Neuroscience
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Comparative Study
Brain afferents to the lateral caudal ventrolateral medulla: a retrograde and anterograde tracing study in the rat.
The ventrolateral medulla (VLM) modulates autonomic functions, motor reactions and pain responses. The lateralmost part of the caudal VLM (VLMlat) was recently shown to be the VLM area responsible for pain modulation. In the present study, the brain sources of VLMlat afferent fibers were determined by tract-tracing techniques. ⋯ The present study gives an account of the brain regions putatively involved in triggering the modulatory actions elicited from the VLMlat. These include areas committed to somatosensory processing, autonomic control, somatic and visceral motor activity and affective reactions. The findings suggest that the VLMlat may play a major homeostatic role in the integration of nociception with other brain functions.
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To test the hypotheses that (i). electroencephalograms (EEGs) are largely made up of oscillations at many frequencies and (ii). that the peaks in the power spectra represent oscillations, we applied a new method, called the period specific average (PSA) to a wide sample of EEGs. Both hypotheses can be rejected. Although the principal peaks in the two spectra agree most of the time, quite often a peak in the power spectrum accompanies no periodicity peak and some periodicity peaks have no power spectral peak. ⋯ In the face of wide variability, we do not report any systematic differences in periodicity among EEGs from different parts of the brain or different brain states or species; it will take many more exemplars of each state, species or brain part to establish characteristic features. The PSA method may be the best so far proposed to demonstrate and quantify periodicity in wide-band time series with noise, but it has serious limitations. Discussion leads to the conclusion that it is time for a new paradigm or metaphor for brain waves.
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Angiotensin II (Ang II) type 1 (AT1) receptors are prevalent in the sensory vagal complex including the nucleus tractus solitarii (NTS) and area postrema, each of which has been implicated in the central cardiovascular effects produced by Ang II. In rodents, these actions prominently involve the AT1A receptor. Thus, we examined the electron microscopic dual immunolabeling of antisera recognizing the AT1A receptor and Ang II to determine interactive sites in the sensory vagal complex of rat brain. ⋯ In the area postrema, AT1A receptor labeling also was detected in many non-neuronal cells including glia, capillary endothelial cells and perivascular fibroblasts that were less prevalent in the NTS. We conclude that in the rat sensory vagal complex, AT1A receptors are strategically positioned for involvement in modulation of the postsynaptic excitability and intracrine hormone-like effects of Ang II. In addition, these receptors have distributions consistent with diverse roles in regulation of transmitter release, regional blood flow and/or vascular permeability.
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Comparative Study
In vivo evidence for an activity-independent maturation of AMPA/NMDA signaling in the developing hippocampus.
Correlated pre- and postsynaptic activity is thought to promote maturation of excitatory synapses in the developing brain by directing AMPA receptors to pure NMDA synapses. However, this hypothesis has not been tested in vivo. Here, we have performed such test by inhibiting correlated neural activity in vivo using a single injection of tetanus toxin into the rat hippocampal CA1 area at postnatal day 1. ⋯ This activity deprivation led to a growth retardation of CA1 pyramidal neurons and to markedly faster decay kinetics of NMDA sPCSs. However, it did not alter the relationship between AMPA and NMDA sPSCs with respect to either their frequency or amplitude. Thus, although critical for certain aspects of neuronal development, correlated neural activity in the neonatal hippocampus does not seem to promote incorporation of AMPA receptors at pure NMDA synapses.
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Converging evidence in schizophrenia suggests prefrontal cortical neuronal deficits that correlate with exaggerated subcortical dopamine (DA) functions: Excitotoxic lesion of the ventral hippocampus (VH) in neonatal rats is widely considered a putative animal model of schizophrenia as they lead to characteristic post-pubertal emergence of behavioral and cognitive abnormalities suggesting a developmental change in the neural circuits comprising the prefrontal cortex (PFC) and subcortical DA. Nerve growth factor inducible-B (NGFI-B, also known as Nur77), an orphan nuclear receptor and transcriptional regulator, is constitutively expressed in the target structures of DA pathways. It acts as an immediate early gene with rapid modulation of its mRNA expression by stress, DA and antipsychotic drugs. ⋯ Amphetamine treatment increased the expression of NGFI-B mRNA in the mPFC, CC, striatum and NAcc in both control and lesioned animals of both ages. Interestingly, however, striatal and NAcc regions of lesioned rats showed a significantly greater effect of amphetamine at PD56. The data suggest that nVH lesions lead to delayed changes in PFC gene expression along with functional DAergic hyperactivity in subcortical regions.