and form the glial scar. These glial cells interact with neurons, blood ves-
sels and the pia materby their stellate processes. Regulation of the microen-
vironment including the concentrations of ions, metabolites and
neurotransmitters (e.g., glutamate) is an important function of astrocytes.
Astrocytes are also the source of the most common glioma, astrocytoma.
The barrier function of the blood-brain-barrier is established by tight junc-
tions (zonula occludentes) between endothelial cells in the blood vessels of
the brain. However, astrocytes establish and maintain the blood-brain bar-
rier and thus control the entry of compounds into the brain parenchyma.
During development the astrocytes are critical to normal migration of
developing neurons. The patient in the vignette suffers from NeuroAIDS.
In that disease, astrocytes are believed to be infected with the AIDS virus.
Astrocytes can be infected with HIV-1, however, there appears to be only
limited replication. Infection can lead to changes in gene expression (of the
cell) and some of the released products can have deleterious effects on neu-
rons. Astrocytes integrate neuronal inputs, exhibit calcium excitability, and
communicate bidirectionally with neighboring neurons and synapses, but
do not synapse with neurons (answer a).Microglia present antigen and
phagocytose dying neurons (answers b and c).Oligodendrocytes myeli-
nate axons in the CNS (answer e).
148.The answer is a.(Kasper, pp 2554–2556. Junqueira, pp 158–161,
166–169. Kandel, pp 265–269.) Clinical depression is associated with
reduced levels of the monoamines, such as 5-hydroxytryptamine (sero-
tonin, 5-HT) in the CNS. The selective serotonin reuptake inhibitors
(SSRIs), such as Fluoxetine hydrochloride (Prozac), bind to the 5-HT reup-
take transporter in the presynaptic membrane, blocking reuptake, and sub-
sequent degradation of serotonin in the synaptic cleft (answer e).
Therefore, serotonin levels increase in the synaptic cleft as a result of SSRI-
treatment. The structure labeled “D” is the postsynaptic membrane. The
electron micrograph of the synapse shows the presynaptic membrane (C),
postsynaptic membrane (D), mitochondria (B), and synaptic vesicles (A).
Recycling of synaptic vesicle membrane occurs at the presynaptic mem-
brane in conjunction with neurotransmitter release by exocytosis. Neuro-
transmitter release is induced by membrane depolarization, leading to
transient opening of calcium channels followed by calcium influx. There is
no cytoplasmic continuity between adjacent neurons (answer d).Trans-
mission from neuron to neuron occurs by chemical transmission in the
248 Anatomy, Histology, and Cell Biology