Joseph D. Bronzino

Developmental protein malnutrition: Influences on the central nervous system of the rat ☆

Our group has been carrying out interdisciplinary studies on the effects of prenatal and postnatal protein malnutrition on the developing rat brain. Anatomical, physiological, biochemical and behavioral approaches using the same animal model have revealed that protein malnutrition affects the brain at various levels, i.e., (1) anatomical, as revealed by Golgi findings of deranged dendritic trees on analysis of cortical and subcortical areas; (2) physiological, as revealed by delayed sleep pattern maturation, disturbances in seizure thresholds, slowing of sensory cortico-cortical and thalamocortical evoked potentials, and changed power in hippocampal theta activity; (3) biochemical, as revealed by marked increases in biogenic amines dating from birth, as well as modifications in tryptophan metabolism; and (4) behavioral, as revealed by various changes in responses to different kinds of aversive stimulation. Reversal studies have revealed that many changes are permanent and not amenable to nutritional rehabilitation even at birth, which is before the brain growth spurt in the rat. Our paradigm closely mimicks the human condition of low level, chronic protein undernutrition and thus reveals the underlying disturbances due to malnutrition. The dietary reversal studies are attempts at pin-pointing critical brain growth periods, beyond which recovery of functions is not possible.

Prenatal protein malnutrition affects synaptic potentiation in the dentate gyrus of rats in adulthood

Long-term potentiation (LTP) was studied in the dentate gyrus of anesthetized normal and prenatally protein malnourished rats in adulthood. LTP was initiated by high-frequency stimulation of the perforant path. Potentiation of both population excitatory postsynaptic potential (EPSP) slope and population spike was studied at various times after conditioning out to 5 h. The results indicate that prenatal protein malnutrition has a differential effect on LTP. Although potentiation of the population spike was relatively unaffected, prenatal protein malnutrition did lead to a significant reduction in potentiation of the population EPSP. Several possibilities are proposed as to the cause of the differential effect.

Neuropharmacology of the afferent projections from the lateral habenula and substantia nigra to the anterior raphe in the rat

Abstract Previous neuroanatomical studies have demonstrated the existence of major afferent projections to the nucleus raphe dorsalis originating in the lateral habenula and substantia nigra. These projections have a predominantly suppressive effect on raphe unit activity. The present acute electrophysiological study in anesthetized rats evaluated: (a) the effects of pharmacological blockade of GABAergic transmission on the suppression of activity of units in the nuclei raphe dorsalis and raphe medianus by stimulation of the lateral habenula, and (b) the effects of pharmacological blockade of GABA, dopamine, acetylcholine, glycine, opiates, serotonin, norepinephrine and histamine on the suppression of raphe activity by electrical stimulation of the substantia nigra. Results showed that the GABA bloeker, picrotoxin, attenuated the effects of lateral habenula stimulation on unit activity in the raphe dorsalis and medianus and that GABA may exert a tonic inhibitory influence on spontaneous unit activity in the raphe. The effects of stimulation in the nigra on raphe dorsalis and medianus neuronal activity were not blocked by any of the 10 drugs tested. Indirect evidence was obtained, however, that norepinephrine and possibly histamine exerted an excitatory effect on raphe units since drugs which block these transmitters tended to enhance the suppressive effects of nigral stimulation. The present results do not permit identification of the neurotransmitter which mediates the marked suppression of unit activity in the anterior raphe produced by electrical stimulation of the substantia nigra.

Paired-pulse facilitation and inhibition in the dentate gyrus is dependent on behavioral state.

SummaryIt is well established that neuronal transmission from the entorhinal cortex through the dentate gyrus via the perforant path is dependent on behavioral state. To further study the modulation of neuronal transmission by behavioral state we employed the paired-pulse technique to study interneuronally-mediated inhibition and shortterm facilitation in the dentate gyrus of freely-moving rat preparations. Precisely timed double pulses of electrical stimulation were delivered to the perforant path in the chronically implanted rat preparation during each of four well-defined behavioral states: slow-wave sleep (SWS), REM sleep (REM), immobile waking (IW) or active waking with voluntary movements (AW). Evoked field potentials were recorded in the dentate gyrus and analyzed to measure the population spike amplitude which represents the total number of dentate granule cells firing in synchronous response to perforant path stimulation. The paired-pulse index (PPI) was used as a measure of the net short-term facilitation or interneuronally-mediated inhibition effective at the time of the paired-pulse test and is computed by dividing the amplitude of the second population spike (p2) by the amplitude of the first population spike (p1). During the course of this study 3754 paired-pulse tests were performed in 9 rat preparations. The three interpulse interval (IPI) values used in these studies were 25, 30 and 35 ms. The results showed that the PPI was greater during AW and REM as compared to SWS and IW. The PPI was significantly greater during AW than during SWS and IW regardless of p1 amplitude or IPI value. The PPI was significantly greater during AW than during REM under most conditions except those corresponding to low p1 amplitude and long IPI. The PPIs measured during REM were significantly greater than those measured during SWS and IW at short IPIs (25 and 30 ms) but not at an IPI of 35 ms. These results indicate that short-term facilitation is the dominant response during AW especially when observed using an IPI of 35 ms. In contrast, interneuronally-mediated inhibition was observed to be dominant during SWS and IW. The net effect during REM was observed to lie between these two extremes using an IPI of 25 ms and tended toward short-term facilitation at longer IPIs of 30 and 35 ms. Septal disinhibition of dentate granule cells is proposed as the mechanism for this effect. The behavioral state modulaion of neuronal transmission through the dentate gyrus is discussed in terms of this hypothesis. We conclude that there are probably at least two mechanisms underlying the behavioral modulation of field potentials in the dentate gyrus: (1) an indirect influence modulating the activity of inhibitory interneurons and (2) a more direct influence modulating the excitability of granule cells themselves.

Power spectral analysis of the EEG following protein malnutrition

In these studies, power spectral analysis techniques were utilized to quantify the EEG obtained from rats reared on either an 8% or 25% casein diet during various vigilance states at two stages of development: (1) adulthood-90 to 120 days old; and (2) immediately after weaning-22 to 23 days old. It was found that the cortical EEG contained relatively more power in the low frequencies (ie., 0.5 to 10 Hz) for the 22-23 day old animals than for the 90-120 day old rats, especially during the slow wave sleep states-SWS1 and SWS2. Theta activity (5-8 Hz) in the hippocampus was shown to have greater power for the 22-23 day old group than for the older animals during both REM sleep and waking. Analyses of power spectral data and other indices of the frequency distribution of the hippocampal EEG indicated that those animals subjected to protein malnutrition have significantly more power in the theta band during REM sleep than the normal adult group. Since it was also noted that the hippocampal EEG obtained from the 22-23 day old group contained relatively more power in the theta band than the 90-120 day old group, the dietary treatment effect might be intrepreted as an instance of retarded development associated with protein malnutrition. Thus, a significant effect of the dietary manipulation used in the study may be largely on the system responsible for regulating theta activity.

Sleep cycles in cats during chronic electrical stimulation of the area postrema and the anterior raphe

Sleep-waking profiles were obtained from 130 7 hr stimulation-EEG recording sessions in a series of cats bearing chronically implanted stimulating electrodes in the regions of the area postrema and anterior raphe nuclei. The results indicated that: (a) during electrical stimulation of the region of the area postrema with 0.5 or 10 Hz at 1 and 2 mA there were significant increases in the occurrence of the deeper aspects of slow-wave sleep and in REM sleep. These elevations were significant in comparison to nonstimulation baselines and to sleep profiles obtained during stimulation of points located dorsal and anterior to the area postrema. (b) Stimulation of the medial reticular formation including the anterior raphe using the same parameters employed for the area postrema did not alter the occurrence of any stage of sleep. These findings indicate that the region of the area postrema may be more involved in the generation of sleep than the anterior raphe nuclei.

Effect of chronic protein malnutrition on non-specific thalamo-cortical evoked potentials in the rat

Abstract Cortical incremental responses to repetitive thalamic stimulation were studied in normal and protein malnourished rats. The rate of cortical incrementation ipsilateral to the thalamic site of stimulation varied as a function of stimulus repetition rate but was unaffected by dietary treatment. The waveform of the ipsilateral response likewise was unaffected by protein malnutrition and a characteristic positive-negative-positive response was observed. In the cortex contralateral to thalamic stimulation, seven of eight malnourished animals exhibited a surface positive peak, in some cases quite prominent, at a latency at which seven of eight normals exhibited a prominent surface negativity. These results are discussed in relation to reported effects of malnutrition on sensory evoked potentials.

Power density spectra of cortical EEG of the cat in sleep and waking

Abstract Power spectral analysis was utilized to study the cortical EEG of the cat during waking, slow-wave sleep (SWS), and REM sleep. The power density spectra for waking and REM sleep differed from that of SWS, with SWS having more power in the low frequencies. Waking and REM differed in the 10–15 c/sec and 30–40 c/sec bands. Characteristic power density spectra of the cortical EEG of the cat provide a basis for distinguishing the three vigilance states.

Power spectrum analysis of EEG synchronization following application of serotonin to area postrema.

The role of serotonin and of the area postrema in synchronization of the neocortical electroencephalogram (EEG) was investigated in the present studies by observing the effects of different drugs (serotonin, norepinephrine, acetylcholine, and Xylocaine) applied topically at the site of the area postrema in cats. Using Fast Fourier Spectral analysis and power density spectra techniques it was found that serotonin increased the low frequency components and decreased the high frequency components in the cortical EEG. Application of serotonin to the floor of the fourth ventrical 6 mm rostral to the area postrema never produced EEG synchronizing effects. Xylocaine applied directly to the area postrema, as well as lesions of this region, decreased the low frequency components of the EEG while norepinephrine and acetylcholine produced variable effects. These results indicate that a serotonergic-sensitive mechanism, which induces EEG synchronization, exists in the region of the area postrema.

A new design for an exploring chemode

Abstract This report describes an “exploring” chemitrode device with the capability of introducing various crystalline chemicals precisely and reproducibly into predetermined target areas in the brain. With such a device it is possible to explore millimeter by millimeter through the specific area under study, thus providing an effective tool for mapping neurobehavioral systems.