Lynn Bengston

Retinal afferents to the dorsal raphe nucleus in rats and Mongolian gerbils

A direct pathway from the retina to the dorsal raphe nucleus (DRN) has been demonstrated in both albino rats and Mongolian gerbils. Following intraocular injection of cholera toxin subunit B (CTB), a diffuse stream of CTB‐positive, fine‐caliber optic axons emerged from the optic tract at the level of the pretectum/anterior mesencephalon. In gerbils, CTB‐positive axons descended ventromedially into the periaqueductal gray, moving caudally and arborizing extensively throughout the DRN. In rats, the retinal‐DRN projection comprised fewer, but larger caliber, axons, which arborized in a relatively restricted region of the lateral and ventral DRN. Following injection of CTB into the lateral DRN, retrogradely labeled ganglion cells (GCs) were observed in whole‐mount retinas of both species. In gerbils, CTB‐positive GCs were distributed over the entire retina, and a nearest‐neighbor analysis of CTB‐positive GCs showed significant regularity (nonrandomness) in their distribution. The overall distribution of gerbil GC soma diameters ranged from 8 to 22 μm and was skewed slightly towards the larger soma diameters. Based on an adaptive mixtures model statistical analysis, two Gaussian distributions appeared to comprise the total GC distribution, with mean soma diameters of 13 (SEM ±1.7) μm, and 17 (SEM ±1.5) μm, respectively. In rats, many fewer CTB‐positive GCs were labeled following CTB injections into the lateral DRN, and nearly all occurred in the inferior retina. The total distribution of rat GC soma diameters was similar to that in gerbils and also was skewed towards the larger soma diameters. Major differences observed in the extent and configuration of the retinal‐DRN pathway may be related to the diurnal/crepuscular vs. nocturnal habits of these two species. J. Comp. Neurol. 414:469–484, 1999.

Neural Correlates of Optokinetic Nystagmus in the Mesencephalon of Rana pipiens: A Functional Analysis

The effects of lesions of the anuran mesencephalic retinal terminal fields on horizontal optokinetic nystagmus (OKN) were examined. Lesion sites which produced effects upon OKN responses were as follows: BOR, nBOR, peri-nBOR, the large-celled pretectal nucleus, and the dorsal tegmental gray and deep tectal layers. Transection of BOR generally resulted in an increase in saccadic frequently at the lower stimulus velocities. Lesions of nBOR produced a decrease in the frequency of both head and eye saccades in the middle to high range of stimulus velocities. The only lesions which totally abolished horizontal OKN were those located medical to nBOR, in the peri-nBOR region. Lesions of the large-celled pretectal nucleus and dorsal tegmental gray substantially reduced both head and eye saccades at all stimulus velocities. Small lesions in the deep tectal layers also depressed OKN frequency. These studies indicate that horizontal OKN may be mediated by a number of structures within the anuran mesencephalon.

Ciliary neurotrophic factor receptor alpha in spinal motoneurons is regulated by gonadal hormones.

Ciliary neurotrophic factor receptor α (CNTFRα) is the ligand-binding component of the CNTF receptor. CNTFRα expression is essential for the normal development of spinal motoneurons and is required for the development of a sex difference in motoneuron number in androgen-sensitive perineal motoneurons. We used immunocytochemistry to examine the expression and hormone regulation of CNTFRα protein in the spinal nucleus of the bulbocavernosus (SNB), dorsolateral nucleus and retrodorsolateral nucleus of the lower lumbar spinal cord of adult rats. CNTFRα immunoreactivity (CNTFRα-IR) was observed in the somata and dendrites of virtually all motoneurons. In all three motor pools, the intensity of motoneuron soma labeling was greatest among gonadally intact males and was reduced in females and gonadectomized males. The density of CNTFRα-IR in neuropil also tended to be highest in intact males. Short-term (2 d) testosterone propionate treatment reversed the decline in the density of soma labeling in the SNB of castrated males but did not reverse any other effects of castration. Long-term hormone treatment, achieved by implanting males with testosterone capsules at the time of gonadectomy, prevented the decline in soma labeling in all motor pools and partially prevented the decline in neuropil label caused by castration. We conclude that expression of CNTFRα protein is androgen-regulated in spinal motoneurons.

Evidence of Retinal Light Damage in Rana cascadae: A Declining Amphibian Species

Diurnal wildlife populations that inhabit high-altitude environments may be at risk of cumulative retinal injury from increased penetration of solar ultraviolet radiation resulting from a declining concentration of stratospheric ozone. Previously, the deleterious effect of ultraviolet radiation on the eggs and hatching success has been shown in Rana cascadae, a high-altitude species undergoing major population declines. To assess whether the retinas of this species may be showing signs of injury resulting from cumulative exposure to solar radiation, both the histological condition and photoreceptor densities were compared in R. cascadae, in experimentally light-damaged R. pipiens, and in control R. pipiens. Distinctive outer-retinal abnormalities observed in the inferior retina of R. cascadae were similar to those observed in light-damaged R. pipiens. These included an abnormal distribution of retinal pigment epithelial melanin, damaged photoreceptors and the presence of large, pigment-filled macrophages. Statistically significant, negative correlations were found between extent of outer-retinal histopathology and cone photoreceptor densities both in light-damaged R. pipiens (r = -0.54) and R. cascadae (r = -0.59). Overall cone photoreceptor densities were lower in the inferior versus superior retina of R.cascadae and in light-damaged R. pipiens compared with controls. In R. pipiens, experimental light damage significantly reduced green-rod and miniature-cone densities in the inferior retina; both contain a short-wavelength sensitive photopigment. The lowest densities of these two photoreceptor types were found in the inferior retina of R. cascadae as well. Similarities between the major abnormalities observed in R. cascadae and in experimentally light-damaged R. pipiens suggest that environmental solar radiation is damaging the retinas of R. cascadae and perhaps other highaltitude species as well.

Alcohol Binge Drinking during Adolescence or Dependence during Adulthood Reduces Prefrontal Myelin in Male Rats

Teen binge drinking is associated with low frontal white matter integrity and increased risk of alcoholism in adulthood. This neuropathology may result from alcohol exposure or reflect a pre-existing condition in people prone to addiction. Here we used rodent models with documented clinical relevance to adolescent binge drinking and alcoholism in humans to test whether alcohol damages myelinated axons of the prefrontal cortex. In Experiment 1, outbred male Wistar rats self-administered sweetened alcohol or sweetened water intermittently for 2 weeks during early adolescence. In adulthood, drinking behavior was tested under nondependent conditions or after dependence induced by 1 month of alcohol vapor intoxication/withdrawal cycles, and prefrontal myelin was examined 1 month into abstinence. Adolescent binge drinking or adult dependence induction reduced the size of the anterior branches of the corpus callosum, i.e., forceps minor (CCFM), and this neuropathology correlated with higher relapse-like drinking in adulthood. Degraded myelin basic protein in the gray matter medial to the CCFM of binge rats indicated myelin was damaged on axons in the mPFC. In follow-up studies we found that binge drinking reduced myelin density in the mPFC in adolescent rats (Experiment 2) and heavier drinking predicted worse performance on the T-maze working memory task in adulthood (Experiment 3). These findings establish a causal role of voluntary alcohol on myelin and give insight into specific prefrontal axons that are both sensitive to alcohol and could contribute to the behavioral and cognitive impairments associated with early onset drinking and alcoholism.

Cell Death Atlas of the Postnatal Mouse Ventral Forebrain and Hypothalamus: Effects of Age and Sex

Naturally occurring cell death is essential to the development of the mammalian nervous system. Although the importance of developmental cell death has been appreciated for decades, there is no comprehensive account of cell death across brain areas in the mouse. Moreover, several regional sex differences in cell death have been described for the ventral forebrain and hypothalamus, but it is not known how widespread the phenomenon is. We used immunohistochemical detection of activated caspase‐3 to identify dying cells in the brains of male and female mice from postnatal day (P) 1 to P11. Cell death density, total number of dying cells, and regional volume were determined in 16 regions of the hypothalamus and ventral forebrain (the anterior hypothalamus, arcuate nucleus, anteroventral periventricular nucleus, medial preoptic nucleus, paraventricular nucleus, suprachiasmatic nucleus, and ventromedial nucleus of the hypothalamus; the basolateral, central, and medial amygdala; the lateral and principal nuclei of the bed nuclei of the stria terminalis; the caudate‐putamen; the globus pallidus; the lateral septum; and the islands of Calleja). All regions showed a significant effect of age on cell death. The timing of peak cell death varied between P1 to P7, and the average rate of cell death varied tenfold among regions. Several significant sex differences in cell death and/or regional volume were detected. These data address large gaps in the developmental literature and suggest interesting region‐specific differences in the prevalence and timing of cell death in the hypothalamus and ventral forebrain. J. Comp. Neurol. 521:2551–2569, 2013.

Additive effects of ciliary neurotrophic factor and testosterone on motoneuron survival; differential effects on motoneuron size and muscle morphology.

Testosterone and ciliary neurotrophic factor (CNTF) each enhance motoneuron survival in the spinal nucleus of the bulbocavernosus (SNB) of newborn rats. Here we directly compared the effects of CNTF and testosterone, alone and in combination, on SNB motoneuron number, SNB cell size, and morphology of the levator ani (LA) target muscle. Female rat pups were treated daily from postnatal day 1 through 6 (P1-P6) with recombinant human CNTF (hCNTF), testosterone propionate (TP), both hCNTF and TP, or neither. Effects of treatment were assessed on P7. TP and hCNTF each increased the number of SNB motoneurons and did so to a similar degree. Females treated with both hCNTF and TP had significantly more SNB cells than those receiving either hCNTF or TP alone. TP administered from P1 to P6 also increased SNB motoneuron size on P7. In contrast, hCNTF alone did not significantly affect SNB cell size, and hCNTF in combination with TP antagonized the effect of TP on motoneuron size. TP also increased LA muscle fiber number and LA fiber size, whereas hCNTF did not significantly influence LA muscle morphology in this study. Immunohistochemistry established that virtually all SNB motoneurons of both males and females express the CNTF alpha receptor (CNTFRalpha) between embryonic day 20 and postnatal day 6. Thus, effects of TP and hCNTF on SNB motoneuron survival were additive, and increases in motoneuron survival were dissociated from changes in target muscle morphology in hCNTF-treated animals. SNB motoneurons express CNTFRalpha perinatally and are therefore potential direct sites of hCNTF action.

Effects of cyclosporine in spontaneous, posterior uveitis

Cyclosporin A (CsA) was administered to chicks of the Smyth delayed-amelanotic (SDA) line from day of hatch to 4, 8 or 12 weeks of age. Animals were evaluated at 8, 12, 16 or 20 weeks with regard to major features of the SDA-line disorder, including extent of feather and choroidal amelanosis, choroidal inflammation, and histopathology of the retinal pigment epithelium and outer retina. A suppression and delay in the onset of both amelanosis and ocular histopathology occurred during CsA administration. However, a rebound enhancement of symptoms occurred 4-8 weeks after withdrawal of CsA that was closely associated with the duration of CsA treatment. These results indicate that CSA may yield therapeutic effects during the period of treatment, but its withdrawal may lead to more severe symptoms that would have occurred without treatment.

Aging and sex-related changes in the outer retina of Japanese quail

Age-related changes in the outer retina of Japanese quail 3 months to 3 years of age have been assessed with light and electron microscopy. A major difference was observed between males and females in the accumulation of lipofuscin in retinal pigment epithelial (RPE) cells. Females showed greater densities of lipofuscin granules, larger granules, and more lipofuscin per RPE cell than did males of comparable ages. In addition, a small but significant decrease (14-16%) in photoreceptor nuclear densities occurred in the temporal retina of both 1-year females and 3-year males. An overall correlation of -.77 between photoreceptor densities and amount of lipofuscin was observed, with a correlation of -.88 for females, alone. No male/female differences were observed with regard to age-related changes in height of RPE cells. Major differences in calcium metabolism and demand associated with egg-laying in females may underlie the observed sex-related differences that occur in the outer retina of this relatively short-lived, domestic species.

Short- and Long-Term Effects of Ciliary Neurotrophic Factor on Androgen-Sensitive Motoneurons in the Lumbar Spinal Cord

Motoneuron death in the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN) of the lumbar spinal cord is androgen regulated. As a result, many more SNB and DLN motoneurons die in perinatal female rats than in males, whereas treatment of newborn females with androgen results in a permanent sparing of the motoneurons and their target muscles. We previously observed that a neurotrophic molecule, ciliary neurotrophic factor (CNTF), also arrests the death of SNB motoneurons and their target musculature, at least in the short term. The present study compares the short- and long-term consequences of perinatal CNTF treatment on motoneuron number in the SNB, the DLN, and the retrodorsolateral nucleus (RDLN), a motor pool in the lower lumbar cord that does not exhibit hormone-regulated cell death. Female pups were treated with CNTF or vehicle alone from embryonic day 22 through postnatal day 6 (P6). Motoneuron number in the each nucleus was then determined immediately after treatment on P7, or 10 weeks later (P77). CNTF treatment significantly elevated motoneuron number in the SNB and DLN on P7; the volume of SNB target muscles on P7 was also greater in the CNTF-treated group. These effects were transient, however, as motoneuron number and ratings of muscle size were not different in CNTF-and vehicle-treated females on P77. Perinatal CNTF treatment did not alter cell number in the RDLN at either age. The finding that effects of CNTF on SNB and DLN motoneuron number are short lived contrasts with the permanent effects of early androgen treatment, and has implications for molecular models of the actions of androgen and neurotrophic factors on the developing spinal cord.