General and Specific Aversive Modulation of Active Avoidance Require Central Amygdala.

Three studies provide evidence that the central nucleus of the amygdala, a structure with a well-established role in conditioned freezing, is also required for conditioned facilitation of instrumental avoidance in rats. First, the immediate early gene c-Fos was measured following the presentation of a previously shock-paired tone in subjects trained either on an unsignaled avoidance task or not (in addition to tone only presentations in naïve controls). Significantly elevated expression of c-Fos was found in both the avoidance trained and Pavlovian trained conditions relative to naïve controls (but with no difference between the two trained conditions). In a subsequent study, intracranial infusions of muscimol into the central amygdala significantly attenuated the facilitation of shock-avoidance by a shock-paired Pavlovian cue relative to pre-operative responding. The final study used a virogenetic approach to inhibit the central amygdala prior to testing. This treatment eliminated the transfer of motivational control over shock-avoidance by both a shock-paired Pavlovian stimulus, as well as a cue paired with a perceptually distinct aversive event (i.e., klaxon). These findings provide compelling support for a role of central amygdala in producing aversive Pavlovian-instrumental transfer.

Anatomical variation of median nerve: cadaveric study in brachial plexus.

Median nerve is formed by lateral root from lateral cord and medial root from medial cord of brachial plexus. Formation of median nerve occur in front or lateral to axillary artery in axilla. In the present study we observed anatomical variations of median nerve formation in the brachial plexus. We examined formalin fixed 60 upper limbs from 30 adult cadavers (15 males and 15 females) which were above the age 40 years from the department of Anatomy. All the cadavers were dissected on both sides according to Cunningham's Manual of Practical Anatomy. Normal formation of median nerve by two roots noted in 42 (70.0%) of upper limb specimen. Variation of median nerve formation noted in 18 (30.0%) upper limb specimen. Three roots taking part in the formation of median nerve in 13 (21.7%) upper limb specimen where additional root coming from lateral cord of brachial plexus. Four roots taking part in formation of median nerve in 3 (5.0%) upper limb specimen, where additional roots coming from lateral cord and posterior cord of brachial plexus. Lateral root crossed the axillary artery anteriorly to join with medial root lying medial to axillary artery. The median nerve formed medial to third part of axillary artery. Additional communication with musculocutaneous nerve with median nerve seen in 2 (3.3%) upper limb specimen. Knowledge of such anatomical variations is of interest to the anatomist and clinician alike. Surgeons who perform procedures involving neoplasm or repairing trauma need to be aware of these variations. Median nerve variation may lead to confusions in surgical procedures and axillary brachial plexus nerve block anesthesia.