The effects of aerobic exercise intensity and duration on levels of brain-derived neurotrophic factor in healthy men.

This study examined the combined effects of aerobic exercise intensity and duration on serum brain-derived neurotrophic factor (sBDNF) levels in healthy human adult males aged 18-25 years. Forty five participants were randomly assigned to one of six exercise conditions based on varying intensity (80% or 60% of heart rate reserve, or control) and duration (20 or 40 min). Vigorous (80% heart rate reserve, "Vig") and moderate (60% heart rate reserve, "Mod") exercise was carried out on cycle ergometers. Control subjects remained seated and at rest during the exercise period. Pre- and post-exercise blood draws were conducted and sBDNF measured. Physical exercise caused an average ~ 32% increase in sBDNF levels relative to baseline that resulted in concentrations that were 45% higher than control conditions. Comparing the six conditions, sBDNF levels rose consistently among the four exercise conditions (Vig20 = 26.38 ± 34.89%, Vig40 = 28.48 ± 19.11%, Mod20 = 41.23 ± 59.65%, Mod40 = 30.16 ± 72.11%) and decreased consistently among the controls (Con20 = -14.48 ± 16.50, Con40 = -10.51 ± 26.78). Vig conditions had the highest proportion of subjects that experienced a significant (? 10%) increase in sBDNF levels, followed by Mod and control conditions. An analysis of modeled sBDNF integrals (area under the curve) demonstrated substantially greater values for Vig40 and Mod40 conditions compared to Vig20 and Mod20 conditions. Collectively, these results demonstrate that neither duration (20 vs. 40 min) nor intensity (60 vs. 80% HR reserve) significantly affects the benefits of exercise if only the sBDNF increase at a single post-exercise time point is considered. However, when comparing either the probability of achieving a significant BDNF gain or the integral (i.e. the volume of circulating BDNF over time) the Vig40 condition offers maximal benefits. Thus, we conclude that the future study of aerobic exercise effects on BDNF-mediated neuroprotection should take the volume of BDNF release over time into account. Key PointsAerobic exercise caused a ~32% increase in serum BDNF in adult human males while serum BDNF decreased 13% in sedentary control subjects.Vigorous intensity (80% heart rate reserve), long duration (40 min) exercise offered the greatest probability of a significant BDNF elevation.Long duration exercise offered the greatest numerical benefits in terms of BDNF integral.Neither intensity nor duration affected the mean elevation in BDNF amplitude caused by exercise.

Zonal organization of the mouse flocculus: physiology, input, and output.

The zones of the flocculus have been mapped in many species with a noticeable exception, the mouse. Here, the functional map of the mouse was constructed via extracellular recordings followed by tracer injections of biotinylated-dextran-amine and immunohistochemistry for heat-shock protein-25. Zones were identified based on the Purkinje cell complex spike modulation occurring in response to optokinetic stimulation. In zones 1 and 3 Purkinje cells responded best to rotation about a horizontal axis oriented at 135 degrees ipsilateral azimuth, whereas in zones 2 and 4 they responded best to rotation about the vertical axis. The tracing experiments showed that Purkinje cells of zone 1 projected to the parvicellular part of lateral cerebellar nucleus and superior vestibular nucleus, while Purkinje cells of zone 3 projected to group Y and the superior vestibular nucleus. Purkinje cells of zones 2 and 4 projected to the magnocellular and parvicellular parts of the medial vestibular nucleus, while some also innervated the lateral vestibular nucleus or nucleus prepositus hypoglossi. The climbing fiber inputs to Purkinje cells in zones 1 and 3 were derived from neurons in the ventrolateral outgrowth of the contralateral inferior olive, whereas those in zones 2 and 4 were derived from the contralateral caudal dorsal cap. Purkinje cells in zones 1 and 2, but not in zones 3 and 4, were positively labeled for heat-shock protein-25. The present study illustrates that Purkinje cells in the murine flocculus are organized in discrete zones with specific functions, specific input - output relations, and a specific histochemical signature.

Discriminative responses of squid (Loligo pealeii) photoreceptors to polarized light.

Cephalopods behaviorally respond to polarized light. Electrophysiology experiments with the squid, Loligo pealeii, demonstrated that spike responses from individual photoreceptors are a cosine2 function of the e-vector orientation of a polarized stimulus. The discrimination limit to this polarization sensitivity depended upon the difference between the orientation of a polarized stimulus with a preferred e-vector. The limit ranged from 2 degrees to 9.2 degrees with a direct stimulus in the dark or 4.8 degrees -22.1 degrees with non-directed background illumination and the cells were least discriminative at the preferred orientations. This limit can be explained partly by the variability in anatomical alignment of microvilli in the photoreceptors around a dominant axis. A few light-sensitive retinal fibers showed no polarization sensitivity. The coding of polarization information suggests that light intensity is transformed into an average spike rate. This average results from silent periods interspersed between bursts of spikes, each burst possessing a consistent interspike interval. The variations in the length and frequency of silent periods depend upon the difference between the polarization e-vector and a preferred e-vector orientation. The minimal discriminated orientation of a squid photoreceptor agrees well with the minimum behavioral discrimination of polarized light by another cephalopod, the octopus.

The making of a complex spike: ionic composition and plasticity.

Climbing fiber (CF) activation evokes a large all-or-nothing electrical response in Purkinje cells (PCs), the complex spike. It has been suggested that the role of CFs (and thus complex spikes) is that of a "teacher" in simple learning paradigms such as associative eyeblink conditioning. An alternative hypothesis describes the olivocerebellar system as part of a timing device and denies a role of the CF input in learning. To date, neither of these hypotheses nor others can definitively be verified or discounted. Similarly, the complex spike evades a clear understanding when it comes to the cellular events underlying complex spike generation. What is known, however, is that complex spikes are associated with large dendritic calcium signals that are required for the induction of long-term depression (LTD) at the parallel fiber (PF)-PC synapse. PF-LTD is a form of long-term synaptic plasticity that has been suggested to underlie certain forms of cerebellar motor learning. In contrast to the PF input, the CF input has been considered invariant. Our recent discovery of LTD at the CF input shows that complex spikes are less static than previously assumed. In addition to depression of CF-evoked excitatory postsynaptic currents, long-lasting, selective reduction of slow complex spike components could be observed after brief CF tetanization. To understand the functional implications of CF-LTD, it is crucial to know the types of currents constituting the specific complex spike components. Here we review the "anatomy" of the complex spike as well as our observations of activity-dependent complex spike waveform modifications. In addition, we discuss which properties CF-LTD might add to the circuitry of the cerebellar cortex.