Coitus-induced activation of c-fos and gonadotropin-releasing hormone in hypothalamic neurons in female rabbits

Copulation induces hypothalamic release of neuropeptides and catecholamines, especially gonadotropin-releasing hormone (GnRH) and norepinephrine, in female rabbits. The forebrain distribution of GnRH cells and the cellular events responsible for the coitally induced GnRH surge have not been identified. We characterized the expression of c-fos mRNA before (0 min) and up to 60 min after coitus in forebrain tissues of mated and nonmated females and compared these findings with those in which single- and double-labeled GnRH/Fos protein cells were identified by immunocytochemistry (ICC). Enhanced expression of fos-mRNA occurred 30 min after coitus, especially in the anteroventral periventricular nucleus (AVPV), the encapsulated portion of the bed nucleus of the stria terminalis (BNSTe) and the ventrolateral hypothalamus (VLH); this increased fos-mRNA activity remained elevated at 60 min in the AVPV and VLH, and was reflected by Fos protein expression 90 min postcoitus. Both ICC Fos-labeled and ICC GnRH-labeled cells were widely distributed throughout the forebrain with postcoital increased double-labeling in the preoptic-septal areas, the anterior-medial hypothalamus and the VLH. The increased number of dual-labeled and unchanged number of single-labeled GnRH cells after coitus suggest some GnRH neurons were non-detected before coitus. Many dual-labeled neurons were adjacent to Fos-labeled cells, suggesting enhanced interneuronal input to GnRH cells after coitus. Collectively, the results suggest that coitus activates hypothalamic GnRH neurons via several loci that include the AVPV, BNSTe and VLH. The distinct anatomical location of the AVPV, BNSTe and VLH further suggests that coital signals may reach the hypothalamus via separate neural pathways that are likely developed within the brainstem.

Retinal innervation of calbindin-D28K cells in the hamster suprachiasmatic nucleus: ultrastructural characterization

The authors have described a subregion of the hamster hypothalamic suprachiasmatic nucleus (SCN) containing cells that are immunopositive for the cytosolic calcium-binding protein, Calbindin-D28K (CaBP). Several lines of evidence indicate that this region may constitute the site of the pacemaker cells that are responsible for the regulation of circadian locomotor rhythms. First, 79% of the CaBP-immunoreactive (ir) neurons express Fos in response to photic stimulation, indicating that they are close to or part of the input pathway to pacemakers. Second, at the light microscopy level, retinal terminals innervate the CaBP subnucleus. Finally, destruction of this subnucleus renders animals arrhythmic in locomotor activity. In this study, the authors examined the ultrastructural relationship between cholera toxin (CTbeta) labeled retinal fibers and the CaBP-ir subregion within the hamster SCN. CTbeta-ir retinal terminals make primarily axo-somatic, symmetric, synaptic contacts with CaBP-ir perikarya. In addition, retinal terminals form synapses with CaBP processes as well as with unidentified profiles. There are also complex interactions between retinal terminals, CaBP perikarya, and unidentified profiles. Given that axo-somatic synaptic input has a more potent influence on a cell's electrical activity than does axo-dendritic synaptic input, cells of the CaBP subregion of the SCN are ideally suited to respond rapidly to photic stimulation to reset circadian pacemakers.

Gonadal steroids regulate the number and activational state of mast cells in the medial habenula

While mast cells in connective tissues have long been associated with allergic reactions, it is now clear that they are also present within the central nervous system under normal physiological conditions. The mast cell population increases 10-fold in the medial habenular region of the brain within 2 h after pairing in doves. The first study explored whether this increase was due to exposure to gonadal steroids. Light microscopic immunocytochemistry indicates an increased number of brain MC following exposure to either testosterone (T) or dihydrotestosterone (DHT) in the male, or 17beta estradiol (E) in the female, but not in cholesterol-treated controls. Thus, the increased habenular MC population is produced by gonadal hormones in the absence of sexual behavior, is not sexually dimorphic, and does not require aromatization of androgen. In the next study, MC activational state was determined using electron microscopy. Cells were categorized into five states: (I) resting; (II) initiation of degranulation; (III) fully degranulated; (IV) piecemeal secretion; and (V) resynthesizing. Hormone treatment (T, DHT, or E) resulted in a significant increase in the percent of cells in activated states. MC granules contain a wide range of biologically active molecules. The release of these granule contents into the neuropil of the central nervous system is likely to have wide ranging effects at multiple levels including vascular permeability and neuronal excitability. In that steroid treatment is known to result in such effects, the present demonstration of a hormonally induced shift in MC secretory state is one avenue by which these effects are mediated.

Changes in brain gonadotropin-releasing hormone- and vasoactive intestinal polypeptide-like immunoreactivity accompanying reestablishment of photosensitivity in male dark-eyed juncos (Junco hyemalis)

In seasonally breeding, photoperiodic birds, the development of photorefractoriness is associated with decreased brain expression of gonadotropin-releasing hormone-like immunoreactivity (GnRH-li ir) and increased expression of vasoactive intestinal polypeptide-like immunoreactivity (VIP-li ir). Dissipation of photorefractoriness and reestablishment of photosensitivity are associated with increased GnRH-li ir brain production, but concurrent changes in VIP-li ir expression have not been investigated. To address this question, we compared the expression of VIP-li ir in the infundibulum (INF) of adult male dark-eyed juncos (Junco hyemalis) that were made photorefractory (PR) by prolonged exposure to long days with that of birds that were not photostimulated (PS), but had regained photosensitivity by exposure to short days for 5 (short-term-PS, ST-PS) or 13 (long-term-PS, LT-PS) consecutive months. Photosensitive males had smaller INF VIP-li ir cell bodies than PR males, but the numbers of INF VIP-li ir cells were independent of photoperiodic condition. Changes in infundibular VIP-li ir were correlated with changes in preoptic area (POA) GnRH-li expression. Specifically, photosensitive males had more and larger POA GnRH-li ir cells and more GnRH-li ir fibers in this region than PR males. Further, LT-PS males had more GnRH-li ir POA fibers and larger testes than ST-PS juncos. Thus, induction of photorefractoriness is associated with increased VIP and decreased GnRH brain expression whereas dissipation of photorefractoriness concurs with decreased VIP and increased GnRH brain expression. These results suggest a physiological role for VIP in the control of changes in GnRH expression as a function of the photosensitive condition.

Mast cells migrate from blood to brain

It is well established that mast cells (MCs) occur within the CNS of many species. Furthermore, their numbers can increase rapidly in adults in response to altered physiological conditions. In this study we found that early postpartum rats had significantly more mast cells in the thalamus than virgin controls. Evidence from semithin sections from these females suggested that mast cells were transiting across the medium-sized blood vessels. We hypothesized that the increases in mast cell number were caused by their migration into the neural parenchyma. To this end, we purified rat peritoneal mast cells, labeled them with the vital dyes PKH26 or CellTracker Green, and injected them into host animals. One hour after injection, dye-filled cells, containing either histamine or serotonin (mediators stored in mast cells), were located close to thalamic blood vessels. Injected cells represented approximately 2-20% of the total mast cell population in this brain region. Scanning confocal microscopy confirmed that the biogenic amine and the vital dye occurred in the same cell. To determine whether the donor mast cells were within the blood-brain barrier, we studied the localization of dye-marked donor cells and either Factor VIII, a component of endothelial basal laminae, or glial fibrillary acidic protein, the intermediate filament found in astrocytes. Serial section reconstructions of confocal images demonstrated that the mast cells were deep to the basal lamina, in nests of glial processes. This is the first demonstration that mast cells can rapidly penetrate brain blood vessels, and this may account for the rapid increases in mast cell populations after physiological manipulations.

Calbindin expression in the hamster SCN is influenced by circadian genotype and by photic conditions

Circadian rhythmicity in mammals, is controlled by the suprachiasmatic nuclei (SCN) of the hypothalamus. We previously described a discrete subnucleus in the core of the hamster SCN containing calbindin-D28k-positive cells which are fos-positive in response to a light pulse. Ablation of this subnucleus results in loss of circadian locomotor rhythmicity even when other parts of the SCN are spared. Here we show that Tau mutant hamsters have significantly more calbindin-D28k in the SCN than do wild type hamsters, and that SCN calbindin-immunoreactivity in the SCN increases in the dark. This is correlated with changes in magnitude of light mediated phase shifts in locomotion. The data are consistent with a role for calbindin cells in light mediated entrainment and phase shifting.

Multiple regulatory elements result in regional specificity in circadian rhythms of neuropeptide expression in mouse SCN

It is well established that the mammalian circadian system consists of pacemaker cells in the suprachiasmatic nuclei (SCN). The mouse has become increasingly important in understanding the circadian timing system, due to the availability of mutant animals with abnormal circadian rhythms. In the present paper, we describe the organization of the mouse SCN, comparing the wild type and Clock mutant animal, with a special focus on those peptides bearing an upstream E-box element (vasopressin, vasoactive intestinal peptide, cholecystokinin and substance P). To this end, we describe the distribution of the foregoing SCN peptidergic cell types as well as gastrin-related peptide, calretinin, calbindin, somatostatin, neurotensin and retinal input to the SCN (determined by both tract tracing and fos-immunoreactivity in response to a light pulse). The Clock mutant mouse has decreased expression of vasopressin mRNA and protein in the SCN, with normal patterns of expression elsewhere in the brain. No other differences were detected between the Clock mutant and the wild type mouse. The results are consistent with the hypothesis that there are multiple regulatory elements of clock-controlled genes in the SCN.

Localization of a suprachiasmatic nucleus subregion regulating locomotor rhythmicity

The bilaterally symmetrical suprachiasmatic nuclei (SCN) of the hypothalamus are the loci of the mammalian clock controlling circadian rhythms. Previous studies suggested that all regions of the SCN are equipotential as circadian rhythmicity is sustained after partial ablation, as long as approximately 25% of the nuclei are spared. In contrast to these results, we found that animals bearing partial lesions of the SCN that spared the subregion delimited by cells containing the calcium-binding protein calbindin-D28K (CaBP), sustained circadian locomotor rhythms. Furthermore, there was a correlation between the strength of the rhythm and the number of spared CaBP cells. Partial lesions that destroyed this region but spared other compartments of the SCN resulted in loss of rhythmicity. The next study indicates that transplants of half-SCN grafts that contain CaBP cells restore locomotor rhythms in SCN-lesioned host animals, whereas transplants containing SCN tissue but lacking cells of this subnucleus fail to restore rhythmicity. Finally, there was a correlation between the number of CaBP-positive cells in the graft and the strength of the restored rhythm. Taken together, the results indicate that pacemakers in the region of the CaBP subnucleus are necessary and sufficient for the control of locomotor rhythmicity and that the SCN is functionally heterogeneous.

Distribution and local differentiation of mast cells in the parenchyma of the forebrain

Mast cells are found in the brain of many species. Although a considerable body of information is available concerning the development and differentiation of peripheral mast cells, little is known about brain mast cells. In the present study, the ontogeny of mast cells in the dove brain was followed by using three markers: acidic toluidine blue, alcian blue/safranin, and an antiserum to gonadotropin-releasing hormone (GnRH). Mast cells first appear in the pia on embryonic day (E)13-14 in ovo, then along blood vessels extending from the pia into the telencephalon on posthatch day 4-5, and in the medial habenula at week 3. Medial habenular mast cell numbers increase during development, peaking in peripubertal birds, and declining thereafter. Several measures indicate that mast cells mature within the medial habenula: there is an increase in the intensity of metachromasia, a switch from alcian blue granules in young animals to mixed alcian blue and safranin granules in older animals, and an increase in GnRH-like immunoreactivity. These results were extended by using electron microscopy. The architecture of mast cell granules evolved from electron lucent with small electron dense deposits at E15 to more electron dense granules with complex patterns of internal structure by 2 months. Ultrastructural immunocytochemistry for the GnRH-like peptide at 1 month revealed both immunopositive and negative cells, suggesting that the acquisition of this phenotype is not simultaneous across the population. Thus, immature mast cells infiltrate the central nervous system and undergo in situ differentiation within the neuropil.

A student emergency: helping school staff cope

A serious illness, injury, or other medical emergency in a student while in school can be upsetting to school staff not accustomed to such situations. A healthcare emergency in a special health needs child in one school district prompted a nurse and a building principal to develop a protocol which would enable school staff to effectively assist the nurse in the event of a student emergency. The plan involved training school personnel to assist the nurse and the administrator in tasks such as answering and monitoring telephones, serving as a runner, controlling unnecessary traffic into the nurse's office, and passing clean supplies to the nurse.

Antiphospholipid antibodies and reproduction: the antiphospholipid antibody syndrome

In women who have a diagnosis of APS (both clinical and laboratory criteria) the chance for successful pregnancy is reduced. In these cases, treatment appears to be a clear option, particularly in the case of prior thromboembolic events. The current preference of treatment for women with RPL and aPL antibodies is subcutaneous heparin and aspirin. This treatment should begin with a positive pregnancy test and continue postpartum. It is unclear, at this time, what treatment, if any, is required for women who do not meet all the criteria for diagnosis of APS, but who are known to have aPL antibodies. In some cases, these women were tested because of a prior false-positive test for syphilis, with subsequent identification of aPL antibodies. More recently, women undergoing IVF were tested and found to have an increased incidence of aPL antibodies. It was suggested that aPL antibodies are associated with infertility and failure to implant. However, a summary of published reports indicate that positive aPL antibodies in patients undergoing IVF do not influence ongoing pregnancy rates. This subject, however, remains an area of active investigation because aPL antibodies were shown to interact with the syncytiotrophoblast and cytotrophoblast layers and could, theoretically, after implantation.

Gender-specific frequency of background somatic mutations at the hypoxanthine phosphoribosyltransferase locus in cord blood T lymphocytes from preterm newborns

Limited information is available regarding the frequency, spectrum, and clinical relevance of somatic mutations in the developing fetus. The goal of this study was to determine somatic mutant frequencies (Mfs) at the hypoxanthine phosphoribosyltransferase (HPRT) reporter gene in cord blood T lymphocytes from preterm infants to gain insight into in utero mutational events. Mf determinations were made by using the HPRT T cell cloning assay on cord blood samples from 52 preterm infants. Natural logarithm Mfs (lnMfs) from preterm infants were compared with results from our database for full-term infants. Our analysis revealed higher lnMfs in cord blood T lymphocytes from preterm compared with full-term infants (P = 0.008). In addition, preterm females had significantly higher lnMfs compared with full-term females (P < 0.001), whereas preterm males were found to have significantly lower lnMfs than preterm females (P = 0.005). Regression analyses also demonstrate a significant relationship between lnMf and gestational age for preterm females that does not exist for preterm males. These results demonstrate the gender-specific association between Mf and age in humans.

Thyroid autoantibodies are not associated with recurrent pregnancy loss

OBJECTIVE

Approximately 1% of all women have recurrent pregnancy loss, defined as >/=3 spontaneous losses of pregnancy; however, a cause is determined in only 50% of cases. Recent studies have associated the presence of thyroid autoantibodies during the first trimester of pregnancy with spontaneous abortion in the current pregnancy among women without a history of recurrent abortion. The objective of this study was to determine whether circulating thyroid autoantibodies were associated with recurrent pregnancy loss.

STUDY DESIGN

Sera from 74 nonpregnant women with a history of recurrent pregnancy loss and from 75 healthy, fertile control subjects of similar gravidity were tested for thyroglobulin and thyroid peroxidase antibodies by means of radioimmunoassay kits. All women had a third-generation thyroid-stimulating hormone assay performed. Samples were obtained >/=6 months after a pregnancy.

RESULTS

Twenty-two of the women with a history of recurrent pregnancy loss (29.3%) and twenty-eight of the control subjects (37%) had positive results for either one or both of the thyroid autoantibodies (P >. 05). Mean thyroid-stimulating hormone levels and the proportion of women with abnormal thyroid-stimulating hormone values did not differ between the 2 groups.

CONCLUSION

Women with a history of recurrent pregnancy loss are no more likely than are fertile control subjects to have circulating thyroid autoantibodies. Testing for antithyroid antibodies is not clinically useful in the evaluation of patients with a history of recurrent pregnancy loss.

Brain mast cells lack the c-kit receptor: immunocytochemical evidence

Mast cells are reported to differ from other cells of the hematopoietic lineage in that as mature cells, they retain the c-kit receptor, and are thus capable of responding to the stem cell factor (SCF) ligand. SCF is important for development and survival of mast cells. In this study, c-kit expression was examined immunocytochemically in the brains of mice, rats and doves. The results indicate that brain mast cells lack the c-kit receptor; those of the leptomeninges and other connective tissues are a mixed population of c-kit positive and negative cells. The mechanisms whereby brain mast cells might survive in the absence of SCF-c-kit signaling are discussed.

Output signals of the SCN

The suprachiasmatic nucleus (SCN) of the hypothalamus controls circadian rhythmicity in mammals (for reviews, see Refs. 33 and 59). Responses modulated by the SCN are numerous and include rhythms in sleep/wake cycles, locomotor, gnawing and general activity, temperature, ingestive behavior, and rhythms of hormonal and peptide secretions. Though a great deal is known about the neuroanatomical organization of the SCN, many elements of the structure-function relationships remain to be discovered. For example, it is not known which cellular components of the SCN function as driving pacemakers or which output signal(s) of these pacemakers are important for each of its functions. While some signals from pacemaker cells reach target regions by neural efferents, there is also evidence that rhythmic responses can be controlled by diffusible signals. This article reviews output signals from the SCN. The data available suggest that neural efferents are not necessary for the control of locomotor activity rhythms. Evidence that a diffusible signal is sufficient to restore activity rhythms in SCN-lesioned animals is described. Finally, possible physiological mechanisms for diffusible signals are suggested.

Insult after injury: pressure ulcers in trauma patients

DESIGN

Nonexperimental-Descriptive.

SAMPLE

The inclusion criteria were trauma patients, ages 15 and older, who were hospitalized for > 2 days, and who did not have preexisting skin breakdown. A total of 148 consecutive trauma patients admitted to the study institution meeting the inclusion criteria were prospectively enrolled.

METHODS

Patients were assessed every 3 days for skin breakdown. Information on the patient's bed type, therapies, medical devices, and nutrition was collected. The Braden Scale for predicting pressure ulcer risk was completed at each assessment.

FINDINGS

Of the 148 patients enrolled, 30 developed at least one area of skin breakdown for a prevalence of 20.3% in patients hospitalized more than 2 days. The most common cause of breakdown was positional pressure (47.4%). Cervical collars were the second leading cause at 23.7%, followed by tracheostomy/endotracheal tubes at 10.5%. The mobility subscale of the Braden Pressure Ulcer Risk Assessment tool was significantly predictive of skin breakdown (p < .001).

IMPLICATIONS FOR NURSING RESEARCH

Skin breakdown is a significant problem in trauma patients who are hospitalized for more than 2 days. Aggressive protocols on positioning, cervical collar use, and airway adjuncts, as well as additional active nursing interventions for immobile patients, may be ways to decrease the skin breakdown prevalence in this population.

Laboratory and diagnostic testing in child and adolescent psychiatry: a review of the past 10 years

OBJECTIVE

To review in a critical fashion the literature of the past decade covering diagnostic and laboratory testing in the field of child and adolescent psychiatry.

METHOD

A computerized search of articles published during the past decade was made, and selected articles are presented. Because of the paucity of articles specifically relating to minors, selected articles from adult psychiatry are cited.

RESULTS

With a few notable exceptions, few controlled studies on the specificity and sensitivity of any laboratory test for any specific disorder of behavior presenting in children have been conducted in children and adolescents. A high index of suspicion will remain the clinician's best ally in utilizing laboratory measures in the assessment of psychopathology. Nonetheless, studies have appeared that will guide the clinician as to what tests are not clinically useful.

CONCLUSION

Indications and the lack of indications for specific laboratory studies are an integral part of the knowledge base that child psychiatrists must have. Much more empirical data will need to be collected prospectively to inform the field and to move the judicious use of the laboratory from an art to a science.

Fiber outgrowth from anterior hypothalamic and cortical xenografts in the third ventricle

Fetal grafts of the anterior hypothalamus (SCN/AH) containing the suprachiasmatic nucleus (SCN) restore circadian rhythms to SCN-lesioned host hamsters and rats following implantation into the third ventricle. Previous studies suggest that intraventricular SCN/AH grafts are variable in their attachment sites, the extent of their outgrowth, and the precise targets innervated in the host brain. However, the use of different methods to analyze graft outgrowth in this model has previously led to inconsistent results. We have reevaluated the outgrowth of fetal rat SCN/AH grafts implanted in the third ventricle of hamsters by using two methods: the carbocyanine dye, 1,1'dioctadecyl-3,3'-tetramethylindocarbocyanine percholate (DiI), was placed directly onto grafted tissue; and a donor-specific neurofilament marker was used in conjunction with xenografts. We examined the specificity of outgrowth by comparing SCN/AH xenografts with that of control cortical (CTX) xenografts. To evaluate whether SCN/AH graft efferents arise from the donor SCN, we used micropunch grafts that contained minimal extra-SCN tissue. The results show that the use of a donor-specific neurofilament marker reveals more extensive SCN/AH graft outgrowth than DiI. SCN/AH graft efferents project into areas normally innervated by the intact SCN. However, this outgrowth is variable among graft recipients, is not specific to SCN/AH tissue, and does not necessarily derive from the donor SCN. The precise functional role of neural efferents arising from SCN/AH grafts in the restoration of circadian clock function and the extent of SCN-derived efferents remain to be determined.

Amniotic fluid glycine-valine ratio and neonatal morbidity in fetal growth restriction

OBJECTIVE

To test the hypothesis that an elevated amniotic fluid glycine-valine ratio predicts neonatal morbidity in growth-restricted newborns.

METHODS

Amniotic fluid (AF) was collected from 122 third-trimester pregnancies (range 31-39 weeks), 49 of which were complicated by fetal growth restriction. Amino acid analysis was performed by high-pressure liquid chromatography. Glycine-valine ratios were compared between normal and growth-restricted fetuses. Neonatal morbidity within the group of growth-restricted fetuses was characterized by evaluation of neonatal hypoglycemia, arterial cord blood gas analysis, and birth weight percentile. We also examined the correlation of AF glycine-valine ratio to the umbilical artery resistance index. The median interval between AF sampling and delivery was 1 day (range 0-8 days). Analyses were performed by Student t test, chi 2 with Yates correction, or simple correlation when appropriate. P < .05 was considered significant.

RESULTS

Growth-restricted fetuses have a significantly elevated AF glycine-valine ratio compared with control subjects (3.31 +/- 1.06 versus 2.61 +/- 0.77, respectively, P < .001). There was no association of the glycine-valine ratio with gestational age for either group. An elevated glycine-valine ratio was not associated with neonatal hypoglycemia within the growth-restricted group (hypoglycemia: [n = 16] 3.19 +/- 1.07; no hypoglycemia: (n = 30) 3.44 +/- 1.09). There were no significant correlations of glycine-valine ratio with arterial cord blood pH (r = -0.10), oxygen pressure (r = 0.04), or base deficit (r = 0.12). There were no significant correlations of glycine-valine ratio and birth weight percentile (r = -.24) or umbilical artery resistance index (r = -.14).

CONCLUSION

Amniotic fluid glycine-valine ratio is elevated in growth-restricted fetuses compared with control fetuses. However, the level of glycine-valine elevation is not associated with neonatal morbidity related to hypoglycemia, arterial cord blood gas abnormalities, or birth weight percentile.

Mast cell number and maturation in the central nervous system: influence of tissue type, location and exposure to steroid hormones

While it is well established that brain mast cells are usually associated with the cerebral vasculature, in ring doves mast cells lie directly in the neuropil of the medial habenula. During normal development mast cells enter the habenula and complete their differentiation in situ. In the present study, we asked what characteristics of the medial habenula contribute to mast cell entry and differentiation. Grafts of embryonic habenula or control optic tectal grafts were placed in the lateral ventricle or anterior chamber of the eye. Transplantation alters the location of the habenula as well as its neural and vascular connections. Three groups of hosts were used for the ventricular grafts: four-month-old and killed three months after transplantation; four-month-old and killed seven months later, and two- to three-year-old gonadectomized males killed three months later. Hosts for the intraocular grafts were four months of age and killed three months later. Mast cells were present in the habenular grafts but not in the control tissue. Mast cells in three- and seven-month-old grafts were phenotypically immature when compared to those of hosts. They contained fewer metachromatic granules, fewer granules immunoreactive to an antiserum against gonadotropin-releasing hormone, and no highly-sulphated proteoglycans. As previously described, gonadectomized adults had fewer mast cells in their medial habenula than did intact animals, but there was no change in mast cell number in habenular grafts. The current experiments indicate that the occurrence and survival of mast cells can occur within the microenvironment of the medial habenula, but that maturation of these cells requires the normal connections of this nucleus. Furthermore, gonadectomy appears to alter mast cell number in the medial habenula by generating a secondary signal which the transplanted tissue is incapable of receiving or processing.

Attachment site of grafted SCN influences precision of restored circadian rhythm

Fetal hypothalamic grafts containing the suprachiasmatic nucleus (SCN) restore circadian locomotor rhythmicity when implanted into the third ventricle of SCN-lesioned hamsters. However, the quality of restored rhythms is variable, and the locomotor rhythms of grafted animals are generally less robust than those of intact animals. The present study explored whether anatomical features of the graft predict the quality of the recovered rhythm and whether such information might provide insight as to the target of the signal from the SCN that controls locomotor rhythmicity. The following graft parameters were assessed: distance between the attachment site of the graft and potential targets for the output signal from the SCN, number and overall size of SCN clusters, the size of the cluster closest to the SCN lesion site, and extent of vasoactive intestinal polypeptide (VIP) and vasopressin-associated neurophysin (NP) positive fiber outgrowth from the graft. The restored circadian activity rhythm was assessed by quantifying the precision of activity onset and the amount, period, and robustness of rhythmicity. The results indicate a significant positive correlation between the precision of activity onset and the proximity of the closest SCN cluster to the site of the lesioned host SCN. A more detailed analysis of the spatial location of the graft indicates that proximity of the graft in the dorsal and caudal directions, but not the rostral direction, is positively correlated with the precision of the recovered rhythm. This suggests two possibilities: the coupling signal may act on a site very near the SCN and travel preferentially in a rostro-caudal direction. Alternatively, the coupling signal may act on a site rostral to the SCN. That the site is not far rostral to the SCN was suggested by the lack of a correlation between the precision of the restored rhythm and the rostrally lying anterior medial preoptic nucleus. Finally, evaluation of NP- and VIP-ergic fibers in nuclei known to receive input from the SCN indicates that the extent of such innervation by graft efferents does not predict either the occurrence of recovery or the precision of the recovered rhythm. Overall, these results suggest that the target(s) of SCN pacemakers regulating locomotor rhythmicity lie in the hypothalamus, close to or rostral to the SCN.