Concomitant highly active antiretroviral therapy leads to smaller decline and faster recovery of CD4+ cell counts during and after pegylated interferon plus ribavirin therapy in HIV-hepatitis C virus coinfected patients.

INTRODUCTION: The impact of highly active antiretroviral therapy (HAART) on CD4+ cell course during treatment with pegylated interferon plus ribavirin (PegIFN-RBV) in patients coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) is unknown. METHODS: We determined CD4(+) cell count in 94 HIV-HCV coinfected patients undergoing treatment with pegylated interferon plus RBV at baseline, treatment weeks 4-48 (W4-W48), and months 1, 3, and 6 of follow-up. Of the 94 patients, 70 underwent concomitant HAART (group A) and 24 did not (group B). RESULTS: Group A showed smaller CD4(+) cell decreases from W24-W48 (P = .027) and greater CD4(+) cell increases after cessation of pegylated interferon plus ribavirin therapy (P = .002) than group B showed. CONCLUSIONS: Concomitant HAART leads to smaller decreases and faster recovery of CD4(+) cells during and after pegylated interferon plus RBV therapy.

Multisensory processing via early cortical stages: Connections of the primary auditory cortical field with other sensory systems.

It is still a popular view that primary sensory cortices are unimodal, but recent physiological studies have shown that under certain behavioral conditions primary sensory cortices can also be activated by multiple other modalities. Here, we investigate the anatomical substrate, which may underlie multisensory processes at the level of the primary auditory cortex (field AI), and which may, in turn, enable AI to influence other sensory systems. We approached this issue by means of the axonal transport of the sensitive bidirectional neuronal tracer fluorescein-labeled dextran which was injected into AI of Mongolian gerbils (Meriones unguiculatus). Of the total number of retrogradely labeled cell bodies (i.e. cells of origin of direct projections to AI) found in non-auditory sensory and multisensory brain areas, approximately 40% were in cortical areas and 60% in subcortical structures. Of the cell bodies in the cortical areas about 82% were located in multisensory cortex, viz., the dorsoposterior and ventroposterior, posterior parietal cortex, the claustrum, and the endopiriform nucleus, 10% were located in the primary somatosensory cortex (hindlimb and trunk region), and 8% in secondary visual cortex. The cortical regions with retrogradely labeled cells also contained anterogradely labeled axons and their terminations, i.e. they are also target areas of direct projections from AI. In addition, the primary olfactory cortex was identified as a target area of projections from AI. The laminar pattern of corticocortical connections suggests that AI receives primarily cortical feedback-type inputs and projects in a feedforward manner to its target areas. Of the labeled cell bodies in the subcortical structures, approximately 90% were located in multisensory thalamic, 4% in visual thalamic, and 6% in multisensory lower brainstem structures. At subcortical levels, we observed a similar correspondence of retrogradely labeled cells and anterogradely labeled axons and terminals in visual (posterior limitans thalamic nucleus) and multisensory thalamic nuclei (dorsal and medial division of the medial geniculate body, suprageniculate nucleus, posterior thalamic cell group, zona incerta), and in the multisensory nucleus of the brachium of the inferior colliculus. Retrograde, but not anterograde, labeling was found in the multisensory pontine reticular formation, particularly in the reticulotegmental nucleus of the pons. Conversely, anterograde, but no retrograde, labeling was found in the visual laterodorsal and lateroposterior thalamic nuclei, in the multisensory peripeduncular, posterior intralaminar, and reticular thalamic nuclei, as well as in the multisensory superior and pericentral inferior colliculi (including cuneiform and sagulum nucleus), pontine nuclei, and periaqueductal gray. Our study supports the notion that AI is not merely involved in the analysis of auditory stimulus properties but also in processing of other sensory and multisensory information. Since AI is directly connected to other primary sensory cortices (viz. the somatosensory and olfactory ones) multisensory information is probably also processed in these cortices. This suggests more generally, that primary sensory cortices may not be unimodal.

Temporal integration of sound pressure determines thresholds of auditory-nerve fibers.

Current propositions of the quantity of sound driving the central auditory system, specifically around threshold, are diverse and at variance with one another. They include sound pressure, sound power, or intensity, which are proportional to the square of pressure, and energy, i.e., the integral of sound power over time. Here we show that the relevant sound quantity and the nature of the threshold can be obtained from the timing of the first spike of auditory-nerve (AN) fibers after the onset of a stimulus. We reason that the first spike is triggered when the stimulus reaches threshold and occurs with fixed delay thereafter. By probing cat AN fibers with characteristic frequency tones of different sound pressure levels and rise times, we show that the differences in relative timing of the first spike (including latencies >100 msec of fibers with low spontaneous rates) can be well accounted for by essentially linear integration of pressure over time. The inclusion of a constant pressure loss or gain to the integrator improves the fit of the model and also accounts for most of the variation of spontaneous rates across fibers. In addition, there are tight correlations among delay, threshold, and spontaneous rate. First-spike timing cannot be explained by models based on a fixed pressure threshold, a fixed power or intensity threshold, or an energy threshold. This suggests that AN fiber thresholds are best measured in units of pressure by time. Possible mechanisms of pressure integration by the inner hair cell-AN fiber complex are discussed.

New insights into the hemodynamic blood oxygenation level-dependent response through combination of functional magnetic resonance imaging and optical recording in gerbil barrel cortex.

Fast, low-angle shoot functional magnetic resonance imaging (fMRI), based on the blood oxygenation level-dependent (BOLD) effect, was combined with optical recording of intrinsic signals (ORIS) and 2-deoxyglucose labeling in gerbil barrel cortex. We observed over the activated barrel a positive BOLD signal and increased levels of deoxyhemoglobin and total hemoglobin during each period of prolonged (30 sec) D2 vibrissal stimulation. These data show that the hemodynamic basis of this fMRI signal is not necessarily a washout of deoxyhemoglobin, as generally assumed. Instead, they suggest that a positive BOLD signal can also be caused by a local increase of blood volume, even if deoxyhemoglobin levels are persistently elevated. We also show that this alternative interpretation is consistent with theoretical models of the BOLD signal. The changes in BOLD signal and blood volume, which are most tightly correlated with the periodic stimulation, peak at the site of neuronal activation. These results contribute to the understanding of the hemodynamic mechanisms underlying the BOLD signal and also suggest analysis methods, which improve the spatial localization of neuronal activation with both fMRI and ORIS.

Preliminary X-ray fiber diffraction studies of cucumber green mottle mosaic virus, watermelon strain.

Fiber diffraction patterns have been obtained for cucumber green mottle mosaic virus, watermelon strain (a distant relative of tobacco mosaic virus), and two heavy-atom derivatives. These patterns and the similarity between the cucumber and the tobacco virus offer the potential of a full structure determination of the cucumber virus.

Effects of unilateral and bilateral cochlea removal on 2-deoxyglucose patterns in the chick auditory system.

The 2-deoxyglucose (2DG) method was used to map functional activity in the auditory system of chicks that had been subjected to unilateral or bilateral cochlea removal. Following survival times of 1 day to 4 weeks, chicks were exposed to continuous white noise in the 2DG experiments. In monaural subjects nucleus angularis and nucleus magnocellularis showed faint 2DG uptake on the side contralateral to the intact ear. In the binaural nucleus laminaris, the asymmetrical and almost mirror-imaged labeling pattern (Lippe, Stewart, and Rubel: Brain Res. 196:43-58, '80) was produced. The superior olive (OS) was strongly labeled on the ipsilateral side, whereas the contralateral OS showed only a slight 2DG uptake at its medial border. The lateral lemniscus and nucleus lemnisci lateralis, pars ventralis (LLv) showed stronger activation on the contralateral side. Both Nissl stains and 2DG patterns provide evidence that nucleus ventralis lemnisci lateralis (VLV) can be subdivided into an anterior (VLVa) and a posterior (VLVp) part. Whereas VLVp is labeled only contralaterally, VLVa is labeled on both sides with similar intensity. Nucleus mesencephalicus lateralis, pars dorsalis (MLD) is strongly labeled throughout contralaterally. The ipsilateral MLD shows a defined ventral portion of high 2DG uptake. Intensity of labeling here is symmetrical to the corresponding area of the contralateral MLD. These symmetrical patterns were related to the tonotopic organization of MLD, which was mapped in intact animals by using tone stimuli. Assuming that symmetrical 2DG uptake in monaural animals indicates excitatory input from both ears (EE-cells), it appears that these EE-cells occupy a sector of each isofrequency plane in MLD. Nucleus ovoidalis (Ov) generally was stronger labeled on the contralateral side. The columnar organization of field L as seen in monaural chicks has already been described (Scheich, Exp. Brain Res. 51:199-205, '83). In bilaterally deafened chicks, MLD, Ov, and layer L2 of field L showed strong but spatially restricted 2DG accumulation in contrast to absence of labeling in peripheral nuclei. The 2DG patterns in monaural chicks are likely to reflect excitatory input within the auditory system. In addition they reveal new insights into the functional organization of some of its nuclei. In particular, they support the notion that MLD contains maps of several interaural integration mechanisms similar to field L. Labeling in the auditory system of bilaterally deafened chicks may result from descending projections or from other than auditory inputs.

Spatial representation of frequency-modulated signals in the tonotopically organized auditory cortex analogue of the chick.

For auditory communication, many birds, including domestic chicks, use a variety of frequency-modulated (FM) sounds. As a first approach to the spatial representation of such sounds in the central auditory system, we have analyzed 2-deoxyglucose (2DG) patterns that were produced by FM stimuli in the tonotopic map of the auditory forebrain area (field L/hyperstriatum ventrale complex) of domestic chicks. Linear FM signals, varying in the depth and range of modulation, and in the direction and rate of the frequency change, were tested. Also included were signals designed to mimic species-specific FM calls. All FM stimuli activated those regions of the map in which frequencies contained in the stimulus spectra were tonotopically represented. However, frequency and amplitude of the FM spectra were not faithfully reproduced by activation of the complete corresponding tonotopic space. FM signals that differed only in the direction of modulation, and therefore had identical long-term spectra, induced maximum 2DG activation at different locations of the tonotopic gradient. FM signals that differed in the rate of change of frequency produced maxima of 2DG uptake at different positions along an isofrequency dimension of the map. These results suggest that the direction of modulation may be represented in a complex fashion along the tonotopic axis of the structure, whereas the rate of change of frequency may be represented along an isofrequency dimension. None of the experiments provided evidence of FM-selective regions within the auditory forebrain complex. However, numerous telencephalic areas, in addition to the primary auditory area, were strongly activated in chicks stimulated with artificial "species-specific" FM signals. These areas could be involved in the processing of biologically relevant stimuli, requiring attention, recognition, and interpretation of the signals.

Auditory pathway and auditory activation of primary visual targets in the blind mole rat (Spalax ehrenbergi): I. 2-deoxyglucose study of subcortical centers.

The blind mole rat Spalax ehrenbergi is a subterranean rodent that shows striking behavioral, structural, and physiological adaptations to fossorial life including highly degenerated eyes and optic nerves and a behavioral audiogram that indicates high specialization for low-frequency hearing. A 2-deoxyglucose functional mapping of acoustically activated structures, in conjunction with Nissl/Klüver-Barrera-stained material, revealed a typical mammalian auditory pathway with some indications for specialized low-frequency hearing such as a poorly differentiated lateral nucleus and a well-developed medial nucleus in the superior olive complex. The most striking finding was a marked 2-deoxyglucose labeling of the dorsal lateral geniculate body and of cortical regions that correspond to visual areas in sighted rodents. The results render the blind mole rat a good model system for studying natural neural plasticity and intermodal compensation. In this report, we confine ourselves to the subcortical levels. The cortical level will be dealt comprehensively in a following paper.

Effect of unilateral partial cochlear lesions in adult cats on the representation of lesioned and unlesioned cochleas in primary auditory cortex.

We examined the effect of unilateral restricted cochlear lesions in adult cats on the topographic representations ("maps") of the lesioned and unlesioned cochleas in the primary auditory cortex (AI) contralateral to the lesioned cochlea. Frequency (tonotopic) maps were derived by conventional multineuron mapping procedures in anesthetized animals. In confirmation of a study in adult guinea pigs (Robertson and Irvine [1989] J. Comp. Neurol. 282:456-471), we found that 2-11 months after the unilateral cochlear lesion the map of the lesioned cochlea in the contralateral AI was altered so that the AI region in which frequencies with lesion-induced elevations in cochlear neural sensitivity would have been represented was occupied by an enlarged representation of lesion-edge frequencies (i.e., frequencies adjacent to those with elevated cochlear neural sensitivity). Along the tonotopic axis of AI the total representation of lesion-edge frequencies could extend up to approximately 2.6 mm rostal to the area of normal representation of these frequencies. There was no topographic order within this enlarged representation. Examination of threshold sensitivity at the characteristic frequency (CF, frequency to which the neurons were most sensitive) in the reorganized regions of the map of the lesioned cochlea established that the changes in the map reflected a plastic reorganization rather than simply reflecting the residue of prelesion input. In contrast to the change in the map of the lesioned contralateral cochlea, the map of the unlesioned ipsilateral cochlea did not differ from those in normal animals. Thus, in contrast to the normal very good congruency between ipsilateral and contralateral AI maps, in the lesioned animals ipsilateral and contralateral maps differed in the region of AI in which there had been a reorganization of the map of the lesioned cochlea. Outside the region of contralateral map reorganization, ipsilateral and contralateral AI maps remained congruent within normal limits. The difference between the two maps in the region of contralateral map reorganization suggested, in light of the physiology of binaural interactions in the auditory pathway, that the cortical reorganization reflected subcortical changes. Finally, response properties of neuronal clusters within the reorganized map of the lesioned cochlea were compared to normative data with respect to threshold sensitivity at CF, the size of frequency "response areas," and response latencies. In the majority of cases, CF thresholds were similar to normative data. The frequency "response areas" were slightly less sharply tuned than normal, but not significantly. Response latencies were significantly shorter than normal in three animals and significantly longer in one animal.

Postnatal shift of tonotopic organization in the chick auditory cortex analogue.

The existence of an ontogenetic shift of tonotopic organization throughout the auditory pathway concomitant with cochlea maturation is a matter of controversy. Using the 2-deoxyglucose method we demonstrate here for the first time the shift phenomenon in an auditory forebrain structure, field L, the auditory cortex analogue of the chick. During the first postnatal month isofrequency contours move to positions where, in younger chicks, lower frequencies (up to half an octave) are represented. This developmentally changing place code of sound frequencies at the forebrain level is similar to the one previously reported for brain stem auditory nuclei. It raises the question of constancy of frequency-related pitch perception during development and may be a complication of early auditory learning and memory.

On determinants of first-spike latency in auditory cortex.

The first-spike latency of neurones at any level of the auditory pathway decreases with stimulus amplitude. As stimuli are generally shaped with rise functions to avoid spectral splatter, a common interpretation of the latency decrease is that the amplitude of the signal reaches the neurone's firing threshold earlier during the rise time. We demonstrate here, for auditory cortex neurones and by varying the amplitude and rise time of tonal stimuli, that this threshold model is inadequate to account for the observed latency changes, particularly when adaptive processes are taken into account. The data raise the possibility that latency may be a function of other properties associated with a signal's onset, such as rate of change of peak pressure.

Invasion of visual cortex by the auditory system in the naturally blind mole rat.

Previously we have shown that the dorsal lateral geniculate body (LGB), which is strictly visual in sighted mammals, receives a strong auditory input in the naturally blind mole rat (Spalax ehrenbergi). Here we show with the 2-deoxyglucose technique and with single-unit recordings that in this species the initially non-degenerated visual cortex, as defined by its connection with LGB, is also activated by the auditory modality. These findings suggest that cross-modal compensation may occur as a natural consequence of the degeneration of a sense organ.

Further observations on the threshold model of latency for auditory neurons.

This paper examines the recent claim of Phillips, that the threshold model of latency is inadequate to account for the changes of latency of auditory cortical neurons in response to tones of different amplitudes and rise times. I argue that Phillips' analysis was based on an incorrect assumption and that he therefore rejected the model for the wrong reasons, though correctly, as the model is in fact inadequate, as demonstrated here and previously. The failure of the model has significant implications for signal processing in the auditory system.

Functional organization of the avian auditory cortex analogue. I. Topographic representation of isointensity bandwidth.

Bandwidth of auditory units in the chick forebrain (field L/Hv complex) was measured with isointensity tone stimuli. Isointensity bandwidth is topographically represented within the four-layered tonotopically organized structure. It declines continuously from rostrodorsal to caudoventral along the longitudinal axis of two-dimensional best frequency planes (frequency band laminae). Layer-specific differences along the radial axis are also obvious. In the input layer of field L and in Hv ON-response bandwidths are relatively broad. The narrower bandwidths of units in the two postsynaptic layers of field L are probably caused by lateral inhibition mechanisms, as derived from the different topographic representations of OFF-versus ON-response bandwidths. A quantitative comparison of the topographic representation of bandwidth is made with the geometry of the tonotopic organization of the chick auditory forebrain complex, as revealed by 2-deoxyglucose data in a former study. A number of possible input-output transformations are derived from this comparison.

Functional organization of the avian auditory cortex analogue. II. Topographic distribution of latency.

Onset latencies of units were measured at 70 dB SPL in the auditory forebrain area (field L/Hv-complex) of awake domestic chicks. Latencies ranged from 8.8 to 75 ms. Latencies of units averaged for octave bands of best frequencies (BF) declined with increasing BF. Latencies were topographically distributed in the radial but not in the longitudinal dimension of frequency band laminae (FB laminae). Latencies were shortest in the input-layer L2 and increased systematically towards the postsynaptic layers L3 and L1/Hv, respectively. This topography visualizes the spatiotemporal spread of onset excitation and reflects the hierarchical processing within the structure. It also indicates a topographical representation of temporal resolution.

Photodegradation of protoporphyrin-dimethylester in solution and in organized environments.

The degradation of sensitizers used in photodynamic therapy (PDT) involves photooxidation either by molecular oxygen or by oxygen intermediates which leads to hydroxyaldehyde and formyl products or to ring opening. Our investigations focused on the spectroscopic changes which protoporphyrin-dimethylester (PP) exhibits upon irradiation. As the microenvironment strongly influences the effects, we used an aprotic organic solvent, L-alpha-phosphatidylcholine dioleoyl (DOPC) liposomes and isogenic fibrosarcoma cells (SSKII) as carriers for PP. Hydroxyaldehyde product isomers develop a new absorption band centred around 670 nm and a new emission band at 676 nm. These characteristics can be used to discriminate them from formyl products and intact PP. In organic solvents, the formation of the hydroxyaldehyde products dominates. In DOPC liposomes and cells, the hydroxyaldehyde yield drops and photooxidation results in attack of the macrocycle. Time-resolved fluorescence spectroscopy of monomeric PP in an organic solvent gives a monoexponential decay time tau of 10.1 +/- 1.3 ns. Upon irradiation a second component with a decay time of 4.9 +/- 0.6 ns, resulting from the hydroxyaldehyde product, was detected. In liposomes and cells the monomeric decay time was significantly longer (15 ns) due to the altered microenvironment. Additionally, we observed in liposomes and in cells a small contribution of a short component (1 ns) which is attributed to an aggregated sensitizer species. In irradiated cells the aggregated fraction doubles, indicating a change in the microenvironment caused by the photodynamic action of the sensitizer.

Topographic representation of tone intensity along the isofrequency axis of cat primary auditory cortex.

The sound pressure level (SPL), henceforth termed intensity, of acoustic signals is encoded in the central auditory system by neurons with different forms of intensity sensitivity. However, knowledge about the topographic organization of neurons with these different properties and hence about the spatial representation of intensity, especially at higher levels of the auditory pathway, is limited. Here we show that in the tonotopically organized primary auditory cortex (AI) of the cat there are orderly topographic organizations, along the isofrequency axis, of several neuronal properties related to the coding of the intensity of tones, viz. minimum threshold, dynamic range, best SPL, and non-monotonicity of spike count--intensity functions to tones of characteristic frequency (CF). Minimum threshold, dynamic range, and best SPL are correlated and alter periodically along isofrequency strips. The steepness of the high-intensity descending slope of spike count--intensity functions also varies systematically, with steepest slopes occurring in the regions along an isofrequency strip where low thresholds, narrow dynamic ranges and low best SPLs are found. As a consequence, CF-tones of various intensities are represented by orderly and, for most intensities, periodic, spatial patterns of distributed neuronal activity along an isofrequency strip. For low--to--moderate intensities, the mean relative activity along the entire isofrequency strip increases rapidly with intensity, with the spatial pattern of activity remaining quite constant along the strip. At higher intensities, however, the mean relative activity along the strip remains fairly constant with changes in intensity, but the spatial patterns change markedly. As a consequence of these effects, low- and high-intensity tones are represented by complementary distributions of activity alternating along an isofrequency strip. We conclude that in AI tone intensity is represented by two complementary modes, viz. discharge rate and place. Furthermore, the magnitude of the overall changes in the representation of tone intensity in AI appears to be closely related to psychophysical measures of loudness and of intensity discrimination.

Sensitivity of neurons in cat primary auditory cortex to tones and frequency-modulated stimuli. I: Effects of variation of stimulus parameters.

In the primary auditory cortex (AI) of barbiturate-anesthetized cats multi-unit responses to tones and to frequency-modulated (FM) tonal stimuli were analyzed. Characteristic frequency (CF), sharpness of tuning, minimum threshold, and dynamic range of spike count--intensity functions were determined. Minimum threshold and dynamic range were positively correlated. The response functions to unidirectional FM sweeps of varying linear rate of change of frequency (RCF) that traversed the excitatory frequency response areas (FRAs) displayed a variety of shapes. Preferences for fast RCFs (> 1000 kHz/s) were most common. Best RCF was not correlated with measures of sharpness of tuning. Directional preference and sensitivity were quantified by a DS index which varied with RCF. About two-thirds of the multi-unit responses showed a preference for downward sweeps. Directional sensitivity was independent of CF and independent of best RCF. Measurements of latencies of phasic responses to unidirectional FM sweeps of different RCF demonstrated that the discharges of a given multi-unit over its effective RCF range were initiated at the same instantaneous frequency (effective Fi), independent of RCF. Effective Fis fell within the excitatory FRA of a given multi-unit. The relationships of effective Fis to CF show that responses were evoked only when the frequency of the signal was modulated towards CF and not when modulated away from it, and that responses were initiated before the modulation reached CF. Changes in the range and depth of modulation had only minor, if any, effects on RCF response characteristics, FM directional sensitivity, and effective Fis, as long as the beginning and ending frequencies of FM sweeps fell outside a multi-unit's FRA. Stimulus intensity also had only moderate effects on RCF response characteristics and DS. However, effective Fis were influenced in systematic fashions; with increases in intensity, effective Fis to upward and downward sweeps decreased and increased, respectively. Thus, for higher intensities FM responses were initiated at instantaneous frequencies occurring earlier in the signal. The results are compared with previous data on tone and FM sensitivity of auditory neurons in cortical and subcortical structures, and mechanisms of FM rate and directional sensitivity are discussed. The topographic representations of these neuronal properties in AI are reported in the companion report.