Neuroscience
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Since metabolic neural activity is accompanied by heat release, measurement of local brain temperature offers a method for assessing alterations in neural activity. This approach, continuous monitoring of local brain (ventral tegmental area, ventral striatum, and hippocampus) and body (temporal muscle) temperature, was used to study intravenous cocaine self-administration in trained rats. The first self-administration of a session was preceded by a strong temperature increase that continued after the drug infusion. ⋯ These data suggest a generalized brain activation associated with cocaine-seeking and cocaine-taking behavior with its phasic fluctuations around individual drug self-injections. While the initial component of brain activation preceding the first lever-press for cocaine is internally determined and closely related to behavioral search, subsequent biphasic fluctuations in neural activity associated with repeated drug intakes appear to be drug-mediated. Cocaine-induced potentiation of monoamine transmission is a possible factor for gradual increases in neural activity that drive cocaine seeking, while a rapid, brain concentration-dependent action on Na(+) transport (local anesthetic action) is the most probable factor determining an abrupt, transient cessation of neural activation associated with cocaine reward.
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Comparative Study
Focal motility determines the geometry of dendritic spines.
The geometry of dendritic spines has a major impact on signal transmission at excitatory synapses. To study it in detail we raised transgenic mice expressing an intrinsic green fluorescent protein-based plasma membrane marker that directly visualizes the cell surface of living neurons throughout the brain. ⋯ In live mature dendrites up to 50% of spines had cup-shaped heads with prominent terminal lamellipodia whose motility produced constant alterations in the detailed geometry of the synaptic contact zone. The partial enveloping of presynaptic terminals by these cup-shaped spines coupled with rapid actin-driven changes in their shape may operate to fine-tune receptor distribution and neurotransmitter cross-talk at excitatory synapses.
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To examine the role of GABA in the respiratory rhythm and pattern generation in neonatal mice, we analyzed the function of the respiratory control system of 67-kDa isoform of glutamic acid decarboxylase (GAD67)-deficient neonatal mice. In these mutant (GAD67-/-) mice, GABA levels in the brainstem were reduced to about 30% of those in wild-type (GAD67+/+) mice. In in vivo preparations, ventilatory parameters were analyzed by whole body plethysmography and electromyography of intercostal muscles. ⋯ Superfusion of the in vitro GAD67-/- preparation with 10 microM GABA prolonged C4 burst duration and partly restored a normal pattern of inspiration, although the restoration was limited. These results indicate that reduced GABA levels during the perinatal period induce malfunction in the respiratory control system. We suggest that GABAergic transmission is not essential for basic respiratory rhythm generation but plays an important role in the maintenance of regular respiratory rhythm and normal inspiratory pattern in neonatal mice.
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Comparative Study
Impaired long-term potentiation in obese zucker rats: possible involvement of presynaptic mechanism.
Electrophysiological investigation of basal synaptic transmission and synaptic plasticity in the CA1 region of the hippocampus was carried out in anesthetized obese Zucker rats (OZR). Comparison of the input/output curves of basal field excitatory postsynaptic potential indicates that these are similar in both the OZR and its lean counterpart suggesting that basal synaptic transmission is intact in the OZR. ⋯ Since post-tetanic potentiation and paired pulse facilitation, forms of short-term potentiation of presynaptic origin, are also severely impaired in the OZR, the results imply that impairment of CA1 hippocampal LTP in these obese rats may be due, in part, to impaired presynaptic function. The results emphasize the potential deleterious effect of obesity on learning and memory functions of the CNS.
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Since metabolic activity is accompanied by heat release, measurement of brain temperatures offers a method for assessing behavior-associated changes in neural activity. To explore this possibility, we monitored local brain (nucleus accumbens, medial-preoptic hypothalamus, and hippocampus) and body (temporal muscle) temperature in an experienced male rat during sexual behavior with a sexually receptive female. Placement of the female into a neighboring compartment increased the male's temperature and additional increases occurred when rats were allowed to see and partially interact with the female through a Plexiglas barrier with dime-size holes. ⋯ These data generally match single-unit and other physiological findings, suggesting that male sexual behavior is accompanied by sustained and generalized neural activation. This activation is triggered by sexually relevant stimuli (arousal), maintained during repeated mounts and intromissions, and peaked at ejaculation. These findings suggest brain temperature fluctuations not only as a sensitive index of functional neural activation, but as a powerful factor affecting various neural functions and an important part of brain mechanisms underlying motivated behavior.