Leonard M. Kitzes

Multiple Organ System Defects and Transcriptional Dysregulation in the Nipbl+/− Mouse, a Model of Cornelia de Lange Syndrome

Cornelia de Lange Syndrome (CdLS) is a multi-organ system birth defects disorder linked, in at least half of cases, to heterozygous mutations in the NIPBL gene. In animals and fungi, orthologs of NIPBL regulate cohesin, a complex of proteins that is essential for chromosome cohesion and is also implicated in DNA repair and transcriptional regulation. Mice heterozygous for a gene-trap mutation in Nipbl were produced and exhibited defects characteristic of CdLS, including small size, craniofacial anomalies, microbrachycephaly, heart defects, hearing abnormalities, delayed bone maturation, reduced body fat, behavioral disturbances, and high mortality (75–80%) during the first weeks of life. These phenotypes arose despite a decrease in Nipbl transcript levels of only ∼30%, implying extreme sensitivity of development to small changes in Nipbl activity. Gene expression profiling demonstrated that Nipbl deficiency leads to modest but significant transcriptional dysregulation of many genes. Expression changes at the protocadherin beta (Pcdhb) locus, as well as at other loci, support the view that NIPBL influences long-range chromosomal regulatory interactions. In addition, evidence is presented that reduced expression of genes involved in adipogenic differentiation may underlie the low amounts of body fat observed both in Nipbl+/− mice and in individuals with CdLS.

Some physiological consequences of neonatal cochlear destruction in the inferior colliculus of the gerbil, Meriones unguiculatus

Physiological consequences of neonatal cochlear ablation were assessed in the inferior colliculus of adult gerbils subjected at 2 days of age to ablation of one cochlea. Responses to tonal stimulation of the unoperated ear were evaluated at 100 microns intervals in the ipsilateral inferior colliculus. Compared with excitatory responses to ipsilateral stimulation in the inferior colliculus of unoperated animals, responses recorded in experimental animals are more widespread, stronger and occur at lower thresholds. The ubiquity of excitatory responses to ipsilateral stimulation in neonatally ablated animals indicates that responses to ipsilateral stimulation in normal gerbils are partly dependent upon interactions during development between pathways conveying information from each ear.

Correlates of combination tones observed in the response of neurons in the anteroventral cochlear nucleus of the cat.

Neurons in the anteroventral cochlear nucleus of the cat respond to combination tones of the forms f2−f1 and f1−n (f2−f1), where n is a small positive integer 1, 2, 3,.... The most easily observed combination tones are f2−f1 and 2f1−f2. In general, a combination tone is effective if three conditions are fulfilled: (1) the combination‐tone frequency must fall within the pure‐tone response area of the neuron; (2) the intensity levels of the primaries must be appropriate; and (3) the separation of the primary frequencies cannot be unduly large. For any form of combination tone, a combination‐tone response area could be plotted by fixing f1 at some level and varying f2 in small steps. The actual frequency of the combination tone could be determined from the timing of the discharges for all neurons whose discharges are phase locked. The combination‐tone response areas indicate that the response to a given form of combination tone is optimal when the combination frequency is at or near the best frequency of the...

Postnatal development of frequency and intensity sensitivity of neurons in the anteroventral cochlear nucleus of kittens

Tuning curves and spike count-vs.-intensity functions were derived form tone-burst responses of single neurons of the anteroventral cochlear nucleus of kittens 4-45 days of age. During the first postnatal week tuning curves are relatively shallow and thresholds are high. With advancing age there is a progressive reduction in threshold and sharpness of tuning. Sharpening of tuning during the first several weeks postpartum seems to be due to a differential reduction in threshold between CF and frequencies below CF. Spike count-vs.-intensity functions are steep in young kittens as compared to adults. During the first few postnatal weeks the dynamic range and shapes of the functions take on the characteristics of adult AVCN neurons.

Response properties of units in the posterior auditory field deprived of input from the ipsilateral primary auditory cortex

The influence of the ipsilateral primary auditory field (AI) on the response properties of neurons in the posterior auditory field (Field P) was examined in three cats anesthetized with sodium pentobarbital. Rate/level functions were obtained, by extracellular recording, from single units in Field P before (n = 38) and after (n = 50) subpial aspiration of AI. The ablations were primarily confined to the medial ectosylvian gyrus, although in one case extended into the high-frequency portion of the anterior auditory field. Comparisons between the behavior of units isolated before and after AI ablation failed to demonstrate any changes in the response properties of neurons in Field P attributable to the ablation. Nonmonotonic response profiles, first spike latency, variability in latency, threshold and maximal discharge rates of the units to acoustic stimuli were not significantly altered by the AI ablation. These results indicate that the basic response properties of neurons in Field P do not depend on input from the ipsilateral AI. This suggests that these properties are most likely determined by thalamic input or by circuitry within Field P.

Cochlear nucleus lesions in the adult gerbil: effects on neurone responses in the contralateral inferior colliculus

Unilateral cochlea ablation in neonatal gerbils has previously been shown to result in transneuronal degeneration of the ventral cochlear nucleus (CN) and enhanced responses of neurones in the contralateral inferior colliculus (IC) to ipsilateral stimulation of the non-ablated ear. Neither effect occurs in adult-ablated animals. To determine whether the lack of physiological change in the adult is due to the persistence of the ventral CN we lesioned the left CN of adult gerbils and recorded neurone responses in the right IC to stimulation of the right ear. Neurone thresholds, latency and intensity/response functions were unaffected by the lesion. The proportion of recording loci in the IC at which excitatory responses were obtained was also unaffected. A transient increase was observed in the maximum unit discharge level. The findings suggest that CN lesions in adults do not produce either the range or degree of neuronal changes resulting from neonatal cochlea ablation and the subsequent transneuronal degeneration of the CN. Thus, the effects of cochlea ablation are age-dependent.

Trophic factors GDNF and BDNF improve function of retinal sheet transplants

The aim of this study was to compare glial-derived neurotrophic factor (GDNF) treatment with brain-derived neurotrophic factor (BDNF) treatment of retinal transplants on restoration of visual responses in the superior colliculus (SC) of the S334ter line 3 rat model of rapid retinal degeneration (RD). RD rats (age 4-6 weeks) received subretinal transplants of intact sheets of fetal retina expressing the marker human placental alkaline phosphatase (hPAP). Experimental groups included: (1) untreated retinal sheet transplants, (2) GDNF-treated transplants, (3) BDNF-treated transplants, (4) none surgical, age-matched RD rats, (5) sham surgery RD controls, (6) progenitor cortex transplant RD controls, and (7) normal pigmented rat controls. At 2-8 months after transplantation, multi-unit visual responses were recorded from the SC using a 40 ms full-field stimulus (-5.9 to +1 log cd/m(2)) after overnight dark-adaptation. Responses were analyzed for light thresholds, spike counts, response latencies, and location within the SC. Transplants were grouped into laminated or rosetted (more disorganized) transplants based on histological analysis. Visual stimulation of control RD rats evoked no responses. In RD rats with retinal transplants, a small area of the SC corresponding to the position of the transplant in the host retina, responded to light stimulation between -4.5 and -0.08 log cd/m(2), whereas the light threshold of normal rats was at or below -5 log cd/m(2) all over the SC. Overall, responses in the SC in rats with laminated transplants had lower response thresholds and were distributed over a wider area than rats with rosetted transplants. BDNF treatment improved responses (spike counts, light thresholds and responsive areas) of rats with laminated transplants whereas GDNF treatment improved responses from rats with both laminated and rosetted (more disorganized) transplants. In conclusion, treatment of retinal transplants with GDNF and BDNF improved the restoration of visual responses in RD rats; and GDNF appears to exert greater overall restoration than BDNF.

Vision Recovery and Connectivity by Fetal Retinal Sheet Transplantation in an Immunodeficient Retinal Degenerate Rat Model

Purpose To characterize a recently developed model, the retinal degenerate immunodeficient S334ter line-3 rat (SD-Foxn1 Tg(S334ter)3Lav) (RD nude rat), and to test whether transplanted rat fetal retinal sheets can elicit lost responses to light. Methods National Institutes of Health nude rats (SD-Foxn1 Tg) with normal retina were compared to RD nude rats with and without transplant for morphology and visual function. Retinal sheets from transgenic rats expressing human placental alkaline phosphatase (hPAP) were transplanted into the subretinal space of RD nude rats between postnatal day (P) 26 and P38. Transplant morphology was examined in vivo using optical coherence tomography (OCT). Visual function was assessed by optokinetic (OKN) testing, electroretinogram (ERG), and superior colliculus (SC) electrophysiology. Cryostat sections were analyzed for various retinal/synaptic markers and for the expression of donor hPAP. Results Optical coherence tomography scans showed the placement and laminar development of retinal sheet transplants in the subretinal space. Optokinetic testing demonstrated a deficit in visual acuity in RD nude rats that was improved after retinal sheet transplantation. No ERG responses were detected in the RD nude rats with or without transplantation. Superior colliculus responses were absent in age-matched control and sham surgery RD nude rats; however, robust light-evoked responses were observed in a specific location in the SC of transplanted RD nude rats. Responsive regions corresponded to the area of transplant placement in the eye. The quality of visual responses correlated with transplant organization and placement. Conclusions The data suggest that retinal sheet transplants integrate into the host retina of RD nude rats and recover significant visual function.

Binaural interactions shape binaural response structures and frequency response functions in primary auditory cortex.

The overall purpose of this study is to examine the behavior of primary auditory cortex (AI) units in the three-dimensional stimulus space that resembles normal listening conditions, viz., level at the two ears and frequency. A binaural-level response area (LRA) is the response to a matrix of contralateral and ipsilateral stimuli presented at a single frequency. LRAs have been examined in the inferior colliculus and AI and found to be highly organized response patterns that are shaped by binaural interactions. The aggregate of LRAs across frequency is the binaural response structure (BRS), a new concept that captures unit behavior in this three-dimensional stimulus space. Since binaural interactions contribute greatly to configuring component LRAs, it is clear that binaural interactions help shape the aggregate BRS. The BRS contains the data required to generate binaural frequency response functions. The frequency range and magnitude of these functions depend on the level of the stimulus at each ear and the configuration of the BRS. Changing either level can greatly alter the binaural frequency response function. Thus, in addition to their classic role in localization, binaural interactions play a fundamentally important role in determining the frequency domain of units in AI.

Organization of auditory cortex in the owl monkey (Aotus trivirgatus)

The best frequencies of single units and clusters of units in the superior temporal plane of the owl monkey were determined using threshold tone‐burst stimulation. Following each experiment, brains were fixed, sectioned, and stained with thionin or cresyl violet. Electrode tracks were reconstructed from these sections and the cortical cytoarchitecture was examined. When the pattern of distribution of best frequencies and the cytoarchitecture are viewed in conjunction, five auditory fields may be defined. The strongest responses occur in two fields: (1) the primary field, which lies on the superior temporal plane caudal to the insula and extends a short distance onto the lateral surface, and (2) the rostral field, which borders the primary field rostrally. Best frequencies are well organized in these fields. Surrounding the primary and rostral fields are three cytoarhitectonically distinct fields. Here best frequencies are more difficult to define. Of these three fields, the most anterior and lateral are o...