop normal morphological features and become structurally integrated into the host brain. It has not been determined whether grafted neurons can form appropriate and functional connections with the host. We have examined this question by transplanting hypothalamic tissue containing vasopressin neurons from normal rat fetuses into the third ventricle of adult Brattleboro rats. The Brattleboro hosts congenitally lack the capability for vasopressin (antidiuretic hormone) production and consequently exhibit a pronounced polydipsia and polyuria. Vasopressin synthesis and secretion by the grafted neurons was evaluated by monitoring changes in the host's drinking and urine osmolality. Hypothalamic grafts, in contrast to sham grafts and control tissue grafts, exerted pronounced antidiuretic influences with water consumption decreasing and urine osmolality increasing in the host animals. The hosts were killed 20 to 40 days after transplantation and the area of the brain containing the graft examined by immunocytochemistry, histofluorescence and radioimmunoassay. The fetal hypothalamus grafts developed cytoarchitectural features of normal hypothalamus tissue and were structurally integrated into the host hypothalamus. Axons from vasopressin neurons in the grafts coursed through the graft-host interface into the host median eminence. Catecholamine-containing fibers from the host similarly crossed the graft-host interface into the transplants. The results of the present study support the interpretation that transplanted vasopressin neurons can make appropriate and functional connections in the host brain with vasopressin being synthesized and released into the systemic circulation.

The development of thyroid-stimulating hormone-releasing factor activity in the neonatal rabbit.

SUMMARY Nine-day chick embryos received grafts of hypothalamus, adenohypophysis, thyroid, and fat (controls) from 0-, 7-, 14- and 21-day-old rabbits to the chorio-allantois. In addition, aqueous rabbit adenohypophysial and hypothalamic extracts were given to 1-day-old chicks. Animals injected with thyrotrophin and saline served as controls. On the 5th day of incubation of treated embryos, or 24 h after the administration of the extracts, the chicks were killed and their thyroids studied histologically. The hypothalamic grafts or extracts activated the chick thyroid gland and a similar trend was found in adenohypophysial or thyroid-stimulating hormone-treated chicks. The degree of activation of the embryo chick thyroid gland was related to the age of the donor rabbit. In general, thyroidstimulating hormone-releasing factor activity in hypothalamic heterografts or extracts appeared first in 14-day-old rabbits and was correlated with increasing thyrotrophic potency of the rabbit adenohypophysis.

Hypothalamic chromatophore-stimulating activity in the amphibians Hyla regilla and Ambystoma tigrinum

Hypothalamic grafts from embryos, larvae, and adults, of the Pacific Treefrog, Hyla regilla, and the Tiger Salamander, Ambystoma tigrinum, homoplastically transplanted to young larvae previously hypophysectomized at the tailbud stage, evoked melanin dispersion and aggregation of reflecting pigment in host chromatophores. To avoid contamination with adenohypophysial hormones hypothalamic tissue was excised from embryos prior to contact with the adenohypophysial anlage and from “albino” larvae and adults hypophysectomized at least one week previously. Sustained responses by adult brain tissue were limited to grafts from ventral parts of the post optic ventral hypothalamus. Responses by grafts from other areas of the hypothalamus and adjacent regions of the brain disappeared within a few days. Histological examination of positive and negative grafts confirmed their exclusively neural origin but did not reveal the cells responsible for the chromatophorotropic activity.

Onset of chromatophore-stimulating activity by the hypothalamus and adenohyphysis in Hyla regilla and Ambystoma tigrinum

Infundibular and adenohypophysial analagen were homoplastically transplanted to subcutaneous tissue of larvae previously hypophysectomized at the tailbud stage. Results indicate that at the stages employed in this study differentiation of the grafts proceeded at a rate reflected by the stage of development of the donor. The onset of chromatophore-stimulating activity by hypothalamic grafts from tailbud embryos of the Pacific Treefrog, Hyla regilla, occurred at post-tailbud stages 20 and 21 (Eakin's series). Adenohypophysial grafts, on the other hand, evoked initial responses in the host melanophores at young larval stages 23 and 24. Similarly in the Tiger Salamander, Ambystoma tigrinum melanostictum, initial pigment responses by hypothalamic and adenohypophysial grafts occurred at post-tailbud stages 37 and 38 and larval stages 39 and 40 (Harrison's series), respectively. By triturating individual grafts the chromatophorotropin was detected approximately one stage prior to the initial release.