Question 81#

Which of the following brain regions shows a preferential degeneration in Alzheimer’s disease?

A. Nucleus basalis

A. Nucleus basalis of Meynert contains a majority of cholinergic neurones. Apart from hippocampal (entorhinal cortex) neuronal loss, selective loss of neurones in the nucleus basalis has led to the pursuit of cholinergic theories of memory impairment in dementia. Currently available pharmacological interventions largely target cholinergic deficiency in Alzheimer’s disease.

Reference:

1. Wilcock GK, Esiri MM, Bowen DM, and Smiths CCT. The nucleus basalis in Alzheimer’s disease: cell counts and cortical biochemistry. Neuropathology and Applied Neurobiology 1982; 9: 175–179. 

Question 82#

Processing of fear conditioning is associated with functions of the:

A. Planum temporale

C. SM, a patient with rare bilateral amygdala damage, was initially reported to lack the ability to recognize fear from facial expressions. Since the report of her case, a number of lesion and functional imaging studies have demonstrated the role of the amygdala in fear processing. It is possible that the amygdala mediates spontaneous fixations on the eyes when viewing expressions of faces. Lack of such fixation may lead to failure of spontaneous processing of fearful emotions.

Reference:

1. Adolphs R, Gosselin F, Buchanan TW et al. A mechanism for impaired fear recognition after amygdala damage. Nature 2005; 433: 68–72.

Question 83#

Which of the following enzymes involved in neurotransmitter synthesis is directly affected by pyridoxine deficiency?

A. Glutamate decarboxylase

A. Pyridoxine (vitamin B₆ ) when phosphorylated to pyridoxal phosphate acts as a coenzyme in the conversion of glutamic acid to GABA, mediated by the rate-limiting enzyme glutamate decarboxylase. The pivotal role of this chemical interaction is evident from pyridoxine-dependent seizures, which can occur in relation to mutations of chromosome 5q31. Dysfunction of this enzyme leads to glutamate accumulation and excitatory damage via NMDA receptors.

Reference:

1. Tan H, Kardas¸lu F, Büyükavci M, and Karakelleoˇglu C. Pyridoxine-dependent seizures and microcephaly. Paediatric Neurology 2004; 31: 211–213.

Question 84#

Which of the following brain areas has a relatively permeable blood–tissue interface?

A. Anterior pituitary

C. The circumventricular organs are midline structures around the third and fourth ventricles. Pineal gland, median eminence, neurohypophysis, subfornical organ, area postrema, subcommissural organ, organum vasculosum of the lamina terminalis, and the choroid plexus are considered as circumventricular organs. These structures lack the blood–brain barrier seen in other regions of brain. These areas enable the brain’s direct response to chemical challenges in blood.

Reference:

1. Johnstone EC et al., eds. Companion to Psychiatric Studies, 7th edn. Churchill Livingstone, 2004, p. 38.

Question 85#

Which of the following terms refers to a substance that influences neuronal activity and originates from non-synaptic sites?

A. Neurotransmitter

C. A neuromodulator is a substance that enhances or diminishes the effect of neurotransmitters but does not usually result in neuronal conduction changes on its own. Substance P, enkephalin, cholecystokinin, somatostatin, and neuropeptide Y are examples of neuromodulators. Neurotrophin is a substance produced to influence neuronal growth. Neurohormones are substances released by neurones into the blood stream to influence effector organs at distant sites, for example corticotrophin-releasing hormone.

Reference:

1. Johnstone EC et al., eds. Companion to Psychiatric Studies, 7th edn. Churchill Livingstone, 2004, p. 41.