Dale R. Sengelaub

Up-regulation of GLT1 expression increases glutamate uptake and attenuates the Huntington's disease phenotype in the R6/2 mouse.

The striatum, which processes cortical information for behavioral output, is a key target of Huntingtons disease (HD), an autosomal dominant condition characterized by cognitive decline and progressive loss of motor control. Increasing evidence implicates deficient glutamate uptake caused by a down-regulation of GLT1, the primary astroglial glutamate transporter. To test this hypothesis, we administered ceftriaxone, a beta-lactam antibiotic known to elevate GLT1 expression (200 mg/kg, i.p., for 5 days), to symptomatic R6/2 mice, a widely studied transgenic model of HD. Relative to vehicle, ceftriaxone attenuated several HD behavioral signs: paw clasping and twitching were reduced, while motor flexibility, as measured in a plus maze, and open-field climbing were increased. Assessment of GLT1 expression in striatum confirmed a ceftriaxone-induced increase relative to vehicle. To determine if the change in behavior and GLT1 expression represented a change in striatal glutamate handling, separate groups of behaving mice were evaluated with no-net-flux microdialysis. Vehicle treatment revealed a glutamate uptake deficit in R6/2 mice relative to wild-type controls that was reversed by ceftriaxone. Vehicle-treated animals, however, did not differ in GLT1 expression, suggesting that the glutamate uptake deficit in R6/2 mice reflects dysfunctional rather than missing GLT1. Our results indicate that impaired glutamate uptake is a major factor underlying HD pathophysiology and symptomology. The glutamate uptake deficit, moreover, is present in symptomatic HD mice and reversal of this deficit by up-regulating the functional expression of GLT1 with ceftriaxone attenuates the HD phenotype.

Prenatal gonadal steroids affect adult spatial behavior, CA1 and CA3 pyramidal cell morphology in rats

The present study assessed whether prenatal androgen and estrogen exposure affected adult spatial learning and hippocampal morphology. Water maze performance, the CA1 and CA3 pyramidal cell field, and the dentate gyrus-granule cell layer (DG-GCL) morphology were assessed at adulthood (70+ days of age) in males, females, androgen-treated (testosterone propionate, TP, or dihydrotestosterone propionate, DHTP) females (2-4 mg/day), estradiol benzoate (EB)-treated females (100 microgram/day), and males treated with the antiandrogen flutamide (8 mg/day). Pregnant rats were injected daily (sc) between Embryonic Day 16 and birth; all pups were delivered by cesarean section. Flutamide-treated males were castrated upon delivery, and adult castrates were used to control for activational effects. Steroid-sensitive sex differences were observed in water maze performance in favor of males. Males had larger CA1 and CA3 pyramidal cell field volumes and soma sizes than females, which were feminized with flutamide treatment. TP and EB, but not DHTP, masculinized CA1 pyramidal cell field volume and neuronal soma size; CA3 was masculinized in both TP- and DHTP-treated females, while EB was ineffective. No effects were observed in cell density, number, or DG-GCL volume or due to adult hormone levels. Thus, prenatal androgens and estrogen influence sex differences in adult spatial navigation and exert differential effects on CA1 and CA3 pyramidal cell morphology. Hence, in addition to the previously reported postnatal component, there is also a prenatal component to the critical period in which gonadal steroids organize the neural mechanisms underlying sex differences in adult spatial ability.

Regressive events in brain development and scenarios for vertebrate brain evolution

The problems of the evolution of varying brain size, the specialization of particular functional systems and overall differences in the relative complexity of brain organization are discussed in terms of alterations of regressive events in neurogenesis (cell death and axon retraction). Three scenarios for evolution, cascade reorganization, parcellation and heterochrony, are considered in light of regressive mechanisms during development.

The spinal nucleus of the bulbocavernosus: firsts in androgen-dependent neural sex differences.

Cell number in the spinal nucleus of the bulbocavernosus (SNB) of rats was the first neural sex difference shown to differentiate under the control of androgens, acting via classical intracellular androgen receptors. SNB motoneurons reside in the lumbar spinal cord and innervate striated muscles involved in copulation, including the bulbocavernosus (BC) and levator ani (LA). SNB cells are much larger and more numerous in males than in females, and the BC/LA target muscles are reduced or absent in females. The relative simplicity of this neuromuscular system has allowed for considerable progress in pinpointing sites of hormone action, and identifying the cellular bases for androgenic effects. It is now clear that androgens act at virtually every level of the SNB system, in development and throughout adult life. In this review we focus on effects of androgens on developmental cell death of SNB motoneurons and BC/LA muscles; the establishment and maintenance of SNB motoneuron soma size and dendritic length; BC/LA muscle morphology and physiology; and behaviors controlled by the SNB system. We also describe new data on neurotherapeutic effects of androgens on SNB motoneurons after injury in adulthood.

Possible conditioned stimulus pathway for classical eyelid conditioning in rabbits. I. Anatomical evidence for direct projections from the pontine nuclei to the cerebellar interpositus nucleus.

Wheat germ agglutinin and cholera toxin-conjugated horseradish peroxidase (HRP) were used to retrogradely and anterogradely trace connectivity between the lateral regions of the pontine nuclei and the anterior interpositus nucleus of the cerebellum in rabbits. Projections from the pontine nuclei were found to terminate in the anterior interpositus nucleus and the interpositus was found to send projections to the pontine nuclei. Projections from the nucleus reticularis tegmenti pontis, dorsal accessory inferior olive, and Larsells lobule HVI of the cerebellum were also found to terminate in the interpositus nucleus and projections from the interpositus nucleus to the inferior olivary complex were observed. The projections from brain stem regions to the interpositus nucleus are discussed as possible pathways that are involved in classical eyelid conditioning.

CEP-1347/KT7515 prevents motor neuronal programmed cell death and injury-induced dedifferentiation in vivo.

CEP-1347, also known as KT7515, a derivative of a natural product indolocarbazole, inhibited motor neuronal death in vitro, inhibited activation of the stress-activated kinase JNK1 (c-jun NH terminal kinase) in cultured spinal motor neurons, but had no effect on the mitogen-activated protein kinase ERK1 in these cells. Results reported here profile the functional activity of CEP-1347/KT7515 in vivo in models of motor neuronal death or dedifferentiation. Application of CEP-1347/KT7515 to the chorioallantoic membrane of embryonic chicks rescued 40% of the lumbar motor neurons that normally die during the developmental period assessed. Peripheral administration of low doses (0.5 and 1 mg/kg daily) of CEP-1347/KT7515 reduced death of motor neurons of the spinal nucleus of the bulbocavernosus in postnatal female rats, with efficacy comparable to testosterone. Strikingly, daily administration of CEP-1347/KT7515 during the 4-day postnatal window of motor neuronal death resulted in persistent long-term motor neuronal survival in adult animals that received no additional CEP-1347/KT7515. In a model of adult motor neuronal dedifferentiation following axotomy, local application of CEP-1347/KT7515 to the transected hypoglossal nerve substantially reduced the loss of choline acetyl transferase immunoreactivity observed 7 days postaxotomy compared to untreated animals. Results from these experiments demonstrate that a small organic molecule that inhibits a signaling pathway associated with stress and injury also reduces neuronal death and degeneration in vivo.

Control of cell number in the developing visual system. I. Effects of monocular enucleation.

Monocular enucleation of hamsters on the day of birth caused an increase in cellular degeneration and a corresponding loss of cells in the dorsal lateral geniculate nucleus contralateral to the enucleation over the first 12 postnatal days. The superficial layers of the contralateral superior colliculus showed a similar increase in cell degeneration, except rostrally where the remaining ipsilateral projection is found. No changes in degeneration were found in either the ipsi- or contralateral ventral lateral geniculate nuclei, the intermediate and deep layers of the superior colliculus, or in the dorsal lateral geniculate and superficial superior colliculus ipsilateral to the enucleation, even though all were denervated to some degree. The disparities in the incidence of degenerating cells normally seen in the central and peripheral regions of the superior colliculus and dorsal lateral geniculate were preserved following the monocular enucleation. The incidence of degenerating cells in early development correlates well with known alterations in adult cell number. Only major denervations of retinal targets appear to be adequate to produce measurable changes in early cellular degeneration.

Androgen Regulates Brain-Derived Neurotrophic Factor in Spinal Motoneurons and Their Target Musculature

Trophic factors maintain motoneuron morphology and function in adulthood. Brain-derived neurotrophic factor (BDNF) interacts with testosterone to maintain dendritic morphology of spinal motoneurons. In addition, testosterone regulates BDNFs receptor (trkB) in motoneurons innervating the quadriceps muscles as well as in motoneurons of the highly androgen-sensitive spinal nucleus of the bulbocavernosus (SNB). Given these interactive effects, we examined whether androgen might also regulate BDNF in quadriceps and SNB motoneurons and their corresponding target musculature. In both motoneuron populations, castration of males reduced BDNF immunolabeling, and this effect was prevented with testosterone replacement. ELISA for BDNF in the target musculature of quadriceps (vastus lateralis, VL) and SNB (bulbocavernosus, BC) motoneurons revealed that BDNF in the VL and BC muscles was also regulated by androgen. However, although castration significantly decreased BDNF concentration in the VL muscle, BDNF concentration in the BC muscle was significantly increased in castrates. Treatment of castrated males with testosterone maintained BDNF levels at those of intact males in both sets of muscles. Together, these results demonstrate that androgens regulate BDNF in both a sexually dimorphic, highly androgen-sensitive neuromuscular system as well as a more typical somatic neuromuscular system. Furthermore, in addition to the regulation of trkB, these studies provide another possible mechanism for the interactive effects of testosterone and BDNF on motoneuron morphology. More importantly, by examining both the motoneurons and the muscles they innervate, these results demonstrate that within a neural system, BDNF levels in different components are differentially affected by androgen manipulation.

Neural activation in the orbitofrontal cortex in response to male faces increases during the follicular phase

Womens sexual interest changes with hormonal fluctuations across the menstrual cycle. It is unclear how hormones modify womens sexual behavior and desire, but one possibility is that they alter womens positive appraisals of stimuli and thus their sexual interest. Using 3 T fMRI, we measured neural activation in women at two time points in their menstrual cycle (late follicular, luteal) while they evaluated photos of men presented as potential sexual partners. Participants were ten heterosexual women aged 23-28 none of who was using hormonal contraceptives or in a committed relationship. In an event-related design, the women were presented with as series of photos of male faces and asked questions to assess their degree of sexual interest in the men depicted. Results demonstrate an overall effect of menstrual cycle phase on neural activation. During their follicular versus luteal phase, women demonstrated increased activation in the right medial orbitofrontal cortex (OFC), suggesting increased positive appraisal. Activation in the OFC was positively correlated with womens estradiol to progesterone ratios. There were no areas that demonstrated increased activation during the luteal versus follicular phase. The observed increase in activation in the OFC during the follicular phase may reflect a hormonally mediated increase in appetitive motivation and may prime women towards increased sexual interest and behavior around ovulation.

Synergistic effects of testosterone metabolites on the development of motoneuron morphology in a sexually dimorphic rat spinal nucleus

The rat lumbar spinal cord contains the testosterone-dependent spinal nucleus of the bulbocavernosus (SNB), whose motoneurons innervate perineal muscles involved in copulatory reflexes. In normal males, SNB dendrites grow exuberantly through the first 4 weeks postnatally. This growth is steroid-dependent: dendrites fail to grow in males castrated at P7, but grow normally in castrates treated with testosterone (T). Treatment with either of the T metabolites, dihydrotestosterone or estrogen, supports dendritic growth in castrates, but not to the lengths characteristic of intact males or T-treated castrates. The present study tested the hypothesis that dihydrotestosterone and estrogen act together to support development of SNB dendrites. Male rat pups were castrated on P7 and treated daily with dihydrotestosterone propionate (DHT) (2 mg), estradiol benzoate (E) (100 microg), DHT (2 mg) combined with estradiol benzoate in either 5 microg (E5) or 100 microg (E100) doses, or vehicle alone. On P28, when SNB dendritic length is normally maximal, motoneurons were retrogradely labeled with cholera toxin-HRP (BHRP). Soma size and dendritic lengths of labeled motoneurons were assessed and compared to those of age-matched, intact male rats. Soma areas of DHT + E5-treated and DHT + E100-treated castrates did not differ from those of castrates treated with DHT alone, although somata of all three groups were significantly larger than those of normal males and E- or oil-treated castrates. Dendritic lengths in DHT + E5-treated castrates were significantly shorter than those of normal males, and did not differ from those of castrates receiving DHT or E alone, although all hormone-treated groups had dendritic lengths that were significantly longer than untreated castrates. However, treatment of castrates with DHT + E100 fully supported dendritic growth to levels characteristic of normal males. These results suggest that somal and dendritic growth may occur through separate developmental mechanisms, and that E and DHT act synergistically to support normal masculine SNB dendritic development.