Transforming growth factor alpha induces angiogenesis and neurogenesis following stroke.

The cytokine transforming growth factor alpha (TGF alpha) has proangiogenic and proneurogenic effects and can potentially reduce infarct volumes. Therefore, we administered TGF alpha or vehicle directly into the area surrounding the infarct in female mice that received gender-mismatched bone marrow transplants from green fluorescent protein (GFP)-expressing males prior to undergoing permanent middle cerebral artery occlusion. Newborn cells were tracked with bromodeoxyuridine (BrdU) labeling and immunohistochemistry at 90 days after stroke onset. We also studied the ingress of bone marrow-derived cells into the ischemic brain to determine whether such cells contribute to angiogenesis or neurogenesis. Infarct volumes were measured at 90 days poststroke. The results show that TGF alpha led to significant increments in the number of newborn neurons and glia in the ischemic hemisphere. TGF alpha also led to significant increments in the number of bone marrow-derived cells entering into the ischemic hemisphere. Most of these cells did not label with BrdU and represented endothelial cells that incorporated into blood vessels in the infarct border zone. Our results also show that infarct size was significantly reduced in animals treated with TGF alpha compared with controls. These results suggest that TGF alpha can induce angiogenesis, neurogenesis and neuroprotection after stroke. At least part of the pro-angiogenic effect appears to be secondary to the incorporation of bone marrow-derived endothelial cells into blood vessels in the infarct border zone.

Direct neuronal projection from a brainstem thermosensitive cell group to the preoptic thermoregulatory center.

The preoptic area orchestrates thermoregulatory responses in homeotherm animals and humans. This thermoregulatory center receives thermal information about core body and skin temperatures, and in turn, it induces thermogenic responses. The physiology of effector mechanisms has been described in detail outlining the brain areas participating in the execution of thermal responses. Previous studies have presented evidence of peripheral thermosensation, existence of skin thermoreceptors, participation of spinal and brainstem sensory neurons in thermal stress, but only recently has been identified the first evidence of an ascending neuronal pathway transmitting thermal signal to the preoptic thermoregulatory center. Nevertheless, a few brainstem areas have not been linked to an afferent or efferent thermal pathway and the neuronal network of thermoafferent signals has only partially been identified. In the present study, we identified a distinct ascending neuronal projection that originates from the thermoreactive cells of the peritrigeminal nucleus in the medulla oblongata, and projects to the thermoreactive cells of the medial preoptic area in the hypothalamus of rats. First, we have demonstrated retrogradely labeled thermoreactive neurons in the parabrachial, pontine and peritrigeminal cells following the injection of pseudorabies virus, a retrograde multi-synaptic tract tracer, into the ventrolateral subdivision of the medial preoptic area. Confirming the existence of a direct neuronal connection, we detected biotinylated dextran amine (BDA) containing axonal fibers and boutons around thermoreactive cells of the ventrolateral subdivision of the medial preoptic area after BDA injection into the peritrigeminal nucleus that is known to respond the temperature changes. Our findings indicate the existence of a so far unrecognized ascending direct neuronal pathway that transmits thermal signal from the lower brainstem to the thermoregulatory preoptic center.

Evidence that peripheral rather than intracranial thermal signals induce thermoregulation.

Numerous effector mechanisms have been discovered, which change body temperature and thus serve to maintain the thermal integrity of homeothermic animals. These mechanisms are driven by thermal signals that are processed by neurons in the hypothalamic preoptic area. To keep a tight control over body temperature, these neurons have to receive accurate thermal information. Although in vitro studies have shown the direct thermosensitive ability of neurons in the preoptic area, other observations suggest the existence of peripheral thermosensation and an ascending thermal pathway to the thermoregulatory center. Direct evidences for either one, or both are still missing. In the present study, brain, rectal, subcutaneous and skin surface temperatures were measured during 15, 30, 60 and 120 min of cold exposure (4 degrees C) in rats and compared with neuronal activation due to cold stress shown by c-fos in situ hybridization histochemistry. Subcutaneous and skin surface temperatures dropped continuously throughout the 120 min of cold exposure by 1.4 degrees C and 6.5 degrees C, respectively. However, during the first 30 min, brain and rectal temperatures increased by 0.3 degrees C and 0.25 degrees C, respectively, and even after 60 min of cold stress, brain temperature did not decrease under the level measured at 0 min. Since the brain temperature did not decrease, it is unlikely that intracranial thermoreceptors are involved in the transmission of "cold" thermal signal to induce thermoregulation. At 30 min of cold exposure, neurons in all known thermoregulatory areas (like the ventrolateral part of the medial preoptic nucleus, the lateral retrochiasmatic area, the lateral parabrachial nucleus and the peritrigeminal nucleus) were already maximally activated. These observations clearly indicate that the activation of neurons in the preoptic and several other thermoregulatory nuclei is induced in vivo by thermal signals originating in the periphery, and not in the CNS.

Activation of brain areas in rat following warm and cold ambient exposure.

Environmental thermal stimuli result in specific and coordinated thermoregulatory response in homeothermic animals. Warm exposure activates numerous brain areas within the cortex, hypothalamus, pons and medulla oblongata. We identified these thermosensitive cell groups in the medulla and pons that were suggested but not outlined by previous physiological studies. Using Fos immunohistochemistry, we localized all the nuclei and cell groups in the rat brain that were activated by warm and cold ambient exposure. These neurons located in the hypothalamus and the brainstem, are part of a network responsible for the thermospecific response elicited by thermal stress. Comparison of the distribution of Fos-immunoreactive cells throughout the rat brain revealed topographical differences between the patterns of activated cells following warm and cold environmental exposure. Among several brain regions, warm exposure elicited c-fos expression specifically in the ventrolateral part of the medial preoptic area, the central subdivision of the lateral parabrachial nucleus and the caudal part of the peritrigeminal nucleus, whereas cold stress resulted in c-fos expression in the ventromedial part of the medial preoptic area, the external subdivision of the lateral parabrachial nucleus and the rostral part of the peritrigeminal nucleus. These neurons are part of a network coordinating specific response to warm or cold exposure. The topographical differences suggest that well-defined cell groups and subdivisions of nuclei are responsible for the specific physiological (endocrine, autonomic and behavioral) changes observed in different thermal environment.

Apoptotic cell death induced by inhibitors of energy conservation--Bcl-2 inhibits apoptosis downstream of a fall of ATP level.

Energy charge controls intermediary metabolism and cellular regulation. Here we show that inhibition of energy conservation at the level of glucose uptake, glycolysis, citric acid cycle, and oxidative phosphorylation induces cell death, leading to fragmentation of DNA into an oligonucleosomal ladder and morphological changes typical for apoptosis. Bcl-2, the prototype of oncogenes that suppress cell death, efficiently inhibits apoptosis induced by metabolic inhibitors. Bcl-2 does not antagonize the inhibitory potential of mitochondrial inhibitors, and cannot prevent or delay the decrease of the cellular ATP level subsequent to metabolic inhibition. Thus, we propose that Bcl-2 blocks apoptosis at a point downstream of the collapse of the cellular-energy homeostasis.