Biomedical subjects

Subhash Saha

Publications and source records attributed to Subhash Saha.

8 recordsLinked to original sources

PubMed2006

Activation of pedunculopontine tegmental protein kinase A: a mechanism for rapid eye movement sleep generation in the freely moving rat.

Cells in the pedunculopontine tegmentum (PPT) play a key role in the generation of rapid eye movement (REM) sleep, but its intracellular signaling mechanisms remain unknown. In the current studies, the role of PPT intracellular protein kinase A (PKA) in the regulation of REM sleep was evaluated by comparing PKA subunit [catalytic (PKA(C alpha)) and regulatory (PKA(RI), PKA(RII alpha), and PKA(RII beta)) types] expression and activity in the PPT at normal, high, and low REM sleep conditions. To compare anatomical specificity, REM sleep-dependent expressions of these PKA subunits were also measured in the medial pontine reticular formation (mPRF), medial prefrontal cortex (mPFC), and anterior hypothalamus (AHTh). The results of these PKA subunit expression and activity studies demonstrated that the expression of PKA(C alpha) and PKA activity in the PPT increased and decreased during high and low REM sleep, respectively. Conversely, PKA(C alpha) expression and PKA activity decreased with high REM sleep in the mPRF. Expression of PKA(C alpha) also decreased in the mPFC and remained unchanged in the AHTh with high REM sleep. These subunit expression and PKA activity data reveal a positive relationship between REM sleep and increased PKA activity in the PPT. To test this molecular evidence, localized activation of cAMP-dependent PKA activity was blocked using a pharmacological technique. The results of this pharmacological study demonstrated that the localized inhibition of cAMP-dependent PKA activation in the PPT dose-dependently suppressed REM sleep. Together, these results provide the first evidence that the activation of the PPT intracellular PKA system is involved in the generation of REM sleep.

Animals↗

PubMed2005

Synaptic distinction of laminar-specific prefrontal-temporal pathways in primates.

Prefrontal pathways exert diverse effects in widespread cortical areas, issuing projections both to the middle layers and to layer I, which are anatomically and functionally distinct. Here we addressed the still unanswered question of whether cortical pathways that terminate in different layers are distinct at the synaptic level. We addressed this issue using as a model system the robust and functionally significant pathways from prefrontal areas 10 and 32 to superior temporal areas in rhesus monkeys. Boutons from prefrontal axons synapsing in the middle layers of superior temporal cortex were significantly larger than boutons synapsing in layer I. Most synapses were on spines in both layers, which are found on dendrites of excitatory neurons. The less prevalent synapses on smooth dendrites, characteristic of inhibitory interneurons, were more common in the middle cortical layers than in layer I. Bouton volume was linearly related to vesicular and mitochondrial content in both layers, though a subset of small boutons, found mostly in layer I, contained no mitochondria. The systematic laminar-specific presynaptic differences in stable cortical synapses in adult primates were independent of their origin in the functionally distinct prefrontal areas 10 and 32, or their destination in architectonically distinct superior temporal areas. This synaptic distinction suggests differences in efficacy of synaptic transmission and metabolic demands in laminar-specific pathways that may be selectively recruited in behavior.

Animals↗

PubMed2005

Pontine-wave generator activation-dependent memory processing of avoidance learning involves the dorsal hippocampus in the rat.

The aim of this study was to test the hypothesis that the dorsal hippocampus plays a critical role in pontine-wave (P-wave) generator activation-dependent memory processing of two-way active avoidance (TWAA) learning. To achieve this objective, rats were given small bilateral lesions in the CA1, dentate gyrus (DG), or CA3 region of the dorsal hippocampus by microinjecting ibotenic acid. After recovery, lesioned and sham-lesioned rats were trained on a TWAA learning paradigm, allowed a 6-hr period of undisturbed sleep, and then were tested on the same TWAA paradigm. It was found that lesions in the CA3 region impaired retention of avoidance learning. Conversely, lesions in the CA1 and DG regions had no effect on TWAA learning retention. None of the groups showed any changes in the baseline sleep-wake cycle or in the acquisition of TWAA learning. All rats showed increased rapid eye movement (REM) sleep and increased REM sleep P-wave density during the subsequent 6-hr recording period. Impaired retention in the CA3 group occurred despite an increase in REM sleep and P-wave density, suggesting that during REM sleep, the P-wave generator interacts with the CA3 region of the dorsal hippocampus to aid in consolidation of TWAA learning. The results of the present study thus demonstrate that P-wave generator activation-dependent consolidation of memory requires an intact CA3 subfield of the dorsal hippocampus. The results also provide evidence that under mnemonic pressure, the dorsal hippocampus may not be involved directly in regulating the sleep-wake cycle.

Animals↗

PubMed2005

Parallel organization of contralateral and ipsilateral prefrontal cortical projections in the rhesus monkey.

BACKGROUND: The neocortical commissures have a fundamental role in functional integration across the cerebral hemispheres. We investigated whether commissural projections in prefrontal cortices are organized according to the same or different rules as those within the same hemisphere, by quantitatively comparing density, topography, and laminar origin of contralateral and ipsilateral projections, labeled after unilateral injection of retrograde tracers in prefrontal areas. RESULTS: Commissural projection neurons constituted less than one third of the ipsilateral. Nevertheless, projections from the two hemispheres were strongly correlated in topography and relative density. We investigated to what extent the distribution of contralateral projections depended on: (a) geographic proximity of projection areas to the area homotopic to the injection site; (b) the structural type of the linked areas, based on the number and neuronal density of their layers. Although both measures were good predictors, structural type was a comparatively stronger determinant of the relative distribution and density of projections. Ipsilateral projection neurons were distributed in the superficial (II-III) and deep (V-VI) layers, in proportions that varied across areas. In contrast, contralateral projection neurons were found mostly in the superficial layers, but still showed a gradient in their distribution within cortical layers that correlated significantly with cortical type, but not with geographic proximity to the homotopic area. CONCLUSION: The organization of ipsilateral and contralateral prefrontal projections is similar in topography and relative density, differing only by higher overall density and more widespread laminar origin of ipsilateral than contralateral projections. The projections on both sides are highly correlated with the structural architecture of the linked areas, and their remarkable organization is likely established by punctuated development of distinct cortical types. The preponderance of contralateral projections from layer III may be traced to the late development of the callosal system, whose function may be compromised in diseases that have their root late in ontogeny.

Animals↗

PubMed2005

Two-way active avoidance training-specific increases in phosphorylated cAMP response element-binding protein in the dorsal hippocampus, amygdala, and hypothalamus.

Previous studies have demonstrated that the activation of pontine-wave (P-wave) generating cells in the brainstem during post-training rapid eye movement (REM) sleep is critical for the consolidation of memory for two-way active avoidance (TWAA) learning in the rat. Here, using immunocytochemistry, we investigated the spatio-temporal distribution of CREB phosphorylation within different parts of the dorsal hippocampus, amygdala, and hypothalamus following a session of TWAA training in the rat. We show that the TWAA training trials increased phosphorylation of CREB (p-CREB) in the dorsal hippocampus, amygdala, amygdalo-hippocampal junction (AHi), and hypothalamus. However, the time intervals leading to training-induced p-CREB activity were different for different regions of the brain. In the dorsal hippocampus, p-CREB activity was maximal at 90 min and this activity disappeared by 180 min. In the AHi, activity of the p-CREB peaked by 180 min and disappeared by 360 min. In the amygdala, the p-CREB activity peaked at 180 min and still remained higher than the control at the 360 min interval. In the hypothalamus, at 90 min p-CREB activity was present only in the ventromedial hypothalamus; however, by 180 min this p-CREB activity was also present in the dorsal hypothalamus, perifornical area, and lateral hypothalamus. By 360 min, p-CREB activity disappeared from the hypothalamus. This TWAA training trials-induced spatiotemporal characteristic of CREB phosphorylation, for the first time, suggests that REM sleep P-wave generator activation-dependent memory processing involves different parts of the dorsal hippocampus, amygdala, and hypothalamus.

Amygdala↗

PubMed2004

Neurotoxic lesions of phasic pontine-wave generator cells impair retention of 2-way active avoidance memory.

STUDY OBJECTIVES: The aim of this study was to test the hypothesis that the activation of pontine (P)-wave generator is critical for the posttraining rapid eye movement (REM) sleep-dependent memory processing. DESIGN: Ibotenic acid was microinjected (0.5 microg in 0.05 microL) into the functionally identified P-wave generator in order to destroy the cell bodies and thus to study the effects of their destruction upon waking-sleep states, P-waves, and 2-way active avoidance memory. SETTING: Sleep research laboratory at Boston University School of Medicine. PARTICIPANTS: Adult male Sprague-Dawley rats (N = 27). INTERVENTIONS: Chronically implanted for recording polygraphic signs of sleep and bilateral guide tubes for the local microinjections into the P-wave generator. MEASUREMENTS AND RESULTS: The ibotenic acid produced a small spherical area (< or = 0.35 mm in diameter) of nerve cell loss centered on the P-wave generator. Bilateral lesioning of the P-wave generator decreased P-waves during REM sleep by > 95% without significantly changing the amounts of time spent in wake, slow-wave sleep, or REM sleep. In these P-wave generator-lesioned rats, acquisition of avoidance learning and posttraining wake-sleep changes were identical to those of the sham-lesioned rats. However, in the test trials, after 6 hours of undisturbed sleep-wake, P-wave generator-lesioned rats had no retention of avoidance memory. CONCLUSIONS: These findings, for the first time, provide direct evidence that P-wave-generating cells are critical for normal REM sleep-dependent memory processing. This evidence supports our hypothesis that the P-wave generator in the brainstem may act as an on switch to provide activating input to forebrain structures for sleep-dependent memory processing.

Animals↗

PubMed2003

Spontaneous REM sleep is modulated by the activation of the pedunculopontine tegmental GABAB receptors in the freely moving rat.

Considerable evidence suggests that the neurotransmitter gamma-aminobutyric acid (GABA)-ergic system and pedunculopontine tegmentum (PPT) in the brain stem are critically involved in the regulation of rapid-eye-movement (REM) sleep. GABA and its various receptors are normally present in the PPT cholinergic cell compartment. The aim of this study was to identify the role of GABA and its receptors in the regulation of REM sleep. To achieve this aim, specific receptors were activated differentially by local microinjection of selective GABA receptor agonists into the PPT while quantifying its effects on REM sleep in freely moving chronically instrumented rats (n = 21). The results demonstrated that when GABAB receptors were activated by local microinjection of a GABAB receptor selective agonist, baclofen, spontaneous REM sleep was suppressed in a dose-dependent manner. The optimum dose for REM sleep reduction was 1.5 nmol. In contrast, when GABAA and GABAC receptors were activated by microinjecting their receptor selective agonists, isoguvacine (ISGV) and cis-4-aminocrotonic acid (CACA), respectively, the total percentages of REM sleep did not change compared with the control values. In another eight freely moving rats, effects of baclofen application was tested on firing rates of REM-on cells (n = 12). Of those 12 neurons, 11 stopped firing immediately after application of baclofen [latency: 50 +/- 14 s (SD)] and remained almost silent for 130 +/- 12 min. Findings of the present study provide direct evidence that the PPT GABAB receptors and REM-on cells are involved in the regulation of REM sleep.

Action Potentials↗

PubMed2003

Serial pathways from primate prefrontal cortex to autonomic areas may influence emotional expression.

BACKGROUND: Experiencing emotions engages high-order orbitofrontal and medial prefrontal areas, and expressing emotions involves low-level autonomic structures and peripheral organs. How is information from the cortex transmitted to the periphery? We used two parallel approaches to map simultaneously multiple pathways to determine if hypothalamic autonomic centres are a key link for orbitofrontal areas and medial prefrontal areas, which have been associated with emotional processes, as well as low-level spinal and brainstem autonomic structures. The latter innervate peripheral autonomic organs, whose activity is markedly increased during emotional arousal. RESULTS: We first determined if pathways linking the orbitofrontal cortex with the hypothalamus overlapped with projection neurons directed to the intermediolateral column of the spinal cord, with the aid of neural tracers injected in these disparate structures. We found that axons from orbitofrontal and medial prefrontal cortices converged in the hypothalamus with neurons projecting to brainstem and spinal autonomic centers, linking the highest with the lowest levels of the neuraxis. Using a parallel approach, we injected bidirectional tracers in the lateral hypothalamic area, an autonomic center, to label simultaneously cortical pathways leading to the hypothalamus, as well as hypothalamic axons projecting to low-level brainstem and spinal autonomic centers. We found densely distributed projection neurons in medial prefrontal and orbitofrontal cortices leading to the hypothalamus, as well as hypothalamic axonal terminations in several brainstem structures and the intermediolateral column of the spinal cord, which innervate peripheral autonomic organs. We then provided direct evidence that axons from medial prefrontal cortex synapse with hypothalamic neurons, terminating as large boutons, comparable in size to the highly efficient thalamocortical system. The interlinked orbitofrontal, medial prefrontal areas and hypothalamic autonomic centers were also connected with the amygdala. CONCLUSIONS: Descending pathways from orbitofrontal and medial prefrontal cortices, which are also linked with the amygdala, provide the means for speedy influence of the prefrontal cortex on the autonomic system, in processes underlying appreciation and expression of emotions.

Animals↗